@LvW: I really appreciate your insisting on precision in analysis of feedback circuits. I completely aggree, that the questioned statement isn't exact.
But using negative feedback in an amplifier with low frequency transistors causes oscillation...........
I however think to know, what is meant here, and I guess, you basically know, too.
The addressed problem, as far as I understand, is phase margin in feedback circuits and available compensation techniques. The above statement and the additional explanations are apparently assuming, that the 2N3055 limited current gain-bandwidth product is directly affecting the amplifier open loop gain, creating a respective pole. If this would be true and there are additional poles affecting the phase margin, reducing the loop gain may be the most obvious means to handle this situation.
There are however, several points contradicting these assumptions.
- the limited transistor current gain can be fight by local feedback
- if unavoidable, the output stage pole can be made dominant
- additional poles in amplifier gain can be shifted by pole-splitting
So a general correct statement would be to say,
low frequency transistors are requiring a higher effort in amplifier compensation.
There's also a certain risk of dynamic instability, cause the transistor bandwidth is strongly current dependant. You have to assure, that you don't get sustaining oscillations after overloading the amplifier. Most catastrophic failure cases of audio power amplifiers are likely caused by effects of this kind.