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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 |
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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. |
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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. |
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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. |
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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. |
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