[Amps] Gassy Tubes/Technology Museum looking for artifacts

[Peter Chadwick]

>Wild guess: to prevent plugging a 6.3v filament tube in a 12.6v socket?  
Maybe 807's were also used in other applications in that era.<
It seems a bit illogical, because  there were 6 and 12 volt octal tubes with the same base connections - 6K7, 12K7, 6SG7, 12SG7 etc. Further back, there were 2.5 volt and 6.3 volt tubes on the same UX base - 2B7 and 6B7 come to mind. So why go to the bother for 1625s, when they needed more metal for the two extra pins? And the quantity of 1625s made meant that must have been a fair weight of brass for those two extra pins.
807s were around pre war, and there was one of the early RAF VHF transmitters used something called an 8018, which my father told me was an 807 selected for more output at 120MHz - he actually instructed on that equipment when he was in the RAF. He said it was awful speech quality, using the device as a sort of linear with low level grid modulation on the preceding frequency multiplier, and running grid current in the 8018. 
73
Peter G3RZP