RCA Type BA-4C Vacuum Tube Monitor Ampliﬁer
From the very beginnings of the broadcast industry RCA components were considered the preeminent choice. Here is a pair of RCA model BA-4C broadcast monitor amplifiers. These were widely used to check broadcast program output and as line or distribution drive amplifiers. They are true full fidelity performers featuring high-quality input and output transformers and variable input gain controls. The amps were designed for two 1620 preamp tubes, two 6SN7 tubes, one 5U4 rectifier tube, and dual 1622 (6L6 type) output tubes. They offer quite a bit of gain and therefore do not necessitate an external preamp, and may require additional input attenuation padding depending upon the sound source.
Download the 652-KB pdf 15-page BA-4C manual.