russel
./_dazed_and_confused
It was specifically the A1, A100, A200, MA50's and MA100's which were terribly unreliable for heat reasons.
The P140, P150, P170, P180, P270, A370, SA470 and power amp section of the B200 are all basically the same topology and IMHO a very good one which sounds great. I'm surprised they haven't become more sought after...
A friend of mine still uses a pair of P140 power amps which I completely "supercharged" to the extent of even fitting extra output mosfets and has had reliable service from them for over 10 years of daily use (presently driving kudos super 20's) and great sound.
My friend had a P170 mebbe P140 in the 80s, he scribbled out the component layout and I letraseted a couple of PCBs, used it for a number of years, nice amp.