deze man denkt hetzelfde als ik denk: de zekering is te zwaar, dus die sneuvelt later bij 240 dan 120 ish. Met later bedoel ik vermogen, niet stroom natuurlijk
It has nothing to do with the voltage rating. A fully functioning amp will draw half as much current off the mains if they are 240v vs 120v. Therefore, to get the same protection, you need a fuse that has half the CURRENT rating for 240 volt mains vs 120v mains.
You could use the same fuse, but there will be less protection provided. Going the other way, from 240v to 120 you have to double the fuse current rating or it will blow on you. It's best to use the proper current rated fuse for the mains voltage you are using. The things are cheap, so do it right!
The voltage rating can be anything higher than the wall voltage you are using. So, at least 125 in the US and at least 250 in much of the rest of the world.