Vintage tube amp resurrection with Variac?

I have acquired some vintage tube equipment that has not been turned on for several decades. I bought a Variac on eBay having read many times to be sure to "bring up" old tube gear "slowly on a Variac". What exactly constitutes "bring up slowly"? Is it some sort of staging perhaps? If so, what voltage at each stage, number of stages, how long per stage. Or does it mean to continuously, but very slowly, crank the Variac from 0 to 117 volts?

Showing 1 response by atmasphere

There is a simple way to do this using an incandescent light bulb. You remove all tubes and put the light bulb in series with the AC power and turn it on.

The light bulb will light up, which means most of the power is being dissipated by the bulb because the caps are likely shorted. However, if they need to 'form up', the bulb prevents them from heating up by limiting the current. If the bulb goes out the caps are formed up and OK.

Time-honored technique BTW; but if this is an amplifier you intend to really play a lot don't screw around- just change out every filter cap in sight... If there is a selenium rectifier change that out too.