Best used Krell two channel amp?

My favorite Krells in the past have been the original KSA 50MkII, followed by the KSA 150/250, along with the KSA80/200, their predecessors. The 50, 80 and 200 are all pure Class A designs, and after warmup can sound quite nice (for solid state); the 150/250 were actually not fully pure Class A in operation, as I recall from the Stereophile review, but heavily enough biased in Class A that they too could drive just about anything out there, and they were pretty nice sounding as well, perhaps a little sweeter and warmer, if possible for a Krell, than the 80/200s. My personal favorite was the 50Mk II, which had a slight sweetness in the highs that the others did not quite match, but that's the oldest model here and used a cooling fan, which is another part that could go in the unit--the other versions have massive heat sinks. All run very hot, and can double as a space heater. After these models (and the Audio Standards), Krell went to a Sustained Plateau Bias system that kept the amp running cooler but in my view lost some of the character, and ultimate power into difficult loads, of the earlier models. The later models have their supporters too, though, as I'm sure you'll find from the answers to your post--I think it's safe to say they may be more accurate in passing the signal, but I always felt they lost a little of the music along the way. My opinion, likely not shared by many others!

I own the Big B&W800's.

Over the years I have owned many Krell amps. Without exception, the newer the model, the better. I think the biggest improvement was with their newest basic technology. the FPB series.

I would aim to try to get the FPB300.

Richard

My Krell experience started with a KSA 100s it replaced 2 Aragon 2004's very much better. Moved on to a FPB 300 again a marked improvement in all areas. I was not ready for the differences, when I got a FPB 400cx.

The improvement in the latest version affirms the genius of all the people at Krell.

You should save your money until you can get the latest version. As far as dizzing array statement, there is only the FPB line that should be considered for music.

If you are watching TV that is a different story.

The newer Krell FPB x-series are the most musical amps they have ever made. Some people like the older KSA series, but I have spent hundreds or thousands of hours listening to both, and none of the older amps are as musical as the newest amps. Depending on how much money you have to spend the FPB 400cx is a good choice, if you have the money the FPB 700cx will dominate a big speaker like the B&W's, and let you hear what they can do with the right amps.