R-744A VHF Surveillance Receiver



Type: Commercial Receiver (may include amateur bands)

Year: 1965 ??

Valves / Tubes

13: 6612 6611 6611 6611 6612 6612 6611 6611 6611 6611 6611 6611 6611

Semiconductors (only for transistors)



Reception principle

Superhet with RF-stage; ZF/IF 4300 kHz; 1 AF stage(s)

Tuned circuits

8 AM circuit(s)     9 FM circuit(s)

Wave bands

Wave Bands given in the notes.


Power type and voltage

Batteries / addl. power jack / 1.45 & 45 or 24 Volt


- For headphones or amp.

Power out

from Radiomuseum.org

Model: R-744/PRR - MILITARY U.S. different makers


Metal case


Table model, with any shape - general.

Dimensions (WHD)

370 x 139 x 168 mm / 14.6 x 5.5 x 6.6 inch


U.S. military communications receiver for COMINT intercept missions. Also used by Canada and Australia. Used during the Vietnam War. Frequency range 20-100 MHz AM/FM/CW. Has three RF stages, a two-tube L.O., four IF stages, AM and FM det. BFO and one AF stage for headphones only. There is also a crystal calibrator for every 2 MHz. Single band: 20-100 MHz continuously with inductive tuning. Two antenna inputs, normal and DF antenna switch selectable. The four IF stages, FM det., BFO, AF stage and crystal calibrator are all plug-in modules for easy replacement. Each module is made of aluminium and has the size and socket of a 7-pin miniature tube. All modules contain a sub-miniature tube with all its components and is sealed. The receiver can be operated from internal dry batteries or from a 24V vehicle system. The receivers were made by various manufacturers and exist in some variants.

Net weight (2.2 lb = 1 kg)

5.8 kg / 12 lb 12.4 oz (12.775 lb)

Literature/Schematics (1)

- - Manufacturers Literature (U.S. Army TM5825-203-20)

General Notes

This small receiver was made by Arvin Industries for the US army during the early 1960s. Its dimensions are about 15 x 6 x 7 inches. Coverage is from 20 - 100MHz in one continuous range and it will receive AM, FM and CW modes. It uses sub-miniature pentodes types 6611 x 7 and 6612 x 3. Each of the 3 x IF stages, the calibration and BFO oscillators, AM detector and audio stage are separately housed in 8 small cylindrical cans about 2" high and 3/4" in diameter with a B9A tube base. The set is operated either by internal batteries or an external 24v vehicle power supply. There is no internal speaker, necessitating the use of headphones.

A variation seen is the R744(XE-3) made by Mallory, which doesn't have a band spread knob. These sets were also used by the Australian Army, where the Contract Number under the makers name has been blacked out. There is also supposed to be a similar set covering 100 - 200 MHz. These sets were designed as surveillance receivers having continuously variable tuning to overcome the drawback that most field military sets were restricted to FM mode with only pre-set fixed frequencies at say 100kHz separation. The R744 was used in Vietnam and possibly other fields.

Very little information seems to be available on the internet about this receiver so I have posted a copy of the schematics in djvu format from the manual TM5825-203-20. I can supply a scanned copy of most of the full manual which is some 2.5Mb in DJVU format.

r744a ID plateCollectability

These sets are very scarce in Australia and rarely come onto the market and even seem to be rare in the US and elsewhere judging by the lack of information on the internet. Here they would be very collectable and in working order probably a useful receiver. Their attraction for collectors would be helped by their functionality and small size in comparison with most military receivers. Only low serial numbers have been seen. The two earliest sets, including this one, have R-744A/PRR as ID and have S/N 12 and 15 whilst the later models, with the PRR suffix removed, have S/N 22, 59 and 60. I think it likely that sequence numbering is within a US contract and not across the full range of sets built. I know of three other sets, 16, 18, 19 all here in Australia.

Current Condition

This particular set, S/N 15,was in good condition, all be it all of the electronic modules in the IF, FM, and RF areas needed attention. Unsoldering the tubes to replace the pencil tubes and re-align the IF transformers is a very difficult task. The IF transformers are glued in adjustment so solvent was needed to free them up so they could be re-adjusted. The adjustments needed to be done with a dummy shield in place due to the capacitance the shield causes, I made one from a scrap price of copper tube with two holes drilled to match the IF screws. The other area that was a challenge was the RF alignment. The Mixer IF can needed adjusting and is the same construction as the ones in the IF cans.

Some Internal Views

RF chassis removed from the Main front panel so that alignment could be done. Note that the RF and IF sub-assemblies come away from the Front panel and are only connected by two RF cables and the power and interconnect plug. Also not that I am using the optional Power Cable extender from the power supply to the radio to do repairs, I was lucky that I found a spares case with parts and this cable in it.




Rear and case interior with 24v power supply with the Front panel hardware in the third shot. It was necessary to remove all of this to extract the RF subassembly.


r744a case interior


Closeup shots of one of the IF cans.Note the Pencil tube 6611, and on the second shot the IF transformers. You can see the Cores with slots that needed to be adjusted. Also in my modules a number of the tubes were damaged and microphonic. They all were replaced.







Assembled views of the top and bottom:
r744a interior 3r744a interior 2