That's the mains fuse, which pretty much works the same as every other fuse you'll see on a guitar amp. (The other fuse, the HT only supports high voltage to the power amp and preamp). Don't worry about the difference - you have a fault somewhere. I'd say it's about a 75% chance it's a bad tube. If someone can open it up for you cheap, you might save a few $$ if they can rule that out. Oh yeah, and they could also save your life, too.
- It looks just like a Telefunken U47 - with leather. You'll love it ...
- Jazz is not dead - it just smells funny.
- It doesn't make much difference how the paint is put on as long as something has been said. Technique is just a means of arriving at a statement.