65' Deluxe reverb reissue Drri hum problem V4?

[Menuiserie]

Hello,

I had a Deluxe reverb reissue for quite a long time, not using it much because it was a bit noisy. A mix of hiss, 50Hz and harmonics.

Changed tubes, nothing helped.

Last month I decided to recap it thinking it might be caps leaking.
No it was not. So I tried twist the AC wires, and added a humdinger balance pot for heaters. As per some advices, 6.3V is now soldered directly to tubes, and heater balance resistors are connected to humdinger, with wiper connected to V8 cathode (ground).

I could remove some of the hum, but not enough.

As I had ROHS tremolo circuit, I bought a Fender optoisolator and reverted it to the regular circuit (removing both added PCB and 7 10k grid resistors that were on the preamp grids, near the sockets.

No more hiss from the tremolo intensity volume, but still general hum and hiss.

Then I removed some of the tubes to isolate the problem.
With only PI and output tubes + rectifier : no hum, no noise, very very clean.

I add V1. I get the normal channel. It is clean, no problem, a bit of hiss when I crank the volume but nothing unusual, beautiful sound, no hum.

I add V2. No noise. The weird thing is I can get the vibrato channel (without vibrato and reverb of course) working, but with low level, and no treble, but still no hum. Looking at the schematic it should be muted as it passes through V4 (absent), isn't it?

I add V3, V5, nothing changes.

I add V4. Hum, hiss. When I crank the reverb button, a lot more of them (tank not attached). As I understand it, V4a is the reverb return driver and V4b is the fixed gain 3rd preamp stage of the second channel. So If V4 is wrong, this should affect both these fonctions.
I tried changing tube. not the solution.

I tried poking with a chopstick, reverb return up : every V4 wire but the heaters are microphonics, also every direct connexion with them (rca hot rev return, R28, etc). I reflowed those connexions. Checked good with DMM, but nothing changed when powered. Still Hum and microphonics wires, even when I change for a known good tube.

Checked again those new filter caps, they are good on the mesure.

I'm running out of ideas here...
What do you think?

Thanks a lot for your answers.

 

[bluesholyman]

I had an issue with hum on my DRRI and it ended up being that it was too close the variac I used to control the line level. I moved the amp away from that and all was well - dead quiet.

At this point, I think you should look at the environment, or possibly ground loop scenarios from the wall to the breaker panel.

Try different outlets in the house, different locations and see if the hum follows the amp. If it does, then either grounding issue in house or something else going on in the amp - seems like you have tried quite a lot so far.

Good luck!

 

[Menuiserie]

Thanks a lot,

I will look at the environment and change outlets. I can filter the power / break ground loop with ifi ground defender.
I don't think it would explain why all the wiring to V4 is microphonic though...
Looks to me that V4 socket or its surroundings are faulty, but how?

 

[Dacious]

Have you tried just changing V4? That is the reverb return and if it's making noise with no tank but reverb turned on its either the tube or a component in that circuit. It could even be the mix pot. Does the noise go away when turned to zero?