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Testing Germanium transistors

A project log for Clockwork germanium

A retro version of Yet Another (Discrete) Clock, with vintage parts

Yann Guidon / YGDESYann Guidon / YGDES 04/05/2016 at 19:482 Comments

So I had 3 transistors in my archives, one 2N1926 and two 2N396.

My first test with the attempted Xtal oscillator failed. I had tested the 3 with my DMM and found inconsistent results.

@jaromir.sukuba pointed this to me : http://www.geofex.com/article_folders/ffselect.htm

Go and read this page then return here ;-)

I built the device and went to work. I had to measure twice because the values varied all the time :

Typeoff (mV)on (mV)leakage (µA)gain
2N1926600, 10001370, 1850242, 40477, 85
2N396170, 122940,85768, 4977, 73
2N396540, 4801600, 1530210, 194106, 105


It's... weird. But also eye-opening !

The leakage changes constantly, but the gain is pretty stable with this system.

A pair of transistors have pretty high leakage and appeared as high gain, my DMM measured 150 for two and 100 for one... But the 2N1926 is the least good of the pack.

When I receive the eBay orders, I'll try to sort each transistor to avoid the highest leakages.


20170119:

I just found some more germanium testing advices from 1967 at http://www.smrcc.org.uk/members/g4ugm/Manuals/wirelessworldcomputer.pdf

Damn, even diodes should be tested for leakage....

Discussions

jaromir.sukuba wrote 04/05/2016 at 19:58 point

Leakage of transistors is temperature dependant - that may be reason of unstable reading.

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Yann Guidon / YGDES wrote 04/05/2016 at 20:01 point

heating through the 2K resistor and the 9V also influences the reading. It's scary :-D
Fortunately, we're doing digital stuff, at only 4.5V, which heats less and is not much sensitive to variations.

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