Ampeg B12XT Tremolo help

[Danlampton]

I'm getting frustrated with this trem circuit. The caps and resistors checked good, pots are clean and work well, and the ground is secure. I put a new VM1 in and it still isn't working. I was checking the voltages to/from the VM1 and when I probe (from chasis ground) the lead going to pin 3 of V6 I can hear the trem through the speaker (it responds to the controls).

What's going on here? I'm missing something.

Thanks for any help.

[Danlampton]

Any ideas?

[Jazz P Bass]

Do you have 60Vdc on pin 3?
Is the 47K firmly at ground potential?
The probe is completing something that is missing.

[Danlampton]

Thanks for the suggestions.

Yes, 60Vdc on pin 3.
There is continuity between 47K resistor and chassis ground as well as traced along the eyelet board.
Tried a new tube - didn't help.

[Jazz P Bass]

Maybe it's time to start changing caps?

[Danlampton]

Thanks again Jazz P.

I've replaced all the caps and the 47K from pin 3 of V6 - still no go. Cleaned the speed and intensity pots and verified ground for those. The VM-1 has continuity to ground. If I jumper from the VM-1 lead that is connected to pin 3 through the .05 cap (now a .047) to ground the tremolo works.

Is there a long term negative effect caused by doing this? I sure need to get this out of the shop. I've spent way too much time so far.

[52 Bill]

It looks like this is a vibrato circuit, are you getting a subtle pitch change here? Grounding out one of the mixed, out of phase signals (from pin 3) will change the effect to tremolo.