TM11-858, "RADIO RECEIVER R-392/URR", April 1954.
TM11-858-5820-334-10, "OPERATOR'S MANUAL, RADIO RECEIVER R-392/URR", November 1960.
TM11-858-5820-334-20, "ORGANIZATIONAL MAINTENANCE, RADIO RECEIVER R-392/URR", December 1960.
TM11-858-5820-334-20P, "ORGANIZATIONAL MAINTENANCE REPAIR PARTS AND SPECIAL TOOL LIST"
TM11-858-5820-334-35, "FIELD AND DEPOT MAINTENANCE MANUAL, RADIO RECEIVER R-392/URR", August 1961
TM11-858-5820-334-35P, " FIELD AND DEPOT MAINTENANCE REPAIR PARTS AND SPECIALTOOLS"
Like the R-390, the R-392 covers the range of 0.5 to 32 MHz in 32 bands (the lowest band covers only 0.5 MHz). Triple conversion is used from 0.5 to 8 MHz, with the first IF being variable 9 to 18 MHz. Double conversion is used on bands above 8 MHz. The common second variable IF is 2-3 MHz and the third fixed IF is 455 KHz. The PTO tunes from 2.455 to 3.455 MHz. Frequency readout is provided via 5 digits of mechanical counter, with the MHz digits controlled by the bandswitch and KHz digits by the PTO. The dial is marked to 200 Hz resolution between the digits. The radio uses 2 stages of RF amplification and *six* stages of 455 KHz IF amplification. Selectivity is similar to the R-390, provided by cascaded LC filters, but there are only 3 selectable bandwidths - 2, 4, and 8 KHz.
The R-392 is equipped with a 100 KHz crystal calibrator and variable BFO. The function switch allows standby, normal, noise-limiter, squelch, and net (relay -- with the T-195) operation. The active plate and filament fuses, along with a spare for each, are mounted on the front panel below the main controls. The dial lamps can be set to OFF, DIM, or ON.
All connections to the R-392 are on the front panel, as the case has no penetrations of any kind. The cases are extremely rugged and can probably survive direct fire from anything short of armor piercing rounds. The radio is designed to be immersionproof when mated with the proper connectors. Contributor David Capshaw has prepared a table detailing the power and audio connections.
The DC power cable for the R-392 uses a nine-contact center screw locking plug with gaskets and O-rings (remember -- the receiver is immersionproof!), Amphenol type 164-4FS. As these connectors were expensive and hard to find, many surplus radios have been hacked to use different connectors.
Audio output of 200 milliwatts into a 600 ohm load or line is provided from two front panel connectors. The proper mate for these is an Amphenol type 164-8.
The antenna input is either a 50 ohm BNC for coaxial cables or a spring loaded binding post for single wire and whip antennas. There is also a 455 KHz IF output via a BNC connector.
The R-392 is easily serviced with normal equipment and a couple of special tools. The special tools (right angle Bristo and Phillips drivers, plus tube pullers) *should* be mounted inside the radio's case, but are usually missing by the time these radios hit the surplus market. Because of the immersionproof design, the inside of these radios are almost always in pristine condition -- no dust, insect bodies or mouse droppings to be found. The only other problem is the tropical anti-fungal varnish common in many mil-spec radios, which must be cleaned from any connections that are being soldered/unsoldered.
Test points on the chassis make troubleshooting and alignment convenient, and the tube complement has enough "built-in" spares in other stages to make tube substitution a viable troubleshooting technique. You will probably want to purchase a few spare 26 series tubes from Fair Radio, Surplus Al, or another source as they are few and far between at most hamfests.
Table of tubes and stages. Thanks to David Capshaw for reorganizing this info.
Trouble-shooting information. Use the trouble-shooting chart, then the stage gain tables, and finally the voltage/resistance tables to localize defective components.
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