(c) 2025 Peter McCollum
Radio Set RS-5, made in Japan for CIA
The proper name of this set is not confirmed, but is almost certainly the CIA’s “RS-5” set. I am awaiting the results of an FOIA request to CIA, which (if granted) should help to confirm the name of this set. About 20 years ago, a CIA Commo veteran (now deceased) told me the following:
“[After seeing the pictures of an example of the set] One of the [retired CIA Commo veterans] remembers [the RS-5] well. During the Korean war the outfit could not get RS-1's fast enough so they had them [the RS-5] built in either Japan or Taiwan. They wanted something similar to the RS-1. Seems they had quite a few of them built.”
Another fact that supports the belief that this is an RS-5 set, is that the power connectors for the transmitter and receiver are the same style as the RS-1, with the same pinout. It would be an unlikely coincidence that they appear on this Japanese-made set. In addition, the dates found on the example set (dates are 1952 and 1953, detailed below) match the Korean War time frame.
The RS-5 is known to have been used in an operation in Albania in September 1952 (operation FIG TREE, see memo below), and in Germany (for the KIBITZ stay-behind), also in 1952. In addition, the RS-5 was anticipated in February 1950 to be used in Ankara, Turkey, and at station MOB for case CARTEL. The number of sets manufactured is unknown, however CIA documents say that in 1960 there were 285 RS-5 sets in inventory that were “surplus”, and would be offered for use on an unidentified project. Meanwhile, collector Takashi Doi (in Japan) reports that the transmitters and receivers became available on the surplus market in Japan in 1956 (advertised in CQ (Japan) magazine), but generally without the matching power supply. For some reason, CIA did not receive all the sets that were manufactured.
This edited extract from a declassified CIA document names the RS-5 as being “principle” equipment in 1951, alongside the SSTR-1, RS-1, RS-6, and URC-4. I am awaiting an FOIA request for the contents of “Appendix 2-M”, which is currently redacted.
A declassified memo, naming the RS-5 in an operation in Albania.
My observations from studying the available photos of the set (reproduced below):
Receiver: The receiver tunes 3 to 7 MC (“Type A”), or 7 to 16 MC (“Type B”), with the range shown on a label on the front panel (some examples do not have the frequency label). So, no band-switching circuitry was required. The schematic says "RSK-253 SW Receiver". Audio output impedance is 10K ohms. Tuning knob is a wartime Japanese version of a National-type vernier dial. Dial is marked 0-100 (not frequency), but there is a graphical tuning chart included so that the operator can guess the operating frequency. This scheme was used on many WWII Japanese receivers. Ground post is marked "E" ('Earth'). Tuning cap is branded "Cosmos" in Roman letters, while the IF cans are the same brand, but in Japanese katakana characters. Chassis says MFP treatment applied in 1953. Coil L7 has another Japanese brand logo - this brand made many crystals during the war. BFO injection is applied to an unconnected pin of the 1S5 detector tube, relying on capacitive coupling to the nearby diode plate inside the tube. The BFO runs at all times. Gain is controlled by adjusting the voltage to the RF amp and IF amp stages. The mixer is a 1R5 tube, probably resulting in lower performance at the higher frequencies compared to the RS-1’s RR-2B receiver, which uses a 1L6 (however, this receiver’s upper frequency range is less than the RR-2B).
Transmitter: The transmitter was made in two versions, similar to the receiver – some examples have a frequency-range label, some do not. The schematic says "SMT-1 SW Transmitter". The design is very similar to the RT-3, but without the neon tuning indicators for the oscillator and final tanks. Bill Howard has examined the key, and says it is clearly a wartime Japanese military key; the same type as used with the type 94-3 A and C transmitters (or the same as a type 94-5 key, but with a different connector). Some of the caps visible in the photos are marked "Mica Condenser", and made by Sanko Denki. Tubes are U.S. made (GE and Ken-Rad brands). Transmitter includes a tuning chart (filled out by hand), which indicates the Plate Tuning and Antenna Tuning settings for a few sample frequencies and for antenna lengths of 18, 24, and 31 feet. The chart has 10 frequencies, but only 3 have been filled in.
