Filament Voltage

[bandersen]

110 had been around a couple years already but with longer necks and conventional guns. Philco repurposed a heater/cathode/grid from a miniature 7/9 pin receiving tube to make the neck much shorter.

[MuzzcoVW]

Thanks guys. It is interesting looking at the gun setup in say an 21EAP4 vs a 21FDP4. The latter looks "conventional" while in the EAP you can see the smaller tube style setup. And it's interesting as far as longevity the few EAPs I have all have decent emissions and cutoff. The one 21FDP4 I have is strange. It has super emissions but pretty much no cutoff. Personally I've never seen that before. Can't wait to test it and see how the picture actually looks