Ground loop between preamp section and power section

[joesatch]

smallbox build. I have the preamp section grounded to near the input jack to the chassis (v1, v2 cathodes, preamp filter caps, input jack, master/gain/middle grounds.

The power section (OT ground, bias, presence, P.I, speaker ) is grounded near the filter cap on that side.

If i jumper a wire from the power section ground to the P.I input , the hum goes away dead quiet (essentially a mute).

If i jumper a wire from the preamp ground point to the P.I. input the hum is still there.

I have solid chassis grounds not sure where this loop is occurring.

what i have tried:

moved mids pot ground to where the presence is grounded (no change)

pull V1, V2  no change

pulling V3 (the PI) the hum stops

[joesatch]

disconnecting the P.I. input noise goes away this would point to the preamp section. However this test is with V1 and V2 pulled so not necessarily? This circuit has a 10M resistor to ground at the P.I. input which i've never seen before

[joesatch]

did a bunch of troubleshooting tonight . the culprit is the presence ground. when i move the presence ground from the power section ground point to the preamp ground the hum goes away. i guess i'll leave it this way. not suppose to be like this but the hum is gone

[Merlin]

Your diagram doesn't show the presence control grounded at the power section ground point

[joesatch]

that is interesting. i generally follow the same grounding scheme for all my builds which is to ground the presence to the power section ground.  i think whoever drew the diagram just did that for simplicity. there is one thing about this build which i rarely have that's a 5k presence pot. these 5k presence appear to be very prone to interference and noise. i generally use a 25k and 4.7k resistor

[Merlin]

When you ask a question it helps to post a diagram of what you actually built, not something different. SISO applies.

[joesatch]

i don't like your tone. be respectful.

[pdf64]

i don't like your tone. be respectful.

People in glass houses shouldn't throw stones.
It seems disrespectful to those whose help you're requesting to provide them with bad info, thereby wasting their time.
If you don't like the tone people take when you send them on a wild goose chase, perhaps you should reflect on the possibility that you brought it on yourself, and you're at least partly to blame?

[joesatch]

[plexi50]

I see very good soldering skills. Ground loops can be very troublesome.
Do you have heater filament resistors to ground? From pilot light or power tube sockets to ground?                    I think i see something. Cathode resistors on pin 8 power tube sockets.