Now, if I was smart, I'd quit. The amp has a low level but very acceptable hum. Really, it's very, very good. There is, however, some white noise when the volume is turned up to about 8-10. I believe this was introduced when I moved the preamp buss ground to the jack end. I'll see if I can leave well enough alone because there is no way to turn this amp up to more than 5 in the house, if that. If I can't leave well enough alone...well...Phil_S wrote: I replaced the plain wire with shielded as suggested. I think it is worse, not better. I am going to pull the shielded and go back to plain.
-Reconnect the ground wire from the 250K/6800 to the ground end of the power tube R/C. I will run a separate wire to the main chassis ground, removing it from the Plate and Screen filters ground on the board. (Yeah, I know that's a 2fer.)
Many thanks to everyone. There were some very good observations and all the comments were helpful in making me think about this.
I looked back at my notes about the ground scheme. What they say is to connect the power tube cathode R/C at the ground point on the chassis. I put that on the buss with the main filters thinking it makes no difference. That's just wrong, especially in this case where there are two things that need to go the that R/C ground in addition to the R/C itself.
