I just joined the forum and posted my first question regarding the use of a variac ahead of a tube amp. I wish I had read your posting first. I posted that I had recently read an article by a botique amp builder that indicated it was not harmful to a tube amp to utilize a variac for overdriving the amp at lower volumes. He indicatd that 80 to 85 volts was typically the lowest input voltage that should be used. He advised that tube life would be affected by that it was not significant. Do you have any advice regarding this issue?
