Recently I modded a Peavey VTM 60 head for adjustable bias. Its running too hot even with the pot all the way down. I get one of the tubes just faintly glowing red. I have a 15K resistor feeding a 25K pot then returning to the power board with a 33K resistor. Plate voltage is 475V running 6L6 power tubes. I was following someone else's mod when I did this and it originally called for a 10K pot. What value resistors should I be running to make this work? I rock with a solder gun but not so much on theory.