Variac Variable Transformer


I have a number of tube amps and tube preamps. Many are stored for a long time. Quicksilver recommends I hook up a Variac Transformer to the amps and bring up the voltage slowly and let it stay at 120 volts for ten minutes. Same process for tube preamps. I was wondering if other Audiogon members do this? I'm thinking solid state amps and preamps would be included as well...
exocet954
It's a problem with electrolytic caps. Layer of aluminum oxide that serves as isolator diminishes over time (years) without voltage and capacitor looses its voltage rating. Applying voltage and keeping voltage at lower levels (for days) will replenish layer of aluminum oxide and capacitors will be OK. Applying full voltage to unit that was in storage for many years can cause capacitor short, thermal build-up and even explosion. Capacitors have fuse (vent) to prevent it (explosion) but it's wise to to test it.
How long should I leave the Variac on for? Bringing up the voltage slowly to 120 volts...Mike at Quicksilver recommended ten minutes. They have been in storage over a year now, originaly built in the last several years. I have an older ARC SP-6B tube preamp stored for over 7 years as a back up preamp. Any recommendations? Thanks..
My personal preference is to bring the voltage up very slowly, over several days, or a week. Have seen guys in a hurry to hear their new (old) tube amps bring the voltage up to 120 and smoke the capacitors. IMO all of the internal components require small voltage increases to prevent malfunction.
If the amp uses a GZ34/5ar4 rectifier it will not do a slow start with a variac.

Think this may be true for other indirectly heated cathode rectifiers as well.

I substituted a directly heated 5Y3GT, for a GZ34, when slowly bringing up a Pilot 240 and it worked (someone @ AA made the suggestion).

A local tech used a DIY solid state plug-in GZ34 for the same reason when using a variac on my Pilot 232.
I agree with Commcat. I found rule of thumb on the internet to apply 5 min. plus 1 min for every month of storage. This would call for 41 min of reforming unit stored for three years. It seems too short and I would do this at least for many hours (if not days). Be patient.

Dekay - similar problem with SMPS power supplies. They will produce full output voltage (regulated) as soon as supply voltage crosses some threshold.