Rec.antiques.radio+phono FAQ
Sorry about the somewhat rough character of what follows. It's too
long for me to take it and clean it up, so here it is, just as I saved
it off the net.
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono General Questions(FAQ: 1/9)
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Rec.antiques.radio+phono Frequently Asked Questions (part 1)
Revision Date Notes
1.1 Oct. 20, 94. Second version---major editing. Added two new
sections for sources-of-supply list.
1.2 Dec. 10, 1994. Minor corrections and revisions.
1.3 Jan. 8, 1995. Put in boatanchor mail list info.
1.4 Feb. 26, 1995 Approval to post on news.answers granted
1.4 May 8, 1995 Charter discussion and revised format notice
1.5 Sept. 3, 1995 Add new newsgroup cross references.
2.0 Nov. 20, 1995 Split FAQ from 5 sections to 9 sections
2.1 March 3, 1996 Revise charter disc., boatanchor pointers
Part 1 - Introduction to the FAQ
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Email vancleef@netcom
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and phonographs. It is intended to summarize some common
questions on old home entertainment audio equipment and provide answers
to these questions.
Regular FAQ postings can help save network bandwidth and maintain a good
signal-to-noise ratio in the newsgroup. However, they can't do it alone - you,
the reader, have to use them.
* If you are a new user, please print and review the FAQ articles and look at
the instructions in the news.announce.newusers newsgroup before posting any
articles. If you don't find the answer in the FAQ and you have tried
elsewhere, then you have "done your homework" and it is acceptable to ask
the question on the UseNet newsgroups. Along with your question, please
state where else you have looked for the answer so others also know that
you have done your homework.
* If you are an experienced user, please help by refraining from answering
frequently-asked questions on the newsgroup if they are already answered by
the FAQ articles. Instead, send e-mail to the user who asked the question.
(It will be helpful if you include the part of the FAQ that answers their
question, but not the whole thing.)
The FAQ cannot always prevent people from posting repetitive questions. But
even if hundreds of questions get posted, it saves you from having to answer
them hundreds of times. Also, a friendly pointer to the FAQ in your first
answer can help that person refer to the FAQ in the future. That is when we
can begin to get a real savings of network bandwidth.
To reduce the size of articles, the FAQ information is posted in 5 parts:
Part 1 - Introduction to the FAQ and general questions.
(Editor: Hank van Cleef, vancleef@bga.com).
Part 2 - General questions about acoustical phonographs.
(Editor: George Conklin, george@nccu.edu)
Part 3 - Sources of spares and services for acoustic phonos.
Part 4 - General questions about vacuum tube radios and phonos.
Part 5 - Sources of spares and services for old radios.
Part 6 - Cosmetic cleanup and cabinet finish questions
Part 7 - Technical questions about vacuum tube radios and phonos
Part 8 - Tools and test equipment
Part 9 - Miscellaneous and other antique home entertainment devices
Please do not E-mail technical questions, requests to identify various
items, or technical questions to the Faq editors. Post them to the
newsgroup instead. You will get better answers more quickly by
posting.
(March '96) My mailbox is getting far too many questions that I don't
know the answers to, and I am responding with a form message that says
"I don't know, post to the group." So I'll repeat:
PLEASE DON'T MAIL QUESTIONS TO THE FAQ EDITORS. POST YOUR QUESTIONS TO
THE NEWSGROUP. The FAQ editors read the newsgroup regularly, and
generally respond where they have information. We have put a lot of
general information in the FAQ, and a lot of it has come from discussion
on the newsgroup, not from our own knowledge. You'll get more and
better answers from posting to the newsgroup, and if we've got something
to contribute, we'll do it there. Trying to use us as consultants
simply wastes your time and ours.
The charter for the rec.antiques.radios+phonos follows immediately,
after which are some of the top frequently-asked questions.
Newsgroups line:
rec.antiques.radio+phono Audio devices and materials of yesteryear.
CHARTER
Discussion of the use, repair, and collecting of early standard-broadcast
radios, phonographs, and any other similarly-related items designed for home
entertainment sound receiving or sound reproduction.
This group is intended to be a forum for those with an interest
in sound-receiving and sound-reproduction equipment that was generally
manufactured prior to the widespread use of transistors. The group's
discussion, however, will not be strictly limited to vacuum-tube and
mechanical devices, and those with an interest in early transistor radios,
early televisions, and other such items that reflect pioneering audio
technology will be welcomed.
Exclusions:
Amateur radio equipment discussion will be directed to the existing amateur
radio newsgroups and to the boatanchors list. This is only done because
those groups present an established forum for people with an interest in
classic amateur radio equipment. Those classic amateur radio collectors who
also share an interest in early standard-broadcast equipment will fully
appreciate the desire to separate the two interests. Their valuable
expertise will, however, be most welcome in all forums.
Since the summer of 1993, there has been an ongoing discussion among
those interested in antique radios and phonographs (and other related
equipment and materials) about the possibility of forming this
newsgroup. That small core of enthusiasts has rapidly grown in
number, and now includes representatives of museums, technical
specialists, collectors, and novices with an inquisitiveness about
sound reproducing and receiving equipment of the past. With
enthusiasm for the preservation and enjoyment of these superb
expressions of human inventiveness steadily increasing, the time has
come to establish a forum through which knowledge of their history,
restoration, and use can be shared by experts and newcomers alike.
This proposal represents the essence of what an Internet newsgroup can
accomplish--it can produce a collective source of knowledge from which
useful information can be drawn for years into the future.
Bill Robie, August, 1994
In general, this means:
1. This newsgroup has the name "antique" in it, and primarily addresses
home entertainment equipment. It is not a "catch-all" group for
discussing things not covered by other groups.
2. Items of particular interest to readers in this group:
a. Acoustic phonographs of all types.
b. Early electronic phonographs, primarily for playing 78 RPM
disks.
c. Radios of the 1920-50's period. Of particular interest are
Atwater Kent, Philco, and Zenith sets, although all radios by earlier
manufacturers are of interest to the group.
3. While much of the discussion the group is about radios and phonos of
US manufacture, we welcome discussion of non-US radios and phonos from
the same period sold primarily to a domestic market.
4. There are a great many opinions about what is "antique" and what
isn't. The focus of the discussion that led to creation of this
newsgroup was on phonograph and radio technology of the 1890-1950 era.
The group does include some discussion of:
a. Monaural vacuum tube "high fidelity" equipment.
b. Early hybrid and transistor home entertainment designs.
c. Early black and white televisions, and a few color sets.
However, post-1950's technology generally diverges from the focus of
this newsgroup. We generally regard 1960 as a cutoff date for
appropriateness in this group.
d. Instrumentation suitable for use in design, repair, and
calibration of antique home entertainment items. This includes
laboratory-grade equipment as well as service shop equipment.
e. Discussions about technological history, recording and
broadcasting practices, etc., have been interesting areas of discussion
in the group.
5. While not originally sold as "home entertainment" equipment, there
is an interest in jukeboxes, early musical devices such as the Hammond
organ, and movie theater audio, particuarly items manufactured before
WW II.
6. We welcome participation by "hams," and include some discussion of
old tube-type communications receivers, particularly from the '30's and
'40's in this group. Amateur radio issues in general are already covered
by the rec.radio.amateur.* groups.
(March '96). The "boatanchor" mail list, which was previously mentioned
here, is, according to the list administrator, a paid subscription list
as of March 15, 1996.
7. Casual buy, sell, swap, and trade, of old radios and phonos, parts,
are within the charter. Please keep in mind that this is a discussion
group, with many non-collectors who have one or two items that they
enjoy. This is not a place to hawk your wares. If you have an old radio
or phono or two, or want to buy a specific make and model of something,
then post here. Do not post blanket "WTB (wanted to buy) notices for
any and all old radios, old transistor radios, phono records, candlestick
phones, etc. Also, do not post anonymously (AOL, Prodigy, and Compuserve
users take particular note, as these systems do not give posters a clear
identity). Give a geographic location.
Before posting a buy/sell/swap item here, consider posting to one of the
newsgroups set up for that purpose. Rec.antiques.marketplace is the
principal group for antique trading, and is regularly read by readers of
this group who want to buy and sell. Rec.radio.swap is a general group
for electronic items of all types. Rec.audio.marketplace,
sci.electronics.marketplace are also good groups to use, particularly
for post-WW II items. Consider using a regional marketplace or forsale
newsgroup, particularly if you are talking about something you do not
want to ship. Remember that this group is worldwide.
Dealers of parts, supplies, and services for home entertainment items
are listed in sections 3 and 5 of this FAQ.
8. Binary postings. Please do not post binary files (picture files,
uuencoded data, mime attachments, etc.) to this newsgroup. This is a
Usenet convention, not a charter issue. A number of system
administrators run software that detect and cancel binary postings in
non-binary newsgroups. If you want to post a binary file, find a group
with "binaries" in the name, post there, and post a pointer to it here.
Keep in mind that binary groups are not available on many systems,
because of the traffic volume involved, and are poorly propagated.
Some of the things that don't seem to fit well with this group are:
1. Stereo from the 60's and later, particularly things with bookshelf
speakers. The rec.audio.* newsgroups are the place to discuss these.
2. Computers. Usenet has hundreds of newsgroups devoted to computers,
including old ones.
3. Tape recorders other than vacuum tube reel-to-reel units.
4. Video recorders.
5. Guitar amplifiers.
6. Amateur radio equipment except for older general coverage
receivers that sold to non-hams as home entertainment SWL
(shortwave listening) sets.
7. Phonograph records---trading should be done in the
rec.music.collecting newsgroups.
8. Off-charter and commercial buy and sell postings. This includes
"wanted to buy, old radios" postings from individuals, and any
buy/swap/trade postings from anonymous accounts where name or location
are not given. Repetitive postings are also unwelcome to most of the
readers.
The above are general guidelines, not hard-and-fast rules. If you
receive a response posting or E-mail indicating that your post was off
topic, it will generally point to a more appropriate group. This group
has been historically free of flames. There are some very honest
differences of opinion about many topics, and some of the discussions
are lively. The focus of this group is on positive things. Ad hominum
attacks, flame wars, along with attempts to use the group for commercial
purposes, are not welcome here. Your questions, and your experiences
with old radios and phonos are the lifeblood of the group. Work to make
this group a happy and positive place.
A note on safety: Virtually everything we discuss in this newsgroups
can present safety hazards of one sort or another. In particular are
the energy stored in phonograph springs and the voltages and currents in
electronics equipment. In addition, processes such as soldering
components can cause fires and serious burns if improperly done.
While the subject of safety hazards and safe operation, troubleshooting,
and repair practices is a topic of discussion on the newsgroup, such
discussions are generally far from comprehensive. Additionally, many of
the processes discussed presume knowledge of safe practices, and do not
go into detail about possible hazards. Safety is your responsibility.
While we may discuss techniques and practices that work well for us, and
that we can use safely, we are not prepared to give supervised
instruction or to audit people's safety practices. If you are unsure of
your ability to work in a safe manner, seek out local assistance and
supervision.
Q. What other newsgroups cover similar items?
A. There are several newsgroups covering broadcast and amateur radio;
and audio equipment. Acoustic phonographs, player pianos, etc. are less
likely to be covered in other newsgroups.
Notable among other newsgroups with similar interests:
rec.antiques General discussion of antiques.
rec.antiques.marketplace Buy/sell/swap antiques of all types.
rec.audio.tubes Discussion of later vacuum tube audio.
rec.music.collecting.* Phonograph records. This hierarchy has both
discussion and marketplace groups.
rec.radio.swap Buy and sell any electronic equipment, new or old. This
includes test equipment and accessories.
rec.radio.amateur.equipment Specific to ham radio equipment.
rec.radio.shortwave Discusses shortwave programming,
stations, and receivers.
sci.electronics.repair Repair information, primarily for modern
equipment.
rec.audio.* Discussion of audio equipment. This hierarchy
includes several categories, as well as a marketplace newsgroup.
rec.woodworking Discussion of woodworking, finishes, veneering,
etc. If you are working with an old cabinet, read this group.
Q. Where can I get needles for my Victrola.
A. Contact the Antique Phonograph Supply Company, Route 23, Box 123,
Davenport Center, NY 13751. Phone 607-278-6218. Remember to change
your needles after every play. The engineering concept was simple:
the needles are softer than the record, and will wear without
stressing the record. Some records had grit in the mix to
wear the steel needle.
Q. Where can I get replacement vacuum tubes for my radio?
A. There are several suppliers of tubes. Best known is Antique
Electronic Supply, 6221 S. Maple, Tempe, Arizona 85283, telephone
602-820-5411. See the FAQ section for electronic parts and supplies.
Q. I would like to get an old radio or an old phonograph. Where can
I find one?
A. Generally, these items are where you find them. There are dealers
who specialize in old radios and old phonographs, and these may be the
best source if you want something that has been restored to good working
condition as well as cosmetically. Second hand stores and thrift shops,
estate sales, moving sales, garage sales all can produce interesting
items, and it is possible to find some real bargains. Keep in mind that
the source of supply is attics, barns, storerooms, where these were
tucked away, maybe as much as fifty or seventy years ago. They may or
may not have been working when they were stored.
Keep in mind that acoustical phonographs have parts in their reproducers
that deteriorate over time, and that lubricants deteriorate as well.
Electronic equipment also has components that deteriorate over time as
well. What you are looking at may have been stored in working condition
forty or fifty years ago, and look clean as a whistle, but be in need of
major work before you can use it.
Q. I found an EtherSnarf model YU4Q radio at an estate auction and got
it for $125. Did I get rooked? It looks complete, has ten tubes and a
big oak cabinet with spool legs and lots of gewgaws, and has four
shortwave bands. I don't find it listed in any old radio buyers'
guide.
A. First of all, keep in mind that there were literally hundreds of
radio manufacturers in the US in the 1920-1960 era, and there were some
manufactures who built "trade" radios to be sold under a store's brand
name. Part 3 of this FAQ will help you figure out when this radio was
built, even if it isn't listed in any of the buyers' manuals or in any
of the maintenance manuals that were published at the time.
What an old radio is actually worth depends on many things. First of
all, what is it worth to you? While there is supposedly a market out
there, what a specific radio is actually worth is, in reality, what
someone is willing to pay to buy it from you. You want to keep in
mind the following:
a. The radio may need a lot of work before it will
operate as it was designed to operate.
b. Most radios were "lo-fi" in modern terms. Many of us
actually enjoy the sound, and many of the consoles, cathedrals, and
tombstones were tuned very nicely to the programs sources of the day.
c. While the number of tubes may give some indication of the
quality of the radio, and a big console cabinet is more likely to house
a good radio than a plastic table cabinet, keep in mind that "number of
tubes" and "big cabinet" both were selling points in the 1930-50 era
that meant "high retail price." Some mid-priced consoles look as though
they have a lot more radio in them than they do.
Some people swear by the Bunis "Collectors' Guide to Old Radios" series
written by Marty and Sue Bunis. Others do not feel that their prices
are particularly supportable when trying to sell. Most collectors do
not buy for resale, and buy because they want the item.
Q. My neighbor's grandfather left him a Victor spring-powered
phonograph he wants to sell me for $100. Should I buy it?
A. As with old radios, the "worth" of an old phonograph is its "worth
to you." There are "price guides" and general ideas of what things can
be bought and sold for. However, there are substantial variables, such
as geographic location, condition of the unit, etc.
Keep in mind that you are going to need some records to play on
your machine, and that they are also definitely "lo-fi." Edison fought
electrification to the bitter end, so some of the later Edisons, as well
as the Victor Orthophonic of the mid-twenties, did incredibly well.
Q. I got an old Westinghouse cathedral radio from my neighbor when he
cleaned out it his attic. He told me he put it up there when Fred Allen
left radio, but that it was working when he stored it. I plugged it in
and turned it on. All of the tubes glowed, but nothing came out of the
loudspeaker. After a few minutes, one of the tubes got very red inside
and then, suddenly, liquid shot out of one of the aluminum cans, hit the
bright red tube, and it broke. When I turned the set off, it was
smoking, and this liquid got all over everything like tom cat pee. What
do I do now?
A. Never ever plug in an old piece of electronics gear that hasn't been
used for a few years without checking it out first. Part 4 of this FAQ
describes some of the things to check. Fred Allen left radio in 1949,
so that radio has been stored 45 years.
DON'T PLUG IT IN UNTIL YOU HAVE CHECKED IT OUT!
What I am describing here actually happened to me around 1948. The
problem was a shorted wet electrolytic condenser. The plates of the
rectifier tube, an 80, glowed red, and I shut the radio off, but the
electrolytic boiled, squirted the electrolyte (nasty stuff) onto the 80,
which promptly shattered. Cleanup was a soap-and-water job.
Q. Can I get spares for restoring my Edison phonograph---for my Atwater
Kent radio.
A. Parts 2 and 4 of this FAQ list suppliers of spares for phonos and
radios, respectively. In addition to spares support, there are
people who rebuild phonograph transducers and other subassemblies.
Availability of specific spares depends on several things. OEM spares
support for pre-1930's items was discontinued before WW-II, but in many
cases, items of new manufacture are available. In other cases, such as
the 6U5/6G5 tuning eye tube, commonly used from the '30's to the '50's,
your best bet is to substitute (and there is an adaptor for this
available).
Q. I've never worked on vacuum tube equipment before, but I'm a ham and
I have worked on lots of transistor equipment and small computers. Can
I just jump in and fix my old radio?
A. No. There are some serious differences between old tube equipment
and modern solid state electronics. Here are a few things to consider:
a. DANGER! HIGH VOLTAGE! We are not talking about 110 volts AC,
we are talking about 250-500 volts with plenty of "oomph" behind it.
You generally won't find any fuses in old electronic equipment, and no
protective circuits.
b. Vacuum tube circuits have components and circuitry that
isn't used in solid state equipment.
While the basics of physics regarding voltage, current, resistance,
inductance, and capacitance haven't changed, you'll want to study old
texts that explain the theory of operation of the circuits used. While
developing the skills needed to trouble-shoot and repair vacuum tube
circuits is not difficult, it is very different work from working on
solid state equipment. And, as noted, the presence of genuinely high
voltages for someone used to working with 5 and 12 volts means that you
will need to develop new safe working habits.
Q. I'm all thumbs around mechanical and electronics devices. Can I
find people who know how to make these things work?
A. Yes. You may find someone locally who still does work on tube
electronic equipment, and a few telephone calls to service shops will
point you in the right direction if there is someone in your area.
There are a few people who specialize in repairing and restoring old
phonographs and old radios. While none are listed in this revision of
the FAQ, we may include a few if there is a demand for this information.
For a price, you can have almost any antique "high-tech" device restored
to like-new condition, if not better.
Q. What's the difference between this newsgroup and rec.audio.tubes.
A. Rec.antiques.radio+phono was created to move discussion of acoustic
phonos and old radios (primarily 1920-40 era) from rec.antiques. The
rec.audio.tubes newsgroup was created a year later as a place to
discuss use of vacuum tubes in "high fidelity" and guitar amplifiers.
Q. How do I subscribe to the boatanchors mailing list?
A. (March '96). The following instructions are the last information I
have, and have been in this FAQ since this version of the mail list was
set up in the fall of 1994. However, this list is being converted to
"subscription only" as of March 15, 1996. "Subscription only" means
"send money." I do not know how the listowner plans to handle new
subscribers after March 15.
To subscribe to the boatanchors mail list send e-mail to
listproc@theporch.com. Put the following in the body of the mail
message:
subscribe boatanchors
(the following is abstracted from the listproc response from
theporch.com).
Please *do not* submit such administrative messages to the whole
list! Such messages only irritate the readers. If you remember
only one thing from this message, remember that a "Help" message
to the list processor (listproc@theporch.com) will get you
instructions on how to unsubscribe or change your address.
This subscription is available in two formats. The first, also the
default is to have each posting to the list mailed to you seperately. If
you want it like that, you don't have to do anything. The second option
is to receive digests which means the messages are collected and mailed
out to you only if it exceeds a length limit or a time limit (one day).
To change to the digest form, sent email to listproc@theporch.com with
the following:
set boatanchors mail digest
If you want to temporarly suspend receiving the list but don't want to
sign off the list, you can set your mail to postpone by sending email
to listproc@theporch.com with the following in the body of the mail:
set boatanchors mail postpone
This will stay in effect until you change your mail status to one of:
ack noack or digest (ack the default reflects your posting to
the list back to you)
If you want to read the FAQ for the boatanchors mailing list please
send email to listproc@theporch.com with the following content:
get boatanchors FAQ
Problems that cannot be resolved by sending e-mail to the list processor
should be addressed to:
listown@jackatak.theporch.com
Newsgroups: rec.antiques.radio+phono,rec.answers,news.answers
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono Phono Spares and Services(FAQ: 2/9)
Message-ID: <antique-radio+phono-faq-2-845766911@netcom.com>
Followup-To: rec.antiques.radio+phono
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is over 3 months old, please obtain a new one.
Keywords: FAQ OLD-RADIO OLD-PHONO
Sender: vancleef@netcom6.netcom.com
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Organization: Bluebonnet Firebottle Works
References: <antique-radio+phono-faq-1-845766911@netcom.com>
Date: Sat, 19 Oct 1996 23:15:17 GMT
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Archive-name: antiques/radio+phono/faq/part2
Rec.antiques.radio+phono Frequently Asked Questions (part 2)
1.0 Oct. 20, 94 First version. This material was supplied by
George Conklin (george@nccu.edu).
1.1 Dec. 12, 94 Revisions by George Conklin.
2.0 Second Version May 3,1995 This material was supplied by
George Conklin (george@nccu.edu).
3.0 Third Version, March 1996. This material was supplied
by George Conklin (george@nccu.edu).
Part 2 - Sources of supply, services, and literature for acoustic
phonos
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Please E-mail comments about comment of
this section to George Conklin (george@nccu.edu)
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and phonographs. It is intended to summarize some common
questions on old home entertainment audio equipment and provide answers
to these questions.
The most frequently asked question so far is "Where can I buy
steel needles for my Victrola?" Answer: Contact the Antique
Phonograph Supply Company, Route 23, Box 123, Davenport
Center, NY 13751. Phone 607-278-6218. Remember to change your
needles after every play. The engineering concept was simple:
the needles are softer than the record, and will wear without
stressing the record. Some records had grit in the mix to
wear the steel needle.
Books about phonographs are written mostly by hobbyists,
not engineers or academics. Below is a listing of common
sources to get you going in the hobby.
1. "The Compleat Talking Machine" by Eric L. Reiss, Vestal Press,
1986, is the most important book for a beginner. It lists not only
many models, but it tells how to oil a machine and how to make
most repairs. Order from: The Antique Phonograph Supply
Company, Route 23, Box 123, Davenport Center, NY 13751-0123.
(607) 278-6218. Order this book first. A second edition is
being advertised as available in the Summer of 1996. It is
supposed to contain new material and added hints.
2. For books about Edison machines, George Frow has written
the "bibles." For cylinder machines, order "Edison Cylincer
Phonograph Companion." It was newly revised in 1994 and
contains about all you can possibly want to know about the
various models. Note: it does not discuss prices. Earlier
editions of this book are found only in rare book rooms of
a few libraries. The only drawback to this book are the
photographs, which are small and dark. The second book
by Frow covers diamond disc phonographs by Edison (the
'thick' records players): "The Edison Disc Phonographs
and the Diamond Discs: A history with Illustrations),
1982. APSCO sells both. You may also contact
George Frow, "Salterns," Seal Hollow Road,
Sevenoaks, Kent TN13 3SH, England.
3. For Victor machines, there is also one book everyone
uses called "Look for the Dog" by Robert Baumbach. A
new paperback edition is out. The illustrations are good,
but the discussion is more limited than what is found in
Frow's books on Edison. APSO sells this book too.
4. The main 'general' book on phonographs
is called "From Tinfoil to Stereo: The Acoustic Years
of the Recording Industry 1877-1929" by Walter L.
Welch and Leah Brodbeck Stenzel Burt. University
of Flordia Press, 1994. Yes, it is somewhat
scholarly and does contain some errors, as do many
of the books about phonographs. Some reviewers
found dozens of errors on dates.
5. Magazines about phonographs are few and far
between. However, I recommend the following for
the beginner in the hobby because they are readily
available, appear regularly and are nicely done:
A. "Victrola and 78 Journal" is a new journal and
a nice mixture of articles on records and how to care
for your elderly phonograph. Contact Tim Gracyk,
1509 River Oak Way, Roseville, CA 95747.
Email: tgracyk@garlic.com (916) 784-1929.
B. "Hillandale News" published by the City of London
Phonograph and Gramophone Society. This is a nicely
produced magazine. Contact Chris Hamilton,
"Ardlarich", 2 Kirlands Park, Cupar, Fife KY 15 4EP England.
C. "In the Groove," a monthly newsletter published by
the Michigan Antique Phonograph Society. Contact
John Whitacre, Editor, MAPS, 2609 Devonshire,
Lansing, MI 48910. 517-482-7996. If you are
looking for parts, this is the place to start.
They publish resource guide and membership
directory which lists about 800 phonograph
collectors and about every known organization
dealing with phonographs and parts in the
world. This is the document to get if
you want to buy parts or look for local
dealers.
6. As for places to get repairs done,
some members of this news group recommend you
contact Dwayne Wyatt of Wyatt's Music
World, PO Box 601, Lakeport, CA 707 263-5013.
The catalog lists all the parts for various Edison
cylider and Amberola phonographs, with a price for
each and every screw, gear and so forth. Columbia
Grafanola, Models AT, AZ, and Q and some Victors and
Brunswicks are also listed. He sells reproduction
Cygnet Horns.
Also, APSO listed above does compete overhauls
of old phonographs and supplies parts.
The above sources are enough to get you started.
They are not a complete listing of very book about
Victors or Thomas Edison. They are, however,
the most important pieces of information and
enough to answer many (if not all) questions.
For the most new information possible, get the
resource guide from MAPS.
---------------------------------------------------------------
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono Phono General Questions(FAQ: 3/9)
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Archive-name: antiques/radio+phono/faq/part3
Rec.antiques.radio+phono Frequently Asked Questions (part 3)
1.0 Oct. 20, 94 First version. This material was supplied by
George Conklin (george@nccu.edu).
1.1 Dec. 12, 94 Revisions by George Conklin.
2.0 Second Version May 3,1995 This material was supplied by
George Conklin (george@nccu.edu).
3.0 March 12, 1996. Third Version. This material was
supplied by George Conklin (george@nccu.edu).
Part 3 - Frequently-asked questions about phonographs
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Please E-mail comments about comment of
this section to George Conklin (george@nccu.edu)
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and phonographs. It is intended to summarize some common
questions on old home entertainment audio equipment and provide answers
to these questions.
Part B: Technical Information
Common Questions about Acoustic Phonographs
The most frequently asked question continues
to be from the very first day of the group: "Where can I buy
steel needles for my Victrola?" Answer: Contact the Antique
Phonograph Supply Company, Route 23, Box 123, Davenport
Center, NY 13751. Phone 607-278-6218. Remember to change your
needles after every play. The engineering concept was simple:
the needles are softer than the record, and will wear without
stressing the record. Some records had grit in the mix to
wear the steel needle.
Question: My phonograph does not work. What can I do?
Answer: There is one excellent book which explains how old
phonographs, gramophones and cylinder players work.
"The Compleat Talking Machine" by Eric Reiss. It is
also available from APSCO listed above. It explains how
to work on a phonograph to get it running again. It contains
detailed photographs.
Question: I have just found this wonderful windup phonograph.
How can I tell if it works? I don't have time to read a book.
What can I do?
Answer: Phonographs are found which look new. Others look as if
they have been sitting in a wet basement for 70 years. But there are
a few quick tests:
1. Does the dealer demonstrate the unit? If it plays and sounds
fine, it probably is in good shape. It is relatively hard to hide
problems with spring motors.
2. Is the spring broken? This means that your turn the crank and
nothing happens. Usually the spring is broken near the center, so the
phonograph does not play. New springs can be found for most
phonographs from the Antique Phonograph Supply Company. Cost: about
$50 if you send in the barrel. If a new spring is not
available, you can patch the old one by following instructions in
the Reiss book listed above. But please note that you may not
want to do this without some experience since you can cut your
fingers off.
3. If the turntable rotates (or the cylinder turns), but you hear
a loud bump while the record is playing, then the spring needs grease.
a. This is not an easy task. Purists will say to take the spring out
of the barrel, clean it and the reload the barrel. Warning: if you try
to do this, you can cut your fingers off. The barrel is a cylinder into
which the spring is wound. Some cheaper units simply have an open
spring. Greasing such a spring is much more easy.
b. Shortcut: You can add grease to the spring without first taking
it out of the barrel. Most barrels had an opening called a graphite
hole. Wind up the unit all the way. Take the plug out of the graphite
hole and force in grease. The original Edison formula, which I have
used, contains 10 parts vasoline to 1 part graphite. Put the screw
back in the hole. Let the unit run down, dispersing the grease.
4. Listen to see if the governor is in good shape. When you play the
unit, is there a high speed vibration. If so, you may need work on the
governor. This is difficult.
5. If the turntable works (or the cylinder turns), then play a
record. What does it sound like? If you hear a lot of vibrations,
or if the sound is bad, you probably need to rebuild the reproducer.
a. Rebuilding an Edison reproducer for a cylinder phonograph is
ususally an easy job. Kits cost $6.00. A new sapphire is $30.00
and is likely to outlast you.
b. Rebuilding a Victor #2 (the most common) is not difficult either.
c. Rebuilding a Diamond Disc reproducer is more difficult. The old
diaphragms take effort to remove without damage. It can be done. Kits
are available. New diamond needles: $60.00. But the old diamond may be
in good shape.
d. Rebuilding the Victor Orthophonic is very difficult and few people
will touch this one. Such reproducers (heads) cost about $100 in
auctions. Many were made of pot metal, and they are gradually falling
apart.
e. Rebuilding other heads requires buying generic parts and doing
the best you can.
6. Ok, I don't know much about mechanical things. What can I do?
You can send the entire works off for repair and cleaning. This costs
about $150 for an Edison unit.
7. What about parts? What if something wears out?
If you buy an Edison or a Victor, most motor parts are still
available. As for the other units around, if something other than
the spring is broken, you might want to look for a different unit
unless you are handy around a machine shop, or are willing to pay to
send the entire motor out for repair.
Question: I just found some 'thick' records. How can I play them?
Answer: Many people think that the standard
78 record is 'thick.' However, the really thick records
were made by Thomas Edison and are called Diamond Discs.
They were made from 1912 until Edison closed his phonograph
business in 1929, one day before the stock market crashed.
In their time, these were the premium records. Do NOT
try to play a diamond disc record with a Victrola steel
needle machine. It will ruin the record and it will not
play. The DDs were recorded vertically, using the hill and
dale method. They were played with a special diamond needle.
You can play such records today at 78 rpm on with a stereo
catridge using either the LP needle or a 78 (3 mil) needle.
Or, better yet, such records still work fine with an
Edison machine.
Question: I just found a "Victrola." What is it worth?
Answer: Most people use the word 'Victrola' as a generic
term, like Frigidaire is used to mean all types of ice box.
Most likely such a term means an upright machine made during
the 1920s and housed in a 'brown box.' Since millions were
made, it is impossible to give a specific value. However,
most upright Victors go for about $400 right now.
Question: Where can I read about my Victrola? Answer:
Buy the book "Look for the Dog" by Robert Baumbach. It
lists all Victor models, starting with the open horn machines.
Some were quite rare; most very common. Production
figures are given. Buy the book from Allen Koenigsberg,
502 E. 17th Street, Brooklyn, NY 11226. Phone 718-941-6835.
Question: Where can I find out about record auctions? Parts?
Supplies for old phonographs? Answer: Join MAPS, the Michigan
Antique Phonograph Society, 2609 Devonshire, Lansing, MI
48910. Phone John Whitacre at 517-482-7996. After you join,
purchase the Resource Directory. It lists hundreds of
dealers and places to buy records and get your phonograph
serviced. It also lists other clubs.
Question: I want to buy an Edison Standard. Can you name
some dealers in my area?
Generally the answer to this question is unfortunately 'no.'
The market for used phonographs remains fragmented. In certain
areas there are well-known dealers. But you are not going to
find one listed in every city. Antique malls often sell machines
that are offered to them. Prices can be high.
Question: I just found a phonograph. I can't remember the name.
Who made old phonographs anyway? Answer: The phonograph was
invented by Thomas Edison. He let it sit on the shelf for 10
years. His patents covered cylinder records, the original format.
Later Berliner obtained a patent for what we call today the 78.
Its virtue was that the 78 could be mass produced easily.
Victor took up the Berliner patent. Edison stayed with
cylinder records. By 1920 it seems as if every furniture
store would put together a case and generic works and a new
brand was born. Sometimes Edison would sell spare cases so
conversion companies would put together parts from different
sources even in well-known cases. Some common brands:
Edison, Victor, Sonora, Brunswick, Silvertone, Zonophone,
Aeolian, Pathe, Granby, Columbia, Vocalian, Harmonola,
Heinman and others.
Question: Where can I learn about the history of the
phonograph? Answer: write to Allen Koenigsberg, 502 E. 17th
Street, Brooklyn, NY 11226. Request a collectors check list.
Most important books can be purchased through him. The
most scholarly is "From Tinfoil to Stereo, 1877-1929" by
Welch and Burt. Unfortunately, the authors concentrate on
the legal fights faced by early phonograph producers, and not
the technological problems the had to overcome to bring talking
machines to market successfully.
Koenigsberg also publishes the "Antique
Phonograph Monthly." It contains interesting articles about
phonographs. Be warned: it comes out every year or so, not
monthly. Since the history of phonographs is a hobby not
a scholarly undertaking, people do this sort of thing in
their spare time. Note: the Monthly has not come out for two
years now, so it may be finished. Check with Allen.
Question: What is a gramophone? Answer: The British refer
to a phonograph which plays flat records as a gramophone. In
British usage, a phonograph plays cylinders only.
Question: I just found an Edison cylinder player.
Where can I find out about how it works? Answer:
There is one authority on Edison players, both cylinder
and the Diamond Disc (DD) type. His name is George
Frow. He wrote two books which define the field.
The book on cylinder phonographs is just about to be
republished in a new edition called "Edison Cylinder
Phonograph Companion, 1877-1929." Available from
several sources, but I have a listing from Koenigsberg
listed above. The book is very complete, but its pictures
are very dark and detract from the excellent material.
The second book covers Edison Diamond Disc machines.
"Edison Diamond Disc Phonographs, 1912-1929." Frow
covers all models, including some which may have never
been made! His research comes from the Edison historical
site in Orange, NJ. Source: write Frow himself at
George Frow, "Salterns" Seal Hollow Road, Sevenoaks, Kent,
TN13 3SH England. He airmails the book, with no delay.
Check for current price. He took my personal check.
Also available from Koenigsberg listed above.
Question: Where can I find a list of cylinders which were
made? Answer: Wax cylinders made up until by Edison 1912 are covered
in a book written by Alan Koenigsberg, 502 E.
17th Street, Brooklyn, NY 11226. Celluloid cylinders
made by Edison are listed in a publication sold by
The City of London Phonograph and Gramophone Society (CLPGS),
Mr. Chris Hamilton, "Ardlarich," 2 Kirklands Park, Cupar,
Fife KY15 4EP, Scotland. Phone: 44 334 543 90.
Question: Are there any magazines which discuss old
phonographs? Yes: Personally, the most interesting
is Hillandale News published by CLPGS listed above.
It is a glossy magazine well produced. It contains
about 40 pages per issue. Also, the Michigan Antique
Phonograph Society has a monthy newsletter which answers
questions from readers.
Question: What are the most common old phonographs?
Answer: The phonographs which have survived today
are Edison, Victor and Columbia. Of the three, Edison
was the most sturdy, although Victor was often well made
also. The Columbia units used more pot metal, which
decays with age.
Question: Are all phonograph cyliders the same? Answer: Not all
phonograph cylinders are the same. The cylinder was the
original format for recording. The most commonly found
ones today are Edison's black wax (Gold Moulded) cylinders.
These play for 2 minutes. Columbia made 2-minute cylinders
wax cylinders until 1902, then switched to making their
cylinders out of celluloid. The celluloid cylinders are often
found today in excellent condition compared to their wax
counterparts.
Later everyone switched to 4-minute cylinders. Edison
always offered kits to upgrade his players. The
4-minute cylinders turned at 160RPM (as did most 2-minute
cylinders) and had 200 grooves per inch.
Edison produced 4-minute wax cylinders and later 4-minute
blue celluloid cylinders. The blue cylinders (called Blue
Amberols) were launched in 1912 and were made until 1929,
long after everyone else quit making them.
I have just found a phonograph in a brown case. When
as it made?
If the phonograph has a large external horn, it was made
before about 1912. After that, the ladies wanted horns inside
a case, hidden from view. If the unit you are looking at has
an enclosed soundbox in a pice of furniture, it was made
from 1910 or so up until the end of the wind up era about
1930. Not many phonographs were made from 1929-1945. The
depression caused a collapse of sales, with one authority
claiming that record sales declined by 90% during the 1930s.
Question: What is the difference between Victor and
Victrola? Answer: The Victor Talking Mahince Company
made external horn phonographs. When they switched to
horns inside of the case, the name -ola was added. Victrola
technically means an internal horn machine. Edison did the
same thing. He called his internal horn cylinder machines
Amberolas.
Question: I have some 78s I got from my family. I am afraid of
hurting them with a diamond needle. How can I play such records?
You can play 78s with a modern phonograph using a diamond needle.
If you have only a stereo stylus, you can still use it to play your
78s without hurting them. Of course, it is best to use about a 3 mil
needle made for the purpose. Modern equipment, tracking at 2 grams, is
quite gentle on records compared to the old Victors, tracking at
several ounces.
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono Radio General Questions(FAQ: 4/9)
Message-ID: <antique-radio+phono-faq-4-845766911@netcom.com>
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Archive-name: antiques/radio+phono/faq/part4
Rec.antiques.radio+phono Frequently Asked Questions (Part 4)
Revision Date Notes
1.1 Oct 24, 94 Was part 2, now part 3. New material and
revisions.
1.2 Dec. 5, 94 Added references to RCA Receiving Tube Manual,
corrections and new material.
2.0 Nov. 19, 95 Move from part 3 to part 4
Part 4 - General questions about vacuum tube radios and phonos.
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Email vancleef@netcom.com
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and electronic phonographs. It is intended to summarize
some common questions on old home entertainment audio equipment and
provide answers to these questions.
Q. I've got a <name of radio>. What's it worth?
A. This is the most frequently-asked question in this newsgroup. It is
also the most unanswerable question. You can count on a small home
entertainment set's being worth $5 or $10 if it is complete but not
working, and maybe twice that if it is in good condition and working. Some
consoles may be worth $40 or $50, and some high-end "boatanchor"
communications receivers may be worth $100 or more if they are
restorable. There are a few radios that are reputed to be worth
considerably more, but one very significant variable is geographic
location (in the US), another is whether the radio is shippable out of
an area with a weak market. You can get all sorts of opinions, but in
actuality, the only real way to determine a radio's value is to try to
sell it and see what you are offered. There are simply too many
variables to be able to place any reliable monetary value on antique
electronic equipment of any sort. You will soon discover that what is
being advertised over here for $500 is available over there for more
like $5.00. Good clean electronic equipment restored to good working
condition is worth more money, but generally much less than the costs of
restoration, if one includes any value for skilled labor in doing the
restoration.
Q. What is published to tell me what an old radio is worth?
A. There are some guides that list prices. The most commonly mentioned
is Bunis, Marty and Sue, "The Collector's Guide to Antique Radios." It
is available from Antique Electronic Supply. There are several other
books available from them for identifying old radios, some with price
information. What a specific radio actually is worth may be quite
different than what these guides list. In addition, the condition of
the radio (both cosmetics and electronics) has to be considered. "Antique
Radio Classified" is a buy-and-sell sheet, probably the most accessible
true market information available for inspection.
Q. I just got an old radio at a yard sale for $5. It is a Radio Wire
Television Model J5. When was this radio built? Can I get it to work?
Is this radio worth restoring? Can I get a schematic somewhere.
A. Requests like this send everyone scrambling for their references,
schematics manuals, etc. etc., and sometimes nobody responds. There is
some very basic information that you could, and should, include, that
would get you an answer instantly. If you included "this radio uses
five tubes. They are 12SA7, 12SK7, 12SQ7, 50L6, and 35Z5." See below
on "how to date radios by design features." Listing the tubes often
says everything.
The example used here is one of an endless long list of AC-DC table
radios built after 1940 using this tube complement. This type of set
is known as an "All-American Five." Most people who repaired radios
in the forties and fifties could draw the schematic for any of these
radios from memory----it's a case of "seen one, seen 'em all." This
particular radio has a grand total of 9 resistors (including volume
control), a whopping 14 condensers (including the tuning condenser as
one), three transformers, one oscillator coil, a loop antenna, a
loudspeaker, and a panel lamp. Add the five tubes, and that amounts to
the whopping sum total of 35 electrical components, and if you want to
insist on including the chassis, five tube sockets, cabinet, panel lamp
socket, and cabinet, we are still talking about 50 parts. No wonder
they sold for $4.98 in 1940. If it has value, it is for its case and
mechanical configuration. As a project radio to learn radio repair
and restoration, an AC-DC 5 or 6 tube table set is probably ideal. Most
of these sets need one tube (burned-out heater), new electrolytics and
paper capacitors to get it "working like new."
Typical schematics for All-American Five radios are given in the RCA RC
series and GE Receiving Tube manuals available in reprint from Antique
Electronic Supply. Actual production radios of this design had a
variety of subtle variations, but the typical circuits in the tube
manuals should help you find your way around one of these sets.
Q. I just looked at a Radio Wire Television model B45. It has 13 tubes
and two loudspeakers. I couldn't see all the tubes but I saw a 6H6, two
6L6's, two 5Y3's, and a bunch of metal tubes with top caps. It
has three bands, two shortwave, and a phono, and is in a custom-built
plywood cabinet. What can anyone tell me about this set. The radio
works, but not well. The owner wants $100 for it. Is it worth it?
A. This is the type of radio you should be asking questions about. The
radio itself is a "class act"---high fidelity, 1938 style. It's the
same manufacturer listed in the question above, and shows that
"brands" could range from absurdly cheap to top quality. It also is
typical of the radios that justified service shops paying good money for
Rider's manuals over the years.
As a "collector" radio, it's a difficult one to put dollar value on.
But as a museum piece, an example of what a high-end thirties radio was,
it is a class act. For those who have Rider XVIII, look at Radio Wire
page 18-8, and notice that only the schematic and a few notes are
published, some ten years after the radio was made. (confession: I owned
one of these from about 1948 until sometime in the sixties, and it was
my first really hard-core restoration project. It also was my "hi-fi
amplifier" for many years). If you want an example of high tech
history, it's well worth the $100, and if you restore it, you'll find
that quality is a lasting thing. But restoring a set like this can be a
major project and take a good deal of skill.
Other "high tech" radios that are more readily identifiable by brand
name are the Farnsworth Capehart sets and the 2-chassis Magnavoxes.
McMurdo Silver, E.H. Scott (Scott Radio Laboratories in Chicago) and
Radio Craftsmen are fairly well know high-end receivers. Many of these
last were sold as chassis only for custom installation.
Q. I saw a little table radio with a very pretty plastic case, but the
owner want hundreds of dollars for it. The case looks like marble, but
the radio inside is just another of those 35Z5 and 50L6 five tube jobs.
Why does the owner think its worth almost a thousand bucks?
A. Well, you've stumbled on the collectors' hot item of the nineties,
the "Catalin" case. The reason the owner thinks it is worth this much
is that the collectors' market seems to be willing to pay these prices
for a catalin case. Whether it will continue to do so is open to
question. It is difficult, in a FAQ item, to explain the whimsies of
the "collector" market, because these tend to change.
Q. Well, if a low-tech radio is worth hundreds of dollars because of
its case, and a high-end console with tremendous sensitivity and a
powerful amplifier with good fidelity is worth a lot less, what's the
correlation between price and value?
A. There isn't any. Some radios, such as the Atwater Kent TRF sets and
the RCA catacombs superhets are valuable because they are relatively
rare today, and represent technological history. An old communications
receiver, such as the Hallicrafters SX42, which was also sold as a home
entertainment radio, has much more value to a ham than an old Magnavox
radio-phono, so has value because of its technology. Novelty items,
particularly if they are rare, seem to be high-ticket "collectibles" in
any area. So you see dollar values attached to radios with reading
lights built in, radios with cameras in them, catalin cases, the Sparton
blue mirror sets, incredibly small portables, etc.
Q. I keep hearing about "Neutrodyne," "Regenerative," "TRF," and
"Superheterodyne." What do these terms mean?
A. The first home entertainment radios were crystal sets which used a
single tuned antenna circuit and a crystal detector. When tubes were
added for amplification, these were set up with tuned circuits that had
to be individually tuned to the station being received. These are "TRF"
sets, for "tuned radio frequency." Later on, manufacturers learned how
to build TRF stages using either mechanical coupling between the tuning
condensors or a single ganged condenser, and to provide adjustments to
get them to track (i.e., all tune to the same frequency across the range
of broadcast frequencies), so later TRF sets have one-knob tuning.
The Neutrodyne refers to a method of "neutralizing," or compensating
for, detuning effect of grid-plate capacitances by feeding back an
opposing signal. These sets are TRF sets with neutralizing circuits in
them---generally, another coil in the tuned circuit used to generate the
neutralizing signal.
The superheterodyne uses the physical principle that two oscillators
running at different frequencies will produce "beat" frequencies equal
to both the sum of and difference between the two frequencies. This can
be heard when tuning musical instruments; the principle is the same for
radio frequencies. The incoming RF signal is "mixed" with a local
oscillator signal and fed to a fixed tuned stage that is sensitive to
the difference frequency between the two signals. Use of one or more
fixed-frequency tuned stages gives the set relatively constant
sensitivity and selectivity, both of which are difficult to get in
variable tuned stages. To illustrate what these words mean, take a
common five-tube US table radio and a station at 1000 Khz ( 1
megacycle). An antenna coil and one section of the tuning condenser
(capacitor) are tuned to resonate at 1000 Khz, "selecting" that
frequency. A local oscillator is tuned by the other section of the
tuning condenser to 1455 Khz. In a set with a 12SA7 tube, the
12SA7 is wired as an oscillator, with the oscillator signal appearing on
the first grid (g1). The tuned RF signal is fed to the third grid (G3).
The plate circuit is connected to a transformer tuned to 455 Khz, to
respond to the difference between the frequencies being injected on G1
and G3. Signals at 455, 1000, 1455, and 1455 Khz all appear on the
12SA7 plate (the two fundamentals and the sum and difference), but the
tuned "intermediate frequency" (IF) transformer selects only the 455 khz
signal. This intermediate frequency is generally amplified by one or
more tuned (455 khz) stages---in our example, a 12SK7 with double-tuned
input and output IF transformers (i.e., both the plate and grid circuits
are tuned to resonate at 455 Khz) is used, and the output of that stage
is fed to the a diode detector.
This may sound a bit complicated, and I've left out all the fine points
of the design to focus on "what's supposed to happen."---a good
engineering text discusses design details beyond this description. One
point of terminology----the mixer stage (12SA7) was often called a
"first detector" in early designs; thus, the 12SQ7 diode detector in our
example is called the "second detector," a term that has persisted
through the decades.
One other common early design was the "regenerative" set. In these
sets, an RF amplifier was designed as an oscillator, but provided with a
control that could be adjusted so that the stage wouldn't go into
oscillation. The positive feedback in the stage provided substantially
more gain than a simple tuned circuit would provide. Misadjustment of
the feedback control would make the stage oscillate, producing squeals
in the output, and quite powerful RFI (radio frequency interference) as
well. The "superregenerative" circuit is a refinement that prevents
sustained oscillation, but was generally not used in home entertainment
sets.
(1/95) Roy Morgan forwarded me a description of the super-regen by Dan
Knierim for inclusion---here it is.
>P.S. What's the diff between a super-regen and a regen detector?
>I basically understand the regen circuit (gain stage near oscillation
>behaving as high Q filter) but I don't recall what the principle of
>the super-regen circuit is. And I'm definitely not an RF kinda
>guy these days.
A super-regenerative detector is a gain stage with positive feedback greater
than unity (so that it will oscillate), but with an RC circuit in the plate
or grid supply, so that the increased current during oscillation will lower
the gain over a period of time proportional to the RC time constant, and
finally kill the oscillation. Of course, once the oscillation quits, the
current draw goes down, the RC circuit recharges, the gain goes back up, and
the oscillation starts again. The frequency of this blocking oscillation is
set (by picking the RC time constant) to be well above audible frequencies,
but far below the RF oscillation frequency.
So how does it detect? Any RF input signal at the frequency of the main
oscillation (not the blocking oscillation) will help the main oscillation
restart when the stage is coming out of the blocking mode. If the RF input
increases, the main oscillation will restart faster, the stage will
spend a higher percentage of its time in the oscillating mode, and the
average plate current will be higher (where the average is taken over several
cycles of the blocking oscillation). Thus the detected audio output is just
the plate current run through a low-pass-filter.
The average plate current as a function of RF input amplitude is not very
linear; in fact it has a 1 / natural logarithm nature to it due to the
exponentially rising nature of an oscillator starting up. This makes the
audio quality from a super-regenerative detector low, but also acts somewhat
like AVC. The pk-pk audio output amplitude is more proportional to the
pk-pk RF input amplitude *ratio*. The steep slope of a logarithm near
zero also implies a high sensitivity with very small input signals, which
is one of the super-regens claims to fame.
Some of its many drawbacks are: it makes a racket when not tuned to an
input signal (in other words, it also has a high sensitivity to very small
amounts of noise, in the absence of an input signal above the noise floor);
it is tricky to keep running right; and it radiates like crazy if not
preceded with a separate RF input stage.
By the way, don't sneeze at regen sets just because they don't have a
lot of tubes. I recently read a posting in another group that talked
about a 1920's one-tube setup that blew smoke around some fancy radios.
Edwin Armstrong, who contributed the straight regen, the super-regen,
and FM, was a real genius.
Q. I have an old radio-phono. The radio works fine, but the phono
doesn't make any sound in the loudspeaker at all. What's the deal?
A. Your phono pickup probably uses a Rochelle salt crystal cartridge,
and the salt crystal has failed. You will need a new cartridge. (faq
editor note---I'm including this, and have a radio-phono with a dead
cartridge. What's available?).
Q. I just got an old radio that I think was made in 1939. But it has a
jack on the back labelled "television." It only has a volume
control/on-off switch and tuning control on the front. What's the deal
with the jack? How can a radio receive television, and why is a 1939
radio labelled like this when TV broadcasting didn't really begin until
after the war.
