June 1958 Radio-Electronics
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Electronics,
published 1930-1988. All copyrights hereby acknowledged.
Having spent many years professionally scouring the Internet while
attempting to identify electronic components as part of a reverse
engineering effort, I can appreciate how difficult life would be
when the only resources available were a few manufacturers' databooks
and a magazine article or two. You might think it would behoove
a company to make certain that its products are clearly marked if
not with a part number, at least with an easily identifiable logo.
That way a researcher could call the company, describe the part,
and get the required information. Even with today's nano-size packages,
laser marking could do the job. Sometimes, the maker of the next
higher assembly (which might be the finished product) purposely
either removes the identification from select components or instructs
the vendor to only partially mark or not mark the package*. That
is done for competition reasons specifically to prevent or make
very difficult the reverse engineering of products. You have likely
seen 'teardowns' of consumer electronic items like smartphones,
Bluetooth headsets, wireless routers, etc., where one of the primary
goals is not to gather information for building a comparable product,
but to figure out what it is costing the OEM to produce the item,
and thereby estimate the profit margin. Typically on things like
smartphones we learn that the product is selling to the end user
at a price less than the cost to manufacture, meaning that the profit
is being made in subscription services.
Anyway, this article might be of assistance to people like me
who like to restore vintage electronic equipment. It is written
in an entertaining detective drama format.
* While working for a defense electronics company back in the
1980s, we would often sand off the identification from key DIP devices
and stamp them with custom company part numbers. Doing so ensured
that replacement parts could only be purchased from us. Usually
it was for a component that had undergone reliability screening
beyond the manufacturer's process, but still, I believe the true
motive was profit.
Identify That Chassis
By Jack Darr
little detective work is all it takes to pin a model number on an
unmarked chassis. Just follow the Old-Timer along as he shows you
The Old-Timer grunted loudly as he burned the tip of the finger
he had unwisely poked into the small TV set he was working on. "Oww!
Dad-burn it!" he grumbled. "I'll bet you I know what would be good
useful equipment for a TV man - a set of asbestos fingers! Ouch!"
and he sucked the damaged digit. The Young Ham, meanwhile, sat quietly
at his end of the long bench, his crew-cut head bent over a car
radio. Suddenly, he exploded.
"Darn it all!" he glared at the little chassis. "Why can't people
put model numbers or somethin' on their radios! You'd think they
were ashamed of 'em !"
"Well, some of 'em may be, and some of 'em ought to be," agreed
the Old-Timer, looking up. "What's your trouble, Junior?"
"Aww, this little stinker!" growled the Young Ham. "No model
number, no nothin'! This resistor's burned out, and I can't find
anything on the set. How the heck do they expect us to fix 'em if
you can't find out something about 'em?"
"Get out your crystal ball!" The Old-Timer grinned. "Let's see
it." He got off his stool and ambled down to the end of the bench.
"Ohh. That oughta be simple. I've seen several of them before."
"Well, I haven't!" burst out the Young Ham. "I can't tell beans
from bones about it!"
The Old-Timer smiled at the young man's use of one of his own
favorite expressions and studied the set closely. "Well, now, look
here," he said, pointing into the upturned bottom of the set. "See
that bypass? Says 'Bendix' on it, very plainly, don't it? Transformer
does, too. Don't that tell you something?"
"OK, OK! So it's a Bendix, but what model? I've looked over the
whole thing, case, lids and all, and I can't find anything on it
"Hang on, help's comin'," said the Old-Timer, reaching up to
the well-filled bookshelf that ran the whole length of the shop.
"You remember what kind of a car you got it out of, don't you?"
"Ford," said the Young Ham. "'53 Ford."
"Now, lessee; Chrysler, General Motors, Ford! Here we are," and
he pulled a service manual down. "Now, look. Here's a Rider manual
covering all the Ford radios from quite a ways back. '53 Ford, you
say. Lessee. '52, '52. Here. See? Here's a picture of the front
of the set. See? Looks somethin' like it, wouldn't you say?"
