Variac or not?

adamant40

Variac or not?

I acquired a Marantz 510M amp that had not been turned on for about 10 years.

Yes a Variac is a must, a little at a time, in 20vac mains increments over an hour to full mains volts, so to "condition (form) all the electrolytic capacitors" again, BUT!!! at the same time with meters hooked up and a scope if you have one you must monitor parameters of the amp while going up in mains voltage EG: dc offset, bias, etc etc and whatever adjustments are in the service manual

Cheers George

"Can you explain why lowering supply voltage (variac) would burn out resistor in series?"           Just thinking there may be a corollary, here:          An AC motor, connected to too long of an insufficient gauge wire/cord and the attendant voltage drop, will usually overheat, do to a higher current draw.      Will the power transformer/filter caps try to draw higher current, at charge-up, at a much lower voltage than intended?      One would think a fuse would go first.      

@rodman99999 SMPS would do that - draw more current at the lower voltage, but 510M has linear power supply. Lower supply voltage shouldn’t result in higher supply current. The issue is relay shorting this resistor, that might not activate at the lower voltage (poor design?). I still don’t see how this resistor can be damaged, unless they assume full operation (2x250W) at the lower supply voltage (not desired for conditioning of capacitors).  At idle power it should be OK, but when they say "short" I would short, just in case.