Let me add this to my other post. After doing some nosing around, I think a price around $400 to maybe $500 would be reasonable (to me, anyway). I also wouldn't expect that 700-800 watts claimed by some, unless they're talking input power. It's a pair of 572's, not a 3-500, so keep it reasonable.
I seem to recall having to make some adjustment to the one I had that involved partially removing the thing from it's cabinet. Can't for the life of me remember what it was, but can say that it wasn't any fun. If you get a chance, a little modification is also a fairly good idea in the input connector. It's an RCA phone-jack instead of an SO-239. Not really a problem, just different, and not very common to have a coax jumper with one of the @#$ things on it.
Something else to keep in mind is that since the tubes 'lay down' in the 2100b, you want to be very careful about replacing them. There are more than one 'style' of those tubes, some have plates and grids that are oriented 90 degrees from standard. If the width of the plates/grids do not stand vertical, they will last about 30 seconds after turning the amplifier on. When they get hot the grids naturally expand and then short out to the plate because of 'sag'. Something to pay attention to with any tube that doesn't stand vertically in use.
It's still a good amplifier...
- 'Doc