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.

The band-switching in this receiver is done by removing (!) and replacing the RF drawer. There is a separate RF drawer for 2-4 MHz, 4-8 MHz, 8-16 MHz and 16-32 MHz. There is also an RF drawer for 500 kHz (480 to about 520 kHz), which was the international SOS signaling frequency. Ships were required to monitor that frequency at all times. The "Gibson Girl" SOS rescue radio that was standard equipment on all Allied bombers (SCR-578) transmitted on 500 kHz.

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.

The receiver is designed with three voltage-control inputs for controlling RF gain, BFO frequency, and tuning frequency offset.
For each of these inputs,
there is a 6J6 "reactance modulator" which basically operates as a variable capacitor that they put in the tuning circuit.
Other than that, the receiver is a standard single-conversion receiver. It has 2 tuned RF stages, a VFO
and a mixer tube. It has three IF stages. All the gain stages are controlled by an AGC voltage. The AGC has two different time constants. There is also a limiter before the audio stage. If you count the number of tubes in the RF drawer, you will note that there are five. Two RF stages, one VFO, one mixer - and - one reactance modulator for fine tuning.

This is a good receiver, but it is not a great receiver. For instance, the bandwidth is fixed at 400-4500 Hz. You can switch in a narrow-band crystal for CW, but that's about it. Plus, being a single-conversion receiver, the imaging at high frequencies is significant and annoying. It is pretty good at 2-4 MHz, but the upper band (16-32 MHz) is quite confusing. You pick up every strong station at least 3 times on the band and sometimes 5 times or more. It is more interesting just for the history, and the incredible construction of the units. This receiver is an absolute dream to work on - you can get to all the parts, nothing is buried or underneath something else. The design is absolutely straightforward and clean.