Tele-Tone with odd socket

[Eric H]

I picked up this Porthole Tele-Tone today and noticed something odd, someone piggybacked an octal socket on the back of the CRT socket (first pic).

The only thing I can think of is it was used with one of those Norelco Duo-Vue projectors (or similar) which were an attachment used with a standard TV but I don't know if this is how they were hooked up?

The person I got it from in fact has a Duo Vue but he told me they came from different places.

This set is in pretty good shape, the grille was broken because it had the wrong knobs installed and they were stuck hard, someone tried to pull the chassis out with the knobs attached and busted the grille into several pieces.

I was able to remove it by knocking out some wood braces and removing some staples, it glued back together nicely but i'll wait till it's refinished to reinstall it.