What are the advantages to a Class A amp & what are the trade offs?

George, Krell never made a mono amp with the designation KSA.

Yes KSA50, KSA100 and KMA100 were all Class-A using chimney heatsinks
I got a letter wrong for the mono's, still talking about the same amps with chimney fan cooled heatsinks as I said and provided a video link to.

Thanks Ralph. Fwiw you have a way of making the complex easy to understand. Are/Were you also a teacher?

I have taught a few classes but mainly I think I got that from working in consumer electronics repair while putting myself through engineering school. I found I was explaining how things worked a lot to customers and quickly learned that converting things to layman's terms was an important skill.

I do believe class A 's design & sonic advantage over Class B. BUT don’t understand  say: 30 W class A vs a 250W class A/B. Isn’t the class A/B has the advantage of both ? Example:Pass Int 250 DON'T leave class A till 15 W and has all the extra class A/B reserve up to 500 W into 4 ohms! Why would a 30 W class A be a better choice over the 250 W A/B??? If 99% of the time I am only playing music at about 2 Watt( under 90db)?

Example:Pass Int 250 DON'T leave class A till 15 W and has all the extra class A/B reserve up to 500 W into 4 ohms! Why would a 30 W class A be a better choice over the 250 W A/B??? If 99% of the time I am only playing music at about 2 Watt( under 90db)?

With many push-pull amplifiers the low level power output below a certain point has high distortion than it does at higher power levels. So its on a case by case basis, but generally speaking if you only use 2 watts its likely that a 30 watt amp will be making less distortion (and noise) than the 250 watt amp will. That distortion is likely audible as harshness and brightness so that right there could well be the advantage.

I'm planning a bedroom system with some small speakers that are remarkably free of breakups. I don't need a lot of power and certainly don't want the size of a 250 watt amp in that environment! Small has its advantages...