Back to Contents…

(c) 1999,2008 Peter McCollum

The RS-6 HF Transceiver

The RS-6 is more-or-less a miniaturized version of the RS-1. It has a very similar design, but uses sub-miniature tubes in the receiver and power supply regulator, and a miniature tube as the transmit oscillator. Physically, the complete radio is in four units: receiver, transmitter, power supply, and power supply filter unit (which also provides storage for some accessories). The power supply uses a 6X4 tube instead of the selenium rectifiers used in the RP-1; presumably because the selenium units in the RP-1 are too bulky (they require more than twice the space of a 6X4). Since the unit is built as 4 pieces, rather than 3, there may have been a requirement that each piece was no larger than a certain size.

The RT-6 tunes 3-16.5 MC in two bands with up to 10 watts output. Maximum keying speeds are 40 WPM with the built-in key or an external hand key (in either case using the internal keying relay), or 60 WPM with an automated keyer that drives the tube cathodes directly. The RR-6 tunes 3-15 MC in two bands, with either VFO or crystal control. The receiver also has a BFO and a crystal calibrator. The power supply operates from 70 to 270 VAC, 42-400 cycles, or from 6 volts DC. Each of the four main units is stored in a plasticized cloth bag, plus an additional bag for accessories.

 

RS-6 Radio Station Specifications

 

 

 

 

Receiver RR-6

Transmitter RT-6

Power Supply RP-6 and RA-6

Weight

3 lb 2 oz

2 lb 14 oz

RP-6: 5 lb 11 oz

RA-6: 3 lb 11 oz

Dimensions

6-3/4" X 5" X 2-1/4"

6-3/4" X 5" X 2-3/32"

RP-6: 8-1/16" X 4" X 2-3/16"

RA-6: 8-1/16" X 4" X 2"

Tube complement

5899 RF amp

6AG5 oscillator (6AK6 in RT-6A)

6X4 rectifier

 

5899 mixer

2E26 final

 

 

5899 oscillator

 

 

 

5899 IF amp (two)

 

 

 

5718 detector

 

 

 

5718 audio/cal. osc.

 

 

 

5718 BFO & bias

 

 

Frequency Bands

3-6.5, 6.5-15 MC

3-7, 7-16.5 MC

 

Power Output

 

6-10 watts

 

 

The RT-6 transmitter, shown with the key extended. Author's collection.

 

There also is an RS-6A, which includes the RT-6A and RR-6A. The only big difference is that the RS-6A tunes 4.5-22 MC, whereas the RS-6 tunes 3-16.5 MC. There are also some minor circuit differences, and the RT-6A uses a 6AK6 oscillator instead of a 6AG5. The manual mentions RT-6A serial numbers between 9000 and 9750. The RS-511 (the "Attache Case Radio" shown in Keith Melton's books) is based on RS-6 components.

During the early production of the RS-6 set, some significant design changes were made. The evidence is seen in an early set that has the following differences:

Note the differences between an early RT-6 (right) and the common version (left). The early model has no provision for the “monitor” connector; and the “rec. ant.” connector was never installed.

Part of the diagram inside an early RA-6. Note the mention of the SSP-11 generator; and white paint has been used to remove the sidetone cable from the diagram.

 

It is reported that the RS-6 was made by GTE in Waltham, MA. A HAM that traded the author an RS-6 set said that a friend of his recognized it, and said that he used to work in the Waltham plant where they were built. GTE has been contacted about this. They said that their Waltham plant was making that sort of thing (secret military commo gear) in the '50's or '60's, but they didn't know specifically about the RS-6.

 

The RR-6 receiver. Author's collection.

 

The RS-6 is known to have been on-board equipment in the following aircraft: B/RB-47E, B-47 ECM, and B/RB-52. A SAC manual (Manual 64-1, see Ref. 15) has been seen which specifically lists the RS-6 as required equipment during certain types of missions. It is listed as "Radio kit, long range, type RS-6". The contents of the kit include a nylon container (NOT the same as the bags for the individual RS-6 components - see picture, below), and a GN-58 generator (the manual says "GN-68", but that is presumed to be a misprint). [The information in this paragraph is courtesy of Danny Cahn.]

One story is that RS-6's were mounted on the bottom of B-47 ejection seats, and that the crew would use them to call for a pick-up after they had released nuclear weapons on a Soviet target. This would be needed because a B-47 wouldn't have enough range to hit the USSR and return, so it would have to ditch on the way back home.

 

The RP-6 power supply unit. Note the AC voltage selector switch. Author's collection.

