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If i add an EF86 tube to my Lightning does it have to have a separate volume pot to go with the contour tone selector? I have added the EF86 and tone selector and wired it to the existing Volume pot and there is a really bad hum when connected. Remove it and the hum goes. I'm struggling for room to put an additional volume pot on, as it is the tone selector has gone on the back of the chassis and the only space left would be next to the IEC power socket.

Would it work if i put the two volume controls on one push-pull 1M pot? How would that be wired up?

Ok, so ignore the two volume controls in one push-pull pot. i added the contour selector switch and a separate volume control for the EF86 channel and it works - but there is ground hum. the only thing i have not done is used a screened cable between the pot and the 0.1 cap on the board. Would that make all the difference? I didn't use screened cable because it is just a quick link up to see if it works.