12a3

12A3 is a designation used in several contexts, but it is best known in the field of vacuum tubes. In the era of tube electronics, manufacturers assigned codes such as 12A3 to specific valve types, with the “12” often associated with a heater supply around 12 volts and the “A3” identifying the particular device within the 12A family. The exact electrical configuration (for example triode, tetrode, pentode, or rectifier) and the pinout vary by manufacturer and model. As a result, a 12A3 found in a radio from one producer may differ significantly from a 12A3 in a television from another.

Today, 12A3 tubes are considered vintage and are primarily of interest to radio and audio equipment enthusiasts, vintage amplifier builders, and collectors. Information about a given 12A3 is typically found in original manufacturer catalogs, datasheets, or tube-collector references. When replacing a 12A3, it is essential to confirm the intended valve type (heater voltage, filament arrangement, pinout) from the specific device’s service documentation.

In other contexts, 12A3 may appear as a model or part code unrelated to vacuum tubes, but those uses are less common and not standardized. See also vacuum tube, valve nomenclature, and list of vacuum tubes.