Hi Simon,
I've had the KSA-100 Mk1 and Mk2 versions, KMA-100 Mk2, KMA-200 Mk2 and now the Krell KRS-100.
I can't say much about the other models you've mentioned but from the KSA-250/150 series onwards none of them are real fixed bias Class A amps. Friends of mine operated KMA-160's and a FPB-600 which became very hot to the touch.
The KSA-80/200 and their mono derivates the KMA-160/400 all had problems with too much heat and too little heatsinks.
My Krell KRS-100's use much bigger heatsinks (and six of them per channel instad of three) than the KSA-80/200 for instance and with 600 Watts AC intake they keep relatively "cool" compared to the other two mentioned. The KSA-250 was throttled down with the quiescent current and got even smaller heatsinks that fitted in with the width of the frontplate.
It's my belief that only the Krell KRS series of amplifiers are truly Class A (I measured 180 Watts Class A @ 8 Ohms for my samples) amplifiers that can power those 1 Ohm Apogees like the Fullrange and Scintilla.
The longtime importer of Krell electronics in the Benelux (Belgium, Netherlands and Luxemburg) told me that they had lots of problems with the KSA and KMA from the eighties and early nineties and not with the KRS Series other than replacing old caps (especially the deep red radial Roedersteins and relays). No reliability problems as with the other Krells.
I love them because they sound so wonderful!
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