Raytheon GA004 transistors, Digitronics 3500 Paper Tape reader

If you find a part that is in the same case style that works you could try to re-mark it with the original part number.

Michael A. Terrell wrote:

Actually, we don't really care what it looks like. If we can't get the original Raytheon part (and I suspect we can't), we're perfectly happy to use a more recent replacement, even if it's in a different case style, as long as it's not too large to physically fit in the available space.

What we're more interested in is finding out the specifications for the original transistor, so we can tell whether any particular candidate for replacement is actually suitable.

Re-marking some other transistor to look like a Raytheon part is not required or even desirable. We do mark all the parts that we replace, so that it is obvious that they are not the originals, and we bag and label all of the removed parts.

Eric

Send me your address and i will send you some Germanium PNP transisors. Betas seem to increase with current on all of them. Have some new "bullet" JAN 2N128; beta seems to be about 40 at 4mA and max 6V operating. Can get lots of these. Have mixed old small cylindrical can, TO-1 or TO-44 (1 ea):

*RCA TO-5 2N398 good to about 60V; beta near 100 at 2mA.

Anyway i will send these to you on an "all or none" basis.

I forgot to say that i had refurbished a paper tape reader that used photo-diodes and Ge PNPs; changed it from a "step" read to a continuous or off/on read and added the sprocket hole as a sync channel using the same photo-diodes but used comparitors. Made a new PCB that was plugin compatible and changed the voltage from -48V to +5V. Speed increased from i step per second to feet per second.

The PCB in your reader should be simple enough to chase it out and draw your own schematic if necessary That is what i had done).

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Presumably you can use the address on the museum's web page.

I'm not involved with this project, but nonetheless I want to thank you for doing your part to preserve history!

Cool! The Digitronics 3500 is rated at 400 lines per second. I'm not quite sure whether the interface is "step" or "continuous". The PDP-1 can definitely make it read one line at a time, but when the PDP-1 read-in mode is used, or software is used that doesn't have a significant delay between the tape read instructions, it appears to operate continuously at the rated 400 lines per second.

Cool!

We may do that at next week's team meeting. It's my understanding that we expect to desolder both the suspected bad GA004, and one that is believed to be working properly, and look at both on a curve tracer.

Eric

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The 2N1305 or similar one in that series were a common part in those years. As you said, a NTE germanium should work okay, since it's in an electromechanical device which probably doesn't put that great a demand on the transistors. Also, you might consider swapping two transistors so that the leaky one is in a later or less critical stage. But it may get worse as time goes on, so it should be replaced.

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This was used as a neon lamp driver, and should be capable of a lot higher voltage than 60V. Manual says 105V.

Of course nowadays a high voltage germanium looks pitiful and pathetic compared to a silicon transistor.

Neon lamp driver? Darn; there was one GP germanium transistor that was made specifically for high voltage and was rather common in those daze - now i cannot remember the 2N number. In any case for that application, you could safely use a silicon PNP high voltage part as a replacement. Will get the package out in the mail later today (Friday).

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Hi Eric When working on this old stuff, I've found that they tend to use the same transistor in many different locations and under different operating conditions. I've aften found that I can swap transitors around and keep original parts. I just attach a lable to let myself know what I've done in case it dies completely. Also, one thing to look out for, other than leakage with the germamium transistors is an increase in the DC resistance of the emitter base connection. This usually shows on the emitter side so it acts like a emitter resistor in circuit. It shows clearly on a curve tracer. Dwight