Silverface Twin (Reverb Hum)

[TDR]

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!

Thanks!

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[eddie25]

So the reverb is still working it just has a lot of hum along with it?

First thing to do is to check the reverb driver 12AT7 tube, and the reverb recovery 12AX7 tube.

[Roe]

try isolated RCA jacks and larry grounding. a separate node for the reverb also helps.

[Cheech]

I just fixed a friends deluxe reverb. He had a issue with reverb squealing past four on the control. This amp has the driver and output tubes for the reverb. They each have a set of capacitor/resistor sets for the tube. These sets are grounded to the chassis. I found one of these sets improperly grounded to the chassis. They do not go into a buss bar like your amp has. The set of two capacitors and resistors ground straight to the chassis.

Squeal went away and after I reflowed some solder joints the hum in the amp just practically went away. I could not even tell the amp was on.
http://www.amparchives.com/album/Fender ... 7dc_b.html

Here is a example picture. You can see the large dual capacitors grounding straight to the chassis. One of these was messed up.

[TDR]

Yes the reverb still works, there's just an incredible amount of hum that increase as the reverb control is increased.

Obviously my first thought was a grounding issue, so I got out my meter and checked continuity to ground on: Reverb pot, cathode bypass stages for the driver & recovery, as well as the RCA jacks.

I'm just scratching my head because before I rewired this amp the reverb did not hum, so I doubt it's a jack, cable, or tank issue....

Thanks for all your suggestions!

[Cheech]

Sounds like you did something in your rewire that it does not like. Even the location of where you ground something can induce hum.