I think I found an answer from a response to my video on YouTube. The Mojo760 PT does not have a center tap on the 6.3v heater supply so it is necessary to use 100 ohm 1/2 watt resistors on each filament wire to ground. I will let you know if this solves the problem. The Weber PT in the book has a center tap on the 6.3v that goes to ground and is also in the schematic.