This is a unique receiver, made by the Technical Materiel [sic] Corporation. This was
part of what they called the "Remote Control Receiver System, Model RCR" that was built
for the US Navy. The idea is that the receivers themselves would be in one room, and
a number of remote-control panels would be in a different room. There would be a cable that
went from the control unit through an encoder into a decoder in the receiver room. The control
unit could control three aspects of the receiver (1) Main tuning (+-2000 Hz) (2) BFO frequency, and
(3) RF Gain. The audio gain was controlled on the operator's end.
Needless to say, the operator couldn't do any significant tuning of the receiver, since it was
in a different room. I believe most of the time, the receivers used the option crystal control
for fixed frequency operation. I have tried tuning this unit myself - the tuning is very twitchy.
If you sneeze while tuning, you can miss the entire band you are trying to tune. In the units
I have, some previous owner has put 10:1 verniers on two of the tuning drawers. That turns out to
be quite a good idea.