George Cornelius wrote:


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.

There's a trick to it. There's a raised dimple on the base. You grip
the dimple and the base on the opposite side and rock the tube out in
that plane. There's a split in the springy retiner on that plane which
should open up. Unless the stupid metal base has corroded to the
retainer. A thin film of grease on the groove of the loctal's spigot
helps.


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.

Most of the locktals were designed to interchange with octals. They
have the same pin circle diameter (with entirely different pins) and the
sockets are the same diameter. I guess Sylvania thought it was some
competitive advantage to doing things that way. Most of the locktals
were direct equivalents of octals but it seems they were popular for
car radios. A car will have a voltage of 7.x volts with the generator
running. There was also a line of locktals for series string radios
which had 14xx numbers as well as higher numbers for the rectifier and
audio output tube.

The metal locking base tube type was devloped by Philips in the
Netherlands. Philips liked a 9 pin type of lock in tube. Sylvania
jumped in on their variation of the format right away. Maybe the
Philips licensing fee was lower than the GE/RCA fee. Or maybe Sylvania
hated giving money to a direct competitor.

Curiously, there are still locktal sockets being marketed out of China.
There's almost always some listed on Ebay.




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.

Huh. I did not know that.

I have a couple of 6AL7 tuning eye tubes. Sometimes I think I'd try to
modify the SX-62 to use one as a tuning indicator. It looks as if that
tall gap between band 2 and 3 would accomadate one quite well. The 6AL7
was a product of the SX-62 design era and it almost seems as
Hallicrafters was considering it.



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

The Golden Ear crowd would INSIST you get your vintage audio working!