Fender '65 Twin Reverb reissue filament circuit overheating

[acorkos]

This amp came to me with complaint not lighting up, no sound, but power transformer is humming like normal. Inspecting the chassis internals, the T10A filament circuit fuse holder had been replaced with an in-line variety...the fuse was blown and in one side of the replaced holder, the metal bit that makes contact with the fuse end was missing. Interesting. I replaced the fuse holder with a similar in-line type. Checked power tube bias...about 34mA@435VDC per tube. The owner took it home, played it for 30 minutes and the same thing happened...no lights, no sound, transformer humming. I opened it again, my fuse holder was popped open, fuse blown...and the plastic holder had melted/deformed to a point that the 2 halves wouldn't fit together. I put a new fuse holder and fuse on and let it idle for 30 minutes,...the fuse holder and filament circuit wiring chain was warm to the touch, none of the other transformer wires were warm. The power tubes were still drawing about 34mA per tube, nothing else looked overheated. Power supply electrolytics appear normal, no leaking. Please direct me, what should I be looking at next? Thanks for your help!

[g1]

It seems to me some of them did have an in-line holder from the factory. Not sure if it was fast or slow-blow fuse.
They use them in cars all the time for low voltage higher current applications like this so I don't think it's a problem of suitability. Check the current rating of the holder though.
If 10A slow blow is blowing, there is definitely a problem. Must be intermittent if it is working for you for a while.

[Tom Phillips]

I have had a few recurring problems with 1/4" size fuse holders fitted with 10 A fuses. In each case the issue was local overheating of the fuse and/or the fuse holder due to a high resistance connection because the fuse holder had inadequate / loose mechanical connections to the fuse end caps. As g1 said "Check the current rating of the holder." If the part you are using does not list a rating then it's a dead giveaway that the rating is not very good.

[pdf64]

I’d change it to a blade type fuse and fuse holder, or link it out.