steffo
Info wanted on Krell KMA 400’s
Don’t believe for one minute they are 400w Class-A, having the 400 figure, they would have been conservatively rated at 400w Class A/B into 8ohms, bench tested usually a Krell will be more, like 450-500 Class-A/B. They do this on purpose (underrate) because then the true 4ohm figure looks like it doubling, to give an even better illusion of current.
As for the Class-A bias, with a rail voltage high enough to give approx 500w into 8ohms, those heatsinks then are only capable of doing 30-40w max of Class-A into 8ohms, as this amp does not have "Plateau Biasing" it’s a fixed bias amp.
If it were just a 100w amp into 8ohms (no more) then those heatsinks "may" support it biased into Class-A maybe all the way to 80-100w. But it’s not and the heat factor goes up exponentially as the rail voltage goes higher for more Class-B output.
EG: The Mark Leveinson ML2 monoblocks are just as big/heavy, and have comparable heatsinks, but are only 25w into 8ohms but it’s all class-A.
Cheers George