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Mk. 119
Clandestine transceiver

The MARK 119 (Mk.119) was a modular clandestine radio station, introduced in the late 1940s by HMGCC (now: GCHQ) at Hanslope Park (UK). It was intended for Special Forces (SF), Stay-Behind Organisations (Gladio), Intelligence Operations and the Diplomatic Wireless Service (DWS) [1].

The Mk.119 is highly modular and consists of three independant modules (transmitter, receiver and power supply) plus a case with spare parts. The set was either supplied as three individual units in water-tight containers (see below), or as the all-in-one unit shown on the right.

The unit shown here is called Mk. 119A and was probably built especially for use by the Army. The lid of the green wooden case is hinged. When it is opened (as shown in the image), the lid acts as a writing desk with the morse key bolted in place in the rear right corner.

The three individual modules are interconnected by cables and can easily be identified. The upper unit is the transmitter. It has a current meter in the top left corner. The unit at the center is the receiver with its wide 5-band scale drum. The unit at the bottom is the Power Supply Unit (PSU) which allows the radio set to be powered from any AC mains source (110 or 220V) or 6V DC.

The remaining space at the right is taken by the spare parts compartment that contains spare valves, cables and other accessories. A large aluminium panel, marked SPARES, prevents the accessories from falling out during transport.
  
Mk. 119A with opened front lid

Although the boxed Mk. 119A was intended for use by the UK Army, it was also used by the SAS (Special Forces) and as a stand-by set for British Embassies [2]. In the case of the SAS, it was often bolted onto a series 1 Landrover. The unit shown here is an ex-Embassy standby set.

Closed Mk-119A wooden case Mk. 119A with opened front lid Transmitter Receiver Power Pack Close-up of the morse key Ml. 119 headphones Opening the spare parts compartment Mk. 119A accessories and spare parts
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Closed Mk-119A wooden case
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Mk. 119A with opened front lid
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Transmitter
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Receiver
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Power Pack
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Close-up of the morse key
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Ml. 119 headphones
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Opening the spare parts compartment
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Mk. 119A accessories and spare parts

Standard version
The Mk. 119A shown above, is the only version in which all units are mounted together in a single case. With all other versions (Mk.119, Mk.119B and Mk.119RT) the three units are housed in water-tight containers, allowing the radio to be stored and hidden for long periods of time.

Each container was made of die-cast aluminium and was closed with a die-cast lid that was bolted ot the four corners. A rubber gasket rendered the containers water-tight, which was particularly useful for Stay Behind applications (Gladio). This version of the set is similar to the same-era RS-1 produced by the United States.

The image on the right was taken from the manual and shows the separate modules (after the aluminium lid has been taken off) plus the accessories. At the bottom left is the Power Supply Unit (PSU) with the transmitter on top.
  

The PSU containes a large transformer that is suitable for connection to the 110 and 220V AC mains. It also containes a vibrator, allowing the radio station to be powered from a single 6V DC battery source. The unit at the right is the receiver with its headphones on top. All necessary interconnection cables are in front of the units. The antennas are not shown in the image.

Mk. 119 manual Mk.119 original manual
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Mk. 119 manual
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Mk.119 original manual

Controls
The image below shows the location of the various controls and connections on the single-case Mk.119A. The radio set is shown here with the hinged front lid open, demonstrating that the lid can be used as a writing desk, whilst using the bolted-on morse key for sending messages.

Controls and connections on the Mk.119A



Parts
The complete set consists of three units, each of which is described in more detail below. The full circuit diagram is printed in the original user manual, which is available for download at the bottom of this page [A].

Power Pack (PSU)
Because of its weight, the PSU is located at the bottom of the stack. At the right is a 11-position rotary switch that allows the unit to be used on five different AC mains voltages, ranging from 110V to 240V (right half of the switch).

In the center position of the rotary switch, the unit is powered by an external 6V DC source. In this position the transformer acts as a power inverter and is used in combination with the built-in vibrator. The transformer can also be used to charge the external 6V battery, in which case the left half of the rotary switch is used.
  
Power Pack

All connections to the outside world and to the other units are at the front. In the unit shown here (Mk.119A) the receiver (REC) and transmitter (TRANS) are permanently wired. Next to these two connections are mains socket (AC MAINS) and the socket for the battery (6V BATT).

