As I recall, Sylvania and National Union both brought
the beam forming electrode out through the envelope.
They were available at Cortland Street 5 for one dollar.
The differences between an 807 (the one without the
pop top) and a 1625 was 12 volt filament on the 1625
and it also had 7 pins versus 5.
Again, I'm getting old and the base pinout is a little fuzzy,
one of the 7 pin bases was empty and could be used for
the new "element" configuration.
Built a 4-1625 amplifier that ran about 400 watts input. Lots
of fun and cheap, real important to me back then.
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