Control Unit, C-149/ARN-6 Radio Compass System B-36 and the course knob is

and the course knob is a little stiff but turns 360 degrees

The instrument is in exceptional but experienced condition given its age

but the stamped service date is illegible

as well as confirmation of the part number below the illustration

A description of the system appears in Flight International in January 20th 1938

Control Unit, C-149/ARN-6 Radio Compass System B-36 and the course knob isThis is a terrific example of a C 149 Control unit for the aircraft receiver R 101 of the Radio Compass AN ARN 6 system for direction finding and homing. The receiver function tunes from 100 1750 kHz across 4 bands, which were selected by rotating the center knob below the frequency band window. The center knob rotates a flexible shaft connected to a rotatable loop antenna. The AN ARN 6 system evolved over time, originally using a control box similar