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MCR-1   Type 36/1
Miniature Communications Receiver

MCR-1 was a modular valve-based clandestine receiver, developed in 1943 by (then) Captain John Brown of the Special Operations Executive (SOE) and built by Philco (UK). It was intended for use by the 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 it is commonly known as Midget Communications Receiver MCR-1. It was used both stand-alone and as part of a complete Jedburgh radio station.

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 mains AC/DC PSU.
  
MCR-1 receiver with coil pack 4 attached

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 the war more than 30,000 units had been made [1]. After the war, the MCR-1 became a desired collector's item, as only a modest quantity had survived. During the Cold 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 (tubes).

Closed biscuit tin Opening the biscuit tin Contents of the biscuit tin Complete MCR-1 set MCR-1 Receiver MCR-1 power supply unit (PSU) Headphones Antenna wire on Paxolin card
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Closed biscuit tin
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Opening the biscuit tin
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Contents of the biscuit tin
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Complete MCR-1 set
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MCR-1 Receiver
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MCR-1 power supply unit (PSU)
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Headphones
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Antenna wire on Paxolin card

Features
The diagram below provides a quick overview of the controls and connections on the body of the receiver (here shown at the centre), the Power Supply Unit (PSU) and the coil packs. The receiver has a fixed wire that should be connected to the power socket of the PSU (here shown at the left).

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

The receiver has a set of contact pins at the right end, on which one of the (four) coil packs can be installed. Depending on the desired frequency band, one of these coil packs must be installed on the receiver. The thickest coil pack (at the far right) is for reception of the MW broadcast band.



Complete MCR-1 set with all accessories

Parts
Biscuit tin storage box
Tin
MCR-1 receiver Frequency plug-in coil packs Battery pack Power Supply Unit (PSU)
PSU
Headphones Wire antenna Instruction booklet and technical diagrams
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.

Bicuit tins of the appropriate size were made by Huntley & Palmer in Reading (UK) and also by Meredith & Drew (M&D) in London (UK). The size of a bicuit tin was approx. 23 x 22 x 12 cm.
  
Contents of the 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.

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

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. 1 A tuning coil is fitted to one end of the receiver and four such coils were supplied, one for each frequency band.

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.
  
Perspective view of the four coil packs

  1. Coil pack (1) is somewhat thicker than the other ones and uses the so-called single-span principle to cover the entire
    MW
    broadcast band.

Battery pack
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 fixed lead of the receiver. The unit draws 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.

The manual provides instruction on how to use improvised batteries when the original battery pack is in short supply.
  

Power Supply

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 [2].

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. For safety reasons it would be better though, never to use the original power supply, and use a battery or a modern PSU instead.
Wire antenna
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 demonstrates the portable use of a the MCR-1 receiver, concealed under a regular raincoat.
  
Antenna wire on Paxolin card

Headphones
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 and the power cable.

The supplied headphones have an impedance of 800 Ohms, to which the 5-8 mW AF signal from the receiver can be supplied.
  
Headphones

Instruction manual
The MCR-1 was supplied with a 14-page instruction booklet, which contained operating instructions, recommendation for the antenna, examples of covert use and full circuit diagrams.

A copy of the original manual — with a 4-page supplement — is available for download below.

 Download the manual
  

Opening the biscuit tin Contents of the biscuit tin Contents of the biscuit tin Complete MCR-1 set 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 Coil pack receptacle Rear view of coil pack number 4 Coil pack 4 fitted to the MCR-1 receiver Frequency adjustment
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
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
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Opening the biscuit tin
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Contents of the biscuit tin
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Contents of the biscuit tin
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Complete MCR-1 set
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MCR-1 Receiver
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MCR-1 Receiver
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MCR-1 receiver with coil pack 4 attached
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MCR-1 ready for use
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Headphones and antenna sockets
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Headphones and antenna sockets
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Headphones
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Antenna wire on Paxolin card
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Coil pack receptacle
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Rear view of coil pack number 4
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Coil pack 4 fitted to the MCR-1 receiver
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Frequency adjustment
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Four coil packs
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Coil pack number 1
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Top view of the four coil packs
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Perspective view of the four coil packs
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Early production coil pack
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Later production coil pack
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Rear view of coil pack number 4
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Coil pack 4 fitted to the MCR-1 receiver
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MCR-1 power supply unit (PSU)
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MCR-1 power supply unit (PSU)
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AC/DC voltage selector
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MCR-1 Power Supply Unit (PSU)
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MCR-1 Power Supply Unit (PSU)
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Power (output) socket
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PSU interior
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PSU interior

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
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MCR-1 interior
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MCR-1 interior
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MCR-1 interior
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Tuning capacitor
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Tuning dial
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Valves
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MCR-1 interior detail
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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 (Bg). 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 and the battery pack, and came with a loop antenna. This receiver was intended for the secret Belgian Stay Behind Organisation (SBO).
  
MBLE-version of the MCR-1

The MBLE receivers came without a mains power supply unit, so it is likely that they were meant for operation with a battery pack. There is enough free space in the canvas bag to carry a suitable battery. 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 in the other pocket of the coat.

 More about the Belgian MCR-1

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 potentially 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

Specifications
  • Model
    MCR-1
  • Part number
    Type 36/1
  • Intermediate
    1730 kHz
  • Valves
    1R5, 4 x 1T4
  • Power
    Dry battery pack LT: 7.5V, HT: 90V, or mains PSU
  • Current
    LT: 50mA, HT: 5-8mA
  • Modulation
    AM R/T, CW
  • Dimensions
    Bare receiver: 212 x 100 x 60 mm
  • Weight
    Bare receiver: 1295 grams
Frequency bands
  1. 150 kHz - 1.6 MHz
    85 x 60 x 40 mm (178 grams)
  2. 2.5 MHz - 4.5 MHz
    85 x 60 x 30 mm (152 grams)
  3. 4.5 MHz - 8 MHz
    85 x 60 x 30 mm (154 grams)
  4. 8 MHz - 15 MHz
    85 x 60 x 30 mm (154 grams)
Power supply unit
  • Current
    AC and DC
  • Input
    107, 127, 205 and 235 V
  • Output
    90V DC (HT) and 7.5V DC (LT)
Documentation
  1. Midget Communication Receiver M.C.R. 1
    Original 1943 Manual (14 pages, with circuit diagrams, plus 4 page supplement). 1
  1. Manual scanned and distributed by The Vintage & Military Amateur Radio Society (VMARS).
    Complete overview of freely downloadable manuals here.

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

  2. Wikipedia, Transformer, Autotransformer
    Retrieved January 2012.
Further information
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Crypto Museum. Created: Monday 28 September 2009. Last changed: Saturday, 23 March 2019 - 16:05 CET.
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