Back to the tube filament wiring issue... My confusion with the filament current arose because of my ignorance of the difference in wiring between 6.3V and 12.6V. I always thought that the filaments were wired in series, using pin 4 for one connection and pin 5 for the other. I thought pin 9 was optional. Thus, my reasoning was that if I put 12.6V across pins 4 and 5 I will get twice as much current when compared to 6.3V across pins 4 and 5. After some research, I have discovered my mistake. The worst part is I now realize that I have miss-wired an earlier project, using a 6.3V supply for a series wiring of the heater, which will only give 75mA of heater current. The funny thing is that the 12AX7 worked in this configuration. I will have to go back and correct my mistake. The reason I am relating all of this is so that others who are new to tubes will learn from my mistake. Please confirm the attached diagram. Also, I believe that the 12.6V heater ground connection is optional.