By the early 1950's most power companies had push their line voltage to 115. So sure if you have a 1930's amp, it was probably ment to use 110 volts, but I think you can safely assume that even if they printed 110 volts on the lable in the 50's, they knew it was more likely 115 - 117 volts in most parts of the US during the 50's and early 60's. Power companies have continued to push the voltage up to improve efficiency. Mine now measures 122 volts. This device does provide an option where needed.

The issue that I have with a separate box is "That one goes to Eleven". Never underestimate the incompetence of a guitar player! Permanently wire the bucking transformer inside the amplifier!!! Using a 12.6 filament transformer to buck the voltage is a great idea! Easily available and running the voltage 2.6 VAC under nominal is just going to increase the tube life. I think that it was David Berning that used slightly lower than nominal filament voltages in his amplifiers to keep the transconductance more consistent over the lifespan of the tubes.

Do you have a web link on the steps and part involved? I would like to keep my 65 BF Deluxe Reverb alive.

Thanks !......................it looks lke an inductor with two coils in series on the AC line, one coil differs from the other in value.............may be usefull to observe if it also filters rubbish out of the mains ?

did you use step down transformer with the premier twin you built ? Does it change the tone at all? I heard lower voltages results in more break up. Would a video on testing tone with and without a step down transformer on vintage amps be useful ? Curious to know. Thanks ! Mike