Transmitter (TX)
The transmitter is mounted at the top of the Mk.119A. It is crystal-based and can be used on all frequencies between 1.5 and 20 MHz, divided over 6 ranges that are selectable with a rotary switch at the center. The antenna is connected at the left, in parallel with the receiver.

A suitable crystal should be inserted into the socket at the bottom right, next to the built-in morse key. An external key can be connected to the 6.3 mm jack at the bottom center. In the Mk.119A (shown here) a fixed morse key is connected in parallel to this socket.
  
Transmitter

When transmitting, the meter is used in combination with the tuning knobs (AE TUNING and DRIVE TUNING) to obtain maximum output power. A separate 7-position switch is available for selecting the desired coupling for aerial loading. The transmitter is powered by two voltages supplied by the PSU: 380V (92mA) and 6.3V (1.5A) and produces a maximum output of 17W.

The circuit is built around two EF91 valves and a 2E26 power valve. A small NE48 neon valve is used for tuning. In the Mk.119RT, which is modified for phone (voice) transmission, two more valves (EL70 and EF72) are used for the modulator. The morse key is gone on that model.

Receiver (RX)
Contrary to the transmitter, the receiver is VFO-based. It is suitable for all frequencies between 0.5 and 20 MHz, divided over 5 bands. The band selector is at the bottom right and a wide drum-type scale is used for tuning. On the drum, each of the five bands has its own scale. A small window to the right of the drum, just above the tuning knob, is available for fine-tuning.

The 6-valve superheterodyne receiver is designed for the reception of telegrapy signals (CW), but is also capable of receiving phone, selectable by a 2-position switch at the right.
  
Receiver

The circuit consists of an HF Amplifier (EF92), a mixer (EF91), an oscillator (EF91), an IF amplifier (EF92), a second detector and AVC (Germanium Crystal) and a BFO (EF91). The IF frequency is at 455kHz which can be tuned ±2kHz by the BFO. According to the manual [A] the sensitivity is 90µV in the 0.5-2.3MHz range and 20µV on frequencies between 2.3 and 20MHz.

Spares
Hidden behind a tall metal panel at the right of the Mk.119A are the spares. This area is also used for storing the various cables and antennas when the radio is not in use. With the other versions of the set, the spares are usually stored in a separate water-tight container.

The image on the right shows some of the spares and cables as they were found in the SPARES compartment of the Mk.119A featured on this page. The cable at the top right is for connection to the mains. A full list of all accessories is given below.
  
Mk. 119A accessories and spare parts

Opening the spare parts compartment Mk. 119A spare parts compartment Mk. 119A accessories and spare parts 2E26 valve EF91/EF92 valves Additional spares in carton box Mains power lamp connector (Edison-screw) Retractable antenna
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Opening the spare parts compartment
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Mk. 119A spare parts compartment
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Mk. 119A accessories and spare parts
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2E26 valve
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EF91/EF92 valves
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Additional spares in carton box
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Mains power lamp connector (Edison-screw)
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Retractable antenna

Models
  • Mk.119
  • Mk.119A
  • Mk.119B
  • Mk.119RT
Parts list
Spares
  • Spare valves (2) EF91
  • Spare valves (2) EF92
  • Spare valve (1) 2E26
  • Vibrator SPC6
  • Headphones
  • Neon indicators
  • Phone plug
  • Fuses, 2 Amp
  • Fuses, 250 mA
  • Egg insulators
  • Small screwdriver
  • Insulated wire (2 mm)
  • Small pliers
  • E-screw Mains Adapter
  • 2-pin Continental Plug
  • Transmitting Key
  • Supply lead (Power Pack to Transmitter)
  • Supply lead (Power Pack to Receiver)
  • Battery cable
  • Main cable
  • Aerial interconnecting leads
Supplied separately
  • Varley Dry Accumulator, type 6.0/50H
  • Crystals
Documentation
  1. Original Manual, Transmitter and Receiver MARK 119
    User instructions and full circuit diagrams. Date unknown.
References
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004.

  2. Personal correspondence with a former owner of the Mk.119A featured on this page
    Crypto Museum #301633. 19 June 2002.
Further information
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Crypto Museum. Created: Sunday 15 April 2012. Last changed: Wednesday, 13 September 2017 - 19:26 CET.
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