Fender Twin losing volume/tone randomly

[Travis Bubenik]

I recently picked up a master volume 70's Twin Reverb with a 15" speaker. Sounds absolutely killer, but every time I use it, after playing for say 10-15 minutes it suddenly loses volume and tone - mostly bass - and becomes real thin sounding. No scratching/cutting out/etc., just that sudden drop in sound and tone. And it stays that way. Seems to only happens on the vibrato/reverb channel.

Any thoughts on what could be going on there? I do have a local tech who's gonna look at it eventually, just figured I'd ask the hivemind for now.

[Dave Grafe]

Check all cables, making certain the speaker cable is unshielded, and change out tubes with known good ones. Everything else - such as cleaning tube bases, pots and switches - requires getting under the hood which you should not do unless you understand how to discharge the filter caps first. Try to avoid joining the 500 volt club.

[Bobby Martin]

Try un-plugging the Reverb/Vibrato footswitch at the back panel. My new in '96 Fender Custom Vibrasonic Steel amp (basically a 100w Twin with a 15" and rev/vib on both channels) gave me the same problem, been a great amp for 30yrs and counting.

[Travis Bubenik]

Try un-plugging the Reverb/Vibrato footswitch at the back panel. My new in '96 Fender Custom Vibrasonic Steel amp (basically a 100w Twin with a 15" and rev/vib on both channels) gave me the same problem, been a great amp for 30yrs and counting.

Don’t have a foot switch - but this is interesting as I’m remembering now the reverb is occasionally cutting out too when this happens (forgot to mention.) Hmmm…

[Dave Grafe]

Don’t have a foot switch - but this is interesting as I’m remembering now the reverb is occasionally cutting out too when this happens (forgot to mention.) Hmmm…

If so that points directly to the reverb recovery tube, a 12AX7/7025 that is the fourth preamp tube from the right looking at the rear of the amp, just to left of the reverb transformer.

[Nathan Pocock]

Yeah and it could be the tube socket not the tube itself. Tube gets hot, socket gets hot and if it’s dirty or loose the connection gets flaky. It’s possible to clean and tighten the connectors on most tube sockets without replacing them. Don’t go poking around if you don’t know how to discharge the caps though!

[Raybob Bowman]

Filter caps in doghouse and bias cap failing most likely cause, but not if the normal channel is fine also. More likely dirty tube sockets in that case.

[Travis Bubenik]

Thanks Nathan and Dave - good leads. I am gonna try just replacing that reverb recovery tube and see what happens. I have zero desire to try and fiddle with anything more involved than that lol. I also noticed most of the preamp tubes are missing those metal shields so gonna replace those too and see…

[Cartwright Thompson]

I doubt that tube shields are the problem. It could be a lot of things, some are mentioned above. It just needs to be serviced, find a competent tech.

[Ken Fox]

Does it do it on both channels?

[Travis Bubenik]

Whoops I thought I mentioned that. No - just on the vibrato/reverb channel.

[Ken Fox]

V1 is for channel 1 (tube one on the right)
V2 is channel 2, vibrato channel

Try swapping those two to see if the problem goes to channel 1

Could be anything from solder joints at V2, solder joints at tone stack caps

Even an input jack may need cleaning or the ground contact partially touching the input signal


Many possibilities. V3 is reverb drive, not likely an issue

V4 is two purpose. Reverb signal recovery. The other half mixes channel 1&2. Not like an issue

V5 is tremolo, not likely an issue

V6 takes the mix of the two channels from V5 and drives the power tubes. Not likely an issue if only one channel is acting up

[Donny Hinson]

Try removing and re-inserting the tubes in their sockets 4 or 5 times.
Sometimes, that's an easy way to improve the connections.