What would make one channel drop out besides the tubes. I tested all the tubes, they test great. So I swapped them out to be sure and the channel is still out.

Swapped leads so I know it's not the amp or speakers. I did open it up and everything looks good, except the resistor ? between the two large gray electrolytics at the rear of the unit near the balanced out. It is black, any body know the size?

Any other thoughts?

Thanks in advance