potatofarmer wrote:If you go to one input jack, you'd make that grid stopper 34k to match the previous "high" input.
Yes, of course!
Have you looked for AC voltage on points D, E, and F? You might want to increase your B+ dropper resistors; each stage is drawing very little current so you can raise the resistors without losing much B+. If you have more of those 10k/1w that would be a good place to start.
V1, 2, and 3 are all pretty high gain stages so you want to make sure they're well decoupled.
These are good thoughts and I hadn't considered that I wouldn't loose much by raising the dropping resistors. I don't have more of those 10K 1W, but I've got some 5K 3W which I think will do nicely. I was too focused on keeping B+ high.
Given the number of filtering stages, I did not check for ACV. I just didn't imagine I'd see much ripple that far down the ladder. I should not assume and it is worth checking. I'll report back.
Lead dress around your 6SL7 input stage could help, as could shielded wire, or lowering the gain of that stage.
Well, given the rat's nest I built, I agree, but it will be challenging. I did not want to lower gain, but maybe I'll have to do it. It feels like surrender.
Are you sure it's 120Hz and not 60Hz? Have you tried referencing the heater CT to the power tubes' cathodes?
Yeah, I plugged in the guitar and it is close to the open A string note, between A and B where 120Hz should be. If there is also 60Hz riding on that tone, it is being masked or isn't very much. The 6.3V CT is now elevated at the power tube cathode. The ~40V was needed to address the H-K differential at the first 6SL7. I did not note a meaningful change in the hum. I can't take credit for elevating the CT as it was recommended earlier in this thread by someone else.
In general, I am coming to the conclusion that the hum is due to a ground scheme that doesn't work, or rather is not implemented correctly. It is a star, where each stage is gathered at the negative side of it's filter cap. Each f/c neg has a wire to the ground side of the first filter cap. There is one wire from the 1st f/c to the chassis. The only other wire directly to the chassis ground is the HT CT. I am thinking that I did not correctly identify each ground to the correct filter cap. I will have to work on this...map it so I can really think about it, then maybe posting for group think.
Thank you very much for sharing your thoughts, potatofarmer!
