The R-2(A)/ARR-3 Sonobuoy Receiver

 Below are views of a much modified ARR3 receiver in my possession.

First is a view as it was after it had been stepped down from operating with a Teasmaid. It had done this for maybe 10 years (1968 to 1978) before I ran out of suitable replacement valves. A plywood front panel was fitted to make it look presentable

 

 The view inside the set shows a previous modification when I added an internal loudspeaker after modifying the set for FM reception.

In those days in the early to mid 1960s, police broadcasts occupied the space above local FM broadcast stations.

You can also see an EF80 in place of a blown 12SG7 and there's another underneath the chassis hardwired to a 12SG7 valveholder.
 

  As you can see above there are four IF transformers which I recall were on about 5Mc/s. The valves were all metal types mainly in the 12S series (12SG7, 12SH7, 12H6, 12A6, etc). There were loads of them and unfortunately their heaters expired one by one over the years until my stock of spares was exhausted. Performance was first class and I used the set up to 1972 when I bought a new Tandberg receiver and was able to receive stereo. From about 1968 and to around 1978 the old receiver was connected to a teasmade and used to wake us up every morning with the Home Service to accompany a cup of tea until yet another 12SG7 heater went and I'd used all my spares. Hence the teastains on the top of the receiver which I hadn't noticed before I took the pictures!

From memory... 3 RF stages, Oscillator, 3 IF stages, Discriminator, Ratio detector, Audio amp, Audio Output & Tuning Indicator. Valves were 6x12SG7, 2x12SH7, 12H6, 12Q7, 12A6 plus "magic eye" and in mine a 5Z4. The wiring had harnesses carrying wires that were all individually numbered and the underside of the chassis had that special sort of war-surplus smell, which is still as strong today as it was 60 years ago, probably from the laquer to protect it from mildew.

As I recall, the modification cheated slightly as one used the second harmonic of the local oscillator rather than the fundamental. This resulted in a higher output from the 12SG7 and provided a wider frequency coverage.

The service career of the ARR3 was interesting. During the war on U-Boats, aircraft dropped equipments called Sonobuoys around a suspected target. These transmitted received sonar signals back to the aircraft where an operator using an ARR3 was able to determine the position of the submarine and thence take appropriate action.

 

 Thanks to David Edsall, W1TDD for correctly identifying the set which I'd incorrectly called an ARR2.. Since removing the plywood you can see the type number!

Above is the front panel as it looked after I'd detached the plywood and rubbed it down and below after the application of a fresh coat of paint.

Originally it had an American black crackle finish. I forgot to paint the two bezels but, as the new paint flakes off the panel too easily, maybe I'll redo it with a black crackle paint sometime? The holes remaining were originally filled with a pair of headphone jack sockets, an IF gain control and something else which I can't decipher... I quickly discovered that by changing the characteristics of the automatic frequency control circuitry I was able to add a fine tuning control whilst still preserving the set's perfect frequency stability. The new control was made from the old IF gain pot.

 
 Back in the days when FM broadcasting started these receivers were advertised as the ones BBC engineers were buying to modify for FM reception! There was even an article in Wireless World in 1958 describing the modifications. It was this article that caused me to visit our local government surplus emporium, Super Radio in Whitechapel, Liverpool whose proprietor was a Mr.Benson, from whom I purchased one. The set tuned a band around 70 Mc/s and was relatively easy to convert to 90 Mc/s by merely snipping turns off the coils and resoldering the ends. In those days FM broadcasting was confined to 88 to 93 MHz. Above that were local police broadcasts. A chap I knew, who was one of the first amateurs to play around with VHF, discovered that there was a local police repeater in the Welsh hills overlooking Liverpool with its output on 146.3MHz (just North of the 2 metre amateur band). This pre-dated amateur radio repeaters by many many years and this daring youth used to activate the police repeater and communicate with his friends. He was technically quite able as he also had a government surplus VHF receiver listening out for meteor scatter signals in the FM band just below the UK's allocation. I recall he used to listen to Eastern European broadcast stations whilst at school, picked up by his receiver and re-broadcast via the police repeater. I don't believe anyone ever guessed what he was up to as the local police probably thought it was just atmospheric conditions. 
 

 Here's an article from the November 1958 Wireless World about converting the set for broadcast reception

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