Is there anyone on here that has experience with germanium transistors used=
 in=20
logic circuits ?

I'm having problems with some logic circuits from the 1960s that use OC42=20
germanium transistors.
I've googled a bit and read about the issues caused by the "high" collector=
-base=20
junction leakage currents, but I'm not sure if the symptoms I'm seeing are =
a=20
consequence of this or not.

The devices are called "minilog"  and the circuit diagram (from the origina=
l=20
documentation) of the "type 7" is shown at the bottom of=20

http://www.peteronion.org.uk/803logic/minilogs0003.jpg

I've put a capture from my 'scope on my web site at=20
http://www.peteronion.org.uk/803logic/WA000009.BMP=20

It shows the inputs (bottom two traces) and outputs (top two traces) from t=
wo=20
gates in the same package driven from a switch.  Logic levels are 0V and -1=
0V. =20
As you can see about 2.5s after the falling edge on the output one of the g=
ates=20
output starts to drift up from -10V towards 0V.  I've also seen gates where=
 the=20
drift starts ~1ms and rises much faster.   As you can see there are no=20
capacitors anywhere in the circuit (other than junction capacitancies and s=
tray=20
capacitance between the components). =20


Any ideas on the cause ? =20

PeterO

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