Transistor history question

[Rhodesplyr]

During the middle of the 20th century, a fairly consistent type-designation system had evolved for vacuum tube types, so I've wondered why, when transistors became commercially available, so many companies in the 1960s had transistors marked only with their own in-house parts numbers, making it very difficult to figure out what a standard replacement should be.

I'm well aware that many transistors are broadly interchangeable, but there are situations, like in combo organ dividers, where certain characteristics are important for them to work properly in the circuit.

I guess I may be able to answer my own question in that, perhaps, manufacturers wanted people doing repairs to have to buy replacement parts only from the manufacturer and wanted to make copying their circuits difficult. I'm sure that they neither foresaw nor cared that techs 40 years later would be trying to figure out how to fix their products--and scratching their head over dead-end proprietary parts numbering systems in the process.

I realize that a standard type designation system for tubes was necessary since they do wear out, but the transistors, especially the early ones, were hardly that much better and were more vulnerable to things like voltage spikes than tubes.

[J M Fahey]

Well, we aren't providing the kazoombing reviglator parameters either for any of the products built today, so repair technicians in the year 90 GE (Galactic Era) .... (sorry, year 2047 for Terran Historians) will be very puzzled too, considering that parameter would allow positronic parts cloning machines produce exact replicas in a jiffy.
In a nutshell: who thinks (or cares) 40 years ahead?
I mean in Electronics manufacturing, of course.

[Jazz P Bass]

In the history of transistor manufacturing, parameters are all over the place, batch to batch.
Parts that meet certain parameters become part# XXXX.
By halving in house numbers on the parts, you can assume that the parts where tested by the manufacturer to meet there specific circuit requirements.
Bob Pease (bless his soul) had an awful lot to say about this.
Without the specifications for the in house items, repairing the equipment is a hit or miss adventure.

[Rhodesplyr]

In the history of transistor manufacturing, parameters are all over the place, batch to batch.
Parts that meet certain parameters become part# XXXX.
By having in house numbers on the parts, you can assume that the parts were tested by the manufacturer to meet their specific circuit requirements.

That makes a lot of sense. So, especially in the early days of transistors, companies like Wurlitzer or Vox would place an order not for a generic transistor type, but for transistors with certain specs that would then have Wurlitzer's or Vox's own in-house numbers printed on them by the transistor manufacturer.

The problem for those of us trying to replace bad transistors from that era is that those parts specs have either been tossed in the trash or are buried somewhere in storage.

[J M Fahey]

Yes, that makes a lot of sense.
I have seen many service manuals where they specifically state to use "factory selected" parts.
And Japanese, even today, rate their transistors with a colour paint dot, obviously applied after the transistor is "finished".
For a high production manufacturer it's good business to pay a little extra and avoid having trained personnel with test equipment twiddling little trimmers.

[Rhodesplyr]

I have seen many service manuals where they specifically state to use "factory selected" parts.

I'd be happy to use factory selected parts--if many of these amps, organs, and electric pianos had not long outlasted the companies that made them

And Japanese, even today, rate their transistors with a colour paint dot, obviously applied after the transistor is "finished".
For a high production manufacturer it's good business to pay a little extra and avoid having trained personnel with test equipment twiddling little trimmers.

Vox and Farfisa did the same thing. In part, I think it was to speed up production. The employee had only to put the right color transistor in the right spot on the PCB rather than trying to read a transistor number. I think some colored dots indicate additional low-noise screening for use in low-level/high gain stages.

[Ronsonic]

I remember reading how the advent of transistors would simplify electronic work and manufacturing by simplifying inventory. Instead of hundreds and hundreds of tube types there would only be signal zistors NPN and PNP and drivers of both sexes and powers of both sexes, so you would only need at most a dozen numbers for all applications.

That worked out about the same way as the paperless office.

[big_teee]

I remember reading how the advent of transistors would simplify electronic work and manufacturing by simplifying inventory. Instead of hundreds and hundreds of tube types there would only be signal zistors NPN and PNP and drivers of both sexes and powers of both sexes, so you would only need at most a dozen numbers for all applications.

That worked out about the same way as the paperless office.

