Transl, FWIW it is possible that one or more of the tubes in the amp when it was blowing fuses had a 'bias' point which exceded the values of the bias circuit. A personal experience (on two different amps - same tube set). One amp had 'auto bias', one tube ran hot (plate turned red). Sub'ed in another set and this same location (V3) ran hot again. Sent the amp (under warranty) back for servicing. They reset the bias - the amp has worked fine ever since, but with different tubes - I thought the initial tube that tuned red might have been the problem.
Next I tried to use that same set in an amp with fixed bias. I reduced the bias pots to minimum as normal. Three out of the four tubes had a normal (minimum reading), but the tube that had turned red in the other amp registered 50ma on my meter with the pot in minimum position. I subsequently figured out that the correct bias point on this tube should have been 75 and it was somehow mixed into a batch with a 50 bias point.
How, or if that applies to your amp, I don't know. Just don't assume that auto bias circuits and tube bias points assigned by tube matchers are foolproof. I'm very carful now when I buy matched tubes to insist of bias points of about 40 and have had 0 problems since.
Or, it might have been an short caused by an undersized pin, or loose contacts in the socket, causing a short too (although with the latter it was always noise, popping etc, and was corrected by tighting the contacts in the socket.
Lost any fuses since you went back to the original tubes. BTW, what were the tube types and brand of the tubes you were trying to roll in?
FWIW.
