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MCR-1   Type 36/1
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.
 
The MCR-1 consists of a rectangular receiver, with four plug-in coil packs that can be attached at one end, a separate 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.
  
Complete MCR-1 set

During WWII the MCR-1 became a very popular receiver with resistance groups in many European countries. It was built under licence by Philco in the UK, and many were dropped over occupied Europe for the reception of the 'civil' broadcasts of the BBC that carried the latest news in various languages, speeches of the British Prime Minister and other heads of states and often coded messages for the resistance (e.g. to confirm the arrival of a VIP or an upcoming dropping).

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 has become a desirable collector's item, as only a modest number of them have survived. After the war, the MCR-1 was cloned by MBLE for the Belgian Stay Behind Organisation (SBO). In 1954, the rather large receiver was succeeded by the much smaller Mk.301 that was built with miniature valves.

Complete MCR-1 (centre) with coil packs (right) and PSU (left)

 
Biscuit tin
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.
  
Contents of the biscuit tin

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.
 
Closed biscuit tin Opening the biscuit tin Contents of the biscuit tin Contents of the biscuit tin Complete MCR-1 set MCR-1 Receiver Headphones Empty biscuit tin

 
Receiver
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.
 
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.
  
MCR-1 Receiver

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.
 
MCR-1 Receiver MCR-1 Receiver MCR-1 receiver with coil pack 4 attached MCR-1 ready for use Headphones and antenna sockets Headphones and antenna sockets Headphones Antenna wire on Paxolin card
Four coil packs Coil pack number 1 Top view of the four coil packs Perspective view of the four coil packs Coil pack receptacle Rear view of coil pack number 4 Coil pack 4 fitted to the MCR-1 receiver Frequency adjustment

 
Power Supply
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.
 
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.
  
MCR-1 Power Supply Unit (PSU)

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.
 
MCR-1 power supply unit (PSU) MCR-1 power supply unit (PSU) AC/DC voltage selector MCR-1 Power Supply Unit (PSU) MCR-1 Power Supply Unit (PSU) Power (output) socket PSU interior PSU interior

 
Frequency plug-ins
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:
 
  1. 150 kHz - 1.6 MHz
  2. 2.5 MHz - 4.5 MHz
  3. 4.5 MHz - 8 MHz
  4. 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 broadcast band.
  
Perspective view of the four coil packs

 
Four coil packs Coil pack number 1 Top view of the four coil packs Perspective view of the four coil packs Early production coil pack Later production coil pack Rear view of coil pack number 4 Coil pack 4 fitted to the MCR-1 receiver

 
Interior
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.
  
MCR-1 interior

 
MCR-1 interior MCR-1 interior MCR-1 interior Tuning capacitor Tuning dial Valves MCR-1 interior detail Adjustable capacitor

 
Post war version (MBLE)
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.
 
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 that had space for the coil packs, headphones, antenna, ground wire, the battery pack and the optional window antenna. This receiver was intended for the secret Belgian Stay Behind Organisation (SBO).
  
MBLE-version of the MCR-1

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].
 
Canvas bag holding the MBLE MCR-1 Looking inside the canvas bag MBLE-version of the MCR-1 Complete MBLE MCR-1 set MBLE-version of the MCR-1 with 4 coil packs Wire antenna Headphones Standard MCR-1 (front) compared to the MBLE-version of the MCR-1 (rear)

Although the MBLE-version of the MCR-1 uses the same valves and is electrically identical to the original version, there are some differences:
 
  • Colour: the MBLE version is finished in brown wrinkle paint, rather than smooth grey.
  • Knobs: modern knobs are used on the MBLE-version.
  • Markings: 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.
An original MCR-1 (left) aside a post-war reproduction made by MBLE

 
Connection
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 far better to use batteries or an alternative (safe) PSU.

Power connections when looking into the power socket of the PSU

 
References
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  2. Midget Communication Receiver M.C.R. 1
    Original Manual 1943 (14 pages, with circuit diagrams, plus 4 page supplement). 1

  3. Wikipedia, Transformer, Autotransformer
    Retrieved January 2012.

  1. Manual scanned and distributed by The Vintage & Military Amateur Radio Society (VMARS).
    Complete overview of freely downloadable manuals here.

Further information

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