Germanium transistors would sometimes become very noisy despite the in-circuit DC bias voltages testing normal. This failure was cured by replacing the offending BJT. I have found this as a teenager and now when fixing classic car radios.
What is the mechanism for this type of failure? Si transistors don't fail this way in my experience, why? It has been said that a particular batch of Ge transistors failed this way. Is there any truth to this or is it an urban myth?
Best Answer
From what I remember Germanium transistors have always been less reliable compared to their Silicon brothers. Using Google, I find that the AF114 is particularly prone to fail.
I guess the failure mechanism depends on the model, likely not all transistors fail in the same way.
Also note that the first transistors were Germanium transistors, at the time manufacturers did not have a lot of knowledge on the subject of transistors. They had gained some knowledge by the time the Silicon transistors were introduced so these had a good head-start.
There are always better and worse batches of transistors, also the bad ones get more attention than the working ones. So stories about failing transistors (from particular batches or not) are always going to be around for longer than stories about transistors working as they're supposed to (as that is not much of a story).