I own a Krell FPB-600c (no longer in service) and it did a fantastic job of controlling the notoriously low impedance woofer sections of my Thiel CS5i’s, often at very high volume. I would submit that few have heard the full glory of Tin Pan Alley the way this combo reproduced it. John Atkinson measured the output of the prior model (FPB-600) at over 6kW (yes kilo watts) into 1 ohm!
But it ran hot, very hot. Much too hot to touch the heatsinks for even a few seconds. Despite running supplemental feeds from a second AC unit to my listening room, I was reduced to listening in my underwear (alone) on many occasions in the summer months. The black anodizing on the massive heatsinks turned the tell-tale purple due to the immense heat the circuitry generated. Alas, the many capacitors inside the unit succumbed to the heat and failed.
@mceljo There are not five ranges of plateau biasing and there are only three lights arranged in a triangle on the front panel. In no way do they indicate the switching of the circuitry in operation. They simple light up progressively as the protection circuitry moves through its cycle upon power up and stay fully lit once the unit switches into operational mode.