No amp in your signature line is Class A (maybe the Schiit?). Your preamp may have Class A stages in it, but draws so little power between idle and full output it may not show on your power meter. Your MC275 is a PP (push-pull) amp. The more power you want the more power it will take from the wall socket. A true Class A amp using KT88s will make about 7 or 8wpc/tube (look at Dennis Had's Inspire amps as an example) while your MC275 is rated at 75wpc. Definitely not Class A.
Class A amps do not run at 100% rergardless. Their large heatsinks & power supplies would have to be even larger (aren't they big enough all ready? - my 25wpc INT-25 weighs 50# - once it is delivered). Class A often makes the most heat at idle as the output devices are at an essentially steady-state mid-band. When playing music the average current draw is lower as it moves up and down around that mid-band bias point.
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Glenn...
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