[Arran]

So in other words one version has 12.6 volts more drop across the filament string, though that still does not add up to 120 volts, that would come to 116.5 volts, but they typically designed around a 117 volt working voltage, though it should still have a dropping resistor. The loctals like a 7A8, 7C6 are actually 6.3 volt tubes, but with a current draw of 150 milliamps, the loctals like a 14A7, 14B6 are 12.6 volt filament tubes, also with a current draw of 150 ma.
Regards
Arran