This was Pioneer's top of the range amp in 1970s and still gets very good reviews. Listed at $300 - 400 on ebay.

Was working fine with excellent sound until 2 weeks ago when the overload protection light stayed on continuously instead of going off a second after switching on. Seems to be a common fault with this amp, and can probably be easily repaired by someone with electronics skills. Plenty about the problem on the forums, and circuit diags / service manuals available.