Request review of my schematic

[DF96]

Because you didn't wire it up this way. You always had DC on the pot.

Yes. He tried everything except the correct solution.

I did wire it up that way as well. Sorry, but I did.

This was never mentioned before in this thread. You had an input coupling cap, but not a grid coupling cap. You need both, unless you are sure that all sources have output coupling caps with ground leaks - in that case you can omit the input coupling cap but still retain the grid coupling cap.

Your final circuit will eventually lead to a noisy pot because you are sending grid current through the wiper-track interface. Lots of people take this short cut and it works fine for a few years. Engineer it properly and it will work for decades.

 

[Wigwam Jones]

I realize that I am a newbie and I freely admit it. I took the advice given in this thread and I was glad to have it. I tried every option for placing capacitors in the input, whether I specifically mentioned it or not.

However, I won't argue what I did or did not do. End of discussion. Thank you for your time.

 

[zigzagflux]

It is acceptable to drop out of the discussion, as you desire, being the original poster. This is, however, a public forum, and for the purposes of those that might stumble upon the thread with a similar problem, it is beneficial to provide them with reliable advice. As a self-proclaimed novice, it does not serve the general public well to leave your statement as accurate.

Assuming the basics, that the individual components are in proper working order (tube is functional, potentiometer working reasonably well, capacitor acting like a capacitor), then the drawing in post #35 will work and will not produce scratching or grinding noises. An extra input cap may or may not be needed as well, depending on the source.

I have no doubt you believe you hooked it up that way. But if you did properly, the problem would have disappeared. The next person that is concerned about the facts of this thread might just be willing to try again, instead of shipping it off with a goofy band-aid and call it "good enough".

 

[BinaryMike]

To find out if there's unwanted DC current flowing in the pot, just measure DC voltage end-to-end across the pot terminals, with no signal applied, input open, and wiper full clockwise (or at least not full CCW). It's important to use a high-impedance voltmeter, such as a modern DMM. Anything greater than a very few millivolts across the pot is likely to cause noisy control operation.

 

[Wigwam Jones]

To find out if there's unwanted DC current flowing in the pot, just measure DC voltage end-to-end across the pot terminals, with no signal applied, input open, and wiper full clockwise (or at least not full CCW). It's important to use a high-impedance voltmeter, such as a modern DMM. Anything greater than a very few millivolts across the pot is likely to cause noisy control operation.

Thank you!