Audiophile quality variacs to decrease voltage?

I have an older 30 w.p.c. tube amp that should be run with 110-115 Volts coming into the unit. The average voltage coming from my AC lines is 124 volts, which puts the operating voltages inside the amp well above what it should be, and will cut short the life expectancy of various components and tubes in the amp. I purchased a newer model 10 amp variac to reduce the incoming voltage to the amp, but quickly found that the sound quality was noticeably reduced with the variac in line, at any voltage set between 100 and 124 volts when in use. Are there any "audiophile quality" variacs available, or some that "sound" better than others? I researched power conditioners that might have the feature of reducing output voltage, but the only solution I found were the new PS Audio Premier power plants that can do this. Unfortunately, they retail for $2,000, and my budget does not allow for such a purchase. Even at used prices, their reliability seems to be an issue from posts I have read on them. Any suggestions from others who have suceeded at reducing voltages without ill effects? Thanks for your help!