From the August 1951 ish of Mechanix Illustrated, a modest HOWTO describing a "Snooperscope" that requires a 4,000 to 6,000-volt power-supply to fire infrared light at and through the materials around you.
Construction of the snooperscope: The image converter tube is mounted in a plastic drinking cup 3-1/2 in. high by 2-1/2 in. in diameter. The optical system required depends upon your intended use. We used a small tripod type magnifier lens of 10 power (1 in. focal length) for the front lens and objects from three inches to one and a half feet can be focused. There is no reason why a greater range cannot be had with this lens by moving it closer or farther away from the tube.
After selecting the lens system mount it in a hole cut into the bottom of the cup. A jeweler's saw or coping saw is ideal for cutting the hole. Paint the inside of the cup with black paint. Black airplane dope works fine. No light other than that from the lens must be permitted to hit the tube. Place an infrared filter between tube and lens to reduce effects of stray white light.
The image converter tube is inserted with the graphite side toward the front lens and the metal ring toward the mouth of the cup. A thin flexible lead from the metal ring connects to the positive side of the power supply. Some tubes were manufactured without this lead, in which case a piece of spring metal pressed against the metal ring will work just as well. The front end of the tube has a graphite ring around it. This is the end where the infrared image is to be focused. The graphite coating is the cathode or negative lead. Connect this lead to the B minus side of the power supply. A piece of spring brass or even the flat sheet metal carefully removed from a tin can should be formed with the fingers so it fits snugly around the cathode terminal.