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Miniature Communications Receiver
The MCR-1 was a small modular valve-based receiver,
developed in 1943 by (then) Captain John Brown of the
SOE and built by Philco (UK). It was intended
for use by the Special Operations Executive (SOE) and
Special Forces (SF), and was later adopted by the Army as well.
The internal designator for the receiver was Type 36/1,
but the commonly used name was MCR-1 (Midget Communications Receiver).
It was used both stand-alone and as part of complete
radio stations.
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The MCR-1 consists of a rectangular receiver, with four pluggable coil
packs that could be attached at one end, a Power Supply Unit (PSU)
of the same size as the receiver, and various accessories.
The sets were distributed in water-tight sealed
tinned-steel biscuit tins,
which is why they got nicknamed Biscuit Tin Receiver.
The receiver has a frequency coverage of 150 kHz - 1.6 MHz (broadcast band)
and 2.5 - 15 MHz (short wave), divided over four ranges. It can be powered
by a combined battery pack (7.5V/90V) or by the external AC/DC PSU.
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The MCR-1 became a very popular receiver. It was built - under licence -
by Philco in the UK, and many were dropped over occupied Europe for the
reception of broadcast transmissions of the BBC.
The receiver was also used as part of complete radio stations, such
as the Type 46/1 (Jedburgh Set) and
the Type 48/1 (Nicholls Set).
Production of the receiver started in late 1943, and by the end of WWII
more than 30,000 units had been made [1].
Today, the MCR-1 is a highly desirable collector's item, as only a modest
number of them have survived.
After the war, in 1954, the MCR-1 was succeeded by the much smaller
Mk.301 that featured miniature valves.
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The MCR-1 and its PSU were constructed in such
a way that they could be stored inside a standard biscuit tin of those days.
The image on the right shows an original (now rusty) biscuit tin with a complete
MCR-1 set, protected by cardboard. The receiver and the PSU are each stored
at one side, with the accessories in between them.
Many MCR-1 units were distributed this way.
The manual was usually stored on top of the items. When the cardboard flaps are
closed, there still is enough room for a couple of real biscuits to conceal the
actual contents.
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Bicuit tins of the appropriate size were made by Huntley & Palmer
in Reading (UK) and by Meredith & Drew (M&D) in London (UK).
The size of a bicuit tin was approx. 23 x 22 x 12 cm.
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The image on the right shows the bare receiver. The flying lead
at the left is for connecting a battery or the PSU. At the right
is the receptacle
(i.e. the sticking-out pins) for the coil pack.
The controls are at the front. The large knob on the right is the tuning
dial. Just above the dial, is a small window with a
linear scale.
Each coil pack has a frequency conversion table
on its body.
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Coil pack 1 is slightly larger that the other three. It covers the MW
broadcast band from 150 kHz to 1.6 MHz using the single-span principle.
The remaining three coil packs (2, 3 and 4) cover a contiguous frequency
range from 2.5 to 15 MHz.
A coil pack can be attached to the pins that stick out at the right,
extending the receiver's length.
The receiver is built around 5 valves (4x 1T4 and 1x 1R5)
and has an IF of 1730 kHz, which lies in between range 1 and 2.
Sensitivity is approx. 10 µV (for 1 mW audio output)
and the AF power is approx. 5-8 mW into 800 ohms headphones.
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A suitable pair of headphones
is supplied with the set and should be
connected
to the banana-type sockets
at the left side of the receiver, close to the antenna terminals.
For a good reception it is necessary to connect a proper
(wire) antenna
to the socket marked 'A' and a sufficient ground (counterpoise) to the
socket marked 'E' (earth).
A suitable wire antenna, wound on a Paxolin
card, is supplied with the set. The manual
even shows the portable use of a concealed MCR-1 receiver.
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For portable use, the MCR-1 can be powered by a combined battery pack
that supplies 7.5V/90V. Such (dry) batteries were readily available at
the time and had a 4-pin socket that mates
directly with the flying lead of the receiver.
The unit consumes approx. 50 mA from the 7.5V LT rail
and 5 to 8 mA from the 90V HT rail.
For domestic use, the MCR-1 was powered from the mains.
