In article , analogdial writes:
George Cornelius wrote:

Actually, though, unfamiliar with such a tube. Is it a tuning eye?
I guess not. That would have been the 6F6, I suppose.

Tuning, yes. Eye, no. 7F8 is a loctal VHF twin triode normally used
for oscillator/mixers in new designs between about 1946 and 1950.

[guess I forgot to post this. I'll trim it a bit, though]

Ah, yes, loctals. Hated those things when I was a kid and
had to figure out how to get them out of their sockets so
I could take them down to the tube tester at the neighborhood
drugstore.

Yes, I see the GE data sheet lists it as a dual triode intended
as a grounded grid RF amp or a frequency converter.

Maybe the 7's were loctal in general. Odd because they are 6.3
volt filaments just like the 6's.

It's too bad the RMA didn't give some sort of clue in the tube numbers
for eye tubes. A letter "I" would have done the job.

The Mighty SX-62 uses NO 6F6s. 6F6s are for plebeian S-20Rs and S-40s.

Yeah, the tuning eye tube I was trying to remember was the 6AF6.

Turns out there's a way to use one of those tubes (it's
actually in the laboratory booklet for so-called PSSC
high school physics) to do the classic electron charge to
mass (e/m) experiment with one of those tubes. You place
the tube in a known magnetic field and measure the
curvature of the boundary between light and dark - basically
the edge of a shadow of some barrier in the tube that
blocks part of the beam.

In that lab we tweaked some parameter - probably the "plate
voltage" - until the curvature matched that of a known object,
in this case the erasor end of a wooden pencil.

The SX-62 uses 6V6s in PUSH PULL.

Yes, of course, variants of the famous 6L6. As was the
807, and the 1625, its 12 volt equivalent. Just about had
that 75W transmitter out of the ARRL Handbook completed but
it 'disappeared' while I was off at school and my father
and stepmother parted and went their separate ways.

I do have a push-pull 6V6 amp in my basement. Just recently
thinking of firing it up for a use I have where the solid
state PA amplifier someone bought at Radio Shack just doesn't
seem up to the task.

Probably a waste of a good tube amp, though. I say
let them eat cake.

George