A. You are looking at a marketing ploy. The jack on the back is an
audio input jack, and if there is no switch for it, it is wired
permanently to the top of the volume control (detector output), so has
whatever signal the radio is receiving on it as well. Television was
"just around the corner" in the 1937-39 period and there were some
experimental stations broadcasting what is essentially NTSC video on
Channel 1 (48-54 Mhz) after 1936. Putting these jacks on the radios was
to convince the buying public that their new radio wouldn't be made
obsolete by television "next year." Commercial television actually
began in 1939, but WW II intervened, and the mass-marketing push for TV
did not begin until 1946-7.
Q. I have a console with 6L6's and a twelve-inch loudspeaker. Is this
"high fidelity?" Just what can I expect to hear from my old radio for
audio quality?
A. (9-95) A few readers have exercised your FAQ editor on the topic of
"high fidelity" in the AM band, generally citing the fact that
broadcast transmitters built after 1930 were capable of modulating at
frequencies above 10Khz. The evidence is clear that notwithstanding
transmitter capabilities, there were very few program sources available
to broadcasters that were capable of getting modulation above 5Khz to a
transmitter. Telephone lines used to transmit network programs had
this bandpass limit, as did standard home entertainment and jukebox
phonograph records. Transcription recordings were made at 33-1/3 rpm,
but were not the "microgroove" technology introduced in 1948.
The existence of "high fidelity" receivers in the thirties (either TRF
or using wide IF) is well-documented, but all evidence is that these
were sold for use with the experimental wide bandwidth stations,
particularly in the Northeast US. The vast majority of programming
matched the limited frequency response of most receivers.
The exception to this would be live music, played either in a studio or
in a local concert hall where a telephone link was not required, until
the advent of Armstrong's FM links between New York and New England in
1939.
Microgroove phonograph records with wide bandpass capability, and
magnetic recording, capable of operating beyond 20Khz, were introduced
in the late 1940's, allowing stations to use prepared program sources
that had a wider bandpass capability.
Q. When was magnetic recording introduced? I keep hearing about
"tapes" that were made in the 1930's.
A. You can rest assured that anything involved with home entertainment
was not recorded on magnetic media until the 1947-8 period, and not
regularly used for broadcast purposes until around 1952. While
magnetic recording, using a magnetic wire, was invented by a Dane,
Poulsen, in 1898, the need for a bias to overcome hysteresis distortion
was not recognized until the 1930's. Magnetic recording was used for
military purposes during WWII, which the Germans being the leaders
through much of the period. Wire technology became commercially
available in 1946, using a magnetic steel alloy (fortunately, corrosion
resistant) wire. Formulations for placing magnetic materials on tape
reliably were not available until around 1948, and reel-to-reel tape
only became common around 1951, replacing wire.
The method for getting response above 10Khz. in early magnetic
recorders was simple: move the medium quickly. Webster-Chicago wire
recorders move the wire at about 25 inches per second. Early tape
units operated at 15 IPS.
Worth noting that magnetic recording is not discussed at all in the
Radiotron Designer's Handbook, 4th edition (1952).
Q. I have a nice old Philco cathedral radio that I have listened to for
years. It only gets local stations, and even at maximum volume, is not
particularly loud. Can I get it to work better than it does now?
A. Probably. You have a sixty-year-old piece of electronic equipment
that has probably had two or three tubes replaced, and maybe one bad
capacitor, in those sixty years. In short, it's a candidate for an
electronic overhaul. Some things that may have degraded over the years:
a. Capacitors. Electrolytic capacitor problems generally make
themselves known quite quickly. However, those little wax-impregnated
"paper condensors" may all be leaking current and delivering less
capacitance than needed for good performance.
b. Resistors. These may have "drifted" to a much higher
resistance gradually.
c. Misalignment of tuned circuits. The "tweaks" on the tuning
condenser and the IF transformers generally don't drift very far unless
the coils have absorbed moisture. Altogether too often, the amateur
restorer will tweak the set out of alignment by fiddling with these.
Don't touch them unless you know exactly what you are doing and have the
equipment needed to align the radio.
d. Tired tubes. I put this last, although a lot of people look
here first, and assume that a tube tester's readings will correlate with
set performance. The best test for tube condition is to substitute a
known good tube in each position and seeing if it changes anything. A
sick pentagrid converter tube (6A7, 6A8, 6K8, 6SA7, etc.) may very well
test normally under DC conditions in a tube tester yet fail to oscillate
reliably in the set, particularly on shortwave.
Q. You say "electronic overhaul." Will that restore my set to like-new
performance?
A. Generally, yes---actually, better than new. Modern resistors and
capacitors are better circuit components than were available in the
thirties and forties. Capacitors in particular are much smaller, and
larger values can be used to advantage in some places, particularly in
the filtering circuits.
Q. Modern components? But if I put modern components like mylar
capacitors in the set, it won't be "original" any more.
A. There is a wide range of opinion about use of modern resistors,
capacitors, and wire in an old radio. Some feel that disguising modern
components in the shells of old wax paper capacitors is important. There
are (at least so far as your FAQ editor knows) no clear-cut guidelines
on the "looks" of components installed under a radio chassis. Consensus
seems to agree that all items that are visible when the chassis is
bolted in place should "look like the original radio did."
Q. I have a Philco battery-powered radio. It has a four-prong plug for
the battery. Can I get a converter at Radio Shack and use it to make my
radio work?
A. No. The battery radios required 1.5 volts for the tube filaments and
67-1/2 or 90 volts for "B" (plate) voltage. The 3-way portables
(AC-DC-battery) had built-in battery eliminators, and the tube filaments
were generally wired in series, requiring a 6 or 9 volt "A" battery.
You'll need to make a supply that can deliver 1.5 volts at about 400 ma.
and 90 volts at about 50 ma. for your four-prong Philco. Both have to
be good clean filtered DC. The power-pak-in-the-plug type power units
sold by Radio Shack and others are made to deliver 6-9 volts at
100-200 ma. unfiltered DC.
DATING OLD RADIOS BY THEIR TUBE COMPLEMENT
The development of vacuum tubes, both electrically and mechanically,
advanced at a rapid pace between about 1925 and 1950. The vast majority
of radios sold for home entertainment between 1920 and the late 1950's
were built to various standard circuits. In most cases, checking out
what tubes are used in the radio will place it's date of manufacture
within a few years, identify which of the standard circuits it used, and
give a some indication of the quality of the set. Most radio repair
technicians in the 1930-60 era did not need to look at schematics most
of the time, even when the problem was not a burned-out vacuum tube
heater or filament.
The tube complement is not always an accurate guide, except insofar as
the presence of a given tube indicates that the set was built after that
tube was placed in production. You won't find any 1932 radios using
tubes with octal bases or 6.3 volt filament heaters, and you won't find
any prewar radios with 7-pin miniature tubes. But you may find a 1946
table radio built to a 1935 design. There are also a few other design
features that are very obvious on casual inspection; I'll mention some
of them as we go along.
(New 12-94) In the following discussion, there are references to the
example circuits shown in the RCA Receiving Tube Manual RC-19, dated
1959. This manual is available in reprint from Antique Electronic
Supply. Examples 19-1 through 19-4 in particular show examples of four
standard circuits that were used, either identically or with minor
modifications, in the majority of the smaller "collectible" radios built
from the mid-1930's on.
1. The five or six-tube AC-DC radio with 150 ma. tube heaters wired in
series. Example circuit 19-4 shows one of these radios, using 7-pin
miniature tubes. This design is colloquially called the "All-American
Five" by some of us. The design was first built in 1939, using octal
tubes (i.e., 35Z5 and 50L6 in place of 35W4 and 50C5), so it is also
called by some a "35Z5 radio" or a "50L6 radio." I list this design
first, not only because it dominated home entertainment radio production
for over 20 years, but because it is a very simple superheterodyne
circuit. If you study this circuit and know what every component's
function is, and study an example radio of this design, you'll be
prepared to trouble-shoot and repair most post-1935 radios.
These sets do not have a power transformer, and could operate
in places like mid-Manhattan, which had 110 volts DC as its primary
electrical service. Most of these were built as table radios, although
some were installed in small consoles and radio-phonograph combinations.
Virtually all clock radios use this circuit. These are generally
AM-broadcast-only. The tube set shown in the example is one of three
common sets, having either octal, loctal, or 7-pin mechanical design,
but electrically equivalent. Some sets, particularly in the early
postwar period, were built with mixtures of tube mechanical types,
because of tube shortages and availability, and some sets used more than
one configuration during their production runs.
The six-tube version had an RF preamplifier, and was more sensitive than
the five-tube. Example circuit 19-3 shows the same
basic design with an RF preamplifier stage, with tuned output
(three-section tuning capacitor). Many of the six-tube versions used
resistance coupling between the RF preamplifier and the converter stage
(see Diagram no. 3, p. 339, in RC-19, for a resistance-coupled pentode
circuit). The six-tube version was often called a "35L6 radio" because
a 35L6, 35A5, or 35C5 was used, allowing connection of one more 12-volt
heater in the series heater string. In the fifties, some of these radios
were built with a selenium rectifier, omitting the rectifier tube.
Also, a few manufacturers built a four-tube version that omitted any IF
amplification.
Several low-end "boatanchor" communications sets used this circuit,
adding multiple tuning coils and provisions for a beat-frequency
oscillator. Notable examples are the Hallicrafters S-38, S-41, S-119,
S-120, and Ecophone EC-1 series; and the National NC-46 and SW-54.
The tube complements are:
a. First version, built primarily 1938-40.
(note: this design is similar to the 19-4 example, but is its immediate
prececessor, so has a few substantial differences, noted below).
12A8 RF-converter, 12K7 IF amplifier, 12Q7 detector-audio, 35L6 power
output, and 35Z5 rectifier. The first three tubes had small top caps
for the signal grid connections, with either metal or glass envelopes.
The original glass tubes had a "G" suffix, indicating use of an ST-12
stepped bulb envelope. The major difference between this design and
that shown in example 19-4 is the use of a 12A8, which uses a slightly
different oscillator circuit than the 12SA7, 14Q7, or 12BE6. The other
top-cap tubes are very similar to the single-ended octal tubes which
followed, varying primarily in mechanical construction. 12J8 and 12K8
were sometimes used as converters as well. RC-19 unfortunately omits
any circuits for these converter tubes. This version uses a series
resistor in the heater circuit because the heater voltages do not add up
to "near 120"). The proper place for this resistor, electrically,
is between the rectifier heater and the power amplifier heater.
b. Second version, built 1939-ca. 1960
12SA7 RF-converter, 12SK7 IF amplifier, 12SQ7 detector-audio, 50L6 power
output, 35Z5 rectifier. This is almost the same radio, but using
single-ended tubes in the first three stages and a power output tube
with a 50-volt heater. The major difference is in use of a 12SA7 in
place of the 12A8---these tubes are different internally. Note that the
sum of the nominal heater voltages adds up to 122.8 volts, allowing
operation without need for any series resistor in the heater circuit.
c. Postwar version, 1945-mid '60's
12BE6 RF-converter, 12BA6 IF amplifier, 12AT6 detector-audio, 50B5 power
output, 35W4 rectifier. The only difference from b., above,is the use of
seven-pin miniature tubes. All are electrically identical to the octal
versions above. Some sets were built using a mix of seven-pin miniature
and octal tubes, however, the presence of seven-pin miniature tubes
indicates that the set is postwar production.
d. Loctal tube version, 1940-ca. 1960
14Q7 RF-converter, 14A7 IF, 14X7 detector-audio, 50C5 power output, 35Y4
rectifier. Once again, the same radio as version b., using loctal-base
tubes in place of octal. Philco and GE were fond of using loctal tubes.
Note that some radios used a 14B8 converter, which is the same
configuration in a circuit as the 12A8.
The six-tube configuration used the same tube type for both RF
preamplifier and IF amplifier, and the 35 volt heater version of the
output tube. In most cases the RF preamplifier is resistance-coupled to
the RF-converter stage, and the radio used a two-stage tuning capacitor.
Some later versions used movable slug tuning in place of a variable
capacitor. This variation began around 1947, and became more common
during the next decade.
2. Five or six tube AC-DC transformerless radios using 300 ma heaters
wired in series.
These radios were the precursors of the 150 ma. series heater
radios. Some of these radios also included a tuning eye indicator,
typically a 6E5. Total voltage drop of the series heater string was
68-74-82 volts requiring an external voltage dropping resistor of
some sort. These radios often used "ballast" tubes or resistance wire
in the line cord for this purpose.
a. Version using large-base 5, 6, or 7-pin tubes, 1935-50.
6A7 RF-converter, 78 or 6D6 IF, 75 detector-audio, 43 power
output, 25Z5 rectifier. Most of these sets were built before 1938,
although a few manufacturers built them in the early postwar era.
There are more variations on this design than on the 150 ma. heater
designs described above. As noted, some sets had 6E5 tuning eye tubes.
Sets with shortwave often had a 76 triode as a separate local oscillator
for the 6A7.
b. Version using top-cap octal tubes, 1936-1950's.
6A8 RF-converter, 6K7 IF, 6Q7 detector-audio, 25A6 or 25L6
audio, 25Z6 rectifier. This reflects the switch to octal tubes in 1936.
The first three tubes had small top caps for signal grid connection.
The 25A6 is an octal version of the 43; the 25L6 is a 25 volt heater
beam power tube identical, except for heater, to the 35L6 and 50L6. The
25Z5 is a full-wave rectifier (two diode sections), and was usually
connected with the two sections in parallel. However, some
manufacturers, notably Philco, used the two sections to provide voltage
doubling for B+. Radios with voltage doubler power supplies are
AC-only, as a voltage doubler requires alternating current to "pump" the
doubler circuit.
c. Version using single-ended octal tubes, 1939-50's.
6SA7 RF-converter, 6SK7 IF, 6SQ7 detector-audio, 25L6 output, 25Z6
rectifier. Once again, this is a "switch," this time to single-ended
octal tubes. Major circuit difference is in the 6SA7 circuit because of
differences internally between the 6SA7 and 6A8.
This version was generally not built as a "price leader" inexpensive
table radio because of the availabity of 150 ma. tubes that didn't
require a dropping resistor in the heater circuit. It was very often
used as the basis for an upscale AC-DC radio. Some configurations that
you may run across:
1. Shortwave receiver using an additional RF preamplifier,
separate local oscillator, and second IF stage. The 6SK7 was used for
the RF and IF stages, and a 6J5 as a local oscillator.
2. Push-pull audio output, using two 25L6 tubes and a 6J5 as a
phase inverter. This may be combined with the RF-IF additions, above,
and a tuning eye tube (6E5 usually).
Note that use of rectified line voltage gives a relatively low B+, a
major limitation in the transformerless design. The primary market for
a "full house" receiver that had all of these features would have been
the DC service metropolitan areas, particularly New York City, and that
is the general area where most "odd-ball" configurations of
transformerless sets can be found today. In summary, all of the designs
identified in items 1 and 2 above either used the circuit shown in RC-19
example 19-4, or fairly simple variations of the design. There are very
few radios with these tube complements that vary markedly from the
design, which was established around 1932, and licensed to builders
through Hazeltine and RCA patent licenses. In general, the sets that
deviate markedly from the standard circuit are a few Philcos and
Zeniths, and some off-brand sets that may have been marketed through
chain stores with chain store brand names.
3. Postwar AM-FM sets, 1945-up. These were made in two
configurations: separate FM front end, and common front end (i.e, RF,
IF, mixer, and IF amplifiers. There are many variations on both
designs, using 7-pin miniature tubes, loctal tubes, or "hot" octal
tubes. The 6SB7Y was a "hot" 6SA7-type tube capable of self-exciting
oscillation at FM frequencies, and the 6SG7 a "hot" replacement for the
6SK7. The presence of 88-108 MC FM in a radio always means that it is a
postwar set, as this band was not assigned to FM until April, 1945.
Manual RC-19 shows an example of an FM tuner in example 19-9. Many
AM-FM sets "merged" AM capability into the FM tuner design by using a
bandswitch in the RF and converter stages, and by connecting IF
transformer coils for 455KC and 10.7 Mc. in series, the idea being that
the desired frequency will cause one or the other to resonate (high
impedance) and the other will appear as a low DC resistance. The
bandswich would also select which IF fed the AM detector, and which
detector's output was used to feed the audio section. Example 19-9 also
shows both the limiter-discriminator and the ratio detector designs
commonly used in FM-capable sets.
This ends the "most common" AC-DC section. Now we will consider
history, and some of the other designs.
Example 19-1 in RC-19 shows a later battery-operated portable, using
7-pin miniature tubes. This design was built after about 1934,
originally using 5-6 pin tubes in ST-12 bulbs; later, octal or loctal
tubes. This circuit also is the basis for most later battery-operated
"farm" sets, some of which were built as floor consoles. Close study of
the circuit will show its resemblance to the 19-4 example. A very
significant difference is the use of filament tubes, and the method of
using a back-bias resistor (R10 in the example) to develop grid bias
voltage for the output tube. Note also that a different local
oscillator circuit is used for the 1R5. This circuit was often used in
the "All American Five" design as well, and is not unique to the battery
design. Resistance values in example 19-1 have been chosen for
operating with a 67.5 volt B battery; otherwise, the circuit is suitable
for operating with a 90 volt B battery.
Example 19-2 shows a typical three-way portable. The term "three-way"
may seem confusing, when the radio can be operated either from the power
line or from batteries. However, the fact that it could operated from
110 volts DC as well as from AC lines was considered noteworthy when DC
domestic service was common; thus "AC or DC or internal battery" are the
"three ways." Note that a modern ricebox radio operating on an internal
battery or with an AC adapter is not "three way" as it will not operate
from a DC line.
Once again, this is the Hazeltine-RCA standard circuit used in examples
19-1 through 19-5, with specific provisions for the three way feature.
Example 19-2 also shows use of a double-tuned RF preamplifier.
Notable are the use of series connection of the receiver filaments,
provision of a rectifier, and a changeover switch. In practise, many
manufacturers provided a dummy line-cord outlet inside the receiver.
Plugging the line cord into this outlet would mechanically actuate the
changeover switch, placing the receiver on battery operation. When
studying this circuit, note in particular the order in which the tube
filaments are wired, and the use of an 1800-ohm resistor (R14) in the
3V4 filament circuit to provide a shunt-feed balance current. The order
of connection of series-wired heaters and filaments is significant in
series-string sets. In this case, the 3V4 is connected to the high end
to provide grid bias for operating, and the shunt resistor provides some
of the plate and screen currents for the tube. The rectifier circuit
shown is typical, although three way portables may use a 35Z5 or a
selenium rectifier. DC output from the rectifier is around 120 volts,
depending on the rectifier used, which requires a large dropping
resistor to feed the receiver filaments. Note the use of two large
electrolytic filter capacitors, C28 and C29, connected to either end of
the 3V4 filament. Small filament tubes require "clean" DC power, thus
these two capacitors filter out both residual ripple from the half-wave
rectifier and audio-frequency variations caused by varying power draw of
the power tube. This circuit arrangement is critical. If any filament
opens, one or both of those capacitors will charge up to the rectifier
output voltage. Also, the design assumes that the rectifier is part of
the voltage-dropping string, and 1.5V filament tubes are limited in
their ability to handle out-of-tolerance filament voltage.
The circuit shown in figure 19-3 for an AC-operated receiver is the same
as that in figure 19-4, with several upscale features, and resistance
values selected for operation at 250 volts B+ rather than 120. Note
that the circuits for the 6BE6 converter, 6BA6 IF, and 6AV6
detector-audio stages have the same configuration as those shown for
those three stages in figure 19-4. An additional 6BA6 RF preamplifier is
provided for higher gain and better selectivity. A pair of 6AQ5 tubes
provides push-pull output. The second 6AV6 placed ahead of the lower
6AQ5 grid circuit inverts the audio signal for grid drive, with
"approximately unity gain," determined by the tapped grid leak
(470K/8200 ohms) in the top 6AQ5 circuit. This particular circuit is a
classic example of older home entertainment engineering, and there is
much to criticize in its selection over the use of a twin-triode
balanced paraphase using a 12AX7 or a 6SN7. Why was it chosen? Habit,
probably---it was a good choice for 1932.
The main feature of this set which differs from AC-DC configuration is,
of course, the use of a power transformer and a 5Y3 full-wave rectifier.
The configuration of the rectifier circuit was one of the earliest and
most durable circuits in the history of tube-type home entertainment
radio. This later configuration uses a 5Y3 instead of an 80, has larger
filter capacitors (20 mfd rather than 8 or 10 mfd), and a resistor in
place of an inductance between the two filter sections. Older radios
most often used a speaker field coil between the two filter sections,
partly because Alnico magnets were not available until the late
thirties, and partly because inductance at this point compensates for
using smaller capacitance values to get good filtering.
Note the configuration of the screen circuit for the 6BE6 and two
6BA6's. All three screens are connected together. This is poor design,
and likely to cause parasitic oscillations. The circuit in figure 19-4
also shows the screens connected together, but in this instance, there
are only two screen, in stages that operate in opposite phase, so any
coupling between the two stages has a negative feedback effect.
Older radios:
Home entertainment radio began in 1920. KDKA in Pittsburgh generally
has gotten credit for being the first commercial broadcast station. The
two major receiving tubes available at the time with the UX201 and the
UV199, as they were called at the time. The UX201, later revised and
called 01A was a low mu triode. The V99, as the UV199 came to be
termed, was derived from a telephone amplifier triode, developed
during WWI. Several manufacturers built sets, but the most predominant
in the collector market is the Atwater Kent neutrodyne TRF set using
01A's driving headphones. A standard inexpensive set used regenerative
feedback to achieve gain. These were prone to oscillate, squawk, and
whistle, and created no end of radio frequency interference, and rapidly
lost favor, particularly in high-density metropolitan areas.
The first commercially significant superheterodyne receiver was the
RCA "catacombs" receiver of 1924. This set used V99's, a 42 KC IF
frequency, and a headphone-driving-a-horn "loudspeaker." Both the
A-K and the RCA sets required three DC voltage supplies.
The A supply (5 volts DC for 01A, 3.3 volts DC for V99) heated the
filaments. The B supply, typically 90 volts, provided plate voltage.
The C supply, ranging between 9 and 15 volts, and connected as a
negative supply, was used to bias the tube grids. RF gain was
controlled by a rheostat which controlled the filament voltage. These
three voltages were supplied by lead-acid storage batteries, with a
Tungar bulb charger for charging the batteries when the radio was not
being used. All of the RF stages, and the catacombs superhet local
oscillator, were tuned by separate dial knobs.
If this sounds like the definition of a kloodge, it was. I had examples
of both an O1A Atwater Kent and an RCA "portable" (ran on dry batteries)
catacombs set, complete with lead-acid batteries and Tungar charger, at
the end of WWII. These sets sold by the thousands, but were obsolete by
1929, and most of them were discarded when their storage batteries wore
out. Worth noting that "Philco" is a contraction of "Philadelphia
Storage Battery Company." It is also worth noting here that RCA, or
"Radio Corporation of America," was not a separate company until 1929,
but a patent pool and sales company owned by General Electric,
Westinghouse, and AT&T. The phonograph fans will, no doubt, describe
how the Victor Talking Machine Company and Radio Corporation of America
became RCA Victor.
Automatic volume control methods were developed around 1925. AVC, which
is synonymous with the term "Automatic Gain Control" (AGC), allowed sets
to operate at much higher input sensitivity, and to reduce that
sensitivity to prevent overloading in the presence of a strong signal.
Methods of tracking RF stages and a local oscillator operating at some
difference frequency were also developed in the mid-late 1920's. The
final developments needed to build a mains-powered single knob tuning
"modern" superheterodyne radio were filaments capable of working on AC
without developing hum, a suitable high-voltage rectifier, and a tube
with high plate resistance. The first two appeared around 1928 in the
form of the 26 and 71A tubes and the 80 rectifier. While these were not
the actual "first" devices, they appear in almost all of the early
mains-powered radios. The third came about a year later in the form of
the UY224 tetrode, later known as the 24A. The 24 also had another
recent innovation, the indirectly-heated cathode, which allowed the
cathode element of each tube to "float" at a different voltage from the
heater supply DC reference.
Problems with secondary emission from the 24 were "cured," more or less,
by processing the plate material to reduce this emission. This produced
the 24A. However, a more permanent fix was to include a third grid to
"suppress" the reverse current resulting when plate voltage was lower
than screen voltage. The 57 and 58 pentodes were the result. Both have
2.5 volt indirectly-heated cathodes. However, the 58 has a
characteristic known as "variable-mu." Actually, with pentodes, one
considers transconductance, and what "variable-mu" actually does is to
reduce the transconductance as the tube is more heavily biased. The
feature is desirable in circuits with AVC. These pentodes showed up
around 1931. The pentode power amplifier was also introduced around the
same time, with the 47 replacing the 45 in many designed of the 1932-34
era.
The last significant development in tube design for AM broadcast radios
was the development of a single tube with two control grids to serve as
a self-exciting local oscillator and mixer amplifier. The 2A7, quickly
replaced by the 6-volt-heater equivalent 6A7, was the predominant
design, and the 6A7 was used very commonly until after 1940. The 6L7
also was introduced fairly early. This is a mixer that is not designed
to operate as a self-oscillator, and was used, particularly in
communications sets, with a separate local oscillator, until the
1950's.
