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...