coupling cap question

[M Fowler]

Do you have center tap wire for the filament to chassis ground? If not two 100R resistors off each filament leg to ground.

I built a 2061 20w Marshall head a while back, it is a simple amp and they are sweet sounding amps.

I've enclosed a schematic for you to follow.

Mark

[Stevem]

At this point I would try splitting up the grounds on the preamp sections, take all the grounds that deal with the function of V1 including the input Jack ground and land that to a screw to bolt them down near the input Jack or at the bolts that hold down the V1 socket.
Next do the same with all the grounds that deal with V2.

[JoshBernstein]

There is a center tap for the filaments, but based on the layout, its currently not being used and there is a pair of 100 ohm resistors being used instead

[Stevem]

That's fine, but if that where a issue it would be 60 hz hum you would be dealing with, not 120 like you have posted about!

[JoshBernstein]

Also ill start rearraging the grounds when i get home tonight.

[Stevem]

Actually in looking at the layout again the main problem I see is that the two 47 uf filters are grounded back near the PT!
Disspite what I posted before leave all the grounds for the two preamp tubes bussed together, but move that bussed ground plus the two grounds for the 47uf filters to a grounding point near the input jacks or the first preamp tube socket and I bet that will cure your issue!

[Phil_S]

Pictures are grainy, so, I'm not sure. It looks to me like the outputs are floating. If that's the case, ground the sleeve connection to the same point as the first filter cap ground.

[JoshBernstein]

Sorry about the grainy pics, ill take some better ones later. But the sleeve is currently grounded at the same point as the 50+50 can.

[JoshBernstein]

I moved the ground bus and the ground on the 47s as far away from the transformer as possible with no improvement on the hum

[JoshBernstein]

Something else i should have added earlier:
A couple of times, the hum has completely stopped and the amp functioned perfectly. Its happened a few times, but it is almost always humming.

[Stevem]

I can't make sence of that!
Do a check of the ac ripple voltage on the positive side of each one of those 47 uf caps if you would and report back what that MV level is .

[JoshBernstein]

The ripple on the 47s is basically zero. I moved the ground bus to a different ground again, which fixed the 120 hz hum. But it has been replaced by an equally loud 60 hz hum.

[JoshBernstein]

But its a very odd 60hz hum. It kind of putts along and makes a weird buzzing noise that is reminiscent of an angry wasp.

[Stevem]

Ok so let's start over, what tube do you have to pull to kill that?

[JoshBernstein]

V2 still kills it