The ST-70 has a pretty good reputation, and IIRC was designed by David Hafler. I've never owned one, but did have some Hafler amps before and they were good. As for price, the $300 seems kinda steep for a Dynaco, but I have not looked at pricing on these in a long time. Is it stock, or has it been modified/upgraded? I seem to recall there being some modification kits and parts floating around; I'd take a look on audioasylum to see what you might find out.