I agree.
Speaking of Trasistor History, I didn't hear anyone say that the Transistor was invented by Good Ole Ma Bell.
Bell Labs that is.
Rock on,
Terry

[Enzo]

Actually transistors HAVE simplified my inventory. The fact that there are thousands of types, often very similar, doesn;t mean any one factory or shop must stock them all. There are not a ton of alternate tube types I can drop into place in an amp that won't alter the tone or performance or even require rewiring. I consider 12AX7, 7025 and some others all the same tube. But transistors are VERY forgiving of substitution. I stock more types than I really have to. And I substitute all the time. "Well I don't have these, but those will do just fine." If I stock MJ15003 and MJ15024/25, there are darn few TO3 situations they won't cover.
J

[Enzo]

And speaking of transistor history, anyone remember the CK722?

[J M Fahey]

Well, I do, as well as the glass case, black painted OC71, but sshhhhhhhhh !!! PLEASE don't tell anybody !!!
EDIT: now the Old Timer label takes on a new meaning.

[Enzo]

It was no 2N109, but that is another story.

[Robert M. Martinelli]

Well, I do, as well as the glass case, black painted OC71, but sshhhhhhhhh !!! PLEASE don't tell anybody !!!
EDIT: now the Old Timer label takes on a new meaning.

Not only I remember them, I still OWN some of them, along with some OC44 and 45, some AC128, and a few of the first 2SA 2SB Japanese ones...still have some OA "black" Ge (cat's whisker) diodes as well...

All of them are remainders (and reminders) of my first experiments, back in the early '70s....Geez, I was only 8 at the time....now, looking back at it with the eyes of a father, I think I have been very lucky to have had two parents that allowed me to play with a soldering iron despite my extremely young age...If I close my eyes, I still can clearly see myself harassing my mom and dad to obtain a (obviously needle) multimeter for my 8th birthday....God bless them both!

Talking 'bout the black OCs, I also remember I "ruined" some of them by removing the black paint to exploit their behavior as phototransisitors...

I guess I, too, should change my "label" to "old timer"...or maybe "surviving dinosaur"...(sigh)....

Cheers

Bob

[jrfrond]

There are now many different types of transistors with many different packages (and throw SMD into the mix!), so it's tougher nowadays to stock just a select few as I used to. I just checked my parts database, and I have 671 different part numbers in stock for transistors.

The beauty of it is that you can sub a lot of types. Enzo cited the ubiquitous TO-3 power transistors, and replacing them with the big guns universally (MJ15024/25 or MJ21193/4). No issues with this. Same for the TIP-series, unless they are Darlingtons. I have substitution books, but I also have them in my heads after all these years. Luckily, I also have a lot of NOS stuff hangin' around. It's all good, when you need them.

[Rhodesplyr]

But transistors are VERY forgiving of substitution.

Enzo,

I grant that this is true *most of the time.* I've read your statement on this topic many times in this forum in various discussions, and I believe you. In fact, I had expected it to appear sooner or later in this thread. However, my fate is that in some of the older keyboards I'm frequently called on to fix, it's not really true. And, in those cases, you don't know how much I wish that it were true.

One of the aftermarket suppliers of redesigned amplifier modules for Wurlitzer electric pianos told me that one of the the main problems with the original designs were that they were far too dependent on the hfe of individual transistors. In a repair on one I did recently, I used a cross-reference list to replace a shorted transistor. It worked, but I had to change resistor values to re-bias the circuit. Had I know what Wurlitzer's part number for this transistor meant, I might have been able to select one that would have dropped in without modifying other component values.

In an Italian-made Vox or Farfisa organ, the idea that transistors are forgiving of substitution is of no help whatsoever; on these, you often have to match gain and Vbe to get all the dividers on a particular card to work. And even taking those steps doesn't guarantee that you'll get good results every time.

Now, you can dismiss these circuits as junk, oddball cases, or exceptions that prove the rule. I might agree with you. But to the people who want to pay me to fix them, they aren't junk, and I have to make them work again to get paid :-)

I certainly believe that as circuit designers got more experience with transistor circuits, they took steps to decrease dependence on individual transistor parameters, and I'm very glad that they did.