Princeton Reverb - reverb hum

[drewl]

Actually a Stewart McDonald kit, decent wiring and looks correct, works good, is quiet except for the reverb which hums fairly loud.

It seems to be a grounding or chassis ground problem, the chassis looks like it's cheap material.

Grounding the input to the reverb return stage kills the reverb signal obviously, but will only get rid of the hum if it is grounded to one of the cathode grounds or the 56K ground.

Grounding the signal to the chassis and the hum is still there

Tried sanding and cleaning the RCA jacks and the chassis mounts, tube, tank and cables all good, tested and tried known good ones.

Just a weird grounding issue.

Any ideas or tricks or something I'm missing?

Thanks.

And how the heck do you post a link/schem? Not working for me.

[Jon Snell]

Re-route the grounds to the cathode ground. Sounds to me like a ground loop.
Take all grounds from one point; the cathode ground.

[Helmholtz]

Maybe double-grounding of tank input and output connectors (type D). Would cause a ground loop via the cable shields. AFAIR, Fender used Hammond type B, where only the tank output connector is connected to the shell.

[drewl]

It does it even without tank connected and with different cables and tank.

[drewl]

Re-routing the grounds is slightly better, but if I ground the tank to the cathode ground it's quiet.


I'll try re-doing the cables, and the RCA Jack's

[drewl]

Just to follow up, I finally got back to this and grounding the return amp cathode to the RCA jacks did the trick.

Reverb nice and full and no hum.