If you continue to have trouble with this you might consider the master circuit. I suggested a change from the typical "replace the 220k bias feeds with a dual 250k pot" circuit once for a poster with a bias wiggle trem. The only difference was that the pot wipers were on the PI outputs instead of the power tube grids. This preserves the trem circuit/bias circuit relationship regardless of the master volume setting. The poster said it worked great (though I never tried it myself ) I found my post on the matter but the image was apparently lost in that site crash when a lot of archives got lost or I would have linked it. It's pretty self explanatory, but I can draw it up again if you need it.