I found this little CRT something tester on the BIN pile at Kutztown. Made by Antronic in Chicago. A smallish company making minimal tube testers and brightners in the late 50's to early 70's. No other info on the web. Now a Filipino restaurant.

It looks to go between the plug and socket of early BW CRT's. The transformer is direct to the CRT. The switch shows various voltage selections but the secondary is 6v direct to the CRT via the parallel 7-pin or 12-pin connections and not switched. There is a 110v in and a strapped cheater plug off of the primary to go to the set. The rest of the usual plate, grid, etc. go to the rotary switch and back to the 12-pin connection on the base of the unit showing various voltage possibilities. And two sand resistors for good measure.

What could this thing possibly do...not that I will ever connect it.

I swear I've come across mention of these in an ancient Radio Electronics ad.

I believe it let you use a different tube than the chassis was designed for which sounds a little....weird.

Looks more like an accessory to a CRT tester. Testers that only provide 6.3V but this adapter lets you test CRTs with other heater voltages.