Class A amplifiers - which are considered the best

I remember being approached by someone in the early 90s that held a patent to a sliding class A bias system (for transistors). As innovative as he is, I don't think Nelson created that. As I recall, it showed up on the Krell amps first.

We didn't go for it because our amps are tube. But I have thought about a tube-implemented class A system over the years. It might cool our amps off a bit!

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.

Class A has two modes of execution, A1 and A2. In A1 the output devices conduct all the time and there is no current flowing in the grid circuit (we are talking tubes here). In class A2 the output devices also conduct all the time but there is grid current flowing during part of the cycle. For the latter there are design considerations required to prevent distortion due to driver circuit issues.

Rleff, our amps are A2. 'Pure class A' has no engineering or technical significance (although it may have marketing significance); IOW an amplifier is 'pure class A' whether it is class A1 or A2.

It does not matter if an amplifier is single-ended or push-pull, it can be class A1 or A2 in any of those embodiments.