Overwhelming 60 Hz buzz in Vibrolux Reverb

[olben1]

I've got a Fender Vibrolux Reverb amp that only produces a LOUD :eek: 60 Hz buzz. My first guess is that the rectifier (5U4GB) is shot, so I'm about to replace it. If that doesn't work, the next culprits are either the filter caps or the heater circuit diode. After that I'm at a loss. Any thoughts?

[Lordathestrings]

I think you have a pretty good handle on it. Please let us know how it turns out.

[olben1]

The buzz is still there. I replaced the rectifier and it seemed OK at first. However, after a while the buzz came back. It seemed to be responsive to the Vibratto volume pot but over time the buzz became constant. It may be temperature related, because I can let the amp sit for a while turn it on and it'll be OK for a while then the buzz shows up. :mad: The buzz volume is constant, either volume control has no effect on it. Is it a filter cap breaking over? I'm going to see if I can find the right kind of caps today. Could a faulty preamp tube (7025) do it?

[pstring]

Questions, You said it only produces hum, does this mean it produces no output from your guitar? Is your amp a Silverface with the hum-balance circuit instead of the bias circuit? Have you tried pulling the pre amp tubes individually, one at a time? I don't know you or have any idea of your competence with amps, so if you pull the tubes, please turn off and unplug the amp before you pull a tube, and remember hot tubes are hot, don't burn yourself, if you know all that, please pay me no mind, I just don't want anyone to hurt theirself on my account, ...............

[olben1]

There is a variation in the buzz when I play so signal is there. The buzz is SO loud and invariant that I can't say if the guitar notes are there (probably are) or the input is just perturbing the buzz.
Thanks for the advice on cooling down and unplugging. I've been around electronic stuff for a long time, but ya nver know. There tooooo many stories of folk geeting zapped messing with live stuff when they didn't have to. The warnings are always warranted.
Thanks

[olben1]

Buzz is gone, in case anyone's interested. Bad 12AT7. Thanx fer the input

[pstring]

Just for reference, which one was it, the reverb driver, or the phase inverter/driver (the one closest to the power tubes), enquiring minds want to know, glad to hear you got'er fixed................. :D

BTW, when is the Blues Fest?

[olben1]

It was the reverb driver. The confusing thing was both 12AT7s were bad. One totaly dead, the problem was the second was prolly gassy. Any way I learned (relearned) a lot about TS'n tube amplifiers and the amp has a whole new set of filter caps. Thanks all fer the help. :D