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Type 3 Mk. II (B2)
British WW-II clandestine radio

The British Type 3 Mk. II, commonly known as the B2, is arguably the most well known spy radio set used during WWII. It was designed in 1942 by (then) Captain John Brown at SOE Station IX, and manufactured by the Radio Communication Department of the SOE at Stonebridge Park. The set was issued to agents and resistance groups and special forces operating on occupied territory. The official designator is Type 3 Mk.II but the radio is also known as Type B Mk.II, B.II and B2.
The B2 came in two flavours. The initial version came in an unobtrusive leather suitcase that allowed an agent to travel inconspicuously. This is the most well-known variant. Later in the war it was dropped by parachute in two water-tight containers, that were more suitable for use by resistance groups operating in the field.

The image on the right shows the Type 3 Mk.II in its original brown/red leather suitcase, which can easily be recognized as it has three locks at the front: two simple locks at the sides, and one that can be locked with a key at the center.
Operating the Type 3 Mark II (B2)

The radio set consists of three units: a receiver (RX), a transmitter (TX) and a Power Supply Unit (PSU), plus a box with spares and accessories. When mounted in the suitcase, the transmitter is located at the center top, with the receiver mounted below it. The PSU is at the right in such a position that the two other units can be connected to it. The spares box is generally positioned at the left, with the Morse key mounted on its lid. When operating the B2, the lid of the spares box should be placed on the table, so that the Morse key can be operated.

The Type 3 Mk.II (B2) was relatively small for its day and produced an HF output power of 20 Watts. Nevertheless, it was too big to carry around unobtrusively especially when travelling by public transport. For this reason, later radios, such as the Model A Mk. III (A3) were made much smaller, albeit with a limited frequency range (3.2-9.55 MHz) and reduced power output (5 Watt).
Red/brown leather case with 3 locks Front view of the suitcase Main lock at the center Snap-on locks at the sides Type 3 Mark II in original suitcase Operating the Type 3 Mark II (B2) Close-up of the tank coil and the tuning dials Antenna wire on Paxolin card
Original morse key Close-up of the original morse key Top view at the controls

The diagram below gives a clear view of the controls, as seen from the top. The case has four compartments; one for each of the modules. At the left is the spares box or accessory kit, here shown without its lid. The spares box has two compartments: one for the spare valves and one for the accessories. The PSU is at the right, with the AC and DC connections at the right edge.

Clear view at the controls of the B2. Click for a larger view.

The two compartments at the center hold the transmitter (top) and receiver (bottom), that both are connected to the PSU by means of a 6-pin plug. The PSU can be powered from the AC mains or from a 6V DC source. The headphones are connected to the socket marked PHONES L.R. at the front. A suitable telegraph key should be connected to the socket marked KEY on the transmitter.

The transmitter further needs a crystal at the top right and a tank coil at the left, just below the meter. The antenna and ground should be connected to the two screw terminals at the top left of the transmitter. A short green wire with a banana-plug connects the antenna to the receiver.
Suitcase version
The most well-known appearance of the B2 is the suitcase version, but hardly any surviving B2 is found in its original red leather suitcase. In fact, the B2 was delivered in a variety of different suitcases, ranging from sturdy leather cases to simple cardboard and even wooden variants.
The original leather case is easily recognised, as it has three locks rather than the usual two. In many cases, the original case was swapped for a more common two-lock version, as it was easily recognised by the enemy. Later in the war, cheaper cardboard suitcases were used instead.

Louis Meulstee's excellent book Wireless for the Warrior, volume 4 [1] even shows an example of a wooden carpenter's toolbox in which a B2 is fitted. The dimensions of the suitcase are pretty standard for the era. The image on the right shows a B2 in a simple cardboard suitcase.
Type 3 Mk.II (B2) in cardboard suitcase

Another reason for the many different types of cases is that, after the war, many container versions (see below) were converted into suitcase versions by collectors. Even today, collectors often move the individual parts from the containers into a suitable suitcase. Given the fact that the dimensions of the suitcase were rather standard, it is relatively easy to find one, even today.
Closed B2 cardboard suitcase Type 3 Mk.II (B2) in cardboard suitcase B2 in suitcase Crystal plugged into the transmitter Close-up of the alternative 6V DC power cable Close-up of the mains connector Close-up of an installed tank coil Spare valves
Close-up of the spares box Coils and mains adapter in front of a B2 Close-up of the alternative morse key Narrow storage compartment for the power cables Mains power lead 6V power lead B2 headphones B2 morse key

Container version
Although the suitcase version is arguably the most popular one amongst collectors, it was by no means the most popular during the war. Many B2 spy radio sets were brought into an occupied country, by means of air droppings or over sea. Most suitcases would not survive such a trip.
Furthermore, many of the radio stations were intended for use by the resistance, in which case they often had to be stored in moist places, such as a forest or a farm. In such cases, a suitcase was not the most appropriate packaging.

