The 6BC4 is a miniature low-mu triode vacuum tube used as a voltage regulator in various amplifier designs. It has three leads and was released in the 1950s by the RCA Corporation. The 6BC4 is a medium-mu twin-triode tube with separate cathodes and individual anodes. It has a high Gm of 16.5mA/V and maximum plate voltage of 250V. It was used in the preamp, phase-inverter, reverb, and phase shifter circuits of Fender amplifiers. The 6BC4 has a closely matched pair of triodes capable of providing relatively high gain, making it useful in applications that require accuracy and repeatability such as voltage regulation. It is also well-suited for low output applications like cathode-follower stages and driver stages.