My father had some ham radio related device with a one
inch CRT in
it. That basically looked like a 6L6 with a white top ? including
having an octal socket (8 pins). That?s even harder than the device you
described.
MY guess is that onyl one of each of the X and Y plates was brought out
to a pin, the other 2 were internally connected to one of the anodes. It
works, but the linearity suffers a bit. OK for monitoring on a 1" CRT,
not for meaking measurements on a 6" CRT...
I once worked with a similar CRT, but ona Loctal (B8B) base. Tubualr
enveleope, it looked like an EBL21 with a white phosphor in place of the
getter.
-tony