Feedback is especially important for SS as thermal runaway can be a huge problem (just imagine the look i a guy's face who recently got his krell toasted, I have seen one). Negative feedback is needed to put SS devices in steady state, sonic consequence is decay and attack. Now, that sound is heavily colorated (even darth hansen will not disagree with this) as negative feedback is a deliberate reintroduction of off phase controlled distortion in the earlier driver stages of an amp to bring the SS operating properties within a predetermined power/thermal ratio envelope.
i can not make heads or tails out of this, thermal runaway has nothing to do with negative feedback!
thermal runaway is a function of operating point, how the output transistors are biased, and the heatsinking quality of the amp.
if the output transistors are operated at or beyond their SOA limits, safe operating area, (or region), thermal runaway is sure to follow, how is this?
even though an ss device is rated at 150watts and 15 amps with a Vceo of 150volts, it does not mean that you can operate them at high volts and currents simultaneously. because secondary breakdown can occur at lower Vceo and Ic than the specs for the transistor would imply.
a malfunction in the bias circuitry of the Krell amp was responsible for its getting fried.