Here is something to ponder: You can't buy them, but Audire made both class A and Class A/B amps with the same basic parts. The A/B was twice the power, 200 vs 100 wpc (Parlando and Otez). Their designer, Julius Siksnius, an honest to god rocket scientist for the Apollo moon rockets, also had an earlier amp, the Forte, which used either bipolar or later, just to prove a point, a choice of the above or MosFets. He never claimed either was better. I have one of each. They sound the same. I have an Otez and a Parlando. They sound the same except on my best speakers, B&W 803's. On my Electrostatic's or older B&W's there is no difference. The 803's are my most efficient speakers, by far.
The difference seems to be that the efficient speakers need less power and the Class A has it, so it has an easier life, despite the heat. I know that makes no sense, but I am not an electrical engineer.
I like Pass designs, including Threshold, and Audio Research. Since Audio Research is available in older models, buy it if you can work on it for small repairs, like changing tubes (especially if you have a great A/C system) but get Threshold for total reliability if you are happy with transistors.
Routine bias tweaks are less important on Classe A , as far as longevity.
Tubes are good, but they age and you won't notice without something to compare them with. By then you have wasted a lot of time that could have been used to listen to great transistor amps that are much more reliable designs.
