5F6a build blows fuses at higher volumes

[haricros]

Hello all,
I hope you can help me out here. I have a 5F6a that I built for a friend a few years ago that he's been using off and on since then. Just recently, the fuse blew. I took it back and realized that the filter caps weren't as secure in the back as I had thought and so I have attached them ala Hoffman's schematic. Anyways, the amp sounds great, except when I get the volume up over 6 or 7, which is when the fuse blows. Any thoughts on what might be causing this? I've tried replacing the tubes and there is no change. I'm keeping my fingers crossed that it's not the output transformer. Is it possible that the primaries on the OT need to be switched?
Cheers,
Darcy

[MWJB]

"Is it possible that the primaries on the OT need to be switched?" Chances are that you'd have discovered that long ago, the amp would howl like a banshee the moment you turned it on if that were the case.

What kind of plate current do you have (in mA) at idle?

[pdf64]

I would remove the amp chassis from the cab and cushion support it well away from the speakers, then try playing it to see if the fuse blows. You need to find out if it's physical vibration or large signals which are causing the problem.
The more fuses the better, even if only fitted temporarily for fault finding. Wire in 0.5AT between the B+ CT and ground, and F250mA fuses between each power tube cathode and ground.
Good luck - Peter.

[Enzo]

ANd try connecting to different speakers. if your speaker momentarily opens at high volumes, it can send spikes back into the amp that could pop fuses.

If you think it might be the OT, disconnect it and clip some other OT in its place for test. CLip a speaker directly to this transformer's secondary, don't bother with the amp secondary wiring.

[haricros]

Thanks

Hey guys,
Thanks for your responses. I'll try these out tonight and get back to you.
Cheers,
Darcy