Help, new reverb, grounding hum

[Garrett335]

Hey guys,
hoping someone can help me out with this one tube reverb circuit I added to my 18W build.
The reverb works, however I have a very large ground hum when turning the Reverb Depth and Level up.
The reverb tank I purchased is the Mod (4AB3C1B) Input is insulated, out is grounded. https://www.cedist.com/products/reverb-tank-mod-4ab3c1b

I've tried isolating the RCA female send on the chassis and then the reverb doesn't work at all. I've tried isolating both RCAs, no luck. I can only get the reverb to work with both Send and Return touching the chassis.

One other thing to note is that the wires coming off of lug 3 on both 1M reverb pots are extremely microphonic. Not sure if this is related or not.

I have 4 grounds on the chassis (Mains, PT B+ Fuse output, buss bar for input and board, and ground tab located on return RCA female jack on chassis.

I've attached a few photos of my layout and inside, sorry for the messy wiring, been pulling my hair out trying different things with connections.

I've also attached the reverb circuit from Tubeit that I'm using, its in the bottom left corner of the schematic.

Thank you in advance for any help or advice, I've heard Reverbs are very tricky.

[tubenit]

Where are you using shielded wiring in the reverb circuit?  Is there shielded wiring going from R and the .001 dwell cap?  And shielded wire from 180k (from reverb pot) to R2?

I would say the microphonic wires off lug 3 on both reverb pots would be a place of focus for me.

Where are the photos that you said you attached?  Maybe I'm missing something but I don't see them?

Do you have a passive effects loop? 

Have you tried a dwell resistor of 1M instead of a dwell pot? 

Have you tried other tubes?   Have you tried a 12DW7?

Can you please give us more information?    With respect, Tubenit

[PRR]

> I can only get the reverb to work with both Send and Return touching the chassis.

The drive MUST connect to the reverb transformer's other lead. This lead does not "have" to also go to chassis, though it rarely hurts.

The return MUST connect to the V2b cathode network. Usually this can be done through chassis. If your chassis is full of crap current you can float the return jack on plastic bushings and run *both* wires right to V2b grid and the bottom of that cathode network.

[Garrett335]

I did originally use shielded wire, with one side grounded to the bus. They were still microphonic and humming, so I snipped the grounds off to see if that would help which it did not.
Sorry I forgot to add the photo. I've attached now, and I can take more and post.
There is no effects loop.

I have not tried a dwell resistor I can try that, so would the grid of the fist part of the 12ax7 go straight to the 1M resistor, and other side go to the.001 cap? (I would still need to reference that resistor to ground right?)

I have not tried any other tubes, just starting with the 12ax7

https://ibb.co/g7bRyB5
(it says my photo is too big to post ha, above is a link)

[sluckey]

Please post a schematic of "your" amp.

I see a couple things that 'may' be a hum issue. Your filament wires are running very near the RCA jacks. And your PT HT center tap (fused) is very near the reverb send jack. That red/yellow wire is one of the noisiest wires in the amp! Temporarily remove the red/yellow wire from the fuse holder and connect it directly to the ground lug of that first cap can, keeping the excess length near the PT and well away from the RCA jacks. Does that help?

Also, it's unclear from your pic which B+ node the reverb transformer red lead is connected to. Can you confirm?

[Garrett335]

Attached is a messy schematic, I haven't drawn a full one with the reverb circuit.
The B+ node for reverb is connected after 30ohm resistor after the rectifier. Same spot as the OT CT.

I'll try moving the HT CT like suggested. Have to do it after work.

PRR, I'm not sure I understand.
"The drive MUST connect to the reverb transformer's other lead. This lead does not "have" to also go to chassis, though it rarely hurts"  Can you talk in colors here? One side is the green / black and other side is Blue / Red

Green goes to reverb send (Drive?) / black goes to chassis (Ground)
Red goes to B+ / Blue goes to Plate (Pin 1) ... is this right?

"The return MUST connect to the V2b cathode network."
Does this mean I connect the reverb return to the cathode? Right now it's connected to V3 Pin 7(Grid)

[sluckey]

The B+ node for reverb is connected after 30ohm resistor after the rectifier. Same spot as the OT CT.

That's what I thought. THAT'S A NO NO! Move the reverb transformer red wire to the screen grid filter cap for better filtering.

[Garrett335]

OOPS
Thank you so much Sluckey, I'll move this tonight when I get home and report back.

[Garrett335]

Good morning,
Okay, I moved the red (Reverb) wire to the 50/50 cap, and then the 32/32 cap.
This did reduce the hum a little but is still very present.

I also disconnected the red/yellow CT for the secondary and moved to the other ground as discussed, this actually added another very small buzz, so I moved it back to the fuse.

My uncle had suggested taking a .001uF cap and connecting to grid/ground tracing the stages, when connecting to the V2A(Phase Inverter) grid, the hum almost disappears.

Should I try removing the 1M pot as suggested by tubenit? How would the connections look?

 

[tubenit]

Should I try removing the 1M pot as suggested by tubenit?

I don't think it's important to try that. My guess is the hum is from somewhere else.  It won't hurt to do it, but my guess is that it won't be the issue?

With respect, Tubenit

[Garrett335]

Should I try removing the 1M pot as suggested by tubenit?

I don't think it's important to try that. My guess is the hum is from somewhere else.  It won't hurt to do it, but my guess is that it won't be the issue?

With respect, Tubenit

Well I appreciate the help. I'll keep working on it, seeing if I can get anything to change.
The reverb sounds amazing, really nice tone and depth, if I could just get rid of the grounding hum : /

[Garrett335]

Hey guys I just wanted to give an update for closure.
Took the amp to my uncles house, and he found the issue.
I placed the reverb transformer next to the PT. Moved it to the other side of the chassis close to the input and that removed about 70% of the hum.
Then I re-installed the shielded cable going to the reverb pots, and on my PI grids, once connecting the shield to ground it removed about 20% more.

Now I get to figure out how to keep the tank from vibrating and creating feedback after turning on the reverb pot past 50%.
Thank you as always guys.