Power supply: The meter indicates input voltage, and has a red mark at 100V. The label says "Input Voltage, set to 100V". Note that 100V is standard AC power in Japan. The voltage-selector knob is marked for -20, -10, 0, 10, and 20 volts; relative to 100V. The output connectors appear to match those on the RS-1 power supplies, and the pinouts are the same (per the schematics). All of the major components are Japanese brands. The transformer was made by "Taiyo Denki" (lit. means 'Sun Electric'), and is dated Showa 27.7 using the Japanese calendar (this date is July 1952). One of the selenium stacks has the same date. The 1.5V for the receiver filaments is produced by a shunt regulator composed of a single-layer selenium rectifier, the same method as the RS-1’s power supply. The transformer is rated for 50/60 Hz only.
Additional info from the late Bill Howard, who had studied the set in person:
The Ammo can set transmitter made use of a 6J5 as the oscillator. Crystal connected between grid and plate [Pierce]. Plate output of 6L6 to tank coil/tuning capacitors has a coil L2 of 25mh between antenna and ground, (assume this is tank coil), L1 is a 2 mH coil with a 10 ohm resistor across it in the plate lead from the 6L6 tube to the antenna line. L3 seems to be a 2 mh coil, (I can not find it in the picture) in the antenna line between the two variable capacitors, and a 6 volt 100 ma lamp in the antenna lead. L4 is the open air coil which is connected across the 6 volt lamp. Power input is 6.3 volts and 400 volts. Capacitors are bolted to the front panel and have a metal panel bolted to their rears. On this panel are two angle brackets mounting the tube sockets so tubes are horizontal mounted. Saves space. The resistors look like WWII Japanese mfg [and the mica caps are marked with Japanese brand names]. This is high quality construction and is not a lab prototype set.
The receiver is the same quality construction as is the power supply. The receiver is a 6 tube set with the following tube line up: 1T4 (three), 1R5, 1S5, 1L4. L4 and L5 are 455 IF transformers. L6 is a 455 IF transformer in the BFO circuit. L7 looks like an IF transformer but seems to be an output transformer. L1, L2 are open air coils wound on coil forms about 1/2 inch diameter, L3/L4 seem to be together, again wound on open air coil forms, same size as L1, L2. All the major components are labeled with a part number from the schematic, R1, L4, etc., and tubes are marked on the chassis. The main tuning capacitor is a three gang capacitor, mounted on top of chassis, and there are three trimmer capacitors mounted under the chassis, but I assume connected to each gang. There is a small capacitor mounted on the front panel which seem to correspond to the control marked BFO. Next to it is R1, a potentiometer which is labeled Volume control. The main tuning capacitor is driven by a vernier which was typical of late war Japanese sets (same as used on the WWII 1568 set). Main tuning capacitor has patent number 363480 stamped on the rear. There is a minimal amount of wire used. It is mostly red wire and blue wire. Resistor and capacitor ends have yellow spaghetti covering to provide insulation. Front panel, underside has the phone jack (standard 1/4 inch), the power cord and the on/off switch (toggle switch). Power requirements were 1.5 volts and 90 volts.
Both receiver and transmitter have spaces in the ammo can case for storage of headphones, antennas, key etc. The power supply has a large transformer, two large electrolytic capacitors, two large selenium rectifiers, two smaller selenium rectifiers and a small OB2 tube. Front panel controls are a voltage selector switch (also used as On/Off switch), an input volt meter, two fuses, 100 volt and 200 volt, the tip of the OB2 tube and the female sockets for power connection to the receiver and transmitter. The wire is post WW II wire with plastic/rubber(?) insulation and looks to be about 12 gauge wire.
Power supply. Note the output connectors on the right side of the panel, which appear to match those on the RS-1 set. The pinouts seen on the schematic are a match also.
Receiver RSK-253.
Transmitter SMT-1.
