It appears that the date quoted on the German web-site for the 1625 was
wrong.
In the 1942 edition of the "RCA Guide for Transmitting Tubes" that
went to press
in October/November 1941 the 1625 was included and
was described as "Similar to 807 but has 12.6 V heater ... Especially
Useful in Aircraft Transmitters"
So the 1625 was around before Pearl Harbor.
Any reasons for RCA to choose the 7-pin base for the 1625 were not
mentioned, and they are probably buried deep into the sediments of
corporate logic. My guess is as good as anyone elses.
Regarding the 8018, it seems to be an interesting variation of the
807.
I found some variants, one with a normal phenolic base but quoting a
higher transconductance than the "regular" 807, and two with ceramic
bases, the RAF VT-60 and VT-60A.
The electrode system in the VT-60 shown at http://www.tubecollector.
org/vt60.htm
appears to be somewhat "skinnier" than the regular 807. If this may
have affected the VHF performance is uncertain.
73/
Karl-Arne
SM0AOM
----Ursprungligt meddelande----
Från: g3rzp@g3rzp.wanadoo.co.uk
Datum: Jul 27, 2007 11:20:22 AM
Till: amps@contesting.com
Ärende: Re: [Amps] Gassy Tubes/Technology Museum looking for artifacts
>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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