Silverface Twin (Reverb Hum)

[chadbbrock]

Hey Guys,

I recently scored a silverface twin reverb on the cheap ($300). The OT had been upgraded to a mercury magnetics, as well as the reverb driver & choke. The wiring was completely redone (and VERY sloppy). I recently rewired most of the amp and everything works great except that when the reverb is engaged it hums very loudly. All of the voltages on the reverb driver and recovery stages are right on the money, I've triple checked all of my wiring and can't seem to locate the issue.

I've attached some pictures of the wiring. The lead dress was much cleaner initially, but I had to chopstick some wires around to get the vibrato to stop ticking.

Any advise would be greatly appreciated!

http://i1073.photobucket.com/albums/...k/DSC00275.jpg
http://i1073.photobucket.com/albums/...k/DSC00274.jpg
http://i1073.photobucket.com/albums/...k/DSC00273.jpg
http://i1073.photobucket.com/albums/...k/DSC00271.jpg

Thanks!

[Wally]

Chad, when you hit 'post reply' or start a thread, you can roll down below the message box and find 'manage attachments'. Click that, and you will be led to a system that allows you to post pics directly from yourcomputer to this board.
Did you recap the amp? Does the hum vary with the reverb control? I amgoing to guess that you have a bad cap in that circuit or you have missed a ground somewhere.
And....welcome.....

[chadbbrock]

Thanks Wally! Unfortunately the file size of the pictures were too large to attach, so I had to post a link.

The power supply (filter) caps have been replaced, and I would assume are operating correctly because all of my voltages are right on.

The hum gets louder as the reverb control is turned up....

[Wally]

Okay...I can't access photobucket....andmy account is there! Old computer.
I am goign to think that you have a ground problem.

chadbbrock wrote: "I've triple checked all of my wiring and can't seem to locate the issue."

Chad, this thought above is a trap and will keep you from looking at the problem and seeing the cure, ime. Robert Pursig in "Zen and The ARt of Motorcycle Maintenance" describes how we can keep ourselves from seeing the obvious sometimes.
YOu need to approach the circuit with a fresh and open mind. Anywhere in that circuit could be the problem....cabels, jacks, plugs, tank, tubes, tranny, components and connections in the circuit, pots and those connections.

[chadbbrock]

Hey Wally,

First off, thank you for your responses and words of encouragement!

This definitely isn't my first rodeo, and I'm certainly not giving up and assuming that everything is wired/grounded correctly. I just thought that maybe a fresh set of eyes could see something that I'm not, or possibly someone else has experienced and fixed a similar issue.

I too initially suspected a grounding issue, so I got out my meter and check continuity to ground from the: Reverb control pot, cathode bypass stages for the driver & recovery stages, and all RCA jacks. They all showed continuity (1 ohm or less) to ground. Also, all of the cables are new and check out.

I'll see if I can resize the pictures and attach them.

[chadbbrock]

Resized and attached pictures! NOTE: Not all of the wiring is mine, this girl was a mess when I bought her.

[1955]

Had this problem once, was solved by the tech soldering a wire across all the pots. Don't know any tech stuff, but guess there wasn't a proper ground?

[Wagster]

I have a habit of stating the obvious, usually to no good, but...

Have you tried swapping out the V3 (12at7) and V4 (12ax7) tubes with known good tubes? Your problem could be as simple as that, no? I would be especially leary of the V4 since it is 1/2 Reverb recovery and 1/2 gain stage for vibrato channel (which you said had some ticking issues).

[1955]

And there's also the tank and spring transducers, all kinds of stuff. Troubleshooting reverb is a tough one. But yes, absolutely check every tube and everything else you can think of.