Availability of a single tube for the superheterodyne oscillator-mixer
function was essentially the death-knell for TRF designs. Another
contemporary development which entered production in 1933 was the 2E5
"tuning eye" tube, which varied a shadow area on a visible target as an
inverse function of the control grid voltage. TRF sets were built into
the 1950's, but are not very common. They tend to be either very cheap
radios for use in metropolitan areas with strong signals or in high end
sets where the broad bandpass allowed "high fidelity" (though the
AM stations actually only transmit a signal that has 5KC as the 3db
half-power point in the modulation).
Availability of components for a vibrator power supply made automobile
sets operating from 6 volts DC practical. There was a wholesale switch
from 2.5 volt heaters to 6.3 volt heaters in 1934. The 2.5 volt heater
series of tubes quickly became obsolete. The switch to 6.3 volt 300
ma. filaments was parallelled by development of a two-diode rectifier
and an output tube with 25-volt 300 ma. heaters, making series string
wiring of the heater circuit practical. These are the 300 ma. heater
transformerless sets described above, which date from about 1934.
Octal-based tubes enter the picture in 1936. Many of the original
designs were built in self-shielding steel envelopes. Metal octal tubes
were built with a flat "button" glass seal, which allowed much shorter
electrode lead connections. Early glass octal tubes continued to use
the older "press" design, with relatively long leads. RF and AF tubes
in the original octal series had small top caps for connection to their
control grids. It was not until about 1939 that single-ended tubes
entered production.
Development of a button seal that could be used with glass envelopes
allowed manufacture of metal-based "loctal" tubes. These entered
production in 1939. At the same time, a cylindrical bulb for glass
tubes also entered production, allowing closer spacing between tubes.
Experimental FM became a commercial broadcast enterprise in 1940. The
original FM band began at 42 megacycles, and production of home
entertainment receivers to receive that band began in 1941. The band
originally overlapped the experimental television band (later channel 1,
48-54 megacycles). The FM band was reallocated to 88-108 megacycles in
the spring of 1945, thus a set with 88-108 capability is postwar.
Another "strictly postwar" feature is the 7-pin miniature tube. The
9-pin miniature followed around 1949.
A few tubes were "survivors" through the 1928-50 period. The standout
among these is the 80 rectifier, which was still being used in new
production in the mid-1950's. The 5Y3GT which replaced it is nothing but
an octal-based version of the 80. The 2A3 and 45 power triodes, as well
as the less-common 6A3 were all used from the early 1930's until well
into the 1950's. There remains today something of a cult that
believes that these triodes are the only audio power tubes worth
considering. All of these tubes use filament cathodes, and the most
practical circuits for using them required a separate filament winding,
elevated to the 40-60 volts needed to bias these tubes near cutoff.
Beam power tetrodes were introduced as octal tubes, although the 807
(very rarely seen in the home entertainment market) continued to use the
older large 5-pin base. The principal beam power tetrodes were the 6L6,
6V6, and 25/35/50L6. The 6L6 in a push-pull circuit required more
current than a 125 ma. 80 could provide, and presence of a pair of 6L6's
with a bigger rectifier means a "high-end" set. Push-pull 6V6's could
be supplied by an 80 and provide very adequate audio power of good
fidelity to the open-mounted loudspeakers used in virtually all home
entertainment equipment until the mid-1950's. Generally, a push-pull
power output stage, using any pair of triodes, beam tetrodes, or
pentodes, means a quality set with other desireable features, low hum,
and good sensitivity.
The various oscillator-mixer tubes used can affect a radio's ability to
perform, particularly on shortwave bands. Historically, the first such
tube was the 7-pin 2A7/6A7, followed by the octal-based 6A8, all using
the same pentagrid construction and circuit. These operated well on AM
broadcast, but had severe problems dealing with higher frequencies.
While they were commonly used (particularly the 6A8) into the late
forties, they generally give very poor performance on shortwave bands
above 10-15 Mc (40 meters). The 6L7 was developed as a mixer to be
driven by a separate local oscillator to overcome some of the
limitations of the 6A8. The separate-section 6J8 and 6K8 were developed
to provide better high-frequency performance without need for a separate
local oscillator. These tubes can operate well up to about 25 mc. The
loctal versions (7J7, which is the same as a 6J8, and the 7S7, which is
a higher-gain 7J7) would operate over 30 mc. (10 meters.). The final
version was another layout of the 6-grid "pentagrid" design, the 6SA7.
The 6SA7 would operate, with the inner section as an oscillator, up to
about 27 mc. The 6SB7Y octal, 6BE6 7-pin miniature, and 7Q7 loctal all
would operate satisfactorily up the commercial FM frequencies. A common
method for getting better high-frequency performance was to use a
separate local oscillator with a 6L7, 6SA7, or 6BE6. Glow-discharge
voltage regulator tubes were commonly used in high-end communications
designs to regulate B+ to the local oscillator, giving improved
stability to the circuit. For serious shortwave listening, you should
avoid a set with a 6A7 or 6A8, and consider one with a separate local
oscillator (typically a 6C5, 6J5, or 6C4) and a voltage regulator tube.
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono Radio Spares and Services(FAQ: 5/9)
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Archive-name: antiques/radio+phono/faq/part5
Rec.antiques.radio+phono Frequently Asked Questions (part 5)
Revision Date Notes
2.0 11-1-94 Revised version from Aaron Field. (this version was
previously posted to the newsgroup).
2.1 1-7-95 Added some material to Aaron's list.
2.2 7-8-95 Removed Aaron Field's address as he apparently no longer
has an Internet account at the address listed. Our thanks to Aaron for
having done the work to get this list started.
3.0 10-95 Did a whole bunch of work on the list. Added material on
tubes and schematics.
3.1 Nov 19, 95 Move from part 4 to part 5
3.2 4-96 Add new sources, tube buyer notice
Part 5 - Sources of materials, supplies, and bibliography for antique
electronics
------------------------------------------------------------------------------
The most frequently asked question is "where can I get vacuum tubes?"
TUBE SELLERS:
Antique Electronic Supply
6221 S. Maple Ave
Tempe, AZ 85283
Tel: 602-820-5411
Contact Daily Electronics
P.O. Box 5029
Compton, CA 90224
Tel: 800-346-6667 (Orders)
Tel: 213-774-1255 (Tech)
Don Diers
4276 North 50 Street #SC3
Milwaukee, WI 53216-1313
DNF
6690 7 Mile Road
South Lyon, MI 48178
Electron Tube Enterprises
Box 8311
Essex, VT 05451
Tel: 802-879-7764
Fair Radio Sales
Lima Ohio
Phone: 419-227-6573
Kirby
298 West Carmel Drive
Carmel, IN 46032
Lippert N61W
15889 Edgemont
Meno Fls, WI 53051
New Tube Co.
P.O. Box 202
Middle Village, NY 11379
Tel: 718-894-2131
Quest Electronics, Inc.
5715 W. 11th Avenue
Denver, CO 80214
303-274-7545 Voice
303-274-2317 Fax
Steinmetz Electronics
7519 Maplewood Ave
Hammond, IN 46324
Tel: 219-931-9316
Michael C. Marx
SND Tube Sales
5389 Ville Rosa Lane
Hazelwood, MO 63042
314-770-0119 phone
314-770-9448 fax
email: tubes@i1.net
(furnished by Dan Schoo)
(Note, this is not a supplier, but a buyer of old tubes. I'm copying
the posting slightly trimmed down).
-----------------------------------------------------
I am the Purchasing Agent for Antique Electronic Supply in Tempe, Arizona. We
purchase tubes (or valves, as the English call them!) for resale. Anyone who
is interested can contact me at tubes@crzyone.com, and I can send them via
email the current bid list for tubes we have a need for and our current bid
prices.
For further information, email me at the above address or call (602) 820-5411.
If you want to check out the web sites for a couple of tube manufacturers, try:
http://www.svetlana.com for Svetlana Electronic Devices
http://www.rell.com for Richardson Electronics.
Edward C. Bender
-----------------------------------------------------
Q: Where can I get tubes, electronic parts, knobs, dial lenses,
grille cloth, schematics, literature, refinishing supplies, etc.?
A: The following suppliers carry a variety of merchandise for
collectors and restorers of vintage radio/phono/TV/jukeboxes. Catalogs
or inventory lists are available from all of them. Following this list
is a directory of commonly needed items, with additional sources.
1. Antique Electronic Supply, 6221 S. Maple Ave., Tempe, AZ 85283,
(602)820-5411: Great source for tubes, components, restoration
supplies, books, etc. If you're new to the hobby, start with
the AES catalog--it's indispensible!
2. Puett Electronics, P.O. Box 28572, Dallas, TX 75228,
(214)321-0927: Incredible supply of literature and service
data, also some parts. Good source for collectors of
E.H. Scott and McMurdo silver radios.
3. Play Things of Past, 3552 West 105th St., Cleveland, OH 44111,
(216)582-3094: Plenty of hard-to-find parts for the earliest
radios, including rare tubes. (Probably the best source for
original parts on 1920's sets.) Lots of literature as well.
Excellent catalog.
4. Old Tyme Radio Company, 2445 Lyttonsville Rd., Silver Spring,
MD 20910, (301)585-8776. Tubes, vintage parts, radios,
test equipment.
5. Great Northern, P.O. Box 17338, Minneapolis, MN 55417,
(61) 727-2489: Lots of stuff for collectors of Zenith radios--
parts, literature, T-shirts, service data.
6. Vintage TV and Radio Supply, 3498 W. 105th St., Cleveland,
OH 44111, (216)671-6712: Nice selection of books, tubes,
knobs, components, refinishing supplies, etc. Much better
knob selection than AES (#1 above). Good catalog.
7. Wade's World of Knobs (Wade and Joe-Ann Terrell), 7109 E. Arbor Ave.,
Mesa, AZ 85208, (602)830-7849: Reproduction plastic knobs and dial
lenses, etc.
8. Antique Radio Labs, R1, Box 41, Cutler, IN 46920, (317)268-2214:
Limited selection of various parts and literature.
9. Don Diers, 4276 North 50th St., Milwaukee, WI 53216-1313:
Nice selection of tubes and vintage parts. Tons of caps!
Fun to read catalog!
10. Triode Electronics, Box 578751, Chicago, IL 60657, (312)871-7459:
Jukebox needles, cartridges, tubes, other parts.
11. A.G. Tannenbaum, P.O. Box 386, Ambler, Pa. 19002;
Tel: 215-540-8055: Vintage parts and literature, test equipment.
NOTE: Tannenbaum has moved. New address per their telephone recording
is PO
Additional sources are contained in the following directory of
commonly needed items. The list is currently geared mainly towards
radio, but phono/TV/jukebox collectors should find useful sources
here as well. The sources listed above are referred to by number.
Books--
Best source for currently published books on collecting and restoring
radio/TV/phono etc. is #1! For vintage literature, see "Literature"
listing below.
Capacitors--
#1, #6, #10 all have good selections. #10 may be the best.
Custom rebuilds on single or multi-unit can caps are available from:
Frontier Electronics, 403 S. McIntosh St. or Box 38,
Lehr, ND 58460, (701)378-2341. Price list available.
Coils--
#1,3,4,6,8,9 all have various coils, chokes, and transformers,
both originals and replacements. (Try #3 first for original
1920's and 30's stuff).
Decals--
Decal reproductions of the following logos are available from
#1,4,6 (and probably others): Philco, Atwater Kent, Zenith,
Stewart-Warner, RCA, Stromberg-Carlson, Admiral, Emerson, GE,
FADA, Garod, DeWald, Belmont, Sonora, Magnavox Lion (for horn
speakers).
Dials--
Reproduction tuning dials available from:
Antique Radio Restorations, 635 S. Lincoln Ave.,
O'Fallon, IL 62269, (618)632-7423. (AK, RCA, Zenith, Philco)
Also try #1,2.
Dial covers--
Reproduction dial covers custom made from broken cover or tracing:
a. #7
b. Doyle Roberts, HC-63 Box 236-1, Clinton, Arkansas 72031,
(501)745-6690.
c. Old Time Replications, 5744 Tobias Ave., Van Nuys CA, 91411,
(818)786-2500.
Limited selections of original dial covers available from #1,2,4,6.
Dial pointers--
#6 has a few generic replacements if you can't find an original.
Grille cloth--
a. Good selections from #1 and #6. Sample cards available.
b. John Okolowicz, 624 Cedar Hill Rd., Ambler, PA 19002,
(215)542-1597: "Deluxe Replica Grille Cloth" (Philco,
Emerson, Scott, Zenith).
Knobs--
Best selection of reproduction knobs from #6 (check here first
for clock radio knobs) and #7. #1 not bad for Zenith and Philco.
Most suppliers say "many available, send us your request".
Lamps--
#1,3,6 and 9 all have good selections.
Literature--
#2 and #3 have impressive archives of vintage radio literature,
with titles listed in their catalogs. #1 and #6 have reprints
of popular service manuals and repair data (AK, Philco, Radiola,
Zenith). Also see "Schematics and Repair Data".
Periodicals--
a. "Antique Radio Classified" (monthly), PO Box 2-V32, Carlisle,
MA 01741, (508)371-0512: Classified ads, radio supplier ads,
articles, meet announcements.
b. "The Old Timer's Bulletin" (quarterly, with membership in
Antique Wireless Association), dues $12.00. Contact AWA, Box E,
Breesport, NY 14816. High quality publication chock full of
articles on all areas of vintage radio, including broadcast,
communications, telegraph, TV, etc.
c. "The Radio Collector" (monthly), PO Box 1306, Evanston,
IL 60204-1306, (708)869-5016: published by Marc Ellis, antique
radio columnist for "Popular Electronics" for many years.
Regular features include repair and restoration advice, vintage
book reviews, company chronicles, Q&A, classifieds. $20.00/yr.
Highly recommended.
d. "Radio Age" (monthly, with membership in Mid-Atlantic Antique
Radio Club), dues $20.00. Contact MAARC, Roy Morgan, PO Box
1362, Washington Grove, MD 20880. "Radio Age" was its own
publication until its recent merger with the "MAARC Newsletter".
e. Electric Radio (monthly). Box 57, Hesperus, CO 81236. Published
by Barry and Shirley Wiseman. This is an amateur radio
magazine. Editorial policy is "Our primary interest is in
"... vintage equipment/operating with an emphasis on AM, but
articles on SSB and CW are also needed."
f. There are many radio clubs across the US, each with its own
newsletter!
Refinishing supplies--
#1 and #6 supply all manner of chemicals (fillers, polishers,
lacquers, etc.) for refinishing both wood and plastic cabinets.
Repair and restoration services--
There is probably a collector's club near you that can steer you
towards an individual in your area who works on vintage equipment.
Otherwise, if shipping your radio is an option for you, try the
following:
a. For Your Listening Pleasure, 368 Clinton St., Binghamton,
NY 13905, (607)797-0066. Four levels of restoration are
available, from "working order only" to "museum quality"!
b. #3 and #4 do repairs--not sure about cabinet restorations.
c. Sunrise Services, 2343 Ballycastle, Dallas, TX 75228,
(214)328-4249. Radio cabinet refinishing, wood or plastic.
d. Check "Antique Radio Classified" for countless ads for this
type of service!
Loudspeaker reconing:
There have been several postings identifying the following as
rebuilders of old loudspeakers.
Mr. Richard Stamer
Sound Remedy
331 Virginia Ave.
Collingswood, N.J. 08108
609-869-0238
Mr. Hank Brazeal
103 N. Lake Point Ct.
Crossville, Tenn. 38555
615-456-2529
Speakerworld
2000 Warm Springs Ct. #6
Fremont, Cal. 94539
510-490-5842
Sound Remedy
331 Virginia Avenue
Collingswood, NY 08108
609 869 0238
Schematics/repair data--
Most schematics on vintage radios come from either the
Rider's Perpetual Troubleshooter's Manuals (earlier sets)
or the Howard Sam's Photofacts (post-war sets). These are
available in many public libraries. Otherwise, the following
suppliers offer schematics at reasonable rates (if you can
provide them with a model number): #1,2,4,5. If you don't
have a model number but can provide the tube #'s and layout,
for an extra fee they can usually find the right schematic.
See also "Literature".
Howard W. Sams began publishing repair data in 1947. Don't look for
schematics, etc. of prewar electronics in Sams.
Rider reprinted manufacturers' repair information, and you should look
for "family resemblances" between the radio you have and radios of the
same make---Rider may have published repair data for only one or two of
a large family of model numbers that are nearly identical. Also keep
in mind that many smaller radios built after the mid-thirties were
built to standard Hazeltine/RCA designs under license, and you may not
need a specific schematic for your set).
Tubes--
A complete list of tube suppliers would be an incredible headache
to compile. Just about all of the suppliers listed at the beginning
of this directory have tubes, and it is unlikely that you would
be unable to get what you need from at least one of them. The ones
that have their inventory conveniently listed in their catalog are:
#1,2,3,6,9. Prices vary.
Some other suppliers for various things:
Local sources. Take a look in the Yellow Pages, and check out any
place that advertises under "radio repair." You may find that your
area has an old-time shop or two that does repair work on old
electronics. Don't ignore possible local sources---a few phone calls
will generally lead you to one, even if you don't identify it from the
Yellow Page listings immediately.
Mouser
2401 Highway 287 North
Mansfield, Tex. 76063
800-346-6873/817-483-4422
Mouser is a "modern components" distributor with a big catalog. They
have distribution centers in California and New Jersey as well. While
they do not stock antique-specific items, they are a good source for
resistors, capacitors, wire (modern only) and a host of other useful
items.
MCM Electronics
650 Congress Park Dr.
Centerville, Ohio 45459
800-543-4330
Most of MCM's inventory is oriented toward modern devices, but some of
their items can be used in old radio restoration. They also stock a
large inventory of Japanese and Motorola transistors.
The following advertise regularly in Electric Radio (a magazine for old
amateur radio equipment)
Fair Radio Sales
PO Box 1105/1016 E. Eureka St.
Lima, Ohio 45802
419-227-6573
Primarily military surplus, plus some test equipment and vacuum tubes.
Purchase Radio Supply
327 East Hoover Avenue
Ann Arbor, Mich. 48104
313-668-8696
(Not specific as to what they carry, but worth investigating---they
state they've been there 60 years and specialize in old items).
On magnetic components (coils, RF-IF transformers, power transformers,
chokes), you are faced with several choices, depending on what you need.
Antique Electronic Supply carries a selection of iron core magnetics
and a few other items, primarily for smaller radios. Several suppliers
offer interstage transformers for 1920's sets. If you need a power
transformer you may need to adapt mechanically and/or electrically.
You will need to know the exact dimensions of mounting holes, chassis
cutouts, space available for mounting, etc. You will also need to know
the voltages and current requirements of secondary circuits. If you
have some idea what substitutions you can make, calling around may
produce a very good substitute. For a price, there are several
transformer shops that will build you a new transformer to your
specifications.
Universal-wound coils (i.e., wound zigzag on forms) are difficult to
replace. Fortunately, they don't often give trouble---main problem is
antenna coils zapped by lightning. There are very few shops today who
are equipped to wind universal-wound coils. Some electrical adaptation
of NOS (new old-stock) items is possible in some cases.
If you are dealing with a radio that needs magnetic components or has a
physically-unrepairable tuning capacitor, you may have a parts radio.
Test equipment:
Most test equipment comes from sellers at hamfests. Fair Radio Sales
has several items of test equipment for sale. One source that
specializes in an interesting variety of test equipment, as well as
some old radios and parts furnished the following self-description:
----------------------------------------
W.J. Ford Surplus Enterprises
We have a wide assortment of surplus electronics for sale. Check out
our electronic listings at:
http://infoweb.magi.com/~testequi/
Our lists are regularily updated as new stock comes in.
W.J. Ford Surplus Enterprises
P.O. Box 606, Smith's Falls, Ont. K7A 4T6
phone: (613)283-5195
fax: (613)283-0637
email: testequi@magi.com
check out our home page at http://infoweb.magi.com/~testequi/
--------------------------------------------
Bibliography:
The following books are relevant to old radio design, repair, and
history.
1. Loomis, Mary Texanna. "Radio Operating and Theory." Several
editions, 1925-30. Washington D.C., Loomis Publishing Co.
2. Ghirardi, Alfred A. "Radio Physics Course" At least two editions,
1931-33. New York, Murray Hill Book Co.
3. Terman, Frederick E. "Radio Engineering." Three editions, 1932,
1937, 1947. "Electronic and Radio Engineering" was published as a "4th
edition" in 1956, but covers different topics. New York: McGraw-Hill.
4. Terman, Frederick E. "Radio Engineer's Handbook." 1st ed. New
York: McGraw-Hill, 1943.
5. Langford-Smith, F. "Radiotron Designer's Handbook." Four editions,
1934, 1935, 1940, 1952. Sydney, Amalgamated Wireless Valve Company
Pty. Ltd.
6. Hund, August. "Frequency Modulation." New York, McGraw-Hill,
1942.
7. Rider, John F., ed. "Perpetual Troubleshooter's Manual." 23
volumes, 1928-53. New York: John F. Rider Publishing.
8. Howard Sams "Fotofacts." Issued as folders, beginning in 1947.
Indianapolis: Howard Sams Publishing.
9. There are several works available through Antique Electronic Supply,
either recent items or reprints of old material.
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono Cosmetic and Cabinet Questions(FAQ: 6/9)
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Archive-name: antiques/radio+phono/faq/part6
Rec.antiques.radio+phono Frequently Asked Questions (Part 6)
Revision Date Notes
1.0 Oct. 15, '95 New section
Part 6 - Cosmetic and cabinet finish questions
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Email vancleef@netcom.com
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and electronic phonographs. It is intended to summarize
some common questions on old home entertainment audio equipment and
provide answers to these questions.
This section discusses some of the methods that can be used to clean and
restore items in acoustic phonos antique radios, and other items. While
the internal construction of phonos may be quite different than that of
electronic devices, many of the cleaning issues are quite similar.
Almost any old device requires a fairly standard cleanup involving
removal of dust and dirt, internally as well as externally. The first
step in restoring an harmonium (reed organ) or a piano, as well as a
phonograph, music box, or radio, is to clean the item thoroughly, inside
and out, and assess its condition. Very often, all that is needed is a
good vacuuming, with the help of some small paintbrushes to loosen dirt,
and a soap-and-water cleanup. Clockwork mechanisms, small electric
motor mechanisms, and electric phono turntable, wire recorder, and
similar mechanical transport mechanism generally need to have old
"petrified" lubricants cleaned off, and reassembly with new lubricants.
Cabinet restoration depends on the method of cabinet construction and
finishing. Items built in the 19th and early 20th centuries generally
had wood "furniture" cases, finished with a shellac process. The
introduction of synthetic varnishes in the 1920's meant a rapid change
to use of synthetics for wood finishes, and shellac finish on a home
entertainment device becomes rare through the 1925-40 period. Post WWII
wood finishes are most commonly one of the urethane synthetics.
Plastics that could be formed by casting and injection molding processes
became available at the end of WW I, and many home entertainment devices
made in the 1920's have visible parts made of "Bakelite," a phenolic
resin with an inert filler that can be injection molded. By 1940, there
were a variety of thermoplastic (i.e., melts when heated) and
thermosetting (i.e., cures under heat and does not remelt) resins were
commonly used in construction of molded radio cabinets, knobs, and
decorative trim items. Many of the plastics used in the later pre-WW II
period were not stable over long periods. Ultraviolet from strong
sunlight and heat above human body temperature would accelerate
distortion and discoloring, for which there generally is no repair other
than replacement of the affected part. Items in good condition should
be cleaned up and positioned where they will not be subjected to strong
sunlight or heat.
Various metals are used both in internal construction and in cabinetry.
Painted steel plates and cabinets are commonly found. Also stamped
brass decorative parts. One very common process was to use steel and to
electroplate it with a brass finish. Die cast white metal parts are
commonly found. The zinc alloys used in the 1910-35 period produced
excellent parts, but are subject to aging and corrosion breakdown.
Typically, they will become larger, then become extremely brittle and
crumble. Once again, the only "repair" solution is replacement of the
affected part. There is a long-standing myth that white metal parts were
made of "floor sweepings" and scrap, and the term "pot metal" is
sometimes used in the US to denote the material. This is not accurate.
Zinc precision die casting technology uses specific alloys and
processes, and produces excellent results. Some manufacturers used
die-cast or sand-cast aluminum alloys after the mid-1920's. These
should not be confused with zinc alloys. Die casting processes for both
zinc and aluminum produce high dimensional accuracy, but require
creation of an expensive metal mold set, so are generally associated
with high-volume parts. The tooling required for sand casting is much
simpler and less expensive, but the as-cast parts require machining of
critical dimensions.
This is a very cursory overview of materials and processes, and the
reader who wishes more information should search out and study some of
the literature written for engineers and crafts people who work with
these technologies. In particular, "Machinery's Handbook" and (in the
US) the SAE Handbook (Society of Automobile Engineers) have extensive
information on metals and manufacturing processes.
Your FAQ editor has some strong feelings about some of the techniques
for cleaning and restoration that have been discussed on various
newsgroups. There is no question that many restorable items have been
ruined beyond repair by use of inappropriate chemicals and cleaning
methodologies. Beyond this there are considerations of "kitchen
chemistry." Almost any solvent or process has safety considerations to
consider. And almost any solvent or process will damage something in a
device. You may want to use it over here on this metal part, but if you
get it on that plastic part or electronic component, in may destroy it.
