Vibrolux Reverb volume at zero

[Sir Cuitous]

Volume at zero and I can still hear a thin distorted guitar sound coming through on the vibrato channel. As I turn the volume up there is no change until I reach 3 and then the volume jumps up (the way it does in many amps) AND it sounds great. Nice sounding and clean like this amp should sound. I'm not concerned about the volume jump, but what is allowing signal to come through when it is turned down?

The normal channel volume does work as expected with the sound shutting all the way off when turned all the way down. I replaced the vibrato channel volume pot, but it did not change the behavior. I have seen this a few times before on other different amps. What causes the volume to stay on? Is it something in the vibrato channel prior to the volume pot?

[Enzo]

Crosstalk. The various circuits radiate enough that later stages can pick up and amplify that radiated signal. Thus it is able to "bypass" the volume control. When the control is up, the tiny crosstalk signal can;t be heard over the main signal.

[Sir Cuitous]

That sounds right because there's not even a slight volume change of the crosstalk signal when the knob is turned. Some signal was bypassing the volume control. With the volume all the way off I correctly saw no signal on the grid of the following stage, but right at the plate there was the signal again. I changed the tube and voila - volume is back to normal. Did that tube cause the crosstalk?

[pdf64]

I think that maybe so. I've got a Mazda ecc83 that does this so much that its a comedy act (for tube geeks). In a Fender V1 or 2 slot, with the vol on 1 (ie off), the signal coming off the plate of the second section is significant, AND in the same phase as the signal on the plate of the first section. Then as the volume is turned up, the signal on the plate of section 2 drops to 0 by 2 1/2 on the volume, then increases after that, but inverted (as it should be) compared to the signal on plate of section 1. Peter.

[Enzo]

Classic phase cancellation. Same deal as the hum that nulls out at 2-3 on the knob setting in some amps.

Just goes to show you that there is a lot more going on in a circuit than just what the schematic shows.