The AM Forum

I've known of the GF transmitter/RU series of early 1930's radio gear for Navy aircraft for many decades, had no interest, but when I found out recently that the receiver had amplified AGC, I was interested, so I acquired a RU-18 receiver off of eBay recently; the last model. This is not my forefront project by any means right now.

It is 6 tubes, designed in 1932 by ARC Corporation. Tuned r.f. design TRF (not superhet) with plug-in coil tray. Used for DF and comm. There are single-band coil trays and dual band trays with a switch, 17 coil tray models in all, covering 200 kc to 13,900 kc. Most coils cover a 1.5:1 frequency range. The earliest also went to the Army. That early version is 4 tubes in the TRF section, a detector tube and an audio output tube. The later version I have, was revised by Western Electric, put in higher gain tubes so the TRF section is 3 tubes, detector tube, AGC amplifier tube and a dual-triode for audio output and a BFO; carried through the end of WWII. The interesting thing here is that the AGC apparently functions with the BFO on!

I only want to get it going to measure sensitivity, bandwidth, and audio output level versus r.f. signal levels and see the AGC operation with the BFO on.

Two photos attached. The coil tray photo shows the dual-band tray I have with a low-frequency band coil section exposed. The shortwave band coil is in the larger can.

I now know where the green-flanged 'tray' around here some time ago came from! I hope you can get it running.