Electronics > Beginners
How to test transition frequency of a transistor
magic:
I would say they look genuine, most fakes are lower effort, but who knows. The scratches may come from storing and shipping a dozen of them in a bag.
The thing is that the amplifier works and is likely made of unobtainium, if something blows up it will be a bad day.
Kleinstein:
The transistors are nothing special - so chances are that these are not fakes, even if from China.
Testing them before use may still be a good idea.
The 4 MHz fT is more or less standard - so even a fake / wrong type may very well be in that ball park. Much to slow or too fast may cause oscillations in a given audio amplifier circuit. This could also happen with different capacitance - so it's not just fT. If the amplifier is not oscillating chances are it would be OK.
If they are fake / wrong type, the main parameter to worry about is the voltage rating / SOA (e.g. if they are actually 2N3055).
So the interesting point is more like how to do an SOA test. No need to record a full curve and find the real limit. It is more like give it a stress test (e.g. 1.5-2 A at 60 V for a few seconds) and see if they survive.
The difficulty may be for the test circuit to survive a blowing / runaway transistor.
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