Postwar American Television
501-D Master Remote Control
This device, made in the late 40s or early 50s, is a set top converter box. It has 3 tubes - a 6AK5 RF amplifier, tuned with the "Picture" control and the Channel knob; a 6AB4 local oscillator, tuned with the Channel knob and the Sound control, and a 6BC5 mixer. On the back is a sticker, indicating it was approved by the City of Los Angeles Building and Safety department, which would suggest that it was installed in a hotel or apartment building. It was made by Coastwise Electronics Company in Los Angeles.
The output is on channel 6. However, the output channel would be inverted, with the sound carrier below the visual carrier.
The Picture knob peaks the RF amplifier to the desired channel. The Sound knob adjusts the local oscillator frequency over about a 10 mHz range.
Here is what the manual says about its operation: