Variac Variable Transformer

What I do is start out at 10 volts (or 10 percent, depending on the scale of the variac) for about an hour and then increase by 10 volt increments for about a half hour at each increment. Takes a good six/seven hours.

I would clarify with QS about what they mean by "bring up the voltage slowly". What works for me doesn't mean it's correct for you.

GS5556 does you procedure include solid state power amp that has been sitting unplugged for 2 1/2 years? Thank you for your contribution to this forum. Joe

GS5556 I'm referring to my old Hafler XL280 that has been sitting for all that time. I'm a little worried about throwing all that current, at start up cold, into the PS caps. So I thought if I would just ramp it up in 10 20 vac increments with my 7amp variac for a period of several hours would be prudent. Any thoughts?

This has nothing to do with tubes. It has everything to do with older electrolytic capacitors.

You don't need a variac! All you need is a light bulb (60 watt will do fine) to put in series with the amp or preamp. Pull the tubes out if the unit is not solid state. Turn it on with the lamp in series with the AC line. If the filter caps are having a problem the bulb will light up. As the caps 'form up', the lamp will dim out to nothing (unless you have a solid stage unit, in which case it will remain dimly lit).

This will prevent serious currents from damaging the caps. If the bulb stays lit, you have a capacitor or capacitors to replace.