Hiss and Hum?

[reddinis]

I have modded an amp. Without the overdrive switched in (it's B+ is disconnected, too), the signal path is Input jack> V1a> TMB tone stack> Volume> V2a> V3 phase inverter >6L6's.

The hum and hiss is pretty bad. The hiss is probably because of wiring.

If I remove the first 12AX7, the hiss is completely gone and the hum is very, very faint. Still there, but can barely be heard.

I'm sure the hiss is wiring, even though I've ruled out the input jack and shielded wire to V1a input. There's also a 33k grid resistor on the input.

What I'm wondering about is the hum. Just thought I'd post this before I tear back into it.

I have a feeling that the tone stack might be wrong, maybe not grounded or wired correctly? The filter caps are brand new. I haven't been able to find any wires that, when moved, change the sound of the hum. I also don't think the heater wiring is the problem.

Edit: Also, the tubes are good and wiggling the tubes a bit doesn't change anything, so I don't think it's a socket problem. The OT is brand new, also.

Any help appreciated. Thanks.

[Jazz P Bass]

Does the hum go away when all of the contols are turned full off?
Sometimes a clue will be revealed when the hum is specific to a control.
I had a Marshall 1987X come through the shop & the tone controls (especially the bass) made the amp hum when they where advanced on.
It was the circuit.
That's the way it was.