Signal leaking through with volumes off

[Greg_L]

If AC-grounding the grid from V6B kills the signal, maybe you should try AC-grounding the R27/C21 node.

This did not get a result. Signal still leaking with that node grounded.

[Greg_L]

Did you try lifting the complete node which connects V1A plate wire, R15, R16 and C6 from the board (for normal input) ?
If your problem is caused by a conductive board, this node will be the point where the leakage enters the board. So the V1A plate signal must not connect to the board.

I removed the V1a plate wire from the board. It did kill the leakage.
I removed V1b plate wire from the board. It killed most of the leakage, but a tiny amount still got through.

With V1b grid totally grounded I checked V1b plate right at the socket. There was a small amount of input signal at that tube pin.

[Helmholtz]

I removed the V1a plate wire from the board. It did kill the leakage.
I removed V1b plate wire from the board. It killed most of the leakage, but a tiny amount still got through.

Did you just disconnect the plate wire from the board? That's not what I meant as it will disable the input tube and thus the whole channel. I meant to reconnect things floating above the board.

[Greg_L]

Did you just disconnect the plate wire from the board? That's not what I meant as it will disable the input tube and thus the whole channel. I meant to reconnect things floating above the board.

Ooooooooohhhhhh. Okay I get it. I'll retry that.

[Greg_L]

Did you just disconnect the plate wire from the board? That's not what I meant as it will disable the input tube and thus the whole channel. I meant to reconnect things floating above the board.

Okay I tried this. Reconnected that node floating above the board. No change. Still got leakage. Does that rule out conductive board?

[Helmholtz]

Okay I tried this. Reconnected that node floating above the board. No change. Still got leakage. Does that rule out conductive board?

If you completely prevented V1A (or V2A depending on which input you used) plate voltage from touching the board, most likely yes.

[Greg_L]

If you completely prevented V1A (or V2A depending on which input you used) plate voltage to touch the board, most likely yes.

I lifted the section circled in green. That junction was connected up in the air off the board. The B+ to the plate resistor was still on the board. The plate wire end was lifted. I mean, it still has to get it's DC voltage.

[Greg_L]

Well I think I had a small breakthrough. I think it's definitely a conductive board. I should have done this weeks ago....

I took the hook attachment off my scope probe so I had just the pointy tip and jabbed it into the eyelet board. Guess what? Signal in the board. Not touching anything else, just the board itself, and there's the signal in the dang ol board. As I moved farther away from the plate wire attachment points it went away. I can't really route the wires any better, moving the wires around yielded no change, and they attach where they attach. So I'm thinking it just is what it is. I'm not changing the board.

[Helmholtz]

I lifted the section circled in green. That junction was connected up in the air off the board. The B+ to the plate resistor was still on the board. The plate wire end was lifted. I mean, it still has to get it's DC voltage.

Ok, looking at your layout it seems a bit more complicated than I thought. The idea was to lift everything that carries plate signal from the board. This means that no wire must connect to the rivet where the node was before but also that both ends of C6 (250pF) should be lifted above the board.

If you feed e.g. a 100mV signal to the normal input, V1A plate signal will be 5V to 6V. You may use your scope (AC coupling) to verify that none of the rivets carries that high a signal.

[Greg_L]

Ok, looking at your layout it seems a bit more complicated than I thought. The idea was to lift everything that carries plate signal from the board. This means that no wire must connect to the rivet where the node was before but also that both ends of C6 (250pF) should be lifted above the board.

If you feed e.g. a 100mV signal to the normal input, V1A plate signal will be 5V to 6V. You may use your scope (AC coupling) to verify that none of the rivets carries that high a signal.

Thanks, but check out my previous post right before yours. I think the board is indeed conductive.

[Helmholtz]

Thanks, but check out my previous post right before yours. I think the board is indeed conductive.

Oh yeah, convincing enough! Great idea directly probing the board. Why didn't I think of this. Anyway you confirmed my idea.

[Greg_L]

Oh yeah, convincing enough! Great idea directly probing the board. Why didn't I think of this. Anyway you confirmed my idea.

Yeah, and thank you very much for sticking with this thread and helping me along. I learned a lot about troubleshooting and thinking my way through things....with some guidance of course.

I'm relieved to have found this. I really didn't think it was anything I did with the build itself. I'm not perfect or anything, but I was very meticulous about lead dress and grounding. The board being conductive is out of my control and I'm totally fine with just living with it.

[g1]

Are you in a humid environment and have you tried the 'hair dryer' trick? Sometimes it works, can't hurt.

[Helmholtz]

Are you in a humid environment and have you tried the 'hair dryer' trick? Sometimes it works, can't hurt.

I don't think the "hair dryer trick" can give permanent improvement. I think a conductive board is the result of hygroscopic (water attracting) fibers and poor impregnation treatment in combination with a humid environment. As with all hygroscopic materials (e.g. wood) equilibrium residual water content only depends on temperature and humidity and can't be permanently changed by short time heating or forced drying.

[Greg_L]

Are you in a humid environment and have you tried the 'hair dryer' trick? Sometimes it works, can't hurt.

I live on the gulf coast - Houston area - so yeah this is a humid environment! Never mind the tropical storm that just passed. It's always humid.

I don't know what the hair dryer trick is. I'm guessing it dries out the board?