Germanium PNP transistor based amplifier (OC36) - diyAudio
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Old 14th December 2014, 02:53 PM   #1
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Default Germanium PNP transistor based amplifier (OC36)

I've just recently been interested in building some amplifiers, which I've done with modern transistors just fine. But I have this box of much older transistors, all in TO-3 packages, and was curious if I could use of these in a project.

Among them is a handful of OC36 germanium transistors, I've seen some 'vintage' schematics use the OC71 for example. The most interesting is that the OC36 is very similar to the 2N278 in specifications, and the 2N278 is a power transistor made for class A and AB stage amplifiers.

Anyone know if the OC36 could be used in an audio amplifier? Anyone know of schematics based on germanium PNP transistors?

Something along the lines of Click the image to open in full size.

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Old 14th December 2014, 07:22 PM   #2
sbrads is offline sbrads  United Kingdom
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When I was 13 in the 60's I made my 1st amp, a 4 watt class A valve kit and it sounded nice considering the cheap speakers and record decks in common use then. I then started learning about semiconductors which was just about all PNP germanium stuff then and I made an amp using a pair of (similar to OC36) OC35's. It did not sound good or go anywhere near as loud as the 4 watt valve amp despite being higher wattage, 10 watt I believe. That experience got me very interested in Hi-Fi and led to a long path of upgrades before I was happy with the sound quality. So, build one for interest's sake but don't expect much, and they blow up really easily! That AD140 class A circuit looks a bit weird and wastes a load of power in R22, I wouldn't use that.

Last edited by sbrads; 14th December 2014 at 07:31 PM.
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Old 14th December 2014, 07:52 PM   #3
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Yeah, I don't expect any high quality audio from it, it's just for the learning part of it. Another schematic I've found using the 2N278 is this one:

I can't find a larger picture of that unfortunately.
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Old 14th December 2014, 08:13 PM   #4
Elvee is offline Elvee  Belgium
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If you search in my previous messages, you'll find large numbers of vintage/Ge amplifiers examples I have posted.
Some of them did sound very good actually.

That said, I agree with sbrads on the inefficiency issues of your circuit.
Even if you constrain yourself to PNP's throughout, there are better solutions.
. .Circlophone your life !!!! . .
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Old 16th December 2014, 12:43 PM   #5
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I used to build lots of PNP Ge amplifiers as experiments because they were cheap and easy to find. They are not tolerant of any overvoltage situation and I got the best result from them using autotransformer coupled outputs. Some of them could make decent power from low B+ voltage and sounded pretty good as booster amplifiers for portable radios, etc. Fun, fun tinkering on the cheap.

I still have a few amplifiers around with Ge output devices. One of them is a Sylvania Exponent 4/40 portable stereo phono system. It sounds very good for a portable system from 1966.

Kind regards.
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