2150B, 3150. Both Hitachi MOSFET application note designs. Residual noise from the gigantic transformer and it's proximity to the front end made for low level, but audible hum/buzz. Otherwise, flawless. But you can't really fix the problem. Later models tried with shielding, but it didn't really work.
The only thing that fails is the power switches in the older Perreaux amps from the massive turn-on arc (no slow/surge turn on).
Yes. The MX-600/800/1000 power amplifiers were pretty amazing, although the APS (switching rail) made them a little unreliable in the 1000. I'd say they would be more than competitive in the noise, THD and power output stakes with modern amps. I only have an MX-600 and MX-630 here I could do limited tests on. They have pretty obscenely high short term dynamic power as well.
The M-80/85 were damn fine amplifiers too, but suffered from bond-glue issues.
I never saw an MX-10000 Centennial (1987) power amplifier in the flesh. I don't know if it was ever properly reviewed, but it should be right up there for sure.
The one I'd like to get my hands on is a 1980 Denon POA-3000 or 3000z.
View attachment 70132
1kVA transformer, 100,000uF filtering. FTC continuous rated 180+180W@8R, 122dB S/N etc.
View attachment 70133
https://audio-database.com/DENON-COLUMBIA/amp/poa-3000-e.html