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A suitable Power Supply Unit (PSU)
was supplied with the set, allowing
the MCR-1 to be powered from a wide range of mains voltages, both AC and DC.
For connection to the AC mains, an autotransformer with multiple taps is used [3].
For connection to the DC mains, an
array of power resistors is used.
The voltage selector
is located behind a metal cap at one end of the PSU.
The desired AC or DC voltage can be selected, by placing the screw-terminal
in the corresponding hole. Mains power was usually 'tapped' from the light bulb
using an adapter.
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Warning - Please note that autotransformers are potentially
dangerous, as they do not isolate, but connect the receiver directly to the mains.
As a result the chassis of the receiver may carry the mains voltage.
If this happens, the mains power plug should be reversed. It would be better
though, never to use the original power supply, and use a battery or a
modern PSU instead.
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The MCR-1 covers all frequencies between 2.5 and 15 MHz, divided
over 3 frequency ranges, plus the domestic MW band from 150 kHz to 1.6 MHz
in a single-span.
A tuning coil is fitted to one end of the receiver and four such coils
were supplied, one for each frequency range:
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- 150 kHz - 1.6 MHz
- 2.5 MHz - 4.5 MHz
- 4.5 MHz - 8 MHz
- 8 MHz - 15 MHz
The tuning scale is linear and a suitable frequency conversion scale
is printed on an metal plate
on each coil. On some of the early
production runs of the MCR-1, the conversion table was
printed on paper.
Such tables will have faded over time and are often hard to read.
Coil pack number one is slightly larger than
the other ones and uses the so-called single-span principle to
cover the MW band.
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The interior of the MCR-1 can be accessed by removing the 20 bolts
around the edges of all sides. The bottom and the U-shaped case can then
be taken off. Despite the rather simple exterior, the interior of the MCR-1
is rather complex and well-built.
The image on the right shows the interior of a typical MCR-1.
The five valves are clearly visible. At the right is the large tuning
capacitor.
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After the war, in the late 1950s, copies of the MCR-1 were produced by
Manufacture Belge de Lampes Electriques (MBLE), a subsidary
of the Dutch electronics giant Philips.
Apart from a few mechanical
and components changes, the MBLE-version was electrically identical
to the original.
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The image on the right shows such a post-war MBLE copy of the MCR-1.
The unit is much better built than the war-time version and uses
higher-grade components. Furthermore, the case and the coil packs are
painted in a brown wrinkle-finish. The text on the body is in French
and the knobs have a more modern look.
The MBLE version of the MCR-1 was supplied in a green canvas carrying bag,
together with the accessories, such as the coil packs, (wire) antenna,
ground wire and headphones. It was probably
intended for stay-behind use (Gladio).
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As the MBLE receivers were supplied without a mains power supply unit,
it is assumed that they were intended for battery-operation. There is enough
free space in the canvas bag to carry one or more batteries. It is also
likely that the MBLE-version of the MCR-1 was intended for portable use,
as it has a much longer power cable, allowing the battery to be carried elsewhere
under the operator's clothing.
Judging from the serial numbers of the surviving receivers (missing from
our unit), it is
likely that no more than 100 of these post-war replica units were produced [1].
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Although the MBLE-version of the MCR-1 uses the same valves and is electrically
identical to the original version, there are some differences:
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- Colour: the MBLE version is finished in brown wrinkle paint, rather than smooth grey.
- Knobs: modern knobs are used on the MBLE-version.
- Language: all text is in French rather than English (and rotated by 90°).
- Power cable: the MBLE-version has a longer and thicker cable.
- Headphones: the MBLE-version comes with a canvas cloth-type pair of headphones.
- Sockets: the sockets on the MBLE-version accept standard banana-type plugs.
- Components: modern tuning capacitor and IF coils are used in the MBLE-version.
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The image below shows the pinout of the power socket of the Power Supply Unit (PSU).
Please note that the common line (LT-/HT-) is directly connected to the mains when
using the original PSU. This is potentially dangerous
and can even be lethal.
Do not use the original PSU unless you know exactly what your are doing.
It is better to use batteries or an alternative (safe) PSU.
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Thursday, 12 June 2014 - 06:32 CET
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