Beat me to it. Super forum. They power up kit that's been standing for years by way of a variac. A substantial transformer than can be altered in ratio by a mechanical wheel.
It's a subject close to my heart. I took out a very weighty Panasonic from 7 years of storage this summer. I should have rigged a major reduction in voltage for the first try. But staying in very restricted flat - so I didn't. Stood back and kept my fingers crossed.
After a week or so of running, I knew two things. The electrolytic capacitors were probably through their crisis period, and that I LOVED that 25 year old amp even if I can't carry it far now.