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 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
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:-
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
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
very 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...
about the restoration of a second R1132A