I have a 15+ year old "Amp Preserver" (I think the name got changed to "Tone Preserver") by Carl Hartmann. Gives me -6 and -12vac drops which work great for my vintage amps. We run about 123VAC wall voltage here, which can increase to 125vac in the evenings. Knocking the voltage down -6vac get the line voltage and the B+ down into the design range. My only gripe, the internal transformer produces a slight vibration and audible hum unless you dampen it. I'm sure Carl's later designs have this sorted.