Additionally, there are issues of fire hazards, fumes, violent reactions
with other chemicals, and safe storage to consider. Know your products,
and know your processes. A kitchen is a place for food preparation, not
chemistry experiments or industrial processes. Be very careful to keep
solvents where they cannot contaminate foods or anything used for food
preparation. Store chemicals separate from food items, and away from
the inquiring hands of small children. Also keep in mind that many of
the preparations sold in grocery stores for kitchen cleaning purposes
are, in reality, very strong chemicals, and may have very little
information on the chemical content or processes. When writing this, I
checked a can of Dow brand oven cleaner. It acknowledges 4% sodium
hydroxide as an active ingredient, and gives a litany of safety
precautions in use. This stuff is more violent than most of the
industrial cleaning processes I've used. Many of the spray can cleaning
products are very easy to use----just spray them on your valuable
antique and watch it dissolve before your very eyes. Remember that
these are proprietary products, and while the labels may disclose a few
"active ingredients," it is often not all that is in there that will
wreak havoc. There is a steady stream of notes in the antique groups
from people who tried a spray can kitchen product and discovered, too
late, that it took markings, finishes, etc. off along with the dirt.
There are two manufacturers who make chemical products specifically for
use around electronics equipment. Caig Laboratories makes "DeOxit,"
which is considered by many people to be about the best contact cleaner
around. They make a number of other chemical products for various
electronics uses, and provide good and specific application and use
notes for their products. GC Electronics, formerly General Cement, make
a variety of products for various uses. These include a good electronic
coil dope, a chemical wire insulation stripper for stripping the enamel
from magnet wire, and a variety of cleaning products and adhesives.
One "easy cleaning" method that gets tried regularly is use of a
household dishwasher to clean things. Don't do it. Almost all
dishwashers use high temperatures in their washing cycle, and the
detergents used are a strong caustic solution. They may wash dishes
well, but for other cleaning, have almost all the attributes and
drawbacks of a hot caustic tank (see "lye," below) with few of the
virtues. I've had the unpleasant experience of spending a day with
precision machine tools reworking the castings in an automotive power
steering pump that were put through a good household dishwasher.
General purpose solvents that are generally mild and easy and effective
to use are:
1. Water, with or without soap. Water is actually the most universal
solvent. A little bit of soap or detergent will increase its ability to
wet the surface. More soap will make an alkaline solution. Safe on
most things, but may dissolve inks used on dial markings, and should be
used with care around electronic components, particularly iron core
chokes and transformers. One of the better detergents to use is a
generic-type dishwashing detergent such as Octagon brand.
2. Household ammonia. This should be the clear non-sudsing type, with
no additives like lemon sent. Straight ammonia is a strong alkali, and
will dissolve shellac very quickly. A mild ammonia solution generally
does a good job of dissolving dirt on painted and metal surfaces. A
plain ammonia solution without additives will dry without leaving a
residue, and may be preferable to a soap/detergent solution for many
applications where a thorough water rinse is not used.
3. 3M adhesive cleaner (an automotive product). This is a petroleum
product sold for removing adhesive residue, road oil, etc. from
automobile painted surfaces. It is safe on most plastics. Excellent
for removing the residue left by old masking tape, cellophane tape, and
removing adhesive labels and their residue. It's made by the principal
makers of several adhesives, so is formulated for removing residues from
their adhesive products.
4. Isopropyl alcohol. Generally sold as "rubbing alcohol." This is an
alcohol/water mix, and sold in various concentrations. What I use is a
70% solution. Alcohol will attack marking inks and painted surfaces,
but will sometimes cut adhesives and things like chewing gum that the 3M
products have difficulty with.
5. Diesel fuel. Excellent for dissolving petrified lubricants and
other petroleum products. It is not as quick as gasoline for this
purpose, but has the advantages of being much less flammable, and leaves
an oily coat in the part surface for several weeks, which will protect
against immediate rusting. Generally safe with plastics and slow to
attack painted surfaces. Diesel fuel is an excellent choice for
cleaning spring phono motor parts.
All of the above are fairly safe and easy to handle. Except for soap
solutions, all have distinctive odors. Ammonia generally requires
ventilation or outdoor use, and diesel fuel leaves a strong "perfume"
that is very slow to dissipate.
Noxious and violent chemicals that are excellent for some controlled
applications. All of these require care and precaution in use and
handling, and present serious safety hazards if not used properly.
1. Automotive lacquer thinner. This stuff will cut right through many
things. It is also extremely flammable. Excellent for cleaning
petroleum and oily residues off metal parts to leave them absolutely
clean. Cuts almost all thermoplastics instantly, and will damage paint
surfaces. Removes most marking inks very quickly as well.
2. Lye. As a commercial cleaner, this is generally used in heated
tanks and called "hot caustic." It is always used as a dip tank
solution. You can make a small "hot tank" by dissolving lye in a
coffee can, placing it in a large frying pan, filling the frying pan
with water, and heating to around 60C (160F). Do not heat directly or
bring to the boiling point. Room temperature lye is a very strong soap,
and should not be allowed to contact skin for any period of time.
Heated it is very aggressive. Lye will dissolve the white metals,
aluminum and zinc, and should not be used to clean them. It will remove
petroleum residues, paint, and a variety of other things. One very good
application of a hot caustic tank, which will illustrate what it can do,
is in cleaning steel automotive engine blocks and cylinder heads, where
it is extremely good at removing carbon deposits, cooling passage scale,
and oil passage residues. Hot caustic tanks are often used for paint
removal tasks.
3. Chlorinated hydrocarbons. These include carbon tetrachoride,
trichlorethane, and various "freon" cleaning solutions. While most of
these are good cleaners, they have a lot of undesirable characteristics.
Many of them are no longer available. GC Electronics sells
trichlorethane in small quantities, but I have not seen it clean things
that didn't clean just as well with other solvents.
4. Strong acids. Hydrochloric, nitric, sulfuric, and phosphoric acids
all have good industrial applications. "Oil of vitriol" and "muriatic
acid" are colloquial names for sulfuric and hydrochloric acid. All of
them are extremely agressive and difficult to handle. A mild phosphoric
acid product with good applicability for rust removal is sold as "Naval
Jelly." Other than this, these chemicals are poor choices for use in
antique restoration.
Solvent application methodologies:
The best methodology for using any of the above solvents is controlled
application, to assure that only the parts to be cleaned by the solvent
come in contact with it. In most cases, soft cloths and Q-tips work
well. The best soft cloths were cloth baby diapers, which have been
largely displaced over the past thirty years by disposable diapers.
Start by vacuuming off the loose dust. A small paintbrush and some
smaller brushes, such as those sold for basting poultry, can help in
loosing dirt. Follow up with a mild soap and water solution applied
with a rag. A soft toothbrush can reach into inaccessible places and is
particularly valuable in cleaning up knurled metal parts and fluted
knobs. Use Q-tips moistened with solvent to reach into inaccessible
areas and to "spot clean" specific areas.
(this area under construction)
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono Radio Technical Questions(FAQ: 7/9)
Message-ID: <antique-radio+phono-faq-7-845766911@netcom.com>
Followup-To: rec.antiques.radio+phono
X-Content-Currency: This FAQ changes regularly. When a saved or printed copy
is over 3 months old, please obtain a new one.
Keywords: FAQ OLD-RADIO OLD-PHONO
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Date: Sat, 19 Oct 1996 23:15:36 GMT
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Posted-By: auto-faq 3.1.1.2
Archive-name: antiques/radio+phono/faq/part7
Rec.antiques.radio+phono Frequently Asked Questions (part 7)
Revision Date Notes
1.1 Oct. 24, 94 Revised and reordered as part 5.
1.2 Dec. 12, 94 Minor edits, added new material on caps and tv
1.3 Jan. 8, 95 More stuff on caps.
1.4 March 3, '95 Include Dan Schoo's writeup on paper caps.
2.0 Nov. 19, '95 Move from part 5 to part 7
Part 7 - Radio and electronic phono technical questions.
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Email vancleef@bga.com, vancleef@tmn.com
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and phonographs. It is intended to summarize some common
questions on old home entertainment audio equipment and provide answers
to these questions.
WARNING: HIGH VOLTAGE. SHOCK and FIRE hazard.
Vacuum tube electronics runs on much higher voltages than transistor or
solid state devices. These sets were generally not provided with
interlocks or power fuses. In certain designs, the power line may be
connected directly to the chassis. Many home-entertainment electronic
devices had 250 volts or higher as a standard operating voltages, and
voltages as high as 750 or 800 volts, may be present in some circuits.
Fault conditions may cause HIGH VOLTAGE to be present ANYWHERE, even
after the set it turned off and disconnected from the power line
(mains). Use a grounding lead to assure that no voltage is present
before working on a set.
There is sufficient power to overheat components to the point that they
will catch fire, and many components used in old electronics will
support combustion. While addition of a fuse can reduce fire hazards,
it is not a sure and complete protection against overloads which may be
adequate to overheat components, but inadequate to blow the fuse. In
addition, soldering irons operate at temperatures of 400-500C (approx
700-900F), and are hot enough to ignite many flammable materials such as
paper and cloth.
Several of the CHEMICALS and PROCESSES discussed in the newsgroup, and
in this FAQ, present safety hazards of one type or another. Fire
hazards are common, and many chemicals and processes require substantial
ventilation as well. Read manufacturers' labels and follow all
instructions for safe handling closely. Above all, do not store
or use chemicals with food or food preparation items.
Small children (and some not so small)---if you have some of these
around, take some precautions to make sure their inquisitiveness does
not get them into something that will hurt them, or damage anything.
Old electronic equipment is full of bright colors that will attract
small fingers. The best thing to do with children is introduce them to
radio. Don't just tell them "no, don't touch," etc. It's amazing how
quickly, diligently, and thoroughly a child will learn mathematics
and physics, with the help of an old radio and someone who will take the
time to explain it to them. Noxious chemicals and children don't
mix.
Do not attempt any process unless you know exactly what you are doing,
have evaluated the risks, and have taken safety precautions. Many of
the regular contributors to rec.antiques.radio+phono have been formally
trained in chemistry and physics laboratory procedures, and use
chemicals and processes professionally. They may discuss techniques that
require substantial safety precautions without noting the hazards
involved.
If there is the slightest doubt in your mind about the safety of any
process or material, don't charge off and "just do it" because others
say "it works." Ask questions. There is no substitute for learning
under supervision. Many community colleges and high schools offer
courses open to adults, including courses in laboratory sciences and
shop practices.
Q. I've got a very nice Philco tombstone radio that is only a
decoration because it doesn't play. What can I do to get it to play.
A. This section of the FAQ addresses getting them to play as nicely as
they look. While not intended to be a comprehensive primer, this
section covers many questions that come up regularly. The topics
discussed in this section of the FAQ presume that you have a working
knowledge of vacuum tube circuits.
Q. Why does a 35Z5 or 35W4 rectifier have a number 40 or 47 bulb
connected across part of the heater?
A. The heater serves as a voltage divider. Resistance of cold
filaments is much lower than when they are hot, and connecting a bulb in
series will put almost the whole 110 VAC across it until the heaters
warm up. The plate current flows through the bulb/heater to balance the
current once the tubes are warmed up. Note that this also applies to
ballast tube setups---the ballast resistance is designed to increase as
the set warms up. It's a way of putting a cheap light bulb in a cheap
radio. (Historical note: This is an interview question I used to use
when interviewing engineering applicants in the fifties and sixties).
Q. I just found a (very old tube) radio in a (barn, attic, junk
sale, etc.). It's complete. Can I plug it in and see if it works?
A. If you didn't hear the radio playing, it would be very wise to do
some resistance checking first.
a. What is the condition of the line cord? Replace it if it is
frayed or the rubber is petrified.
b. Condition of filter capacitors. Wet electrolytics, which
were used in the 1930's, should be replaced without question before
applying any power. These are identifiable by the metal cans with vent
holes on them. Dry electrolytics (which aren't really dry inside) can
also lose their film and be low resistance. If DC resistance between
the B+ line and circuit ground (this may not be chassis ground) is not
500K or more, find out why. Make sure the speaker is included in this
check if it has a field coil or has the output transformer mounted on it.
With electrolytics and any voltage divider resistors out of the B+
circuit, DC resistance should be several meghohms.
c. If it's an AC-DC set, check to see if one side of the line is
wired to the chassis. Many of them were. If so, keep the set away from
any metal objects to avoid shock hazard. Some of the early AC-DC sets
would hum like crazy if they were plugged in with the chassis "hot."
d. If it's an AC set, consider installing a fuse in the line
circuit. 2 amps 250 volts for sets with 80/5Y3, 4 amps 250 volts for
sets with 5Z3/5U4.
e. Do a cosmetic inspection. You'll want to vacuum off any old
dust, dirt, cobwebs, etc. first. Look for things like charred
resistors, melted wax from capacitors, coils, and transformers, and any
indications that the radio go put in the (barn, attic, etc.) because
something was wrong with it.
f. Take a look at the bias circuit for the power output stage.
See below for discussion of typical bias circuits. If there is an
electrolytic in the circuit, make sure it isn't "low ohms." If your
output stage is 6L6's, or if it is filament tubes like 2A3, 6A3, 45, or
47, take a very good look at things.
g. Condition of old wiring is important. Don't fool around
with petrified insulation that is breaking off the wires.
A few hours spent doing a good visual inspection and some ohmmeter
checks can pay off handsomely. If you've got to replace a charred
resistor, find out what burned it out and fix that too, before applying
power to the set.
Remember that 99% of vacuum tube failures are due to open heaters or
filaments. The other 1% are due to gas or interelectrode shorts. This
leaves the item that tube testers have a big BAD-?-GOOD meter to
measure, emission, down in the mud as a tube fault that makes a radio
play poorly. Except for rectifier tubes that have been "sucked dry" by
a gassy output tube or shorted filter cap, most of the tubes I have
diagnosed as causing problems because of low emission would not exhibit
that low emission in a tube tester. Example: a 6SQ7 diode that quit
conducting after 15-20 minutes of playing. Diagnosis was confirmed by
soldering a 1N34 diode across the terminals.
If the getter material (you can see it on glass tubes) is white instead of
silver, the tube is probably gassy----most common on power output and
rectifier tubes. A few sets used gas-filled rectifiers. The 0Z4 is
most common in auto radios, but you may find and old set with an 82 or 83
mercury vapor rectifier.
Also remember that with tube equipment, DANGER, HIGH VOLTAGE. applies.
In home entertainment transformer sets, we are talking about as much as
500 volts, and most smaller transformer sets used somewhere between 250
and 350 volts as the main B+ voltage. The transformerless sets
generally provide 135 volts, and have the mains power (to use the British
term) hooked directly to various circuits and often the chassis as
well.
Q. The chassis of my radio is covered with a thick layer of dust, fine
dirt, and underneath is a film of brown crud. How can I clean this
thing up without damaging it?
A. This particular topic gets a lot of discussion and advice, some of
it very bad. Your radio has some irreplaceable components, and if you
use the wrong methods, you can make a junker out of a restorable set in
a hurry. There are some things to keep in mind:
a. The chassis is probably cadmium-plated steel. Some radios
were made with nickel-plated steel (looks green when corroded),
copper-plated steel, or chromium-plated steel. A few chassis were made
of aluminum. If it is a dull silver color, check with a magnet. An
aluminum chassis is non-magnetic, all of the steel chassis are magnetic.
b. The dial face may be a water-soluble paint or a decal.
c. Colored knob markings (lines and dots, as well as letters
filled with color) may be water-soluble.
d. Any silk-screened surface markings may come right off.
These include tube layout information on the chassis, inspector's marks,
and other printing.
e. The tuning mechanism may be stiff because of petrified
lubricant in various shafts and rotating elements.
f. Coils, IF transformers, and tuning condensers may be
difficult or impossible to replace if you damage one.
g. If the radio is complete, tubes in place, the crud and dirt
is on top of everything, not in the electronics. You want to get it off
the radio, not melt it down so that it flows into the working parts.
You can remove the tubes. Make sure that the tubes are clearly marked
as to tube type, and make sure you have an accurate diagram so that you
can replace the tubes in the same sockets you removed them from. Get a
pencil and piece of paper and make notes about things you move,
disconnect, or take apart, so that you can get everything back together
the way it was originally. Begin by vacuum cleaning the set, and use a
soft brush to loosen dirt while keeping the vacuum nozzle near the brush
so that it will pick up loosened dirt. If you find mouse droppings, be
prepared to examine the set closely for damage from mouse pee. Gently
brush off the tuning condenser, being careful not to bend the plates.
Once the surface dirt is off, you can begin to consider how best to
remove the crud, and how far to go with the cleanup.
There are two things that are very poor to use around electronics: steel
wool and soap-type detergents. Steel wool will shed little particles
and raise havoc. Soaps and liquid detergents leave residues that can be
hard to remove. Liquid detergents also do a fabulous job of softening
and removing silk screen inks, water soluble dial markings, and tube
markings, even those that may be safely soaked in water for a few
minutes.
Start on the chassis crud by using a damp rag moistened with plain
water. Don't slosh water onto things. Most tap water is safe to use
around electronics, and is an excellent solvent. I note that I have
refurbished electronics that have been immersed for days in fresh water
after they have been allowed to dry out, and found very little damage,
mostly to capacitors. If the crud comes off with water alone, continue
with the damp cloth treatment. It may be slow, but it will leave a
clean surface with little residue. Finish the job with moistened Q-tips
to get into various nooks and crannies. Be careful that you don't
remove marking inks and paints.
A stronger alkiline solvent is clear household ammonia. This also
evaporates without leaving a residue. If water is not melting the crud,
try a little ammonia on a Q-tip. Use the ammonia straight, and if it
gets results, use it on a damp rag to moisten the chassis. Generally,
once ammonia-sensitive crud has been melted, it will come right off
using a rag dampened with water. Be careful not to get ammonia on a
shellac wood finish---it will cut the shellac and leave marks.
If this doesn't get results, try a mild acid---clear cider vinegar. Use
the same methods as with ammonia, finishing with a rag dampened with
water.
By this time, you should have most of the removable crud off the
chassis. Some other solvents to try---only in small areas with Q-tips:
Isopropyl alcohol. This dissolves a great many things, including flux
rosin, some marking inks, etc.
Trichloroethane (GC Electronics "Chloro-Kleen"). Also dissolves many
things. Don't use on plastics until you have checked to make sure it is
safe. Chloro-Kleen works very well on phenolic and ceramic-mounted
switches such as bandswitches and pushbutton switches.
Lacquer thinner. This is a "court of the last resort." It is a
powerful solvent that will damage many plastics, remove a lot of marking
inks in a jiffy, and generally raise merry hell if you get it in the
wrong place. Use on metal parts only.
Also pay attention to the various warnings about flammability and use
only in well-ventilated areas.
Corrosion on cadmium-plated chassis generally does not respond very well
to anything. You can use Naval Jelly to improve the situation,
particularly if there is visible rust. Light fingerprints often will
respond to automobile polish (Dupont No. 7 is good). This treatment
(followed by an application of Simoniz paste wax) will make many
lightly-scratched plastics look like new.
The best solvent for use with petrified lubricants in tuning mechanisms
is diesel fuel. If there are separately-mounted shafts or gear
mechanisms, you can often take them off----just make sure you can get
them back on again, and positioned properly. Watch for spring-loaded
double gears in gear mechanisms that need to be preloaded when you
assemble them. Shafts should be relubricated with a light grease like
white Lubriplate---use only enough to leave a film on the parts needing
lubrication, and wipe off the rest. Gear trains generally work well
with a little 3-in-1 oil on axle pivots and a film of lubriplate on the
gear teeth. A stiff volume or tone control will generally respond to a
drop of 3-in-1 at the end of the bushing---use only a drop, and wipe it
off after about 5 minutes.
Tube washing gets a lot of attention. Keep in mind that washing most
tubes won't make them work any better. Before you start, make sure that
the tubes are clearly marked as to what they are. While there is no
mistaking a 6A7, a T-9 beam power pentode with no markings may be a
a 6W6, a 25L6, a 35L6, a 60L6, or a 6V6. A 50L6 plugged into a 25L6 or
35L6 socket can produce interesting symptoms that can be very hard to
diagnose. Contrary to popular opinion, tube markings on glass will come
off, some more easily than others. During the 1950's and 60's, tubes
were specifically marked with easily removable markings in an attempt to
thwart a grey market in used tubes being washed, reboxed, and sold as
new. Generally, just holding the tube under flowing water will rinse
off most of the dirt--- a little help from rubbing the surface with a
thumb where it is not marked generally gets fine results. Use a china
marker to marked the type on any tube that isn't clearly identified, and
let them dry thoroughly before reinstalling. Tubes that are loose in
their base, or have a loose top cap, respond to squirting a little
superglue into the gap. Make sure, in the case of a loose base, that
the leads aren't twisted (and shorted).
Q. What about AF power amplifier bias circuits?
A. You can do a little inspecting to see what your radio uses.
a. By far, the most common circuit is to use a cathode resistor
with an electrolytic capacitor for AC bypass. This is what you will
find in all of the transformerless sets. AC bypass is less critical in
push-pull output stages, although most of them operate class AB (i.e,
both tubes biassed near cutoff). If the capacitor is shorted, the output
tubes will over-dissipate and their plates will glow red in a few
minutes. If the capacitor is open, audio output will be low and
distorted.
b. Back bias. I was somewhat surprised in checking Terman
"Radio and Electronics Engineering" 4th edition (1955) not to find this
circuit. It uses a power resistor in the B- return to develop a bias
voltage, typically 10-30 volts, and may be used in conjunction with the
cathode resistor self-bias circuit. The center tap of the power
transformer will be connected to one end of the power resistor and B-
circuits will be connected to the other end. On sets using filament
power tubes, the filament supply may be connected here, and the power
tube grids returned to the power transformer center tap. Most of the
bias voltage is developed by output tube plate current. If there is a
leaky electrolytic here, it will generally overstress this resistor and
burn it out.
c. Separate "C" bias supply. In this case, the set will have
second rectifier tube, filter, etc. These are not common in home
entertainment equipment, much more likely to be found in theater and
public address amplifiers.
Q. OK, I've checked that the tube heaters are continuous, that the
filters are OK, and generally walked through and done the visual and
ohmmeter inspection. I want to plug it in. What do I look for?
A. This is the moment of truth, even for an old grey-hairs. Fortunately,
tubes will take abuse that transistors won't tolerate. But you want to
have your eyes and ears wide open, and be prepared to shut the thing
back off instantly. Some people like bringing them up on a Variac,
which is an expensive piece of equipment unless you are in the
restoration business. So I'll assume you are going to plug the thing
into the 100 volt line, turn it on, and see what happens. Make sure you
have some sort of antenna connected on sets without a built-in loop.
a. On AC-DC sets, turn it on. The tubes should light up, and in 10-15
seconds (when the rectifier and power tube heaters warm up) you should
hear 60 cycle hum in the loudspeaker. Indeed, hum is a built-in feature
of these sets. If it is overwhelming, you've got a bad filter cap.
Check for smoke signals and signs of overheating. If you can tune in a
station, you are probably in business. On 35Z5/35W4-type radios, if the
pilot lamp burns out after the set warms up, you've got a short in B+
somewhere---probably a shorted filter cap. Turn the set off and find
the problem---if you've got a short, the rectifier heater will take the
load and burn out after a while.
b. On transformer sets, I like to connected a 600 volt DC meter across
B+, preferably in the supply to the IF screen grid or plate. If the
rectifier is a filament type (80, 5Y3, 5U4, etc.) you'll see full B+ a
couple or three seconds after turning the set on, and it should drop to
about 100 volts on the IF screen when the cathode tubes warm up (around
10 seconds). Check for smoke signals, burning, and that all the heaters
glow. A low level of 120 cycle hum is to be expected, though a really
fancy set will give almost no hum at all. Once again, if you can tune in
a station, you are probably in business.
Watch in particular for a violent purple glow in tubes, particularly the
power output and rectifier, plates beginning to glow red, and other
signs that there is a short circuit. If the radio doesn't play, keep a
close watch on things, although if you have good B+, no gassy tubes, and
no red plates, and things are OK after five or ten minutes, you are
probably safe in continuing on to do trouble-shooting. A few sets use
tubes with mercury vapor in them, which normally glow purple between
the elements. Typical are the 83 (not 83-V) and 0Z4 rectifiers, and
the gas-discharge VR tubes (0A2,0C3, etc.).
Trouble-shooting. If all the tubes light up, you've got B+, and no
smoke signals, you can begin your walk through the radio. If the radio
is completely dead---no stations, no static---try rocking the bandswitch
if the radio has one. Also, the volume control, any tone controls, etc.
I've found that on ancient sets, it's a good idea to walk right through
and do voltage checks everywhere, no matter how well the radio seems to
play. If you have a schematic with voltages marked on it, so much the
better, although some of the voltages given by manufacturers can
disagree rather markedly from actuals that can be figured by
reverse-engineering the design.
a. Power output stage: Check screen and plate voltages. These should
be close to B+ at the rectifier. Check for positive bias voltage at the
cathode on self-bias circuits or negative voltage at the grids if
separate bias.
b. Audio amplifier. Usually a triode. If the 6SQ7 diode-amplifier
type, the only thing to check is plate voltage, which should show a drop
across the plate resistor. On resistance-coupled output circuits, make
sure the coupling cap is not leaking current to the output tube grid
circuit, which will pull up the grid voltage and make the output tube
plate(s) glow red. Probing the AF amplifier grid generally shouldn't
show any voltage, but should make plenty of noise in the speaker.
c. IF amplifier. Check for screen voltage. If you don't have any,
you've got a shorted bypass cap and a dead radio. Plate voltage should
be near the supply voltage (generally fed by a blue wire to the 2nd IF
transformer). Cathode should show some bias being developed (i.e.,
plate current through the tube). The grid will generally show the AVC
voltage, though your meter will shunt a lot of it, unless it is a
high-impedance type, such as a VTVM.
d. Mixer. If the pentagrid type, tetrode, or pentode, check screen
voltage. Check for proper bias voltage on the cathode.
