1950's GE closed circuit monitor

[Olorin67]

Dug this out of my storage locker. I rescued this from MSOE when they tried to throw it out about 1989. Despite the appearance of the mask, this unit has a round CRT. I found 1957 date codes on some of the tubes, so that might be the date, even though that is late for a round tube. it has 4 UHF connectors on the back, with separate inputs for vertical and horizontal. Inside above the tube are two knobs labeled vertical and horizontal frequency. What kind of signal would this need to drive it?
I'll probably put this on my sell pile, i have too many other projects and need to unload some stuff.