DRRI Static Issue

[Mesotech]

Hey folks. My DRRI began acting up when I powered it up and took it off of standby. There is a fairly bad static noise happening, even with nothing plugged in. I did notice while doing some basic troubleshooting (basically looking around and wiggling tubes and such) that the static deminishes slightly after a few minutes of being on. It gets bearable and then once I plug in an instrument cable the static gets feirce again. It remains so for a long while after I've unplugged the cable, but will eventually settle back down to the almost bearable level again.

I swapped the power tubes, reasoning that since the static was not affected by the volume or tone controls, that it must be in the power section. That didn't help any. I even put each 6v6 into a Champ one at a time and the Champ worked fine with each tube.

Taking out all of the preamp tubes and only leaving the power tubes and rectifier exhibits the same static. I didn't try adding an instrument cable during this test to see what happened because with no preamp tubes in the amp and still having static, I figured the cable symptom was either an annomally or having a signal present only makes the problem more noticable, as opposed to being the cause of the problem.

Next, I opened the amp and visually inspected the components and the solder connections. All seems fine from a visual test.

Where would you think I should start looking first?

Oh, and the amp reproduces the guitar's sound just fine, except for the static that is not related.

One other thing I just noticed while double checking the above mentioned symptoms. V7 seems to be glowing brighter than V8. Swapping those two tubes has no effect, V7 still glows brighter regardless of which 6V6 I put in there. I suppose that should tell me something right there, but I'm hoping someone will chime in with a quick "test X, Y, or Z" answer before I can dig too far.

[Mesotech]

Ok, more poking around today with an orangewood stick looking for loose components or bad solder joints while the amp was on. At one point, I touched a capacitor, C29, and the static became worse. Repeated touching and gentle wiggling of this cap didn't change anything. I then poked on R56 and there was a pop and the static stopped completely. Additional prodding of this resistor or the capacitor didn't result in the static coming back. Both components seem firmly seated in place, and I haven't gone as far as pulling the PCB to take a peek underneath because it looks to be a pain to remove, especially if the amp is working normally again.

I suspect this problem isn't gone for good, and will show back up at the worst time. I would pull the PCB and look underneath, but I'm not totally convinced that the poking around caused the changes in symptoms. Meaning, I didn't touch either component with any force when things changed, and I couldn't cause any additional change afterwards by poking, no matter how much force I tried. I had also touched these and every other component in the amp at least twice before with no change in symptoms.

There is obviously a bad solder joint somewhere that re-fused itself into a working condition. I had the amp on for about 3 hours prior to the 'fix' and about 4 hours afterwards. It works just fine now, and the V7 tube is no longer brighter than V8. Fully cranked, there is only a slight hiss from the speaker (as expected).

[Kap'n]

R56 would make sense - it's a bias feed resistor, and part of the circuit even if the preamp tubes are pulled. C29 is in the PI, and not in the circuit under those circumstances.