The 920 is a 4-pin UX-base gas-filled phototube designed for light-operated relay circuits, sound-on-film motion picture equipment, and industrial photoelectric control systems. Engineered with a light-sensitive cesium-coated cathode surface, it converts variation in light intensity into proportional electrical current. The gas filling provides internal ionization amplification, boosting current sensitivity compared to vacuum phototube types. It operates within a standard 4-pin socket layout and is built for directional light sensing applications. Available NOS and tested used.