How does Transition frequency affect a transistor?


#1

I have a customer looking at transistor 2N5886GOS-ND which is showing a transition frequency of 4MHz compared to 0.6MHz in the one being replaced.

He is looking to replace this out of a solid state guitar amplifier.

Anybody know the implications of transition frequency in an application such as this?


#2

There shouldn’t be any. The transition frequency describes how the transistor’s current gain is affected by the input frequency. This is a low pass effect, so frequencies beyond 600 kHz on the original part or 4 MHz on the new one would start to be attenuated. Audible frequency range is 20 Hz - 20 kHz which is far below the transition frequency of both parts. No effects should be noticeable.


#3

I’d offer the observation that faster devices generally increase the risk of high-frequency instability, RF interference, etc. May or may not be an issue, depending on the design and it’s implementation.

That said, it seems likely that such a transistor would be used as an output stage driver, which are/were often paralleled in audio amp applications. In such a case, the chance of problems increases as a result of dissimilarities between a replacement device and its teammates.