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

@viridian The Krell you refer to (KSA 250) is an older model. The KSA 300S was the next series that were designed precisely to run completely Class A unless the amp gets very hot. Here's the article that explains the difference:

https://www.stereophile.com/audaciousaudio/krell_ksa-300s_power_amplifier/index.html

BTW, with my low sensitivity speakers (Mirage M3si) I can drive the amp into the highest bias level - and it gets really, really hot. What I don't know is whether or not the top two bias lights still turn on when the thermal protection kicks in. It may be that for some of my extremely loud listening the amp goes into Class A/B. For the great majority of my listening the amp never goes past the third bias level and according to the article, and everything else I've read, the amp operates in pure Class A. I think it's worth noting that this amp weighs 185 lbs. It was obviously built to an extremely robust standard.

To clarify further, operating in Class A was the whole point of this amp's design and explains the design differences between it and the KSA 250.

“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 

George, Krell never made a mono amp with the designation KSA.
they were KMA 100s and there were also KMA 50s and 200s. They all used fan powered chimney heat sinks and they were all class A to rated power. I owned a pair of KMA 100s for 20 years and they were great amps.