Germanium Transistors.

Thread Starter

zophas

Joined Jul 16, 2021
143
After playing around with the little siren circuit here. https://forum.allaboutcircuits.com/threads/siren-schematic.181313/ I noticed that germanium transistors where mentioned. At the bottom of my parts bin I found two OC71 and five OC77. Judging from the leads (straggled with loops) I think I took these out of some old valve radio in my teens. Just out of curiosity, I wonder if they still work? Can anyone suggest a small circuit to test them with? Maybe get these 70 year old transistors to blink a modern day LED or something.
 
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Thread Starter

zophas

Joined Jul 16, 2021
143
Oh @SamR , how boring is that? Surely a 70 year old transistor deserves more than a diode check. Lol.
Yes, but I did check them and sadly one of the OC77 has gone to that great germanium place in the sky.
The others show a +/- 1.4 voltage drop on b/e and b/c. Clearly different to silicon.
 

LesJones

Joined Jan 8, 2017
3,523
There is a transistor tester kit that Banggood sell that will probably give the results you want. Normally germanium diodes have a lower forward voltage drop than silicon diodes. (About 0.25 volts compared with about 0.6 for silicon.) I could not find any germanium transistors in my junk but I found a diode from that era. It is an OA5. it looks the same as an OC71 but with only 2 leads. It showed a forward voltage of 0.255 volts using the Banggood tester. This is a link to the tester.
https://uk.banggood.com/Original-Hi...r-p-929603.html?cur_warehouse=CN&rmmds=search

Les.
 

Thread Starter

zophas

Joined Jul 16, 2021
143
There is a transistor tester kit that Banggood sell that will probably give the results you want. Normally germanium diodes have a lower forward voltage drop than silicon diodes. (About 0.25 volts compared with about 0.6 for silicon.) I could not find any germanium transistors in my junk but I found a diode from that era. It is an OA5. it looks the same as an OC71 but with only 2 leads. It showed a forward voltage of 0.255 volts using the Banggood tester. This is a link to the tester.
https://uk.banggood.com/Original-Hi...r-p-929603.html?cur_warehouse=CN&rmmds=search

Les.
Thanks, Les, but I don't think I want to spend money on this type of musing. I can make do with my DMM and whatever else is in my junk box(es).
 

Ian0

Joined Aug 7, 2020
3,533
Just test them as you would a silicon transistor Using the diode test function on a multimeter. Expect a forward voltage drop of 0.2V instead of 0.6V.

By the way, they wouldn‘t have been out of a valve radio!
 

Thread Starter

zophas

Joined Jul 16, 2021
143
Just test them as you would a silicon transistor Using the diode test function on a multimeter. Expect a forward voltage drop of 0.2V instead of 0.6V.

By the way, they wouldn‘t have been out of a valve radio!
Yes they were out of an old valve radio. Electronics was not used for much else in those days.
 

bertus

Joined Apr 5, 2008
21,605
Hello,

Here I have some data and a book on germanium transistors.
And a mullard databook with vacuum tubes and transistors.

Bertus
 

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Thread Starter

zophas

Joined Jul 16, 2021
143
Well, I just built a multivibrator with two 70 year old OC 77. I have built many of this kind of circuit before but this one I liked the most because of how old those transistors are. And they are blinking led's that had not yet been invented. The transistors are marked NKT OC77p 7510. Maybe I'll try a Fuzz Box next. Lol.
 

KeithWalker

Joined Jul 10, 2017
1,947
If you scrape the paint off an OC71, you turn it into a OCP71, which is photosensitive. (That's why the glass case is painted black!).
 
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