Twin Reverb tremolo motor boating

[goldenGeek]

So I thought I was done with the 76 twin reverb but I guess not. It has that well known ticking in the tremolo and it’s a bit more than I can bear. So I looked up the trick with the 0.01uf 600v cap at the 10meg resistor. I tried a few and a orange drop (715-series) killed the ticking the best. But now I have a motor boat inside my amp when playing low notes, check out the included clip. Is this a normal side effect of this mod or is there something else going on? It was a bit unclear but I put the cap across (parallel) the 10meg...

Edit: I see now that fender says to put the cap at the junction between 10m and the opto to ground. Same result, there is an old Diesel engine in there still

Tremolo motor boat.m4a

[martin manning]

I see now that fender says to put the cap at the junction between 10m and the opto to ground. Same result, there is an old Diesel engine in there still

And if you lift one end of that cap the thumping goes away and the ticking returns? Can you post a good photo of the board and control leads?

[goldenGeek]

And if you lift one end of that cap the thumping goes away and the ticking returns? Can you post a good photo of the board and control leads?

Thats the case, yes, lifting one leg ticking is back, thumping is gone. The wiring was originally tucked under the potentiometers on the way over, I’ve tried to move it around several ways, and I also tried to wrap a cable tied to ground around the cables (as seen in the photo) hoping it would somehow shield the thing or whatever.

E34ACEA5-E465-4F36-9227-3FBFAA819090.jpeg

[martin manning]

Any indication that the board is conductive, such as if you probe the board around the neon bulb eyelets, do you see any fluctuating voltage when the trem is on?

[goldenGeek]

Any indication that the board is conductive, such as if you probe the board around the neon bulb eyelets, do you see any fluctuating voltage when the trem is on?

There seems to be a slight voltage build up around the bulb end of the roach, but it's not the pulse of the trem. It builds up to about 600mV and then loads off it seems, the build up time is about 3-5 seconds (only measured counting so its not accurate).

However, I read up on some mods at Rob Robinettes page and there was one tip that if you replace the wire from V5 pin 6 to the spot with the bulb and 10meg with a shielded wire it would drastically dampen the ticking. This seems to have dampened the ticking to a low enough level. However, the thumping is present without the cap as well but it's a little less than with the cap.

[Stevem]

Do you see the V+ thumping in time to the Tremolo rhythm with the amp at idle on the plates of the PI and the plates and screens of the output tubes?

If so then you may have power supply filters that are not decoupling as they should!