"Yeah! That's it!" said the Young Ham. "Now, let's see what that
resistor was, before it burned up. Here it is. 1,800 ohms. Now,
"Ah, Junior," said the Old-Timer quietly. "Ain't you a mite previous.
Are you sure that's the same set?"
"Sure. Look at that front panel and the controls. Same set, see?"
and the Young Ham pointed at the photograph.
"Well, that's true, but there might be one little difference.
There was three people made Ford radios that year, Sylvania, Zenith
and Bendix, according to the book. The one you're lookin' at happens
to be a Zenith. Since when did Zenith start usin' Bendix capacitors
and transformers? Huh?"
"Huh? Oh! I see what you mean," said the Young Ham sheepishly.
"Got too previous, didn't I? Now, let's see in the Bendix set. Hmm.
1,000 ohms. Oopp !"
"Yeah, you did get a mite quick," agreed the Old-Timer. "Now,
you see what too much speed can do. It's a good idea to check up
on everything before you make any rash moves, especially in a case
like this !"
"Tell me, why in the world don't people put the model numbers
and the maker's names on their radios and TV sets?" asked the Young
Ham, as he replaced the resistor. "You'd think they were ashamed
"Junior, that's somethin' that'll never be known, I guess," opined
the Old-Timer, as he replaced the cover on his little TV set. "That
problem's puzzled radiomen since 1920, and it would have before
that, except they didn't begin to make sets until that year! Only
way you can find out anything about 'em is by a long and painful
process of deduction. Got that resistor in yet? I want a coke,
while I let my fingers cool off. Danged little tubes sure do run
Let's go for a coke
He was answered by a burst of rock and roll music from the car
radio, and the Young Ham snapped it off. Leaping up, he announced,
"I'm ready! Let's go!"
The pair trotted down the long hall and out the back door. As
they crossed the alley and took their regular shortcut through
the drugstore, the Young Ham said, "Gee, I wish I could find 'em
that quick! ·I'd have been hunting all day, and you found it in
just a second!"
"Hi, Hop!" said the Old-Timer, as they passed the pharmacist
at his prescription counter. "How's the poison shop today?" Ignoring
the rude reply, they passed on out the front door and across the
street. When they were seated at a table in the soda shop, the Old-Timer
got around to replying to the young man's question. "Well, Junior,
it ain't so much a matter of genius as it is a combination of experience
and patience," he explained. "Time you've had that button nose into
as many of the things as I have, you'll be able to recognize 'em
on sight, too. Main thing is, you gotta take advantage of every
little clue you can find as to who made the thing and when."
"Maybe so, but what do you do when you find a set that hasn't
got any clues as to who made it?" asked the Young Ham.
ain't no sich," said the Old-Timer, truthfully but ungrammatically.
"I don't believe it's possible to build a set without leavin' some
kind of a clue. Y'see, the only ones we'll have trouble with is
the sets from the mail-order houses and other outlets like that.
They don't build their own sets; they buy 'em from the manufacturers
who make a business out of makin' sets just for such people. In
fact, there used to be set makers who sold more sets under other
people's names than they did their own-Wells-Gardner, for instance.
Haven't seen one with their own name on it for more than 20 years,
but there was more WG's than you could shake a stick at. Sears Roebuck,
Montgomery Ward, Walgreen, Spiegel - everybody at one time or another
sold Wells-Gardner sets, I reckon!"
"Well, what do you do then?" asked the Young Ham. "Hey, how about.
a coke over here?" He pounded the table, then ducked quickly as
the waitress flung a water-soaked paper napkin at him.
"Well, Y'see ... glupff!" said the Old-Timer, as the wet paper
wad took him squarely in the mouth. "Hey! Phoo! How'd I git into
this argument? I'm just an innocent bysitter!"
The waitress rushed over and mopped the Old-Timer's face with
her apron, much to the delight of the Young Ham, then brought their
cokes. The Old-Timer stirred his, then tasted it, gingerly. "Well,
that takes the taste of that paperwad outa my mouth," he commented.
"Wow!" said the Young Ham. "They sure do make it cold!" and he
ducked again. This sally was ignored by both waitress and proprietor,
and the two finished their cokes in peace. Going out the door, they
trotted back across the street, through the drugstore and back to
the shop. Reaching up to the bookshelf, the Old-Timer took down
a thick blue-backed book out of a set there. Opening it on the bench,
he located a diagram.
"Here's a good example of what I mean, about some of those old-timers,"
he said. "See here? Here's a Sears Roebuck set listed under their
trade name, Silvertone. Now, looky here," and he turned to the back
of the book. "See? Under Wells-Gardner, here's the same set - Look
at the tube lineup, the circuit and so forth."
"Yes, I can see that," said the Young Ham, "but how are you going
to tell just who made the thing if you've never seen one like it
"Well, that's the hardest part," admitted the Old-Timer, "but
there's a kinda method you can use on all of 'em and find out what
you've gotta know. It's a kinda combination of every little thing
you can see: the cabinet, the chassis, the tube lineup, the general
appearance of the set and everything else about it. If they all
agree, then you're home free. Some people use a code in the model
numbers, that's a big help. Montgomery Ward's Airlines, f'rinstance,
since about - lemme see, 1939, I think. Yeah. See here?" and he
pointed out a listing in the index.
"How can you tell anything by that?" asked the Young Ham. "Just
looks like a mess of numbers to me."
"Nope; they're just full of information, if you know how to read
'em," said the Old-Timer. "Look at this model number here. '93BR508A.'
Turn the first two numbers around and you've got the year it was
made: 93-1939. Then the 'BR' tells you that it was made by the Belmont
Radio Co. or, if it was 'WG,' by our old friend Wells-Gardner, and
so forth. That'll help, if you can find the year it was made."
"Where do you go from there?" asked the Young Ham. "Even if you
do know the year, how do you find it in all that stuff," indicating
the 20-foot bookshelf, filled with manuals.
Lots of service data
"Well, that's not too hard, either," said the Old-Timer. "All
these Rider manuals are roughly numbered according to the year they
came out, beginning with Vol. 1, which came out in 1930. So, if
you wanted a set made in 1940, you'd be like to find it in Vol.
10, and so forth. Feller needs a pretty complete set of all the
service data he can git his hands on, to do much of anything with
this kind of work."
"Well, you've got that, I'll say that for you," said the Young
Ham, eying the well-filled bookshelf and the stacks of assorted
service information which covered nearly every fiat surface in the
"Yep, I have," admitted the Old-Timer. "And I use it all at one
time or another too. Tell you what though. One of these days I'm
gonna git in here and straighten out all of this stuff and file
it like it oughta be! Lessee now, where were we?"
"You were talking about Airlines," said the Young Ham.
"Oh, yes. Now, look here. Here's another helpful soul - the Truetone
sets sold by Western Auto Stores. They give you model numbers with
codes in 'em, too. See this one? Model D-1191WG: 'Factory No. 6C18-3.'
This means Wells-Gardner again. If it was BRC, Belmont; DRT, Detrola,
and so on, just like the others. Then, you can look this up under
Wells-Gardner and probably find it listed under model 6C18."
"Tube lineups are helpful, too," he continued, "especially on
the older sets and once in a while on the new ones. Take this guy
here, f'rinstance. Look. He's used a 12J5 as an oscillator and a
12SA7 as only a mixer tube, instead of using the 12SA7 as both.
Well, all you have to do is look through your manuals until you
find somebody else using the same circuit with the same tubes, and
you've got him. Lots of other little peculiarities like that, if
you take the time to look 'em up. Certain designers have certain
habits and the chances are they'll use 'em over and over again,
for several years, anyhow. If a certain guy uses a kind of trick
circuit one year, you can be fairly sure that you'll find the same
circuit in several sets, especially if it works fairly well!"
"You mean they use the same circuits in all the sets?" asked
the Young Ham, with a bewildered look.
not at all," answered the Old-Timer. "What I meant was just certain
parts of the circuit, like the if's, the oscillator stage, the front
end and so on. Take Philco, for instance. One year they used an
if stage with a little tertiary winding in the if amplifier screen
circuit. Well, they used that same circuit for at least three years.
