So glad I found John who was able to advise on repair and upgrade options for these old amps, they’ve been repaired twice before so I wanted to make sure they stand the test of time. Decided to go the whole hog which entailed:
– upgrading the toroidal transformers from 500VA to 1000VA (custom built and main cause for the delay)
– upgrading the smoothing caps from 4×10,000uF to 4×22,000uF in each amp
– upgraded the MOSEFETs to higher voltage modern Profusion devices ECF10N/P20s (6 pairs each amp)
– new binding posts, internal cabling replaced and sorted.
After many months with work delayed due to COVID impact on suppliers, they’re back home. Its clear there is a LOT more dynamic range, lower noise floor, more details coming through, timbre of drums is richer etc. And the bass – I’ve never heard bass so deep and controlled before on my system. The overall signature from my ATC SCM40s is anything but lean – the amps now really show what these speakers can do and I expect they would drive the bigger SCM50s well. The original character of the amps (or lack therefore) is retained but with a lot more of everything.
While not cheap, the cost has been a great investment and I hope these amps will last many years to come, I am thoroughly enjoying them.
Thank you John!