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.

“The Krell KSA amps are pure Class A.”

The only Krells that were full Class-A biased into 8ohms were the KSA50 and the KSA100 and KSA100 MkII monoblock, all these were internal chimney heat sinking and fan forced.
https://youtu.be/kqSkh08AmKM?t=1

Cheers George 

Threshold 400A class A

I believe it's a push pull 100w Class-A/B amp. And with those heat sinks, about a max of 15w of Class-A,  with rail volts for 100w Class-B.

Cheers George 

A big advantage of Class A amps is that by the standards of any AB amp they have a hugely overbuilt power supply and they can drive low impedance loads without faltering.

Yes they should have, but not all have, I’ve seen them with supplies that are close to saturation in the Class-A idle state, which means there’s nothing left for any Class-B transients, so they sound like a limp ****.

This amp I have here can do 3-100w user adjustable of pure Class-A, then to 180w Class-B, and it has the power supply to back it up, 5kva transformer with 300,000uf of supply caps. But it also weighs close to 60kg
https://ibb.co/Yp956yN
https://ibb.co/qW4qSc8
https://ibb.co/rdKwDgc

Cheers George

Class-A has yet to be equaled in my experience.

Correct, if done right.

Why do many of us spend $$$K's on our equipment especially BS cables, for only 10% "if any" in sound quality increase over something that cost a 10th or 100th of the price.
Yet we cry murder for nowhere near the extra cost of using Class-A amps and the power they consume, (Class-D users are especially known for this)

Cheers George