# Determine the Vcbo of a germanium transistor and the voltage drop along the connected components.

#### Colin Mitchell

Aug 31, 2014
1,416
The base-emitter junction has 0v across it when the input voltage is zero. At 100k the base will rise 1mV and the base-emitter junction will not be turned on.
It is pointless putting a 400 ohm resistor in the emitter when no current is flowing.

Show me a germanium transistor with a leakage of 0.5mA !!!!!!!

#### Ratch

Mar 10, 2013
1,099
The base-emitter junction has 0v across it when the input voltage is zero.

Doesn't matter. With that much resistance in the base circuit, and no resistance in the emitter circuit, all the 10 ua of Icbo will pass through the b-e junction and raise the Ic to at least 0.5 ma.

At 100k the base will rise 1mV and the base-emitter junction will not be turned on.

The b-e junction does not have to be turned fully on. If the 10 ua amps passes through it, it will be betatized and the Ic will be 0.5 ma even if no voltage is applied to the base terminal..

It is pointless putting a 400 ohm resistor in the emitter when no current is flowing.
The 10 ua current will be present since it is being diverted from the base terminal.

Show me a germanium transistor with a leakage of 0.5mA !!!!!!!
Never said the leakage was 0.5 ma. I said the effects of the leakage increased the Ic to 0.5 ma even when the base voltage was zero.

Ratch

#### Herschel Peeler

Feb 21, 2016
401
Theory aside, I built a version of the circuit. I didn't have a germanium NPN but I had a germanium PNP, so I flipped it and used a germanium PNP and a silicon NPN. Yes I can get enough leakage in the germanium PNP to get the LED to turn on.
My germanium was a 4JX1D872. Measured leakage at 5 V was about 1.5 uA, but at 12 V it was about12 uA. I think I might have hit the BV of the B-C.
NPN used was a 2N3904. Its collector current was about 2.5 mA. Enough to light the LED at 12 V. but not at 5 V.
I have no specs for the 4JX1D872. The rated leakage for the AC127 is 10 uA, so it is in the ball park of the exercise, kind of.

#### Colin Mitchell

Aug 31, 2014
1,416
Now put zero ohms in the emitter and then 400 ohms and then 10k and let me know if it makes any difference.
Make sure you have no base resistor and take the base to emitter.
Or the equivalent for PNP

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