The R1132A Receiver

 This receiver was used in RAF control towers during WWII together with the R1392. The latter was crystal controlled and had a slightly better valve line-up than the older R1132A.

The dial is marked "0 to180" and is not directly calibrated, the operator relying on a card next to the meter to let him know where to set the dial for a particular frequency.

Here's the circuit diagram

 

 Here's a second example I have. Clearly these old sets haven't had an easy life.

 

 The second example (above & below) also has corrosion on its chassis and is missing it's valves, but it does have a screening cover which my first example was missing.

It's tuning chart runs from 100Mc/s (=171) to 124 Mc/s (=16). Using basic arithmetic this makes the full coverage 98 to 127 MHz, bearing in mind the dial has a few calibration marks below 0 and above 180.

 Although the first example has suffered somewhat from exposure to damp, as you can see from the following pictures, the interior is in excellent condition.

Both this and the companion R1392 used an external power supply, typically the type 234A, which provided HT and LT. It's possible that a version of the 1132 was planned, or exists that has a built-in power unit because, as you can see below there's plenty of room available for this to the right of the RF section.

The receiver uses ten octal-based valves (a mixture of International and Mazda types) and a single UX4 (stabiliser) as follows:-

 Read the original manual

1st RF amplifier VR65 (CV1065/SP61); Mixer VR65 (CV1065/SP61), Oscillator VR66 (CV1066/P61); 1st IF amplifier VR53 (CV1053/ARP34/EF39); 2nd IF amplifier VR53 (CV1053/ARP34/EF39); 3rd IF amplifier VR53 (CV1053/ARP34/EF39);

Detector and AGC VR54 (CV1054/ARDD5/EB34); BFO VR53 ((CV1053/ARP34/EF39); AF amplifier VR57 (CV1057/EK32); Audio output VR67 (CV1067/L63/6J5G); and Voltage stabiliser VS70 (CV1070/AW2/7475)

The majority of wartime receivers sold in the period 1946 to the 1970s were modified for amateur use. This particular receiver was probably converted for operation on the 2 metre amateur band, 144-146MHz. The only modification necessary to do this was to reduce the coil sizes by snipping off a turn or two.

These were the days when AM was the norm and SSB and narrow band FM the exceptions.

My own 2 metre activity was pretty typical. I used an ex-RAF transmitter and an R206 receiver with a nuvistor converter.

I had a yagi aerial mounted on an ex-MoD self-supporting mast made from plywood tubing and rotation was achieved with a prop-pitch motor. At night a torch had to be pressed into service to check on your beam heading, but during the day a car wing mirror served the purpose.

In the days before a 2 metre band plan was in use most amateurs used crystal control. The procedure was to call CQ on your fixed frequency, then tune the whole band listening for a reply. A bit hit and miss, but it certainly worked and you can't beat AM for fidelity, something no modern radio ham will ever experience.

Note, in the R1132, the use of valve type VR57 which is an octode. Why use this strange valve as an audio amplifier? My guess is that it's connected with the large range of received signals in a control tower, ranging from very weak transmissions from distant aircraft to local high power transmitters on the airfield. The audio amplifier instead of being the usual triode is this octal variety which is wired up to enable lots of control over the audio amplification to keep the loudspeaker output more or less constant. I've never seen this before and it might have been undertaken after the design of the receiver had been completed as a "PDS" task following complaints from users? Another odd thing for a WW2 design is the attenuation switch. Clearly the AGC wasn't powerful enough to deal with all eventualites.

Maybe somebody knows about this??

I started to restore the first set which had been modified for use on 2 meters. I got as far as re-establishing the coils which are chunky silver-plated copper and found that the valves were being pushed to their limit. I used basic copper initially and discovered the Q of the oscillator coil was too low to maintain oscillation right across the band and the gain of the RF amplifiers was pretty low. I decided to shelve the job until I bought a spectrum analyser so I could see what was going on. I now have the latter but not the time...

Read about the restoration of a second R1132A

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