as an arm chair tube tech, I can tell you there could be many reasons why a fuse blows in a tube amp. power tubes, driver tubes, rectifier tubes, if you have diodes...those too....
best bet....find someone who is not an arm chair tech.
If you can't do that...test all the tubes (you will need a transconductance tester) ......measure all capacitors (cap tester will run you 40 bucks for a cheap one)....test all transformers (volt meter for power suppy trannies...inductance meter for output trannies is better than DCR ing a tranny)....use a variac (but you need to bring them up super slow over hours.....theres a lot of articles on how to be an instant tube amp arm chair tech) ...cross your fingers.....then after the smoke clears...find a tube amp tech accept your lecture from them...hand over the cash...they will fix your amp.
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