10-22-2015, 11:49 PM
Arran, if you look at the schematic, you will see that the tubes are biased by a resistor on the center tap. One could set the circuit up with the filaments in series and it would work OK. Besides the filament voltage, the other tube specs are really fairly close between the 71A and the 45. http://www.nostalgiaair.org/pagesbymodel...029582.pdf. I only suggest it because it is the only plausible reason to have 2 45s in the push pull section. As I said, I think someone just stuffed them in to fill it up.
