They do wear out. :) And they are simple to replace. It is probably time to open up that amp, and clean it out of dust, replace the fan, and maybe the main power caps too.
I have a KSA 50, though I rarely listen to it anymore. Erik is giving you excellent advice. I actually took my fan out, removed the motor label and lubed the motor with some light weight motor oil and then put it all back together. It’s extremely quite now.
If this amp has been used regularly for the last 25 years it’s time for a recap. That class A heat really shortens the life expectancy of the electronics.
Thanks to both so far. While I am really impressed with quality sound matching my Audio Research LS5mk2 and the Krell Ksa 50, I'll have the Krell opened and carefully checked to be double sure about my perspective purchase. Any suggstion about original or different/better caps? Thanks again. Maurizio
If you can, upgrade the temperature rating. The higher the rating, the longer the operating life at a given temp.
Nichicon is the go-to brand for the big power supply caps. Replace distributed, smaller isolating power caps with Panasonic FM where there are equivalents. These are usually in the 10-100uF range.
Replace the fan it's over 30 years old, but don’t get sucked into buying expensive roller bearing type they are noisy, use good quality bronze sleeve bush type, these are the quietest.