On voltage checks: if you have a schematic and voltages, these can be a
general guide to the voltages you should see on the tube elements. If
you don't have voltage measurement data, most of the tube manuals give
standard values for circuit DC levels as "typical operation." Most
designers used these "typical operation" values in circuit design.
Q. I have a nice old fifteen tube radio. It's got problems with
insulation falling of the wiring, and a couple of repairs that were
badly done. There is a lot of dirt in the coil boxes and bandswitch,
and I can't get at them to clean them up. All of the paper capacitors I
checked were leaking electrically, and several resistors have drifted
way out of tolerance. What can I do with this set to get it working
properly?
A. There is a point where the best thing to do with an old radio is to
take the thing completely apart, clean up everything, and build it up as
a new radio. While this may seem like a lot of work, it actually is
easier than a major piecemeal restoration. For one thing, taking major
components off the chassis will open up areas and make the rest of the
set easier to work on. You will need an accurate schematic for the set,
and you will need to make copious notes as you take it apart. Note how
the bandswitch and other tap switches are wired, and identify the
connections on the schematic. Make notes on what components are where,
the hardware used to mount them. You will want a bunch of containers,
typically one for each type, to keep parts in. Mark the
containers---don't rely on memory for anything. Your notes are going to
be "kit building instructions" for putting it back together. Clean off
all the old solder to make it easy to install components.
The results can be little short of astounding. You can start with a dog
that has parasitics, won't align properly, and has been butchered by
hackers who fixed everything except what was wrong, and end up with a
brand new radio with superb performance. Work? Yes. But take it one
tube circuit at a time, one subassembly at a time, etc., and you'll be
surprised and pleased with the results.
Q. What about electrolytic capacitors? Can they be re-formed?
A. Roy Morgan sent me a drill for re-forming old caps. Keep in mind
that some caps won't come back to life. The "wets" from the early
thirties generally have internal problems and corrosion, and a lot of
the axials have dried out internally. Note that a "dry" electrolytic
has a moist gauze with electrolyte inside---what makes them "dry" is
that the electrolyte doesn't slosh around. "Dry" can types, like the
Mallory FP series, often will come back to life with a re-forming. I
used the procedure that follows on a 20/20/15 mike 450V Mallory FP with
a date code of June 1945 that probably last saw power in the 1960's,
and the cap came back to usable condition. Here's Roy's procedure:
To Re-form electrolytic capacitors:
With the "patient" set off, set the external supply at the rated voltage
of the cap(s), and feed the old set at the input to it's B+ filter through
a 100K, 2W resistor. The old caps will slowly come up to voltage as
their elecrolytic layer re-forms after long storage. You may want to
unhook bleeders or screen voltage dividers if present in order to get no
dc load other than the caps. Once re-formed up to nearly the cap rating,
increase the external supply voltage to the point where increased voltage
only increases the current drawn (the electrolytics begin to "leak".) You
can vary the series resistor depending on the voltage of the cap you're
trying to reform.
If the final cap(s) voltage is high enough, it doesn't need to be
replaced. If it's too low, put new one(s) in (leave any original cans in
place for appearance, and substitute new axial lead ones under the
chassis.)
Some caps take only a few minutes to re-form. Some take a day or so! Be
patient. Your Adjusta-Volt or Variac can be well-used for this if your
external supply is solid state, or has a separate hv supply transformer.
I have one good for 900 volts no-load having 5R4's and separate filament
transformers. This lets me re-form 500 volt electrolytics if I need to.
With a 500 volt supply, and a number of 100k or 200k resistors, you can
re-form a number of caps all at once. Measure the voltage on the caps as
time goes on with a high-input-resistance meter (VTVM or solid state
DVM). Allowing an electrolytic to idle with a small leakage current of 1
to 5 ma won't hurt it, so if the thing re-forms to it's limit during the
night after you've left it on the re-former, no harm is done.
Most electrolytics in good health will leak at a voltage from 125 to 200
percent of the continuous rating. If the leakage voltage is only a little
above the needed circuit voltage, or is below about 110 percent of the
cap's rating, then you can excpect it to not live too long. New axial
lead caps are fairly cheap, and are good peace of mind in my opinion.
(I didn't have a separate power supply. What I did was disconnect B+
from the caps and feed the rectifier output through 100K resistors to
each section. With a 670VCT plate winding, and only a few ma. current
draw, an 80 will come very close to delivering 500 volts peak (1.41*370
is a little over 500. Once the caps settled down, I put 20K's in the
circuit to pull them up even further---they had about 480 volts on them
at the end).
Q. What about testing other caps?
A. This is also from Roy Morgan.
PAPER COUPLING CAPS:
Test interstage coupling caps (e.g. from an audio driver tube to the grid
of the output amp tube) by measuring the dc voltage at the grid (across
the grid resistor if it's not going to ground). Use a high-impedance
voltmeter like a VTVM or DMM. If it's above zero, you need a new cap!
The vast majority of paper caps from the 30's through the 60's are at
least moderately leaky now. Your tubes will thank you with long life for
replacing these caps. Ceramic caps have indefinite life expectancy, as do
good quality modern film caps.
You can do this kind of testing while you are re-forming the filter caps
in-circuit. The tubes are off, and will not be harmed by excessive plate
current while you find all those leaky paper caps. The voltages across
them will be higher than normal running conditions, because the driving
stage is not drawing any plate current.
SCREEN BYPASS CAPS:
With B+ applied and the tube pulled or set off, the voltage at the screen,
again measured with a high-impedance voltmeter, should be the full B+ or
value at the other end of the dropping resistor. If not, the cap is
leaking.
LOOSE CAPS:
Set your high-impedance voltmeter to a high-enough range and clip one end
of the cap to the DC probe and connect (carefully) the other end to a B+
supply corresponding to the rating of the cap. The meter will jump up
briefly and then settle down toward zero. Analog meters (VTVM's) are good
for this because you can watch the movement of the needle. Once the
reading settles, any indication much above zero indicates leakage. A
quick ohms-law estimate with the input resistance of you meter will give
you a value for the leakage. DVM's are often 10 megohms.
Q. I looked under my radio and there are a lot of parts with several
color markings on them but no printing. What does this mean?
A. There has been a color code for marking part values since the early
1930s. The numbers are always the same:
Black = 0
Brown = 1
Red = 2
Orange = 3
Yellow = 4
Green = 5
Blue = 6
Violet = 7
Grey = 8
White = 9
There are several mnemonic sentences for remembering this series, some
lewd, some not. "Bad Boys Ruin Our Young Girls Behind Victory Garden
Walls" is one of the politer versions.
Resistor markings: early-mid 30's was "body-end-dot" where the
resistor body was the first significant digit, one end was the second
digit, and a dot in the center of the body was the multiplier. After
about 1935, resistors were marked with color bands; the first
significant digit is the band nearest one end. Silver is used to
indicate 10% tolerance; Gold, 5%. These are either on the other end of
a body-end-dot resistor or a fourth band on band-marked resistors. The
scheme is simple to decipher: a resistor marked yellow-violet-green is
47 mulplied by 10 to the 5th (100,000), or 4.7 megohms.
Mica and molded paper capacitors, in little rectangular plastic
packages, used the same color values, but there were about twenty
different schemes for locating the dots, and most of them use six dots,
with three or four giving the value. These can be a nightmare to
decipher. Generally, either the first or second dot in the top row is
the first significant figure, and either the rightmost dot in the top
row or the rightmost dot in the bottom row is the multiplier. The size
of the capacitor (bigger values are physically bigger) and the circuit
application will give a clue as to the approximate value. The left
bottom dot generally gives the voltage rating in 100s of volts (red is
200; green, 500), and the center bottom dot generally gives the
temperature characteristic. The left top dot may be a significant
figure or may be a type indicator. Some types have six dot positions,
but one or more with no marking, which may mean "not used" or "brown."
Knowing the series of standard values for resistors and capacitors can
help in deciphering color codes. These were changed during WW II.
Prewar 20% resistors (no tolerance color) were 1000, 1500, 2000, 2500
ohms, etc. Postwar were 1200, 1800, 2700, 3300, 3900, etc., replacing
the old 0/5 scheme with approximately 20% jumps in value. Mica
capacitors in old radios were generally 50, 100, 150, 200
"micromicrofarads" (picofarads---term did not come into use until the
early 1960's in the US). Molded paper capacitors are generally in the
1000 pf. (0.001 microfarad) to 10000 pf. range, with 0/5 as second
figures. Postwar production switched to 12, 18, 22, 27, 33, 39 as
significant figures, although the old scheme was still commonly used.
Wattage ratings of resistors in different package sizes have been
revised several times, always increasing the rating for a given package
size. When replacing resistors, modern 1-watt metal film resistors
generally are about the right physical dimensions for older 1/4, 1/3,
and 1/2 watt resistors. Values should be derated 50%; that is a 1 watt
resistor should calculate to a dissipation of 1/2 watt or less in a
circuit.
An overstressed resistor will overheat, and discolor its color bands,
sometimes very deceptively. In particular, the red and orange
multipliers may look brown, and it may require inspection with a
magnifier to see that the center of the resistor is charred. Any
resistor that looks as though it has been heated to the point of
charring or discoloring its markings should be replaced . Also, some
compositions used for composition resistors were unstable over time,
and a resistor that looks perfectly good and is in a circuit location
where overstress is nearly impossible may be wildly out of tolerance.
Use an ohmmeter to check, but check your ohmmeter against some
known-good new resistors of similar value.
Typical resistor failures:
240 ohm 1 watt cathode resistor for a 7C5---looks like it might have
gotten warm, colors still normal, actually is 150 ohms. Inspection
with a magnifying glass after removal found more signs of overheating
on a side that was not visible with the resistor soldered in place.
Failing "low" like this is not common, and generally comes from using a
resistor with too low a wattage rating for the application. The
coupling capacitor to the 7C5 grid was leaking, pulling the grid up
enough to over-dissipate the resistor. Oddly enough, the tube survived.
240 ohm 1/2 watt screen resistor for a 6K7. This was found on visual
inspection, connected to a replacement bypass capacitor in a
suspicious-looking repair. Ohmmeter showed about 10K ohms, and the
circuit location should have a 2K ohm resistor. Closer
inspection after removal disclosed a charred center which had turned
the red multiplier brown. This resistor was originally 2400 ohms, used
to replace a 2K.
33K 2 watt screen resistor for a 6BA6. The screen bypass capacitor was
shorted, "killing" the set. Ohmmeter showed about 250K. This resistor
showed no signs of distress. A shorted bypass capacitor often takes
out the resistor in the circuit, but a further check in this radio
showed about 2/3rds of the resistors over 20% high, some as much as
twice the value, even though they were not discolored. It got 100%
resistor replacement.
A resistor that is physically broken generally has been subjected to a
short circuit condition that overheated it until it exploded. Look for
a hard short in the circuit.
Q. My old radio has a lot of tubes covered with wax, and some of the wax
has melted out and is on the bottom of the cabinet. What should I do
about this.
A. These are inexpensive wax-impregnated paper-dielectric
capacitors. They were notorious, even when fairly new, for developing
opens, shorts, intermittents, high dissipation, and tend to be rather
fragile as well, particularly when soldering around them. Melted-out
wax is common, and may be only the result of heat developed under a
chassis in normal operation. From reliability and other engineering
points of view, replacing all of them with newer capacitors of other
types is part of a refurbishment/overhaul. Some collectors feel that
40-60 year old capacitors are "survivors," that wholesale replacement is
unwarranted. Also, there are two schools of thought on replacing
components with others that are very dissimilar-looking, even in areas
that are not normally visible when a radio is installed in its cabinet.
A few restorers go so far as to melt the wax out of old capacitors,
remove the foil-paper "innards," install a new capacitor, and refill the
body with wax. Other restorers feel just as strongly that consistent
appearance is more important, and that 100% replacement with no attempt
to disguise the appearance of new components is to be preferred. Alfred
Ghirardi, in "Radio Physics Course," has a lengthy discussion of
failure modes of these capacitors, and states an expected service life
of 10,000 operating hours.
Whether to do a wholesale replacement or not is a decision
you'll have to make yourself, and whether to use modern radial-lead
components or to try to find lookalike replacements or disguise the new
ones, also has no uniform consensus. Your radio may not give you much
choice about wholesale replacement. If you find more than one or two
bad ones, or if the set has mysterious ills, parasitics, or poor
performance, or is intermittent, 100% replacement is indicated. If the
item you are repairing is "blue collar" or "high tech," 100% replacement
with obviously new good-quality components seems to be preferable. By
"blue collar," I refer to test equipment and items such as Hammond
organs and studio equipment that worked for a living. By "high tech," I
mean good communications receivers and genuine high-fidelity equipment.
Many of these items used higher quality components originally.
One item that has complete consensus is quality of workmanship.
You will want to learn how to remove component leads completely, clean
up old terminals, and make neat new solder joints.
Q. I found an RCA model 630 ten inch TV set at a flea market. The
power cord is shot, and when I pulled the chassis out, I found the wires
to the switch appeared to have had the insulation burned off. I found
that the 5U4 plates were melted together. I put in a new 5U4 and
plugged the set in, but it doesn't do anything---no picture, no sound.
What should I do now?
A. First of all, a TV set draws substantially more power than a
radio. Do yourself a favor and install a fuse in the primary power
wiring to the switch. Use a slow-blow fuse rated at about 150-200% of
the set's power consumption. For a set drawing 250 watts, a 4 amp
should give reasonable protection.
On a 630, there is a black box mounted on the left rear of the
set, with some power resistors inside. Open the box and check the
resistors. These are back-bias resistors, in the B- circuit. If they
are open, check all the filter caps. Replace the resistors, if
necessary.
Bringing up an old TV takes some care, and the order in which
you check things out is important. As with all old electronics, assume
that it has several things wrong with it. Check that the CRT heater is
continuous (ohmmeter)---you should be able to see it glow when you turn
the set on. The first thing to fix is the power supply. Once you have
good B+, and all the tubes are lit up, do you have a raster? If not,
check the horizontal oscillator and amplifier. Note that the horizontal
amplifier has very high voltages in it, and that some faults may cause
these high voltages to appear where they shouldn't be. Don't go probing
around in the horizontal circuit with the set turned on. Horizontal
amplifiers on magnetic deflection sets ran with voltage and current
levels appropriate for a transmitter, and several postwar sets continued
to use the 807 beam tetrode as a horizontal amplifier tube, rather than
one of the purpose-built tubes. Shut the set off, connect your probes,
then turn the set on, take your readings, then shut the set back off again.
Don't touch anything in the set without first assuring that it is shut
off, then touch an insulated probe connected through a 1K resistor to
ground to all of the terminals in the circuit to assure that there isn't
a high voltage charge somewhere. If the horizontal circuits are OK, the
1B3 high voltage rectifier filament will glow. Make sure that the high
voltage cable isn't shorted somewhere, and that there isn't a lot of
dust or crud to bleed off the high voltage---problems here are usually
pretty obvious in the dark, where you can see corona discharges, arcing,
and other leakage problems. Unless you have equipment of measuring
10KV, you can't measure the high voltage directly, but if the 1B3
filament is lighting, and the flyback plate winding to the 1B3 is not
open, you probably have high voltage. If you have high voltage, and the
tube does not show any light (this may be a spot or a line, rather than
a raster), check the CRT grid-cathode bias voltage---once again, keeping
hands completely away from the CRT socket unless the set is turned off
and you've grounded terminals through 1K. The brightness control should
be able to swing the voltage back and forth from about -20 to -60 volts.
Check grid 2 voltage---should be around 250.
If you have a horizontal line on the CRT, you are not getting
vertical deflection. Check that the oscillator is oscillating, that the
output stage is operating.
Once you have a raster, then you can start debugging any
problems in the video and audio circuits. Prewar and early postwar TV
sets trapped the audio right behind the tuner and used separate IF
strips for video and audio. Later sets use "intercarrier" IF's, with
one IF strip and a sound trap at the end of the IF chain. In either
case, "raster, no picture, no sound" means that the problem is between
the tuner and the sound trap. "Picture, no sound," or "sound, no
picture" means the problem is after the sound trap. Don't fuss with the
tweaks on the IF strip (strips) unless you have the proper equipment and
instructions for doing an alignment. Unlike most radios, these are
stagger-tuned, and you don't just "tweak them up" for best performance.
The video comes from a conventional AM detector and a "high fidelity"
voltage amplifier, connected to the CRT cathode. Note that the bandpass
of the video amplifier is very wide, and the term "video amplifier" has
become a generic term from a wideband untuned amplifier. The audio is
through a conventional ratio detector and single-ended audio amplifier
to a (incredibly cheap setup for something that cost $400 in '46) small
speaker.
One fairly standard complaint is loss of raster sync. If the
tubes are OK, this is generally the paper capacitor bugaboo at work.
Loss of both horizontal and vertical means that the coupling out of the
video amp has a problem. Horizontal sync comes from differentiating the
video signal, and vertical sync from integrating the double-speed
interlace "trick" pulses that ride on the "pedestal" portion of the
video signal (the vertical sync portion).
These are some basic things about forties TV sets. Note that
the CRT's on early magnetic deflection sets had offset guns and "ion
trap" magnets. This was to prevent burning a spot in the center of the
CRT. Around 1948, the aluminized phosphor coating, which was impervious
to ion burns, went into production, eliminating the need for offset
guns. If the ion trap is misadjusted, the electron beam won't be aimed
at the phosphor screen properly, so the raster will be dim or
nonexistent, or have "neck shadows" at the edges. This, like the IF
tweaks, another "if it's working, don't fix it." Electrostatic
deflection sets that used tubes like the 7JP4, did not have ion burn
problems, so are mounted with nothing on their necks. These sets also
did not require transmitter-like power for horizontal deflection, so did
not have high voltage derived from the horizontal circuit. Instead, a
separate RF oscillator was used. CRT circuits in electrostatic
deflection sets are quite similar to oscilloscope CRT circuits.
There are several books on servicing television sets that
generally apply to forties sets, although they are generally oriented
toward later sets. Compared to later sets, most forties TV sets were
powered through transformer supplies, did not have any tricks like B+
boost.
Q. My radio plays, but the audio is distorted. Announcers sound like
mush-mouths, and music sounds as though gravel is rattling in the
instruments. I checked it with another speaker, and it sounds just as
bad.
A. The most common causes of distortion are in the power amplifier
circuit.
(Note that in the following I am assuming class A or AB1 operation,
where tubes do not draw grid current. If the grids of your power
amplifier tubes are driven by power tubes, such as a 6N7 or 6V6's, most
of the following applies to operation at low output).
1. Check that the coupling cap (or caps, in the case of
push-pull) are not leaking DC from the preceding stage and pulling the
output tube grid high. Most circuits use a 180K to 500K grid leak to
ground and a .05 or .1 microfarad coupling cap. At low-moderate audio
output, there should be no measureable DC voltage across the grid leak
resistor. Check the grid leaks themselves for proper value and good
connections (typically to ground). Wax paper coupling caps here are
notorious for giving problems, and are candidates for replacement even
if they appear to be good. The tube itself may be developing excess gas
current in the grid circuit. Disconnect the coupling cap, turn the set
on, and make sure there is no voltage developed across the grid leak. If
there is, replace the tube. Note that most tube testers won't disclose
this problem. With larger tubes (6V6, 6L6), replacement tubes made
after the mid-70's often had poor gas current characteristics, and some
designs were built with higher-value grid leak resistors than specified
by the manufacturers on the assumption that replacements would "never be
that bad." Most beam tubes specify a maximum impedance in the grid
circuit of 500K for cathode bias, 100K for fixed bias operation.
2. Check the value of the cathode resistor. Be careful here,
because a resistor that has overheated may not only have changed value,
but have charred the color bands so that they look like a very different
value resistor. If the circuit uses a cathode bypass capacitor (usually
an electrolytic, 20 mfd. 25 volt typical), check that it isn't leaking
current, and check that it has capacitance.
3. Check grid bias with the set running. Proper bias for
various tubes can be estimated from tabular data in tube manuals, and
ranges from around -7.5 volts for a small high-gain beam pentode like a
50L6 to around -60 volts for a large low-gain triode like a 2A3.
4. On a push-pull output stage, check that both sides are
operating. An easy check is to jumper across the grid leak resistor
with a clip lead, and see if things change. If jumpering one input
kills the audio, the other side is inoperative. Prime things to suspect
if one side is dead are the power tube on that side, open transformer
plate winding (no B+ on that tube), open coupling cap, or problems in
the voltage amplifier ahead of the output stage.
5. If you haven't found the problem yet, check the quality of
the audio coming out of the preamplifier stages.
6. DC imbalance can cause problems in push-pull circuits. Most
old radios don't have any place to measure this. You can wire 100 ohm
resistors into the plate circuits, in series with the output
transformer, and measure the quiescent DC voltage across them. For most
old radios, a 20% imbalance is tolerable. Keep in mind that the
voltage developed across a cathode resistor is total cathode current,
both screen and plate, and that a common cathode resistor in a push-pull
circuit is looking at the effects of two tubes simultaneously.
Q. I've got an "All American Five" 50L6 radio that has new filter caps,
but the hum that comes out of the speaker is really out of sight. I can
hear it in the next room when the volume is so low I can't really hear
the station it's tuned to. I know these sets hum, but should it be that
bad? All the tubes test good on a mutual conductance tube tester.
A. No---you've probably got a very common tube fault that a
tube tester doesn't detect, heater-cathode leakage, probably in the
50L6. In these sets, the low end of the 50L6 heater is about 38 VAC
above ground, and the high end, up at 88 volts. What you are getting is
AC on the cathode, and the only real solution is a 50L6 that doesn't
have heater-cathode leakage. 12SQ7's can also have this problem,
although they are always wired at the ground end of the heater string.
The only real diagnostic is to scope the cathodes of both tubes.
One item that aggravates this situation is that many "All
American Five" sets had no bypass capacitor across the power amplifier
cathode bias resistor. Hanging a 50 mfd. 50 volt cap here often will
improve set performance and reduce hum, although it won't solve a
serious case of leakage.
Before trying to diagnose hum problems, particularly in a series
string set, try turning the plug to the wall socket around the other
way, to reverse the polarity of the chassis. Many of the older 300 ma.
series string sets were very sensitive to primary power polarity, and
would have very loud hum if the power plug were connected the wrong
way.
Q. What sort of tools and test equipment do I need.
A. A 20,000 ohms/volt multimeter is indispensible. They are relatively
inexpensive, and modern multimeters have protection circuits in them.
You can trouble-shoot and fix almost anything discussed in this
newsgroup with a multimeter and some knowledge of circuit theory. Many
prefer an analog meter with a needle over digital. You can watch the
needle move and see what's happening.
While not "test equipment," tools for unsoldering and soldering
components and wire are also mandatory. Soldering is discussed in
another FAQ question.
Other small hand tools include screwdrivers, allen wrenches (for knobs
with setscrews), nut drivers, and small diagonal cutters and
needle-nosed pliers. There is only one kind of tool, a good quality
tool. Buy the best. They'll last forever, and do their jobs well.
Don't buy cheap knucklebusters. They are hard to use, will make
scratches, bend, and break, and scar up the work. Buy the best---many
of the good tool manufactures have sold the same tools for over fifty
years, and many of us use tools that old today.
Beyond the basics are the following:
a. Oscilloscope. This has become the primary instrument for use in
electronics work of all sorts. While they were not commonly used for
radio repair in the 1930's and '40's. There are a great variety of
scopes, ranging from the old relaxation oscillator sweep type used in
the thirties (and sold by Heath as late as the 70's) to the very latest
solid state scopes with triggered delaying sweep and multiple trace
vertical inputs. Almost any scope that works is fine for working on old
radios and vacuum tube amplifiers. While you can get old vacuum tube
scopes for very low prices, keep in mind that you may find yourself
trouble-shooting and fixing it.
b. RF signal generator. Once again, these come in many sizes and
shapes. These are used for aligning tuned circuits (RF and IF
amplifiers). For an AM-shortwave radio, you need 100 kc. to around
15-20 mc, with AM modulation capability, and for FM, you should have
88-108 capability as well. A sweep signal generator (i.e., able to
swing the frequency back-and-forth over a small range electronically,
with a voltage output to drive an oscilloscope horizontal amplifier) and
a suitable scope are very nice to have but not mandatory.
c. Tube tester. The value of tube testers as a primary diagnostic tool
tends to be overrated, but a good mutual conductance tester (Hickock
made several) can be of value if it is used appropriately. Cheap "tube
checkers" will test filaments (an ohmmeter will do as well) and whether
the tube conducts or not, and may detect hard short circuits (these do
happen). A Tektronix 570 curve tracer (a specialty oscilloscope that
gives graphic displays of tube characteristics) is the ultimate in test
devices. However, the ultimate "tube tester" is the equipment in which
the tube is used. The function of tube testers, more than anything
else, was to sell replacement vacuum tubes. And many really nasty
tube-related problems will only show up in the socket in the equipment
where they are supposed to function properly.
If you have a good scope, multimeter, and signal generator, and know how
to use them, you have all the tools you need for radio work. Here are
some other items, some of which were popular as radio shop tools, and
some of which aren't primarily test equipment.
d. Signal analyzer, signal tracer. These were very popular in radio
shops. They are an AF amplifier, small speaker, and a diode detector
that can be switched in and out of the probe circuit---in essence, a
small radio without any tuned circuits. If signal is getting into the
antenna, you can probe each stage and hear it, and quickly locate a
"dead" or "distorted" stage.
e. Condenser tester. Also "radio shop" stuff from the 1930-50 era.
