Uneven bias meter travel when chording

[Gman]

Hi Guys,
I was rebiasing my 85 watt Twin reverb (AB763) and after setting the bias I played some chords through it to see how it sounded. I noticed that there was a much bigger swing on one side of the meter than the other. I'm using an Alessandro BTW.
After some swapping around I determined that it's happening on the V9 and V10 power tube positions. It's not the tubes or the meter.
I should add that the amp sounds fine.
I don't know why this makes a difference but I just noticed that it doesn't happen playing through ch2 only ch1 (???)

1. Is this normal?

2. If so why does that happen?
I'm wondering if it has something to do with the different size coupling
caps (.001 & .1) on the grids of the PI.

3. If this isn't normal, does anyone have an idea what what might be causing it and how to trouble shoot it?

Thanks,
G

[Enzo]

Troubleshoot it? The amp sounds fine, there is nothing wrong with the amp.

You are looking at an amp design that has withstood the test of time for over 50 years. It doesn;t need redesign at this late date. The coupling caps are fine.

WHy would tube currents be assymetrical, and especially only in one preamp channel? Perhaps the waveform being sent to the power amp is not symmetrical. Scope the signals and see.

Other possibilities might be uneven output transformer winding resistance. How much difference in currents do you see?

[Alex R]

the caps on the grids of the PI are not both performing the same function.