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RE: Sony Class A, think not

Yes but Krells sliding bias amps were still huge with huge power supplies and huge heat sinks. Even then they never ever reached full rated power Class A...only Krells earlier true Class A amps did that.

Look at the reviews of like the Krell KSA200S
http://www.stereophile.com/content/krell-ksa-200s-power-amplifier-measurements

It was only Class A for the first 15 watts or so on the lowest plateau setting (125 watts at idle). Even with full ramp up though it never could do full power in Class A.

The KSA50S could never draw 800 watts for long...it would simply burn up due to lack of heat sink capability for that kind of power consumption. Where did you get those numbers anyway...I didn't see them in the stereophile review. They mentioned bias levels of 765mW and 25.2 watts. I could believe something like 400 watts make consumption for a 50 watt Class A amp. The old Sumo Nine I had in the past had about 420 watts consumption (all the time) for 60 watts Class A power.

"If continuous high powers are required that would lead to overheating, the amplifier reverts to classic class-AB operation.

For a contrast, my NAT Symbiosis consumes 800 watts continuously for 100 watts max output. That is single ended Class A.

Compare the Krell KSA50S or Sumo 9 power supplies and heat sinks (the Sumo also had a fan) to the Sony and it becomes clear that there cannot be more than a few watts Class A or the thing will simply overheat.

"to the touch, the top panel of the Sony is quite warm and there's been no signal going to it for an hour now"

Warm is good but I had for review an AcousticPlan Santor amp some years ago that was 50 watts per channel and it ran VERY warm. I asked the designer to what level of Class A it was biased...he said "about 15 watts". It had bigger heatsinks than what I see in the Sony. I had a SimAudio Celeste W4250 that was 10 watts biased Class A...it ran rather warm as well with rather good sized heat sinks. Like I said, I doubt there is more than a few watts Class A operation with the Sony.

A single pair of transistors is good. I never understood why some companies insist on using dozens of output devices.

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