So, if you had if troubles and couldn't find the right diagram,
you could look up the same circuit in another set, even if it was
a year later. See?"
"Oh, I get it, now," said the Young Ham : "You can kinda make
up enough information to get what you need, even if you have to
use the diagrams of several different sets!"
"Now you're getting the idea." The Old-Timer applauded. "It's
not where you find it, but what you find! There's a heck of a lot
more service information available now than there was when I started,
too. Why, they're even pasting schematics inside the cabinet on
a lot of sets now, and that's a big help. TV sets, well, that's
a different story. A TV set's a heck of a lot more complicated than
a radio, and there's still a heck of a lot of variation between
makes as to the different circuits. Thank goodness, they're beginning
to settle down some by now, though. Different manufacturers are
beginning to use the same circuits in the same places, with only
minor variations here and there. Like the high-voltage supply -
I guess about everybody uses the same general circuit by now. You
don't find any more line-voltage supplies with the tremendous transformers,
or rf power supplies with the separate oscillators and stuff like
that, that we had in the early-day sets, and hurray for that!"
"No, sir, TV sets are not all alike, yet," agreed the Young Ham.
"Not with all the funny tubes they're coming out with now."
TV set clues
"Well, that's sometimes a hindrance and sometimes a help." said
the Old-Timer. "Some manufacturers have a habit of using certain
tubes. That'll help you identify their sets, no matter what name
they're under. For instance, Zenith used the 6BN6 tube as the sound
discriminator for several years and no matter what set you had,
if it had a 6BN6, chances are it was a Zenith. Now, we've go the
same situation in TV that we had in radio. Different makers are
selling sets to chain stores, mail-order houses, and so on. The
only way you can tell what kind of a set it is is to give it the
same treatment. Look it over carefully, check for brand names on
the tubes, transformers and so forth. Look at this one here. This
is an easy one." The Old-Timer indicated a small TV console in the
finished-work department. "Says 'Truetone' on the cabinet, but look
at it closely. What does it look like? We've had several of them
in here lately, from ol' Walker's, down the road. Recognize it?"
"Why, it looks just like those - Oh, what was the name of that
set - Oh, yes! Raytheon! That's what it is, a Raytheon!" said the
Young Ham, excitedly.
"Kee-rect the first time," said the Old-Timer. "You'll also find
that same set under Silvertone - had one the other day, out on 15th
St. And, you know Ol' Dingbat's Stewart-Warner? The Gasman's? The
9300 series? I found one of them the other day, carrying a Silvertone
nameplate, but it was a Stewart-Warner 9300 'cause the first thing
I spotted was that characteristic heavy metal bridge over the yoke.
That's another thing you want to remember. Look for characteristic
construction features - like that bridge, or something distinctive.
For instance, maybe some company always mounts their tuners way
out to the side, actually off the main chassis. That's a trademark.
Maybe they use a certain given kind of printed-circuit assembly
- like Westinghouse or Admiral or G-E. Why, I even identified an
Airline TV set one time by the dern knobs! It turned out to be a
Bendix and they had those peculiar cutout knobs, with the inside
shaft on the outside knob, and so on. Nobody used them that year
but Bendix, and I spotted it that way!"
"Gosh, it'd taka you a lifetime to learn all of the darn things,"
sighed the Young Ham in discouragement.
"No, not necessarily," said the Old-Timer. "All it takes is a
pretty good memory for those little quirks and characteristics I've
been talkin' about, and the ability to put 'em all together and
make 'em spell out the name of the set. That, and somethin' you
could use just a wee bit more of - patience!"
"Who, me?" said the Young Ham, aggrievedly.
"You," rejoined the older man. "In common with all kids, you
want to git everything done today! Don't forget, there's always
tomorrow, and you've got plenty of time! Take it slow and easy,
and be sure you're right before you go ahead.
"But, back to the subject of identification. It's only once in
a while you really need a schematic, especially since so many people
got thoughtful and started puttin' tube layouts inside the cabinets
on TV sets. Why, some actually put the heater string layout in the
sets with series heater circuits and don't think that ain't handy!
