>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
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