Voltage for a tube amplifier fuse?
 

Is it ok to use a fuse that is rated at 6 1/4 Amp 250 Volt, if the amp is rated for a fuse that is 6 1/4 Amp 125 Volt? If not could someone please point me in the direction of a good website to purchase the correct fuse? I live about 40 miles from the nearest hardware store so I don't go into town often, so a hardware store isn't ideal. I have also searched on Radio Shack and could not find the correct kind of fuse.

Sorry is this was a stupid question, but thank you guys in advance for whatever help you can give me.

Here's how it works. The voltage rating is referring to how it will behave after the fuse blows, not before. A fuse with a low voltage rating may continue to conduct after it blows due to residue if it's across a high voltage. It is only really a concern if using a low voltage fuse like 30V in a high voltage device like 230V (higher really).
A fuse cannot be rated too high in regards to voltage for an application and the difference between 120 and 230 isn't enough to really be a concern anyway. Using a 250V on a 120V system is actually better than using a 120V fuse. The only reason we don't use 1000V fuses in everything is that they cost too much, otherwise nobody would ever use smaller voltage ones.

tl/dr: a 250V fuse will work just fine.

Thank you very much. I appreciate the help.