Biasing Question

[Firestorm]

Let's completely isolate this. Disconnect the in and out cables from the chassis and disconnect the footswitch and tell us if it still buzzes.

[martin manning]

Good strategy. What about the 220k to ground from the reverb recover tube's grid? Is that well connected and grounded

[Celery_Strat]

Let's completely isolate this. Disconnect the in and out cables from the chassis and disconnect the footswitch and tell us if it still buzzes.

...yep

[Celery_Strat]

Good strategy. What about the 220k to ground from the reverb recover tube's grid? Is that well connected and grounded

I "chopsticked" the entire board yesterday, and all seemed well. No microphonic or loose parts. Wfhen I get home today, I'll check again with more concentration in the reverb area. For grounding, I have the pots and jacks on a buss, the trannys on a chassis lug, and the 4 reverb / vibrato rca jacks on a mini bus, soldered to a ring terminal under one of the RT mounting nuts.

[martin manning]

Does grounding the reverb recover input with the pedal (grounding the pedal jack's center conductor) kill the hum?

[Structo]

So you are positive this is coming from the reverb pan and not the power transformer?

[Celery_Strat]

So you are positive this is coming from the reverb pan and not the power transformer?

Pretty sure its the reverb circuit, pretty sure it's not the pan.

[Firestorm]

Pretty sure its the reverb circuit, pretty sure it's not the pan.

Specifically, the reverb recovery circuit. Did you see Martin's suggestion to see what happens when you ground the grid on that triode? You can just short the ends of the 220K load resistor. Whether that shuts it up or not will be significant.

[Celery_Strat]

Stand by...

[Celery_Strat]

Pretty sure its the reverb circuit, pretty sure it's not the pan.

Specifically, the reverb recovery circuit. Did you see Martin's suggestion to see what happens when you ground the grid on that triode? You can just short the ends of the 220K load resistor. Whether that shuts it up or not will be significant.

Doesn't go away, but gets much more "bearable". Also, gets louder as I move towards it with the short, then terribly loud for the split second after i touch the short to it until good contact is made across the resistor.

[martin manning]

Are you shorting across the leads of the 220k resistor? Seems like the grid is not well grounded when you are doing this, so the path from the resistor lead to the grid may have some resistance. Try shorting the recovery stage's grid directly to ground. Best to do this away from the socket to stay well away from the plate lead, but make sure that the solder joint at the socket looks good.

[Celery_Strat]

Yeah, shorting straight to ground from the grid (pin 2) shuts it up. (well, makes it "fine with me").

[martin manning]

So maybe check all the signal and ground connections from that grid pin back to the reverb tank. Also, are you sure that the cables are good?

[Celery_Strat]

everything seems OK there. Cables are good according to meter. Tank seems fine. Does it without the tank cables connected anyway. I have noticed that the lead from pin 7 to the place under the board where the grid resistor? is soldered is VERY microphonic and gets scratchy and makes the buzz louder when manipulated...

[martin manning]

Reflow the eyelet that the wire from pin 8 is connected to, to see if you can stop it from being sensitive, but I think that must be another unrelated issue. If you can kill the hum by grounding pin 2, and the reverb pot increases it, then the hum has to be originating in the recover stage. If you can't kill the hum by grounding the lead from the 220k (which goes from the pedal jack to ground), then there is a bad joint somewhere between that resistor and pin 2.