I don't know much about biasing but it can have a lot to do with the heating as well as the sound of the amp.
Perhaps the hot one's biasing has been calibrated at a substantially higher level than the other. If it is biased too high, then that can destroy parts of the amp also.
Perhaps the hot one's biasing has been calibrated at a substantially higher level than the other. If it is biased too high, then that can destroy parts of the amp also.