After a long, long sleep: ML-335

That’s a gorgeous amp. I recommend sending the amp to ML’s authorized service center for complete check-up before you insert in your system.

Fire it up, its an amp, not a land mine.

Have it looked at first.  It's an expensive amp to repair so a little caution is warranted.  It doesn't have to be an ML service center.

Don't plug it in and turn it on. You will need to invest in a Variac. Set the Variac to 5 volts (AC) and turn on the amp and leave it at that voltage for at least six hours and then increase the voltage in 10 volt increments, with each increment at least two hours. This process will reform the power supply filter capacitors, which after 25 years are almost certain to be "dried out".

Or you can recap the amp. Pyramid Audio was quoting $1400 for cap replacement more than five years ago. 

+1 for the Variac