You're going to want a slo-blo (time delay) fuse. Since this is a low power, two power tube amp I'd go with what the Princeton or Princeton Reverb use which is a 1 amp. Unless it blows constantly (and you know that the amp is working properly) you should be fine with this value. The 2 and 3 amp fuses go up in value as the power of the amps goes up.
Good luck, have fun, and stay safe.
Playing with amps gets kind of addicting, doesn't it?
