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  • Author Author: jc2048
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Transistors: Some Very Old Ones

jc2048

The other day, I was sorting through some old boxes and found a small bag of old transistors. There were two types, both

of them PNP devices. One kind was an OC204 part, made by the old British company Mullard, the other a 2S3220 device made

by Texas Instruments. I presume they date from the 1960s.

 

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I wondered if they still worked and what their characteristics would be like compared to a modern device so I built up

this circuit of a simple common-emitter amplifier on a breadboard (shown with a modern 2N3906 PNP transistor) so that I

could test them.

 

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For the base bias resistor (R2), I actually used a pot so that I could adjust the collector voltage to be -4.5V (half the

supply voltage). Both devices needed just 13.6k for R2 to bias the collector to -4.5V, unlike the 2N3904, which in the simulation

needed 430k. The gain worked out to be approximately 7 (at a collector current of 2mA). Yes, that's not a typo, the hFE

really is just 7 for both parts.

 

Here are the waveforms of the 2S3220 amplifying a 10kHz sinewave - yellow trace is the input and the blue trace is the collector (AC coupled)

 

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I was curious about the frequency response, so I plotted a crude graph of the amplifier's response for both parts. As you

can see, the response is starting to drop off at just 100kHz, so they'd have been ok for low frequency work - audio

amplifers, etc - but not much use above a couple of hundred kHz.

 

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For contrast, here's what the 2N3906 does in simulation

 

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  • in reply to jw0752

    I am going to have a look into my parts graveyard for some moldy oldies to test out.

    You had me worried for a moment, I had missed the PARTS in the sentence. image

  • Hi Jon,

    I love these explorations into the foundations of electronics. Just like DAB I am going to have a look into my parts graveyard for some moldy oldies to test out.

    John

  • Now you have me wondering about the types of interesting components my be hidden in my stash.

     

    Sounds like an excuse to do a treasure hunt.

     

    DAB

  • in reply to shabaz

    Unfortunately, I've only got four of the OC204s. The rest are 2S3220s, which a webpage tells me are silicon. I don't know what the date of them is, but the TI parts have codes like 610, 612, 615 on them, so I would guess that's showing 1966 followed by a week code (week 10, 12, etc). The American companies were well into silicon by then. The OC204s have a code of '3 R 5' which might be 1965. [I would have bought them in the early 1970s as a bargain pack of usable, but no longer state of the art devices.]

     

    The construction of the Mullard parts is fascinating because inside the metal cover there's a glass envelope that houses the semiconductor. That shows their heritage in valve (vacuum tube) manufacture - they knew how to work with glass, so that's what they though to do.

     

    Both cases predate having a tab for the emitter - the Mullard part has a red dot and the TI part has the leads arranged in a triangle.

  • This is very cool : ) Germanium transistors sell for a lot of money these days, even with that gain of 7 probably ; )