These 1950s RCA Model BA-2C (MI-11226-B) booster amplifiers were widely used in the broadcast, film, and recording industries as the first-stage amplifier for high-fidelity recording. They utilize two of the highly regarded 1620 (or 6J7) vacuum tubes, coupled to large input and output transformers. The amplifiers are self powered (with built-in AC supply), and feature an input gain control and easy solder eyelet termination. The multi-impedance input and 50 dB gain make them an excellent choice for use with ribbon type microphones, but they also excel with tube condenser types. The pair came mounted in an RCA rack-mount shelf (MI-11599) with mating connectors.