Struggling With Reverb Circuit Hum

[Cosmo]

Cyg & TT, the reverb circuit and RCA jacks are on the far opposite end of the chassis, away from the power supply. I have move the tank all over the place (outside of the cab), but to no avail.

I'll report back once I've reworked the ground schema. It may be a bit due to time constraints.

[M Fowler]

Well now its time to start checking the reverb pan hookup cords, then lift the RCA jacks, then check grounding, then you might have to use shielded wiring.

Man what a bummer to go through all this but you will find that annoying problem.

Remember one very important point that you have already discussed is dirty AC in your home or work place as the cause I know first hand about that.

I found an old landscaping light transformer plugged into an outside recepticle behind a bush as the main source of all my problems besides those helical bulbs and santa village lights my wife had on for the last 4 years. All gone now.

[tubelectron]

One source of noise in the reverb circuit can be the placement of the reverb tank.

If the output of the reverb tank is oriented towards the power transformer end of the chassis it can pick up noise from the power supply.

The reverb tank should be positioned so that output of the tank is on the input / preamp end of the chassis...

TT

Well, obviously, that seems logical, but in fact, I had one time to do conversely, finding that the most hum-induction sensitive transducer of the tank was the INPUT (drive), not the output...

Then I had to place the input side at the preamp side of the chassis, far from the power transformer. Quite surprising but true...

So trying both orientation is a good tip !

A+!

[tubeswell]

Some simple stuff.

If you touch the back of the pan with your finger, does the hum go away?

[Cosmo]

I did some unscientific experimentation and incorporated most of your grounding recommendations. What I didn't do was try each change by itself to see what specifically was the root cause.

Here's what I did:
1) Wrapped the tank in tinfoil
2) Isolated both RCA jacks from the chassis
3) Ran the RCA jack grounds to the circuit ground buss
4) Ran the level pot (100K) ground to the circuit ground buss
5) Ran the ground for the second gain recovery stage 220K grid
resistor to the buss

This was a quick test. I didn't have the power tubes installed so I just used the scope. Sure looks like the noise is gone. I've ordered the proper RCA jacks so I'll have to wait until the first week in January to finish this as I'm heading out of town for the next couple of weeks.

When I return I'll retrace my steps and determine which of the mods contributed to most.

Thanks again guys!