Fender 94 Twin cut-out at high levels

[dave_arrow]

Hi, new amp garage user here. I hope this is appropriate for this forum.

I've had a Fender 94 Twin since about 1996, and short of having to get the power trans replaced under warranty and one speaker blowing, it has served me well for hundreds of gigs.

Now, being a newbie amp builder and having 2 successful amp builds under my belt, I got a bit over-confident and decided to do some cap upgrades on the Twin when I last replaced the 6L6s and PS. All of the smoothing caps, Orange Drops in the vintage and Mullards on the drive channel, tested at home, all sounding great, at neighbour friendly volumes.

Next rehearsal, after half an hour or so, on kicking up the volume for a solo (amp footswitch or a drive pedal), the output intermittently cuts out. Not like a dodgy cable "on and off", more like a quick fade out and back in, sort of like a strange and unwanted tremolo. It's fine again when it's quieter. My guess is that heat is playing a part here, but where?

I'm unable to replicate it with a dummy load (a 200W 6.8R resistor) taking output from the XLR on the back of the amp, which comes from an OT tap.

Can anyone offer any advice, please? It happens on all channels and I've ruled out cables, pedals, etc. Could dry joints cause this? I would expect dry joints to be more "on and off". Had I not done the cap upgrade, I would wonder about the OT shorting when it gets hot, but I never had the problem before my "upgrade".

Help would be most welcome before I poke around any more!

Thanks,
Dave

[TUBEDUDE]

I'd try reheating the joints on the smoothing cap /resistor junctions. The fade in and out sounds like draining of the filter caps after the rectifier path is interrupted. Look at the rectifier thru the filter caps / resistors.

[selloutrr]

If you are comfortable safely working on amps.

next time it happens you should be able to pin point the problem by chopsticking the amp.

the PCB fender amps are known for having solder issues.
I could make a living off of resoldering fender boards.

[dave_arrow]

Thanks guys.

I'll get it back on the bench soon and update the thread when I have something to report. I'm a bit confused as to why I couldn't replicate it with a dummy load, although I appreciate a resistor isn't a speaker. Chopstick at the ready...

Dave

[ampdoc1]

Taking a speaker load and applying it to the XLR line out is not going to "load" your amplifier like connecting a load to the output jacks (Speaker or load resistor). Although it is a OT winding, the use of an XLR suggests it is designed for low voltage out, say, to feed a microphone.

Connect your load to a speaker jack.

a'doc