The heater cable toasted

[Kensel]

hello friends "music electronics forum". I have a problem. I recently built a "Fender Bassman" based on the layout of "Ceriatone. Everything was fine, the amp sounded. Two weeks ago I noticed that the box was vibrating (a combo) so I proceeded to disarm till I found the fault. The amplifier worked well throughout this process. Solve the problem (the vibration in the box) and then mount the amplifier, plug the guitar, I light and sound, but after a minute starts to smell of burning out so quickly turn it off. Dismount and I realize that the earth wire of the heaters was toast. I have carefully reviewed all the amp and the only thing toast is wire of ground (0 volt) of the heater. All other pieces are OK as filters, capacitors and resistors. Do not know what happened. I thought there was a bridge between the "plate" of any of the "tube" and heaters, but after a visual inspection is not no cable dangerously close together. I also thought that the power of 0volt heater had been disconnected, but when my tester measures had continuity. The fuse (2A) does not blow. What will be the problem?

pd: in the primary 220volt
pd2: heater: 3.15volt 0volt 3.15 volt
pd3: I bought another power transformer