An inexpensive L-R-C bridge with an electronic oscillator. Used
properly, it can be a handy tool. I use the term "condensor" because
it was the standard term for a "capacitor" in the US until the late
1950's.
f. VTVM (stands for "Vacuum Tube Voltmeter"). The virtue of these is
the high input impedance (generally megohms) and their ability to
measure resistances into the megohms range. Largely supplanted by
oscilloscopes, which draw a picture of the signal, but of value today
for their ability to measure high resistance.
g. Grid dip meter. This is a small oscillator that comes with a set of
plug-in oscillator coils that can be poked into tuned circuits. They
rely on the fact that a resonant circuit near the oscillator coil will
cause the grid current of the oscillator tube to drop, hence "grid-dip."
A very simple and handy little device, though generally used with things
like transmitters that have to be tuned before power is applied. Since
they oscillate, they are also a fine "poor man's signal generator."
There were several specialty houses in the US in the 1930-50 era that
built very good measurement equipment. I'll mention them by name:
Boonton Radio, built Q-meters and R-X bridges. These measure the
inductance and other characteristics of RF coils and tuned circuits.
Generally used to support coil design efforts. The British Marconi
Q-meters are excellent as well.
Measurements Corp. Built very nice signal generators, much higher
quality than those from repair equipment manufacturers like Hickock.
General Radio (Cambridge, Mass.). This company moved to the suburbs in
the late 1950's and is now known as Genrad. Their 650 impedance bridge
was the general use DC/400 cps L-R-C bridge. It used a small battery
and a 400 cps "hummer" (a small vibrator) to generate AC for measuring
impedance of things like audio transformers. Over the years, General
Radio built a broad line of devices, primarily for engineering use, only
some of which are applicable to radio electronics.
Guildline of Canada. I mention them because they built some of the very
best calibration standards. Their potentiometers and other products are
not only "not test equipment" but can easily be damaged if used for
testing things. The proper use of such equipment is calibration of
working equipment, and the appropriate place for it is a calibration
shop.
While I mention equipment common in the US, I am familiar with products
of Marconi in England, who built engineering support products similar to
the Boonton, Measurements, and General Radio products. I believe that
Telefunken, Phillips, and Thompson-CSF (spelling?---French company) also
built and sold similar equipment. The US stuff often shows up at things
like ham swapfests, and is bought and sold by several companies, notably
Tucker, of Dallas, Texas.
Q. My radio is supposed to have 295 volts on the screen of the 6L6
amplifiers. I read 303.5 on my digital voltmeter. Is something wrong?
A. Yes, both your expectation that the screens are supposed to read 295
volts, not 295 +/- 20%, and that your DVM is precise just because it
gives you a lot of digits. When was that DVM last calibrated (or was it
ever calibrated) against a known standard of some sort?
Most shop test equipment is wildly inaccurate to begin with, and has had
enough use and abuse (and time) since last checked that you can't trust
the readings at all. At best, they will tell you "around 300 volts" or
"around 455 Khz" unless you have some way to check against standards.
Don't trust anything to be telling you other than "approximately" unless
you have had it checked against standards recently, know what accuracies
you can expect, and things that can affect accuracy. Most major cities
have services which have standards against which to check test
equipment, and if you have something like a GR 650 bridge that is
working properly, it may be worth the tariff to have it's calibration
checked by one of these shops.
When selecting test equipment, keep in mind that that nice old Tek scope
may have 35 or 30 tubes and 50 adjustments, and pose much more of a
maintenance problem than any radio.
Q. I don't trust the calibration of my instruments? What can I use to
check them?
A. There is a good frequency standard available for free: WWV, which
broadcasts on 5, 10, and 15 Mhz. If you have a signal generator with a
crystal calibration oscillator, you can tune in WWV on a shortwave
receiver, tweak the crystal tank circuit, and have a fairly good
reference to WWV for other frequencies----though it's a long stretch
from 5Mhz to 455 Khz. Fresh dry batteries generally are fairly close to
their nominal voltages, and an automobile battery that is fully charged
is a first cut "standard" 12.6 volts. Accurate voltages above that are
hard to find in the basement workshop. Ohmmeters tend to be wildly
inaccurate, but you can measure a bunch of resistors of different values
to get "somewhere near."
(Faq editor note: other countries have frequency-standard time
stations; if someone familiar with them could E-mail me the information,
I will include it here).
The rule of thumb is that two-figure accuracy is readily achievable, and
more than what is needed for service work. However, if you are using
flea-market test equipment, it may have been discarded or surplussed
because it could not be calibrated, or may not have been checked and
calibrated for thirty or forty years.
Q. I tried to use a Tek scope to trouble-shoot my AC-DC set, but when I
connected the probe ground, I got sparks and burned out the wire.
What's wrong?
A. US AC-DC sets typically have one side of the line connected directly
to chassis ground. Some European sets may also have a direct connection
between one side of the supply mains and the chassis. Virtually all US
test equipment built over the last 40 years uses a three-prong plug with
a direct connection between the ground prong and the test equipment
chassis. What happened here is that the radio was plugged in with the
high side of the line connected to its ground, and you connected the
ground strap across the line voltage. While in US power distribution
systems, the "neutral" wire is connected to earth ground at the
distribution panel, grounding the line neutral at the radio may cause
currents to circulate in the neutral-ground circuits (ground loop).
The best way to avoid a shock hazard with an AC-DC set is to use an
isolation transformer. It is possible, but not recommended, to "float"
the test equipment ground by using a two-prong "cheater," but this may
cause other problems. Plugging the set in so that the grounded side is
neutral may also work, particularly if you use a .01 mfd or larger cap
in the ground circuit to the scope. However, with any method other than
an isolation transformer, the scope and the radio may have some voltage
between them, posing a shock hazard as well as problems making
measurements.
AC-only sets were often connected with a .02 mfd cap from each side of
the AC line to the chassis to provide an AC reference ground between the
chassis and the AC line. If either of these capacitors is shorted, the
chassis is directly connected to one side of the line. Find these caps
and check them before doing any trouble-shooting.
Q. I want to fix my old radio myself, and have never used a soldering
iron before. What do I need to do?
A. Soldering equipment for radio work is discussed in section 8 of the
FAQ.
Q. Replacing all those capacitors is a lot of work. Somebody told me
that I could just clip the leads and solder new caps to the old leads.
That sounds a lot easier. Should I do that?
A. Going back to Frye's "Mac's Service Shop," a column that appeared in
the old "Radio News" in the 1940's, a proper repair is to make the radio
"like new," using the methods that were used to build it originally.
The Yiddish term, "schlock," was invented for folks who do things like
clip out old parts and solder new ones to the leads. Yes, removing
solder from terminals and prying the ends of tightly-wrapped leads open
so that you can remove an old part is hard work, and it will take a
while to learn to do it with any ease. Take those old components
completely out, clean off the terminals, and install the new components
neatly. In many cases, particularly if you are replacing wax paper
capacitors with axial-lead mylars, you will find the old leads bent
around quite tightly to connect one end of the capacitor to the nearest
ground that could be reached. The new capacitors are much smaller, and
may install much more neatly, particularly if an appropriate ground
point is nearby for bypass caps.
If you take pride in good workmanship, you'll end up with a set that
works well, isn't a fire hazard, and doesn't have mysterious squawks and
squeals. Sloppy workmanship is a red flag to anyone who looks at the
radio---it says that there is probably extra trouble installed by
whoever did the poor work. And, most of the time, investigation shows
miswires, wrong-value components, and a host of other problems.
Q. I have an early 1930's radio and want to replace the wax paper
capacitors, but want to keep the chassis looking original. Where can I
get look-alike wax paper caps?
A. The manufacturers who made these discontinued them years ago. You
will probably find repairs from the 1946-70 era in old radios using
paper capacitors molded in plastic, and even these are difficult to find
nowadays. While recent axial lead caps with mylar and other plastic
dielectrics work well, as long as the voltage rating is adequate.
Generally, 400 volt caps will work, but 600 or 630 volt caps are safe
in any set with an 80 or 5Z3 rectifier. However, they don't look
anything like the old axial lead capacitors.
It is possible to melt the wax out of old capacitors, salvage the
cardboard sleeves, and install new axial lead caps inside. While
axial-lead caps are somewhat hard to find, and tend to be expensive,
they are still made, and are usually small enough to fit in the old
cardboard sleeve.
Dan Schoo, who does this type of restoration regularly, kindly wrote up
a procedure for salvaging the old sleeves and putting new caps inside,
and made it available for inclusion in the faq. Here it is:
Rebuilding Wax Filled Paper Capacitors
by Daniel Schoo
From: schoo@fnal.gov (Dans Cockatoo Ranch)
A paper capacitor is a type of capacitor that was used
extensively in radios from the thirties through the fifties. They
are made of wax impregnated kraft paper and two thin metal foils
cut into long narrow strips. The foils were placed one on each
side of the kraft paper and rolled up along the long dimension
into a rod shaped assembly. The foils were skewed such that they
extended a little past the paper at the ends of the rod, one on
each end. This provided an electrical connection point to each
foil over it's entire length. The voltage rating of the capacitor
was controlled by the thickness of the paper. Thicker paper could
hold off a higher voltage. The capacity was controlled by the
surface area of the foils. Longer wider foil wraps would have
higher capacity. This is why higher voltage and/or higher
capacitance values would require a larger size for the capacitor.
The lead wires were attached to the foils extending out from the
ends of the rod. The entire assembly was then slipped into a
cardboard sleeve and the sleeve was filled with wax. Later types
were molded into plastic shells and had paper labels attached or
were printed with colored bands or text to indicate the values.
The black band around one end of the sleeve and the words
'outside foil' indicate the lead that is attached to the foil
strip wound on the outside of the kraft paper. This is important
in some applications and tells the assembler which lead to use
during construction. Paper capacitors were used for higher
voltages at medium to small capacities. The voltage ranges are
usually from 100 to 600 volts and from .0001 to 1 microfarad in
capacity. They typically fail by becoming leaky and allowing DC
current to pass.
The purpose of rebuilding an old type paper capacitor is for
appearance only. When restoring an old radio to operable
condition, some owners desire to keep the appearance of the
components under the chassis as close to original as possible.
When certain components fail such as capacitors, it is not
possible or even desirable to replace them with original types.
To keep the original appearance, the old component is taken apart
and a new one is hidden inside the old shell.
After you have determined that a capacitor is bad, or if you just
want to replace one because you have a basic dislike for them,
remove it from the radio. Begin by melting out the wax potting.
Wear eye protection and use a heat gun, blow drier or small torch
with a hot air attachment like a Master Ultratorch. Do not use a
torch or other open flame on the capacitor as this will apply too
much heat in a small area and probably cause it to burn. Not much
heat is required to melt the wax but it has to be steady and even
to heat up the entire body of the capacitor. Hold the capacitor
sleeve with a long nose pliers and heat it slowly until all the
wax has dripped out. Discard the old wax. Some paper capacitors
have cardboard end disks. For these, the ends of the sleeve are
rolled inward to retain the disks. Unroll the end crimps and
smooth them out. Remove the end disks with a small screwdriver.
After the end disks are out continue to heat the capacitor until
the rest of the wax is out. After most of the wax has run out,
hold the capacitor with an insulated pad, grab a lead with a
pliers and pull the insides out. If the wires come off, push the
insides out with a small screwdriver. If the insides are stuck in
the cardboard sleeve, it may be necessary to drill them out. Pull
out the wire leads and drill a small pilot hole down through the
center of the capacitor. Drill another larger hole about half the
diameter of the sleeve. You should be able to dig out the rest of
the insides with a small screwdriver. Be careful not to puncture
the sleeve.
Once the sleeve is cleaned out you can install the new modern
capacitor. The most difficult part of this is to find a suitable
capacitor that will fit into the paper shell. You can substitute
a new capacitor with an equal or higher voltage rating than the
old one but try to get as close as possible to the original
capacity. Fortunately many of the modern capacitors are much more
compact than the old paper ones. Modern capacitors use plastic
films like polycarbonate, polypropylene, polystyrene, and
polyester which is also known as Mylar. The most common is Mylar
and is suitable for many replacement applications. These do not
degrade with time like paper does and should give years of good
service. The popular Sprague "Orange Drop" is a Mylar capacitor.
These are not suitable for use in this application because they
are designed for printed circuit mounting and the leads are
radial. This means that they extend out the side of the capacitor
at a right angle. You must use an axial lead capacitor with the
leads extending out in line with the capacitor body.
Slide the new capacitor inside the old sleeve and center it. If
there is a lot of space around the new capacitor such that it is
loose you can wrap a few turns of plastic tape around it to build
it up. Slit the tape down to about a quarter of an inch wide and
wrap it in a band around the middle of the capacitor until it
fits snugly in the sleeve. After the new capacitor is centered in
the sleeve you can fill the ends with wax. You can get beeswax at
any well stocked hardware store. It comes in small tan blocks
about three inches square and one inch thick. Cut off a small
chunk and place it in a small metal can. Prepare the can by
bending a pour spout into the top edge and make sure it is clean
and dry. Wear proper eye and skin protection when heating the wax
just in case it spatters. Heat up the wax slowly with a heat gun,
a hair dryer or small torch. Remove the heat when all of the wax
has melted and be careful not to overheat it. If it begins to
smoke remove the heat immediately. Support the capacitor in a
vice or tape it to the edge of a table top. When the wax has
melted thoroughly, pour it slowly into the end of the sleeve just
up to the edge. If the capacitor had end caps leave enough room
to reinstall them. When the wax has cooled sufficiently, flip
over the capacitor and fill the other end. Allow the capacitor to
cool completely before installing it in the radio.
V
Daniel Schoo (o o)
Electronics Design Engineer ( V )
Fermilab, Batavia, Illinois, USA .......m.m......Dan's Cockatoo Ranch
vvv
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From: vancleef@netcom.com (Hank van Cleef)
Subject: Rec.antiques.radio+phono Tools and Test Equipment(FAQ: 8/9)
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Archive-name: antiques/radio+phono/faq/part8
Rec.antiques.radio+phono Frequently Asked Questions (part 8)
Revision Date Notes
1.0 Oct 28, 95 New section
Part 8 - Tools and Test Equipment
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Email vancleef@netcom.com
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and phonographs. It is intended to summarize some common
questions on old home entertainment devices and provide answers
to these questions.
[faq editor note Oct.'95. This is a new section, which includes material
previously covered in other sections, as well as new material].
This section of the FAQ is divided into two parts: tools, and test
equipment. The section on tools is intended to be general, covering
tools suitable for working on acoustic phonos and other mechanical
devices as well as electronics. The section on test equipment is
primarily electronic.
TOOLS:
If you are going to work on anything yourself, you will need some hand
tools. Keep in mind that "tools" and "trades" go hand-in-hand. Most
tradespeople are expected to own their own hand tools, and the best
sources of good tools are those that sell to crafts trade users. Anyone
whose livelihood depends on use of hand tools will tell you that there
are two kinds of tools: good tools and no tools. A cheap tool is worse
than no tool. It will cost you some money to buy a suitable assortment
of proper hand tools for various jobs. Good tools properly used will
last a lifetime, and you'll get a good return on the investment. I have
tools that I bought over forty years ago that still work "like new."
Craftsmen (and women) who use tools professionally will tell you that
cheap tools are "knucklebusters" (and worse). There is no substitute
for having the right tool for a job. Trying to get by without proper
tools for jobs, or with cheap tools, you'll damage the work and hurt
yourself.
Take the time to learn how to use your tools properly. A quick trip to
the library will produce books on various crafts trades that include
selection of tools, use of tools, and maintenance of tools (such as
cutting tools) that require maintenance. Talk to crafts people in
various trades. The automobile mechanic may tell you that Snap-On tools
are overpriced and frosting on the cake, but that same mechanic buys
every week from the Snap-On truck. And the welder will question whether
Linde double-diaphragm gas regulators are really needed, but that's
probably what he is using for gas welding. There is an old adage that
"the poor workman blames his tools." Develop your skills in using good
tools, and you'll get good results.
One point of etiquette: If you are talking to a crafts person, don't
charge over to his/her toolbox and start looking around. Ask permission
before handling someone's tools. Most crafts people will gladly show
you what they use, and tell you why they value particular tools.
Q. What do you consider basic tools for working on old phonos or
radios?
A. There are a number of common small tools for working with any small
device. These are:
a. Flat-bladed screwdrivers. You will need an assortment of
these in various sizes.
b. "Phillips" cross-point screwdrivers. The also come in
various sizes. The most common is #2, but you will also want #1 and #0.
The tips on these wear out, and the only solution for this is to buy
good quality replacements when the tip becomes worn.
c. Hex socket keys, commonly called "Allen Wrenches." Start
with a kit that has the common sizes, from .050 through about 1/4 inch.
The most common are the "L"-shaped keys. They are also available in
screwdriver shanks with straight bits. Once again, these wear out. You
can grind the worn tip off one to give it more life, and buy the various
sizes individually. Most people working on old electronics have several
.050, 1/16", and 5/64" keys as these are the ones most frequently used
in small work.
d. Socket wrenches. A 1/4 inch drive set in a box, with
ratchet, screwdriver handle, and extensions, is a good choice. You can
also buy nut drivers, which are screwdriver shanks with socket tips.
The "six point" (or hex) sockets are best unless you actually need to
work with 12-point hardware. Most commonly used are 1/4", 5/16",
11/32" nut drivers. 3/8", 7/16", and 1/2" are used on binding post,
switches, and potentiometers. For these, a ratchet and deep socket is
best.
e. Box and end wrenches. These come in a variety of styles. A
box wrench has a hex shape at either end, two different sizes. An "open
end" wrench has fork-shaped tips with parallel sides, also made with
tips at both ends, two different sizes. A "combination wrench" has an
open end at one end and a box at the other, same size at both ends. Box
wrenches are generally made with the box ends offset from the wrench
shank. Open end and combination wrenches don't generally have this
offset, but the box end of a combination wrench is generally set at a
small angle to the shank so that the wrench shank has clearance above
the work. Which is best? Most people use all three types in their
work. The open end wrench will tend to spring and round off the corners
of the hardware if a lot of torque is required, and most people feel
that the box ends should be used except where clearance requires use of
the open end. Note that there are specialty "tubing wrenches" for use
with hex fittings on tubing. These are box sections with a cutout to go
over the tubing, to get a good grip on the fitting. These should be
used only on tubing fittings, not as general wrenches.
f. Pliers. These come in a bewildering variety of sizes,
shapes, and tip types. Many people also try to use them instead of
wrenches or other more suitable tools, which is not good. Pick pliers
for pliers applications, and get the right tools for other hardware
tasks. For small work, needle-nose pliers get steady use. You will
want to have a set with a very long narrow set of jaws and another that
is larger and more blunt, generally called "round nose." Both have long
parallel jaws and a rounded tip cross section. A pair of "duck bill"
pliers is also quite useful.
The common slip-joint "gas pliers" can be useful, but many
people consider them a tool that works poorly on a variety of tasks and
not very well on any of them. For large work requiring sturdy jaws, a
set of "Channellock" (TM) pliers is much better. The originals were
made (and patented) by Channellock in Meadville Pa., originally named
"Champion Dearment." Get a set that have the interlocking channels for
adjustment.
g. Diagonal pliers, wire cutters, side cutters, etc. These
names are all applied to plier-type tools with cutting tips. You will
want a small set for cutting wire. Some of these are made with the
cutter tips ground all the way to the very end, which is useful for
nipping wire loops on old electronics terminals. They are intended for
cutting soft materials, like copper wire, and can be damaged by trying
to cut hardened steel with them.
h. Hemostats: These look like scissors, but have duck-bill
tips on them and a latching mechanism on the handle. Originally used in
medical work for clamping off blood vessels. They were used in
electronics as "heat sinks" for soldering germanium semiconductors, to
bleed the heat off the lead. Also valuable for use in applying clamping
pressure to thin sections.
i. Magnifying lenses and eye protection. You will want some
sort of magnifying glass, jewellers loupe, or bench magnifier, for
examining things in detail. A 5X magnifier is a good choice for most
work.
Always have eye protection when using tools. If you do not wear
eyeglasses normally, get some safety glasses. Corrective lenses must be
the "shatterproof" eye protection type, and if you wear corrective lens
eyeglasses, get a pair that is suitable for close work that has
shatterproof lenses. Contact lenses do not provide eye
protection---have something in front of them.
j. If you are going to do really small work, like meter
movements, a set of jeweller's screwdrivers is a good investment.
Brookstone sells a kit in a box that includes an assortment of small
flat-bladed and cross-point screwdrivers, tweezers, small cutting
pliers, and a magnifying glass.
Q. Where do I get good tools?
A. You can get them from sources that sell primarily to the crafts
trades. Most independent automotive jobbers carry automotive tools such
as SK and Herbrand. Snap-On tools are sold by independent sales people
whose "store front" is usually a step-van type truck (similar to a UPS
or bread delivery truck). Other brands are also sold by independent
people operating out of delivery trucks. These people make regular
rounds of automobile and aircraft repair shops, and are often not listed
in the telephone book Yellow Pages. Look under Snap-On, SK, and
Herbrand in the white pages. It may be necessary to inquire at an auto
repair shop or two, or at an airport fixed base operator maintenance
facility, to find out when the various tool dealers normally arrive, and
how to get in touch with them. You can generally arrange a mutual
meeting point with these people, either on their normal route, or by
appointment. Almost all of them know their tool lines and their uses
extremely well, and can advise you on what to buy, knowing what uses you
plant to make of them. Be prepared to spend money. Most electronic
distributors carry good selections of specialty tools for electronics
work. The best sources are those to sell to the trades. Don't look for
prices, look for quality. Those who sell tools will sell to an
individual for the same price as they sell to crafts people in the
trades.
Keep in mind that good tools are, by and large, not "consumer items"
that you'll find in "low price" type stores, such as K-Mart and
Wal-Mart. The one exception is Sears, Roebuck, who have historically
sold good quality tools under their in-house "Craftsman" name. I have
recently heard reports that Sears quality has become less reliable.
Also, while Craftsman tools were historically good tools, there are a
good many tools that are much more refined, and are worth the extra
money in productivity. SK, Herbrand, Blackhawk, Krauteur (pliers in
particular), and Channellock are all excellent in the USA. Snap-On is
the "Rolls Royce" in automotive type tools, and generally cost more for
tools that may or may not be superior to some of the other brands, but
you'll find all of these brands in a mechanic's toolbox.
Q. What about soldering equipment for electronics work?
A. All of the manufacturers that use solder to connect electronic
components run "solder school" for new employees. Electronics soldering
is not the same as soldering pipes in plumbing or doing auto body lead
work. There is only one way to learn, and that is to do it. You will
need:
a. Soldering iron. A Weller or an Ungar "solder station" with
a 35-50 watt "pencil" iron and thermal control in a soldering iron
holder is best. If you are going to unsolder components directly
soldered to a chassis, you will need at least 50 watts, and maybe a
larger 100 watt iron. Do yourself a favor and buy a good soldering
station. It will cost more than a cheapie Radio Shack iron, but you
will find that the tip stays in good condition a lot longer, and that
you do much less damage with heat, using a good iron. The solder
station holder provides a place to put the iron down that is safe, a
real "plus." Also, buy an iron with a plated iron tip, or get one for
it. There is just no way to keep a copper tip well-tinned for this type
of work, and solder eats away the copper, ruining the tip after a
while.
b. Solder. Kester or similar ROSIN CORE solder is sold
specifically for electronic use. It is "eutectic" solder, that is, 37
percent lead, 63 percent tin, which melts at the lowest temperature.
Don't use 60-40 plumber's solder, which is 60 percent lead.
c. Small tools for use when soldering. You will want some fine
point needle nose pliers, some medium point needle nose pliers, and a
small set of diagonal cutting pliers. Also, a small screwdriver and a
solder "pick" that has a pointed piece on one end and a v-notched piece
on the other. Round this out with a solder sucker (a little pump with a
high-temperature plastic piece that you can safely shove into hot
solder, and a button trigger to trip the pump). Solder "wick" works
well, but remember that when you are removing solder from a 1934 radio
terminal, you are removing 4 or 5 times the amount of solder used on a
modern printed circuit board---use the pump to remove most of the solder
and the wick to remove the rest.
Tin your new iron, and keep the tip well-tinned at all times. This
means keeping a coat of unoxidized solder on the tip. The solder
stations come with sponges. Wet the sponge, and wipe the hot iron on it
to clean off residue. To tin the first time, just melt some solder on
the tip. The rosin in rosin core solder is a mild flux---that is,
chemically active to deoxidize and clean the surface so that solder will
flow onto it. Wipe the iron back and forth on the sponge to distribute
the solder. When properly tinned, the tip should be shiny with fresh
solder all around back about half an inch. Keep the tip looking like
this, and you'll eliminate half the problems people have when soldering.
To remove components, heat the old joint until the solder melts, and
remove the solder with the solder sucker. Bend the old component leads
back, and slide the lead out. You'll have to keep the joint hot until
you've got the bent-over part of the old lead away from the terminal.
This sounds easier than it is. You will want to learn to use the solder
pick, small screwdriver, and needle-nose pliers on various joints. If
the component you are removing is scrap, clipping the lead and leaving a
short loose end often makes getting the loop open easier, and once the
loop is open, the lead can be removed by pushing the wire through the
terminal. Also, using the nippers (carefully!) to nip the wire loop so
that it will break often helps when removing components.
