US Coast Guard Receiver R-138

Jim Novak, WA9FIH owns this unusual unit and has provided all of the material for this page.

The R-138 is a transformerless 110V AC/DC multi-band receiver in a black wrinkle finished metal cabinet 19 inches wide, 10-1/2 inches high and 12 inches deep, with rounded corners and a hinged top lid. The cabinet closely resembles those made by Middletown (CT) Manufacturing Co. Frequency coverage is in six bands, from 200-420 kc and 490-18000 kc, so the IF frequency is probably about 455 kc. A 7 x 5 inch chromed bezel surrounds a plastic cover over a half-round dial scale. There is a terminal strip for 500 ohm audio output to an external speaker, and another strip for relay muting, indicating that the radio was designed to be used with a transmitter. Among the front panel controls are a variable noise limiter, crystal filter, antenna trimmer, BFO, and RF gain.

Overall view of the R-138 receiver	R-138 front panel view

The unit has eleven octal-based tubes, including an OA3/VR-105 voltage regulator, fairly standard lineup of six volt tubes including a 6SG7 RF amp, 6SB7Y oscillator-mixer, a pair of 6SG7 i.f. amps, 6H6 detector, a 6SF7, two 6SL7s, and a pair of 25L6GT audio output tubes. The tube filaments and two dial lights are all in series across the 110 Volt line.

Although there is no band-spread tuning, the main tuning dial has about a 40:1 reduction ratio and reasonably accurate calibration, resulting in relatively easy operation, at least in the AM mode. Tuning is a little fast for single sideband signals, but with a little care both SSB and CW transmissions can be copied, and the crystal filter does provide additional selectivity when needed. Oscillator stability seems reasonable after a 15 or 20 minute warm-up.

An AC/DC transformerless military receiver is unusual. It is very likely that this radio was intended for use on CG ships where the power was normally 110-120 VDC. Use at remote ground stations or lighthouses where AC power might not be available is also a possibility. Jim's search through his collection of radio references yielded nothing about the unit, nor any Coast Guard radios for that matter. Although the Internet has numerous sites devoted to military radios, there is little information about Coast Guard equipment, and absolutely nothing about the R-138. His inquiry to the Coast Guard Museum in Connecticut resulted in a kind reply from a curator who was unable to find any reference to this model or the contract in their files. The manufacturer, L. R. Dooley Inc. is a mystery. His Google search yielded one hit, a reference to a piece of personal correspondence from that company in 1949 to an apparently well known professional dancer whose personal archives are stored in the New York City Public Library! Who knows, perhaps in between stage appearances she might have worked on their assembly line – still another mystery!