Hi,
You could do the following:
Remove all power and preamp tubes and replace the fuse. Does the fuse still blow?
a) If yes, remove the rectifier tube. Does the fuse still blow? If yes, there is a short in the wires coming from the power transformer or your power transformer is bad. Take the amp to a qualified technician.
If the fuse does not blow, replace the rectifier tube.
b) If no, replace the preamp tubes. Does the fuse still blow? If yes, there is a short somewhere - take the amp to a qualified technician if you do not have experience with working on amps.
If the fuse does not blow with the preamp tubes in, put in one of the power tubes. If the fuse now blows, the power tube is most likely bad. Try a different tube in that socket. If the fuse then still blows, the socket wiring of that tube needs to be checked - again refer to a technician if you don't have the experience. If the fuse doesn't blow you have isolated the tube as the problem. Replace the power tubes, have the amp rebiased and you should be back in business.
Cheers Stephan