Watch out what you are heating, and watch out what you are pushing and
pulling on. That iron is hot and will burn wire insulation, melt
polystyrene (clear plastic coil forms), etc. Move things out of the way
so you have a clear shot at the joint you are working on.
Don't bend terminals back and forth---they'll break. The worst ones for
breaking are on the 7 and 9-pin miniature tube sockets, and if you break
one, you get to replace the socket, which is a major task. Coil form
terminals are not far behind, and most of those old coils are
irreplaceable. The big terminals mounted on phenolic terminal strips
are fairly rugged, and components fastened to them are a good place to
get some experience before tackling finer work. On fragile terminals,
once the solder is removed (use solder sucker and solder will to remove
as much as possible), a little judicious use of nippers to cut wires,
and other little tricks you will learn as you go along, to avoid any
stress on the terminal, is the only way to go.
Another trick is to make a cold solder joint. Just wiggle the lead a
little while the solder cools, and it will stay free. You can then work
with two hands to get the joint opened up and the lead out of the hole.
When installing new components, run the leads for all new components
going to a particular terminal before soldering any. Form the leads
into new loops and nip off the excess. Place the iron against the
terminal and melt some new solder by pressing it against both the iron
and the terminal. It will melt on the iron first, then into the
terminal. Don't use too much solder, and make sure that the solder
flows onto all the wires and onto the terminal. Once the solder has
flowed into the joint, remove the iron and wait for the joint to cool
and solidify. This is where cold solder joints occur. A cold solder
joint happens when a lead gets wiggled as the joint is cooling,
preventing formation of a solid bond. They are generally easy to see,
because the solder ball on the terminal will often be very frosty, and
not have a smooth surface. They are also very easy to make, and you
should experiment with some scrap---just wiggle the pieces as the solder
is cooling, and you'll get a cold solder joint. If you've got any doubt
about a joint, reheat it and reflow the solder.
Cold solder joints are the single most common solder defect. Inspect
your work carefully after soldering, and if there is the least doubt
about the joint, reheat it. Excess solder and solder bridges (where the
solder flows between adjacent terminals) are other quality
problems---remove excess solder, and inspect carefully. Many radios
were "unrepairable" simply because of bad soldering somewhere.
Attention to producing the very best workmanship, and close inspection,
will produce quality solder joints----anything less will produce
trouble.
While the people who originally built these radios were very skilled,
you'll occasionally find a cold solder joint or a joint with no solder
at all on a lead that has been there as long as the radios has been
around. Don't be afraid to inspect, reheat, and reflow a fifty year old
solder joint that looks suspicious just because it has been there for
fifty years.
There are two schools of thought on rosin removal. You can leave the
rosin on the joint, and most radios were made that way. However, if you
do want to remove it, isopropyl rubbing alcohol on a Q-tip will melt it
right off.
Q. I need to solder some sheet metal, and my soldering iron won't melt
the solder onto the metal.
A. The soldering process for electronics work is conceptually the same
as for sheet metal, but uses small irons, mild fluxes, and eutectic
solder (63/37 or 60/40), which melts from solid to liquid state very
quickly.
For sheet metal work, there are several processes that are used,
depending on the metals to be joined and the strength needed. These can
be divided into three categories:
a. Soft solder, using pewter (tin-lead alloys). Requires use
of a large soldering iron or a flame such as a propane torch. May
require strong fluxes and use of 50/50 or 37/63 solder, which has a
mushy state and can be worked with paddles or a damp rag. Most radio
sheet metal work is done with cadmium plated parts, which will solder
with rosin flux.
b. Brazing, which is a similar process, but uses copper or
silver alloys and a much higher temperature than soft soldering.
Requires an oxy-acetylene torch and appropriate fluxes. The principal
difference between brazing and soldering is that non-pewter alloys and
much higher temperatures are used. Silver brazing is often called
"silver soldering."
c. Welding, which involves melting the metal of the parts and
using a similar alloy as a filler to join the parts together. This
requires use of high temperatures to melt the metal. Principal
methodologies are oxy-acetylene "gas" welding, traditional electric
"arc" welding, and inert gas electric welding, such as "MIG" or "TIG."
There are other electrical processes such as resistance, or "spot"
welding.
I mention all of these because you need to recognize where these
processes were used in original manufacture. For radio work, soft
soldering on sheet metal parts generally involves lead attachment, and
is best done with a 75-100 watt iron, using radio solder and rosin flux.
Don't attempt to repair brazed or welded parts with soft solder if any
strength is required. While brazing and gas welding are conceptually
simple, most hobbyists do not purchase the equipment necessary, and both
require some experience to do well, particularly on small work.
TEST EQUIPMENT
The most frequently asked questions are about tube testers, and many
people who are attempting to get their first radio working assume that a
tube tester is the first piece of test equipment needed. This is not
the case. In a recent discussion between "old-timers" on the boatanchor
list who had worked professionally in manufacturing plants during tube
days, it developed that none of them recall seeing a tube tester in
places like Tektronix, James Millen, or Automatic Radio. While vacuum
tube (or valve, to the British speakers) faults are historically the
most common faults found in old electronics, most of them can be quickly
diagnosed in the application circuit. Also, there are many subtle
faults that a tube tester won't find. We'll discuss tube testers
further down, but will put discussion of other test equipment first.
Q. People talk about using a "Simpson meter." I'm tired of hearing
about Simpson. And what do Simpsons have to do with electronics?
A. The Simpson model 260, first produced right after WW II, is the most
common VOM (volt-ohm-milliameter) found in both manufacturing and
service establishments. It is a 20,000 ohms/volt (DC) multimeter, that
measures DC and AC voltages, currents, and DC resistance. Simpson is
the name of a manufacturer of meter movements, as well as complete
multimeter products. The Triplett 630-series is a direct competitor,
and some people prefer the 630-NA over the Simpson 260. Both are still
produced, and cost around $150-175 for the basic models.
A good VOM can be used to diagnose about 99% of the faults in old
electronics if you know how to use it effectively. It is the first and
most important piece of equipment to have on your bench. You'll rarely
see a used VOM for sale, because they are workhorses, and everybody who
has one is either using it or has managed to reduce it to junk by using
it for decades in all types of conditions. There are inexpensive VOM
multimeters for $25-$50 available from places like Radio Shack, if you
don't want to pay the price for a good commercial quality meter like the
Simpson or Triplett. Either you have a VOM or you need to get one now.
Q. What other test equipment is "basic" for working on old radios.
A. For most work, the basic instruments that will do almost anything
are a VOM multimeter, a signal generator, and an oscilloscope. This has
been true since the mid-1950's, when oscilloscopes that were
sufficiently versatile for general purpose use became available. There
are a variety of signal generators that can be found in the flea markets
and hamfests. For radio work, you will need something that produces
modulated and unmodulated signals between the IF frequencies and the
high end of the receiver bands, as well as a suitable audio signal for
testing audio circuits. A generator capable of generating signals from
100 Khz to 110 Mhz, and a fixed 400 Hz audio tone, will cover the needs
of AM long wave, medium wave (US AM broadcast) and high frequency (1.6
to 30 Mhz) radios, and cover the 88-108 Mhz. FM band as well.
Two items that were very common in service shops in the 1940's, but
which are more-or-less forgotten today are the VTVM (vacuum tube
voltmeter) and signal analyzer, or signal tracer. We'll look at both
below.
Used test equipment is generally available at very reasonable prices.
Unlike the costs of hand tools and soldering equipment, it is easy to
build up a very adequate bench full of useful items for about $100.
Q. I saw a Hewlett Packard signal generator at a hamfest, and, at a
nearby table, a Hickock signal generator. I know that Hewlett Packard
is supposed to build top-notch test equipment, but the Hickock generator
was a lot less expensive, is smaller, and seemed to cover almost the
same ground as the HP generator. What's the real difference here?
A. Essentially, the "real differences" are that Hickock equipment was
generally low-price test equipment targeted toward service shops. HP
equipment was costly, and generally bought by research and engineering
organizations. As you note, the Hickock unit is smaller. Look inside,
and you will see home entertainment type construction, with light sheet
metal work, inexpensive components, etc. Inside the HP box, you'll find
things like huge aluminum castings, top quality components, and more
refined circuitry. The products may have performed similar functions,
but were designed with entirely different philosophies, and targeted
toward entirely different markets. One I would call "service grade,"
the other, "laboratory grade." Generally laboratory grade instruments
were used by highly skilled professionals in laboratory environments.
The service grade boxes were often hauled around in the back of a sedan
delivery or pickup and pretty well beaten up, and weren't expected to
last forever. The reason you see so much laboratory grade equipment in
the used market today is that it is thirty or forty years old and lived
all its life either in a laboratory environment or in storage in the
back of an test equipment pool area. Below are some of the brand names
generally associated with the two grades of instrumentation.
1. "Service Grade."
RCA (signal generators, oscilloscopes, meters, tube
testers).
Hickock (signal generators, tube testers).
Supreme (signal generators, multimeters, tube testers).
Radio City Products (signal generators, multimeters).
Eico (a broad line of manufactured and kit instruments).
Heathkit (a broad line, kits only).
Simpson (multimeters).
Triplett (multimeters).
2. "Laboratory Grade."
Measurements Corp. (Signal generators, grid dips),
Boonton Radio Corp. (Q-meters, other LC instruments).
Allen B. Dumont Laboratories. (Oscilloscopes).
General Radio (A broad line, including RLC bridges,
signal generators).
Weston instruments (meters of all types, standard
cells).
Hewlett-Packard (broad line of test equipment).
Tektronix (Oscilloscopes and related equipment).
Marconi (British. broad line of test equipment).
Philips (Netherlands. broad line of test equipment).
Leeds and Northrup (voltage and current calibration).
Guildline of Canada (voltage and current calibration).
Waterman (oscilloscopes).
James Millen (grid dips, frequency standards,
specialty oscilloscopes).
Wavetek (signal generators).
Q. What about VTVM's? I notice that you can get a "service grade" RCA
VoltOhmyst or a "laboratory grade" HP or Ballantine unit. Are the HP
and Ballantine meters really superior to the VoltOhmyst.
A. I have WV97A and WV98C VoltOhmysts, and HP400D AC and 412A DC
VTVM's. The meters that get the most use in my work are the WV98C and
the HP412A. I like the WV98C because it has both AC and DC capability,
and a reasonably good ohmmeter. It is also much more responsive to
signal changes, and is much easier to use for a lot of service tasks.
The 412A is extremely accurate across the scale, much better than the
WV98C, and has a maximum full-scale sensitivity of 100 microvolts,
compared to the WV98C's 500 millivolts. It also has a much wider ohms
range, and is more accurate there, too. It won't measure AC voltages,
and the design cuts off AC response at only a few Hz, so it is slow to
respond to changes. In short, the tradeoffs are not only construction
quality, but in flexibility. The WV98C required some component
replacement when I got it, but it is a much better setup for general
service work. The HP meter needed a light bulb replaced in the chopper,
but was essentially "plug 'n play" and didn't need recalibration.
The HP400D is an "AC meter," and the WV98C has "AC" voltmeter functions.
However, the 400D is a true RMS meter, while the WV98C is peak-reading.
That is a major difference. If you are looking at the calibrator output
of a Tek scope, which is a square wave, the WV98C reads the peak value,
and you have to read that value on the "P-P" scale. The 400D reads the
equivalent DC energy value of the square wave, information that is not
particularly useful if you want to see if the calibrator is anywhere
near accurate. RMS measurements have plenty of value when looking at
something like a class C amplifier. The 400D was also something of a
bear to get working properly, because it had been "fixed" by someone who
did not know the principles of operation, and who "repaired" all sorts
of things except what was actually wrong with it. In short, all three
meters have their place on my bench, and in several applications, one
will not substitute for another very well.
One point that should not be overlooked is that the sophisticated
circuitry of a laboratory grade instrument can be a nightmare to trouble
shoot and repair. The WV98C does not have a chopper with lightbulbs, a
clock motor, and optical switches, which had problems in the HP412A, and
has only a rudimentary power supply, so does not have the regulator
problems that were the actual fault found in the HP400D.
You can get a great deal of good use out of a service grade VTVM over
and above what you can get from a passive VOM. Input impedance is much
higher, so you can accurately measure things that the VOM can't see.
You can invert the DC sensing and measure negative voltages directly,
and the ohmmeter function has a lot more capability than is available
with a VOM. While one quickly gets used to the backward-reading
ohmmeter scale on a VOM, I still like the VTVM's forward-reading
ohmmeter.
Q. What about signal tracers/analyzers. You mentioned these. What do
they do?
A. These came in several configurations. The fanciest ones were the
RCA "Rider Chanalyst" and Meissner Chanalyst. Essentially, what they
are is a substitute radio receiver, in sections, that you can use to
duplicate the functions in a receiver under test. The simpler units
had only a crystal video receiver (i.e., an untuned detector and an
audio amplifier). The RCA Rider Chanalyst has a built-in signal
generator and VTVM.
The trouble-shooting methodology for using one of these boxes
effectively is to start at the receiver front end, and use the probe to
listen for signal. Simply trace forward with the probe until you find
where the signal disappears or becomes garbled, and you've found the
area that is faulty. Instead of reading meters or scope traces, your
ears tell you what's going on.
The RCA Rider Chanalyst was in a self-contained box that could be tossed
in the back of a car, taken out to a customer's home for a house call to
visit a sick Philco Chairside. Probes, power cord, and even the
instruction manual clipped inside the front cover. Armed with a tube
caddy, a soldering iron, and an assortment of resistors and caps, the
set could be brought back to life in short order. Needless to say, the
customer could watch all this, be impressed by the "doctor's" widget box
and bedside manner---and hear for himself (or herself) the walkthrough
that located the trouble. The smaller units, like the Philco, Sprague,
and McMurdo Silver units, were not all-in-one boxes, but worked with a
signal generator and multimeter alongside.
Q. I have a chance to get a Tek 535 oscilloscope with some plugins for
a very reasonable price. Is this a good thing to have, particularly
when you say that oscilloscopes were rare in service shops in the 30's
and 40's?
A. Grab the scope, if it is working and calibrated, and has had the
selenium rectifiers replaced with silicon (Tek made conversion kits for
this).
There's been some thought given to coming up with a Tek Scope Faq. Stan
Griffiths published a very good little book (available from Antique
Electronic Supply) on old Tek scopes named "Oscilloscopes: Selecting and
Restoring a Classic." Both Stan and I worked for Tek, and we've been
holding something of a steady forum on the boatanchors list on the
topic. In the used market, Tek scopes abound, for quite low prices,
considering what they are. The most common models are the 545A, 535A,
and 547. Almost any of the others in the 530-540 line are good scopes
that come back to life quite well and give yeoman service. The common
plug-ins for these are the CA, K, and G, and you will want at least one,
if not all three. The 547 requires a 1A1 for full bandpass, but will
work with any of the letter series. These scopes are big and heavy,
around 65 lbs, and gobble up about 500 watts of power.
On smaller scopes, the 561A with plug-ins is a good scope, although
limited to 10 Mhz bandpass. The 310 is a little (3" tube) cutie that
can be very handy, although they are somewhat prone to overheating if
you try to run them all day. I'm not going to try to sum up what is in
Stan's book here. He has 200 pages devoted to descriptions of old
scopes and plug-ins, and the vast majority of the equipment described is
good for working with radios. The later 7600 series scopes with the
right plug-ins are also good choices, but tend to be more expensive, and
more difficult to repair.
I'd pick any of these over the 585 (which does NOT work with
letter-series plug-ins unless you have a special adapter), some of the
specialty scopes like the 517, 519, and 502.
On other brands of scopes, Hewlett-Packard tried to compete with
Tektronix for a while. Some of their scopes, particularly the lower
performance units, were fairly good, and some others were marginal. The
Fairchild-Dumont 766H was at least the equal of the Tek 547. However,
so far as I know, they are more or less orphans today, with very few
people having documentation, spares, parts units, etc.
Other scopes? Most of the others are much lower performance scopes than
the Tek 530-540, and a good many of them are lower quality as well.
Unless you are a scope collector, don't bother with the WWII-era P4
synchroscopes, the old RCA's, or the pre-Fairchild Dumonts. One
particular group of scopes to avoid is the Lavoie, Hickock, and
Jetronics "Tek wannabe" scopes that government agencies bought in large
quantities. These, along with "Tek wannabe" plug-ins, are easy to spot.
They look like Tek stuff, but don't have any manufacturer's name on
them. Identification is by a screwed-on nameplate. Genuine Tektronix
has the Tek logo, the name "Tektronix," and other very clear markings on
it. These are, to be blunt, nothing but electronic junk.
My personal preference is for simpler scopes. I use a 533A or a 310 for
most work, and don't find myself at all hampered by 15 Mhz bandpass
(533A) or lack of a delaying sweep (useful for pulse and digital work),
or a dual-trace setup. The real value provided by an oscilloscope is in
qualitative graphic displays. For serious quantitative measurements,
other test equipment is simpler and more accurate, and it takes a good
deal of skill and experience to set up and use an oscilloscope to make
good quantitative measurements.
While you can buy "repairable" Tek scopes and plug-ins regularly for
$10-$50, I feel reluctant to advice the novice to run right out and to
this. Stan Griffiths has about as much experience working with Tek
scopes as anyone, and I certainly would not want to get into a
productivity contest with him. Both of us feel that trouble-shooting a
sick scope is fairly straightforward and easy, and we buy "repairables"
and fix them fairly quickly and easily---most of the time. But a 545
has something like 75 vacuum tubes (I never counted all of them---there
are eight here, ten there, seven more another place, etc.), and someone
who is not familiar with Tek scopes and trouble-shooting methodologies
in general might have a terrible time. Both of us have bought stuff
and found, when we started trouble-shooting, that someone had been there
before us and "fixed" almost everything except the real problems. It's
obvious that somebody else tried to fix some of these, and couldn't.
Both of us have specialized test equipment, and both of us know how to
set up a completely uncalibrated scope. For someone who isn't really
prepared to play "scope wizard," and who wants a solid, reliable scope,
finding someone who knows Tek scopes and who has
clean-working-calibrated units for sale for $125-$150 may be a lot
better bet.
Q. Ok, I've read through all the blather about meters, signal
generators, and oscilloscopes, and my question was about tube testers.
When are you going to talk about them?
A. Ok, fair enough. Roughly, tube testers can be divided up into a few
categories. (Your FAQ editor is flying somewhat blind here. I don't
own or use a tube tester of any type, and it has probably been forty
years since I tried to use one. Dan Schoo has kindly furnished
material on tube testers, which is included after this general
discussion).
1. Emissions testers. These are the type that used to be seen
in drug stores, and the Heathkit "Tube Checker" type of box. They are
fairly simple, have a heater/filament supply, a "good/?/bad" meter.
They generally operate by connecting the tube as a triode and seeing how
much current will pass through. Short circuit testing is by applying a
voltage across element pairs and seeing if enough current will pass to
light a neon bulb.
2. Transconductance testers. The best known of these are the
Hickock testers, both the civilian and the military models. As with the
emissions testers, they are provided with a heater/filament supply and a
shorts test arrangement. However, they are provided with separate DC
supplies and controls for setting the tube elements at one or more
operating points. Readout, as with the emissions tester, is on a meter
which indicates plate current. Most of these have two sets of settings
for the meter readout. In one mode, the meter reads the current as DC
transconductance. In the other, the meter reads on a "Good/?/Bad"
scale. The controls for setting the operating point parameters and
meter sensitivity maybe either potentiometers and switches, or sets of
contacts operated by a punched card. The type that uses potentiometers
and switches is generally used with a tabular listing (a roll chart in
the machine) of switch settings and readings. I am not sure how the
pots and switches are calibrated, and how easily one can reset the
operating point parameters, or read current values on the meter, for
taking a series of operating points to plot on a graph. I haven't seen
any discussion indicating that anyone is using them other than with the
tabular chart values for specific tubes.
3. Tektronix 570 Vacuum Tube Curve Tracer. This is a specialty
oscilloscope that can trace out families of operating curves on a CRT
X-Y display. The box is provided with a heater/filament supply, two
adjustable "fixed" voltages (i.e., they remain static during tracing), a
step voltage, and a sweep voltage. The display monitors current
(vertical) vs. voltage (horizontal), and may be switched to different
suppiies. Connections to the tube are via a patch panel at the front of
the unit, which uses jumpers to go to an adapter plate. Two of these
are provided, to allow side-by-side comparison of two tubes, and there
is a switch to select which set of jumpers is active. While the
switches are marked "plate," "screen," "grid," etc., the patch panels
allow connection of any of the voltages to any of the elements. This
device is not really a "tester," because it has no built-in settable
criteria or indications for "pass" or fail. The box can be set up to
provide a dynamic display of any set of curves, including such things as
suppressor and screen grid transconductance. These were low-volume
products, and the 570 was discontinued in the mid-1960's. So far as I
know, principal use of them was to match pairs of tubes for various
characteristics. Prices on the used market have been bid ought of sight
by the golden-ear tube audio crowd, and the last I heard, the going
price was well over $1000.
All of the above devices are DC tests only. While the Tek 570 provides
a dynamic display, it does so at very low audio frequencies. The
emissions type tester is clearly a rudimentary "pass fail" device whose
strength is in determining whether the tube will work at all. The
transconductance tester is somewhat more sophisticated in setting
parameters at an operating point, which may or may not represent the
actual application conditions that the circuit imposes on the tube.
Some of the major issues in selecting a tube tester involve the
configuration of sockets and socket adapters, and availability of test
data for specific tubes. Also, the condition of the tube sockets has to
be considered. The useful life of a tube tester was relatively short,
because of socket wear. While the sockets could have been replaced,
introduction of new tube types and socket configurations continued
steadily into the mid-1960's, and replacement rather than repair of a
worn unit was justified to support newer configurations. One must keep
in mind that the vast majority of tube testers of both the
emissions and transconductance type were sold and positioned in a
prominent place in a point-of-sale retail business. They were uncommon
in engineering and manufacturing operations.
What faults can a tube tester find? Obviously, it will cull out tubes
that are totally non-functional, such as those with open heaters. Tubes
that light and conduct, but indicate either "?" or the high end of the
"bad" range on a tube tester may function perfectly well in the actual
circuit. The real problem comes when a tube tester indicates "good" but
the tube won't operate properly in the application circuit. Hard faults
are fairly easy to find in-circuit. The only really valid test for tube
condition is in a test under actual operating conditions, and the device
under repair provides those conditions at the application socket. The
easiest and quickest test at the socket, beyond doing some simple meter
and scope checks, is to plug a known good tube into the socket and see
if that solves the problem. Even in a shop where sales policy required
100% testing of tubes in a tester, a significant percentage of tube
replacements were for faults found in in-circuit testing involving tubes
that tested "Good" on the tester.
(The following was furnished by Dan Schoo)
Q. Does anyone have advice for the make and model of the best tube
tester for restoring and maintaining communications receivers
I've seen units made by Hickok (600, 6000, others) as well as
military (TV2C). What are the advantages/disadvantages of each? Thanks.
There are many good testers available. A mutual conductance type is a
better choice than an emission tester. Many times the choice is a matter
of personal preference about the layout and cost. Hickok made many good
instruments. All of them were of similar design and should work equally
well. The 600A, 800, 800A, 6000 and 6000A were very similar. They were
aimed at the radio/TV service industry and were designed to be easily
transported. The 6000 is a nice machine but way overpriced in the current
market. I'd take an 800A any day of the week over a 6000. The 800 and
800A used the meter to measure shorts/leakage instead of a neon lamp in
that capacity. With the meter you could measure leakage to a much lower
level than with the lamp. The only difference between them is the
socketing. The 800A was updated to include Compactrons and Nuvistors but
still retained the old sockets.
The 500 series was a bit larger and not as portable as the 600/800/6000
but similar in function and about equal in performance. The top of the
500 series was the 539C which was closer to a laboratory type tester than
the others. It had three meters and several features you might use in
circuit design. It would test the firing voltage of VR tubes and small
thyratrons. It tested for leakage with the meter but also had a neon
lamp for fast short tests.
The 700 series was larger too and more or less aimed at the industrial
and communications market. These were a little classier than the other
series but not as advanced as the 539. The best machine they made was
the 700. This was closer to a TV-2 than any of the others. It was
designed for laboratory use and had seven meters. If you are just doing
repair and restoration on receivers any of the Hickoks will suffice. The
752A is a good choice because it has some of the desireable features for
communications equipment like VR tube tests, has newer and older type tube
sockets, and reads the leakage on the meter. The TV-2 is a big machine
and for normal service work probably way more than you need.
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Subject: Rec.antiques.radio+phono Miscellaneous Questions(FAQ: 9/9)
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Archive-name: antiques/radio+phono/faq/part9
Rec.antiques.radio+phono Frequently Asked Questions (part 9)
Revision Date Notes
1.0 Nov. 15, '95 New section
Part 9 - Miscellaneous and other home entertainment items
------------------------------------------------------------------------------
FAQ editor: Hank van Cleef. Email vancleef@netcom.com
This is a regular posting of frequently-asked questions (FAQ) about
antique radios and phonographs. It is intended to summarize some common
questions on old home entertainment devices and provide answers
to these questions.
This section is being added to the faq to cover questions on things like
Regina music boxes, jukebox-specific questions, and other items that
cover home entertainment devices included in the charter which are not
acoustic phonographs or old radios.
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Last changed: 25-JUN-1997 18:33:43
David Barts | davidb@scn.org |
http://www.scn.org/~davidb/