11-29-2016, 09:52 PM
I doubt it's a socket for an additional tube, probably for some sort of accessory. Maybe an 100kc calibrator.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry