A few weeks ago, there was some discussion of the 1625. I started reviewing
my old QST magazines (my wife thinks keeping them on the book shelf is a
waste of space) and found a tube announcement for the 1625. It took awhile,
because I got sidetracked by the many other articles and ads. Well, I did
not find the 1625 tube.
Last night I brought home a real treasure - a newly purchased Hallicrafters
S-30, a very rare radio direction finder. I was looking through the same
QSTs to find an ad that showed a photo of the external power supply and
finally found a birth announcement for the 1625. It is in QST, February
1941. The announcement simply says that "the type 1625 is similar to the
type 807 except that it is provided with a 12.6 volt heater and a 7-pin
base." So, the information adds little except a time frame. More useful,
though, may be the announcement of the 1626 in the same article. This is
much more unique. It is designed for rf oscillator service "requiring
unusual stability". It is a new design and not a copy of one of the 6 volt
tubes. If you carefully examine the sequencing and timeing of the 16XX
series tubes, you will find that they were released to solve a special need.
It was not simply a 12 volt series of tubes. For example, the 1624 2.5 volt
filament, as I recall. I expect the 1625 and 1626 were designed by RCA to
meet specifications for a particular transmitter series. I would guess that
soon after, the 1629 was released. It is almost as if these tubes were
designed to meet the specifications set forth by the designers of the ARC-5.
Well, back to work so I can finish the 1941 QST binder before work.
73, Colin K7FM
Amps mailing list