Identify That Chassis
June 1958 Radio-Electronics Article

June 1958 Radio-Electronics [Table of Contents] 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

A 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 how

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 at all!"

"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, by golly!"

"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 of 'em!"

"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 hot!"

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.

"They 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 before?"

"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 shop.

"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.

"No, 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 sets, see?"

"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.

"Huh?"

"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