voltage question

[Toney]

Gonna chip in here myself.
I want to import a tweed era Champ or possibly a kit and I've been through similar crap with transformers.
The best solution is definitely to have the device converted to the correct spec. transformer internally.
I used to live in Japan and there they run 100v at 50hz. Why?
Who knows- just to be annoying???
When I came back to OZ I brought back some audio amplifiers and the correct 240v step down transformers. Guess what ?.....hummm!
Yeah, they hummed. Two different brands of good quality transformer.
Annoying background hum.
Have a question though.
Exactly what voltage is standard at the wall in the US?
I have read (even in this thread) 110, 115,117. Whats the truth???
I need to know exactly to get my champ running right, they are a simple,  single ended amp and need exactly the correct voltage to sound good.