Good day. I have just run into a rather odd scenario that I was hoping you fine folks could help me out with.
I just completed a PPP 6L6 amp with a a split fixed bias adjustment. One bias control for the two tubes on one side of the output transformer and the other bias control for the other side of the output transformer. I am getting proper negative voltage on both sides, however I noticed something strange when I was trying to give it a quick ear balance (yes i know that is not the proper way, I just wanted to see if a little tweak would reduce a little hum that was coming through). Let's call either side of the push pull left and right for the sake of my description. I increased the current to the left side and the hum increased as expected, then reduced the current back to it's original place and increased the current on the right side. Here is where I got a little confused. The hum dropped and continued to get quieter as I increased the current. I tried bringing the left side current up to match the right side and the hum increased with it.
Ideally I would like to have no hum, but having the tubes so imbalanced that one side is glowing blue and the other has almost no blue glow at all causes me a little bit of concern.
Any ideas on this would be greatly appreciated.
Cory.