[Milsurplus] Some odd tubes - what are they?

[KD7JYK DM09]

: The bases are not like anything I have ever seen though. They are a
: brown-bakelite like material with is almost 2" square with what looks like
a
: silver-plated banana plug at each corner, one (or two) a bit larger in
diameter
: than the others.

Maybe from one of the giant "breadboard" type radio kits found in schools?
I remember one in my high school, was about the size of two sheets of
plywood and everything plugged in.

Kurt