Class A amplifiers - which are considered the best

Question: NAD "Power Envelope" amps....Hope I'm not
going too far off topic, but with the recent comments
about sliding bias circuitry, I'm genuinely curious
about what, if any, similarities exist between the
NAD 2600a method (mid 1990's) and the Krell method.
The NAD's have never been called Class A, have they ?

I believe the "power envelope" did nothing extra for the class A bias.
What I believe it did do was to aid in transient ability with a bit more short term current from the power supply. This way they saved on big expensive power supplies, and got a result that was better than using a mediocre supply.
I lifted this explanation from DIY audio, make of it what you will.
"The cheaper PE receivers used two ± power supply rails with a fast diode on the lower rails feeding the outputs, a polyswitch was in series with the upper rails."

Cheers George

Rleff, The idea was an analog setup that used a feedforward system so that the bias is mapped in sync with the output signal. In effect there would be no 'decision point', merely a minimum level that represents no signal at all- as soon as you have some signal, the bias is increased or decreased in exact synchronization with the signal, so the amplifier is always operating in the class A region. However so far things have gone if favor of the KISS principle- So far the evidence suggests that such a system will produce some artifact.

Ralph, are the M60s pure class A? Not that I care, except theortically. I do remember when I bought my CAT JL2 that Ken Stevens scoffed at claims others made about being Class A (he had an SS design in mind), but I think his amp was pur Class A, it sure was hot enough, raising the room temp 5-7 degrees.

Reference Line Silver Signature from the late '90s. 100 watts into 8 ohms, doubles all the way down to 2 ohm loads. Designed for passive preamps and runs hot, so you have to be okay with those features. Top quality internal components. Built to last forever. Amazing transparency and ease.