Twin reverb loud hum when volume at 0.

Bad solder joint in the doghouse. Did you clean up behind the controls earthing plate? All knobs right? MV model, right?

 

Check all of the solder joints carefully along the brass strip under the pots. That's notorious for what you're experiencing.

 

Does that zero have a 1 in front of it?

 

IMHO, loud hum - I think about :

- a problem in the PSU.
- a problem in the Phase Inverter or Output Stage.

---> Check all plate voltages and bias voltages with a DMM. Tolerance = +/-10%. It may help you to locate the issue.

Be careful and ready to turn off : your amp may be in danger...

-tbln.

 

pull the tubes one by one , clean the contacts on each tube with DeOxit and a Q tip reseat the tube rince and repeat for each tube one at a time see if that might help to clear it up , take a chopstick tap on the tubes to see if a tube is the culprit ,( microphoning) if no tap, on the components is side to see if something comes to light (one hand rule always)

before you go balls deep into rewiring

 

Try putting another tube in the PI position. Any tube will do, the tube you pulled from the normal channel. All you're doing is seeing if the tube's gone bad.

 

Are all of your jacks and pots down tight? Nothing loose?

 

Bad pot...what brand did you use, seen some cheaper ones do that very thing new out of the box

 

Agree. Had this issue with 77 AC30. It’s bad volume pot. Tha shaft works, but at 0 position it’s lifted and not grounded as it should be. Chamged the 1M/A pot and works perfectly now.

 

Since the twin has two channels, I would doubt that both of the pots are bad... Generally, @BlacknWhite please give a bit more clarity of how the hum behaves. Is it consistent or random? How does it change with volume or other controls? Is the reverb on or not? Does it start immediately or when the amp gets warm...

And another stupid question - is your amp earthed? Have you tried plugging it into an another outlet?

 

I've seen this as an issue before, if you're using an isolation transformer (maybe some variacs) then it may be something you've over looked.

 

Did it hum before you modded the MV? The MV was stock when you got it? That can at least narrow it down to driver error

 

The hum does not go away when you pull V2, which is the input gain stage for the Vib ch. When you pull V4, which has one triode as the reverb return and one triode as a gain stage in the Vib ch, the hum goes away. Good info. So, when V4 is out of the circuit, does the Normal channel operate with no buzz? If so, then you can isolate your search to that V4 tube and the associated circuitry and components.