[HBR] Looking for an octal equivalent of the 12AT7

[Walt Hutchens]

Define 'equivalent.'

The 6SN7 and 6SL7 are octal twin triodes, both have 12-volt
equivalents.  The 6SL7 is (like the 12AT7) considered a high-mu trode
but has an amplification factor of 70 (vs. 60) and a transconductance
of 1600 (instead of 5500).

However the lead lengths in nearly all octal tubes are several times
greater and interelectrode spacing is also greater so they can't be
used in the VHF applications for which the 12AT7 was intended. I'd
expect the 6SL7 to poop out pretty fast above 10 meters.

There are a couple of LOCTAL tubes that were intended for use in early
FM receivers: SOME of these have miniaturized structures right down
near the base. However no dual triode comes to mind.  There's the
octal 717A sharp cutoff PENTODE with very short leads -- 1-3/8" seated
height.

It's a problem, trying to unwind applications, circuits and
construction approaches of the 60s-70s back to the tubes of the late
30s to early 40s. With very rare exceptions (the 1940 6J6) the
consumer tubes came along when the consumer applications did. VHF and
UHF applications in the war years were handled either with tubes that
were memorably awful performers -- the 6SH7 at over 100 Mcs? -- or
with tubes having a special structure: peanut tubes (the 955),
doorknob tubes (316A), lighthouse tubes (2C40), and so on.

There's an almighty interesting collection possible, just in 'VHF/UHF
tubes of WW II.'

The 6J6 is an impressive piece of work and I wish I knew the story.
It's not only ancient as UHF tubes go, it's still a good performer in
in oscillator/mixer applications up through VHF.  AND it's available
in a 150 mA version -- the 19J6 -- although these are hard to find at
times.

Anyway, if you explain your application some other possibilities might
come to mind.

Everyone here knows about Frank's electron tube pages, right?  The
largest collection of tube data sheets I know of, all available
through one web site at:

http://www.tubedata.org/

Invaluable!

Walt
KJ4KV