The 83 is a heavy-duty 4-pin UX-base mercury-vapor full-wave power rectifier vacuum tube introduced in the early 1930s. Designed for high-current power supplies in commercial radio transmitters, public address systems, and precision tube testers (such as Hickok models), it utilizes ionized mercury vapor to maintain a near-constant 15-volt internal drop across varying load conditions. Featuring dual directly heated filaments, it operates on a 5.0V filament supply and provides exceptionally tight voltage regulation. It fits standard 4-pin sockets. Available NOS and tested used.