The 12J5GT is an electron tube made by General Electric. It is a miniature, top-contact, indirectly-heated triode tube of the "loctal" type, meaning that it is designed to fit into a socket with a narrow, octal-type base. It has a maximum plate voltage of 450 volts and a maximum plate current of 15 milliamperes. It has a typical amplification factor of 50 and an internal resistance of 10K ohms. It was primarily used for audio applications, functions such as amplification or tone control, or as a voltage regulator. The 12J5GT was popular in radio and hi-fi sets of the late 1940s and 1950s.