Sunday, February 10, 2019

effect of reversing an alloy junction transistor in the circuit

Making an amp is fairly simple at first glance. Just put some forward bias on the transistor and apply a signal. The circuit can misbehave is several different ways. A transistor has three regions it can be biased to.
1. saturation
2. cutoff
3. active
With no bias it will be at cutoff.
With to much bias it will saturate.
When it is biased in the active region it will amplify.
It can be biased too much and then be over driven and distort too.
So the question is why a circuit will not operate when built "properly" but will work when the transistor is rotated.
I took two transistors and put them in my transistor hfe testers.
The one on the left is in the socket properly. The one on the right is reversed. They both show hfe but the one connected properly is much higher.
I reversed them both. The one on the right is correctly inserted now. So what does this tell us about the circuit in question?
hfe is the forward transfer or ß. The collector current will be Ib * ß. If the circuit is biased into saturation with the transistor inserted properly and you reverse it ß is reduced so it is no longer saturated. In order to give more help I would have to see the circuit in question but the simple answer is to reduce the bias.

Note: The transistors being tested are germanium micro alloy.


  1. In one of the British electronics hobby journals from the late 60s (?), there is a column where a young man and the older owner work in a repair shop. In one story the old man shows the younger some circuits that shouldn't work (per schematic) but do on the breadboard. All the transistors were germanium PNP.

  2. That would be an interesting read. One article at the radio museum they interview a clock maker turned transistor maker who tells the process he used. He used a strip of phos bronze to make his points. Both points were the same material so his transistor emitter and collector would be interchangeable as he made them. The forming process made the contacts act differently. The point in contact with the surface would act as a schottky barrier. The forming process would cause diffusion and create the alloy for the transistor hook. Rufus Turner wrote some articles about his homemade transistors. Some of his books are available at the American Radio History site. A good one is "Transistor Theory and Practice" in the Gerback lib section. I'll post a link to it.