 

The RA-6 Filter-Accessory unit, with the lid open. Visible are the AC power plug, and the red and black DC power cables with battery clamps. Author's collection.

Because of the design similarities with the RS-1, it is possible that the RS-6 was designed with involvement from RDR Corp., and that the volume manufacturing was done by GTE (and/or others). Some of the design similarities between the RS-1 and RS-6:

Based on the observed serial numbers, a large number of RS-6 sets were manufactured - possibly about 10,000 sets of RS-6 and RS-6A combined (It is possible that numbers were randomly skipped, to hide the true amount, but it is not clear what the benefit would be. Why give the impression that the production was higher than it really was?). RS-6 components are known to number from 33 up to over 10,400. The RT-6 and RR-6 units are seen in the range up to about 8000, while RT-6A and RR-6A units cover the 8000-10000 range, and RP-6 and RA-6 cover the entire range of numbers (there is no RA-6A or RP-6A). So it appears that RS-6A manufacturing continued the numbering where the RS-6 left off – the numbers were not reset to “0” when the “A” model was introduced.

It is unknown how many were made for CIA, as compared to SAC or other users. It is interesting to note that all of the observed serial numbers (except for one early set) are above 2300, although the manual (or the Addendum) mentions numbers as low as 33. Perhaps the low-numbered units are the ones that were delivered to the CIA, and the remainder were delivered to the military, and thus found their way into surplus channels via the MARS program, etc.

The RS-6 probably started production in about 1951. An early unit appears to have component date codes in 1951. Most other units have codes for 1952 and 1953. By observation of markings in the RR-6 receiver, the IF transformers are marked with a number such as “119-3-25” – the “3” represents 1953, and the “25” is a week number for that year (the ‘119’ is an EIA manufacturer’s code, representing Automatic Manufacturing Corp., a major maker of IF transformers at that time). The Manual Addendum is dated May 1953, and mentions serial numbers up to 2614 with certain hardware differences. RR-6 production appears to have stopped in 1953, while production of the RS-6A probably stopped about mid-1954, as determined by the “119-4-14” marking seen in an RR-6A.

A complete RS-6 station ready for use from AC mains power. Note the many cables and connectors – a total of 10 cable-ends must be connected (including antenna and ground, which are not shown in the picture).

The RS-6 is not a very "user-friendly" design - too many cables and wires, with the possibility of hooking things up wrong, and exposed high voltages on male connector pins. The sidetone connection between the transmitter and receiver seems to be an afterthought: an alligator clip is used to connect to one of the pin plugs on the earphone. The manual also discusses a situation with the keying relay that requires the operator to press the key when changing modes, etc. - it would seem that there are many opportunities for error. Very little field maintenance is possible. Apparently, miniaturization was a priority in the design, and this was accomplished at the expense of ease-of-use. And, there may have been a design requirement that no single part of the set would be larger than a certain size; therefore the power supply was designed as two units. The author suspects that the RS-6 never really saw favor with the CIA - the RS-1 was better in every way except size, and new solid-state sets were not far away. It may be that SAC was involved in the project early on, and provided the support necessary to keep the project alive for so long.

Receiver RR-6 schematic (258 KB)

Transmitter RT-6 schematic (176 KB)

Power supply RP-6 schematic (174 KB)

Filter/accessory unit RA-6 schematic (127 KB)

 

A SAC RS-6 bag. Image courtesy of Danny Cahn.

 

Comments from Jess Guarderrama:

I was a radio operator (CW) with the 24th Division LRRP from 1960 to 1963. We used the RS-6 on all of our field operations. We could load just about anything. I remember one operation when I ran a wire along side of a laundry line and maintained contact with our base station throughout the entire operation. The transmitter was easy to load and the receiver was unbelievable when it came to picking the base station signal out of the noise.  I remember using this rig to operate on the ham bands during some of the field operation (DL4TU was my call then). I ran many a commo check cranking the GN-58 generator with my right hand and sending with my left hand while the key was strapped to my left thigh.

RS-6 Notes (from Dennis Starks):

At the Warrensburg Mo. HAMfest I was related a very interesting story from a ham upon his noticing my RS-6 on display. He tells me his (first) RS-6 was purchased in 1960 while he was serving with the 77th Special Forces Group at Ft. Bragg, NC. It seems that at this time several hundred RS-6 sets were surplused from this unit (he also noted that it was possible the radios came from a Special Warfare Group also stationed there). Many others were purchased by Hams on the Base for $10.00 ea.

Regarding RS-6 parts, for persons wanting to have authentic-looking accessories:

Next section…