what is diff: Class "A", "A/B", and "B"

Perhaps this will help resolve the explanations. In class A, the output devices conduct more or less as the input varies, but never cut off. In other classes, output stages can be cut off (not conducting) during art of the input signal variation while the other half are conducting. That is why one could say that "different parts" of the signal are being handled by "different parts" of the circuitry. This is not a precise technical explanation, but intended to resolve the verbage. The real deal performance wise is whether the output stage is operating on the most linear portion of its characteristic curve. In class A, they are. :)

It is indeed Hitachi I have. Is this a good thing? Apparently it didn't do so well, or was it not cost effective? Please forgive my ignorance, I've had this thing for twenty years + or - and I've never had any info about it.

I'll think about this over a USDA Class A sirloin steak.

Now that we all have a good idea (?) of the class A, B, A/B, was there something else I missed? Oh yeah, private first class :) The bottom line is, just go out and listen to the amp/preamp. If you like the way it sounds then buy it.