If they ever stop doing that, we'll sure be up that well-known creek
without any form of propulsion!
"Anyhow, like I said, the only time you've got to have a schematic
is when something's burnt up, like a. resistor or a coil and you
can't get the identification from it. Although, come to think of
it, coils, transformers, yokes and the like ain't too much of a
chore. Look here." He dug a catalog from the file. "Here's a catalog
put out by Merit that lists all kinds of TV sets and their components,
especially yokes, transformers and stuff like that. Sets are listed
"by make and model number, and it's very little trouble to look
up one and find out just what part you need. Thordarson, Sprague,
Miller and several others put out similar catalogs. You can get
'em from your parts supply house or direct from the manufacturers.
Sure are handy, too!
"Do you know that you can even use these books backward? Instead
of looking up the parts from the make and model of the set, you
can look up the set from the make and part number of the part!"
"How's that again?" queried the Young Ham. "Run that by slowly,
and let me get a better shot at it."
"All right, look. You've got a TV set. You know it's a Silvertone,
say, but the model number's been scratched off or something. From
the tubes, you've got a reasonable suspicion as to about what year
it is, and -"
"How's that, now?" interrupted the Young Ham. "How can you tell
from the tubes what year a set was made?"
"Well, you can't, too definitely, but you can get a general idea,"
admitted the Old-Timer. "Take the 3-volt series. When'd they come
out, first? Last year, was it? Anyhow, if the set has 3-volt tubes
in it, you know it was made sometime within the last 2 years, on
account of they didn't make the tubes until then! Older sets, if
they have tubes that haven't been in common use for several years,
you know they aren't newer than a certain year, and so forth. Oh,
just f'rinstance, if you find a 6AC7 in the video output, the set's
apt to be over 3 years old because they haven't, as a rule, been
using 6AC7's there since about that period. It's just a general
hint, that's all."
"I see - I think," admitted the Young Ham.
"Now, where was I? Oh, yes. I was lookin' up sets by part numbers.
Yeah. All right. First thing, you take the part numbers off two
or three big parts, like the yoke, power transformer, fly-back transformer,
vertical output transformer and so on. Copy 'em down on a piece
of paper, and start lookin' through the catalog for a set, of the
right make, which has all of those numbers! Chances are, when you
find it, it'll be the right one. If it ain't, you can usually get
so close that you can use the diagram of that set to find out what
you want to know! Why? Because, if it uses all of the same parts,
there's bound to be a pretty good similarity between the two
"I think I'm beginning to get a glimmering of the idea," said
the Young Ham.
"Well, it's usually a lot of dern trouble, any way you look at
it," said the Old-Timer, "but sometimes that's the only way you
can get the information you have to have. Guess the only way you
could sum it up would be to compare it to a detective, lookin' for
clue . You've got to take every little clue you can find. The cabinet,
the shape and size of the chassis, the tubes, even the kind of parts,
the type of construction used and every little detail. Why, I remember,
a long time back, I even identified a radio because one part had
a big long part number! Happened to think that the Colonial people
had a fancy for great long part numbers, looked one up and there
it was! So, if you take advantage of every clue, no matter how small,
and add 'em all up right, you come up with the right answer, just
like Friday. All you gotta do is get the facts, ma'am."
"Dum-di-dum-dum!" agreed the Young Ham.
"Yes, sir!" said the Old-Timer, leaning back on the bench, "that's
gotta be your motto. No fact too small, no clue too insignificant!"
"Well, I can tell you one small insignificant fact you're overlookin'
right now," said the Young Ham.
"There," pointing to the clock. "It's 5 after 6, and I've got
a heavy date. We're on overtime right now!"
"Ye Gawds, we can't afford that," cried the Old-Timer, leaping
off the bench. "Let's git outa here. My wife's gonna kill me. I
told her I'd be home early tonight, too!"
"Down scope, crash dive, all ahead flank," yelled the Young Ham,
his voice fading rapidly as he dashed down the hall. " 'Night!"
The Old-Timer grinned, pulled the master switch, looked around for
cigarettes left burning and ambled after him.
Posted June 27, 2014