by sKiZo 7th October 2014, 12:19 pm
May be some confusion between using a variac to reduce average high VAC or using one to bring up old gear that's been sitting a while.
For line voltage reduction, just set it and forget it, but remember that the variac will cut voltage the exact same amount no matter what's coming in. Set to provide 115vac, if the average incoming level drops a couple points, you're now down to brown out conditions that can do damage over time. In my case, I was running an average of 124vac, but that's down to around 120vac after some recent changes by the power company. Good to double check every now and then to see what's happening.
For bringing up vintage equipment, the 80-90vac setting would be a great place to start, as it's just tickling the components and giving them a chance to wake up. Especially critical for reforming some types of older capacitors. Leave it go a bit at that setting, and bring it up to speed in stages over an hour or so, ready to pull the plug at the first sign of any of the magic smoke attempting to escape.
PS ... I built a bucker that I used here when the line in measured 124vac consistently. That drops the power supplied by 7vac, which gave me 117vac into the amp. Kewl! With an average of 120vac in, that does put me into brown out territory, so I took the bucker out of line. I just checked with the Kill-A-Watt, and I'm seeing 122vac - if that starts to look consistent, I might have to consider putting the bucker back.
Or plugging the system into my variac ..