As the war progressed, more and more sets were supplied in two water-tight metal containers with sufficient padding to survive a dropping. Several brackets were present at the sides of these containers, allowing them to be attached to a parachute or to carry them at the back of the agent by using appropriate webbing.
The two containers side by side, connected via 2 cables

The transmitter and receiver were packed together in a container that was marked 'G'. A second - slightly smaller - container, held the power supply unit and the spares box. It was marked with the letter 'H'. After removing the lids, the two containers would be placed side-by-side and the transmitter and receiver were connected to the power supply unit. A nice example is in [1].

The example shown above is from the collection of Museum Jan Corver in Budel (Netherlands). The accessory box is missing from this one, and has been replaced by a carton box, which is visible at the right. The marking 'G' is visible at the front of the leftmost container.
The two containers side by side, connected via 2 cables Container 'G' with transmitter and receiver Container 'H' with PSU and spares (spares box here replaced by brown carton) Close-up of the PSU Accessories Morse key Headphones Front view of the container version

Transmitter (TX)
The transmitter is usually mounted above the receiver and is the larger of the two. It is crystal operated, produces an RF output power of approx. 20 Watts and is suitable for CW only (Morse). Furthermore, the full frequency coverage is divided over 4 ranges (or actually 8), each of which needs its own tank coil (with A and B side) to be plugged into a 6-pin socket below the meter.
Furthermore, the appropriate PA grid frequency needs to be selected with the WAVEBAND switch (7 steps) and the optimum fundamental crystal frequency with the CRYSTAL selector (6 steps). The circuit is based on just two valves: an EL32 for the oscillator and a 6L6 for the PA. Provisions are made to allow the crystal to be use in fundamental, second or third harmonic mode.

The image on the right shows the transmitter after is has been taken out of its protective casing. The flying lead is the power cord that is normally connected to the TX-bus of the PSU.
TX unit

For the transmitter, external tank coils are used. Each coil is suitable for a limited frequency range and should be inserted into a 6-pin socket just below the meter. In order to cover the entire frequency span, four coils are supplied (L1 to L4) that each have two sides (A and B). Besides the correct coil, the WAVEBAND selector should be used to select the appropriate range.
The following frequency ranges are available:
  • L1-A: 3.0 - 4.0 MHz
  • L1-B: 3.75 - 5.25 MHz
  • L2-A: 4.5 - 6.25 MHz
  • L2-B: 5.5 - 7.5 MHz
  • L3-A: 6.5 - 9.0 MHz
  • L3-B: 7.0 - 10.0 MHz
  • L4-A: 9.0 - 13.0 MHz
  • L4-B: 12.0 - 16.0 MHz
The four tank coils

TX unit TX-unit interior TX-unit interior TX interior TX interior detail TX interior detail TX interior detail TX interior detail
The four tank coils Tank coil L3 B2 close-up of the Transmitter and Receiver Coils and mains adapter in front of a B2

Receiver (RX)
The receiver is usually mounted below the transmitter and is the smaller of the two. The entire coverage from 3.1 to 15.2 MHz is divided over three ranges that are selected by the WAVEBAND-selector at the left.

To the right of the band-selector is the tuning knob that has two wheels: one for coarse and one for fine tuning. Above the tuning knob is the scale readout that has a magnifying plexiglass lens over it.

RX-unit RX-unit interior RX-unit interior RX-unit interior Close-up of the RX tuning scale

Power Supply (PSU)
The Power Supply Unit (PSU) is normally mounted to the right of the transmitter and receiver in such a position that the two modules can be connected directly to the corresponding power socket at the front. It allows the radio set to be powered from the mains and from a 6V battery.
The connections for the external power supply (mains and 6V) are both at the right. The upper two pins (the thick ones) are for connection to a 6V DC source. The (+) terminal is marked with a red dot. The lower two pins (the thin ones) can be used for connection to the AC mains.

In order to avoid mistakes, it is not possible to use both power sources simultaneously. A large selector-plug is used to select between mains and battery. Above this selector are four selector plugs that are used to select the appropriate mains voltage by adding the indicated values.
PSU interior

Unfortunately, the B2 needs its own non-standard proprietary plugs, which are often missing from the surviving sets. The 6V DC plug can easily be replaced with a domestic (mains) plug from the 1960s and 70s. It fits nicely over the thick pins and can safely be used, but you would need to mark the (+) terminal of the connector, preferrably with a red dot like on the PSU itself.
The transformer inside the PSU is suitable for virtually all mains voltages in the world, but it is also used when powering the B2 from a 6V DC battery, in which case a vibrator is used to convert the 6V DC voltage into an AC voltage. A spare vibrator is usually present inside the PSU.

Unfortunately, in most original vibrators, rubber was used as an insulating material and its sulfur vapors have often ruined the vibrator contacts beyond repair. In such cases the original vibrator is best replaced by a solid state version, that can easily be (home) made from a few components.
Empty socket for spare vibrator

Caution: please note that the PSU works with high - potentially lethal - voltages. Be careful when connecting the set to the mains and be very careful when touching metal parts whilst the set is connected to the mains. You should only experiment if you know what you are doing.
B2 cased Power Supply Unit. Note the two ground strips at the side (for TX and RX grounding). PSU interior PSU interior with the two vibrators at the right Empty socket for spare vibrator Power terminals. Left (tick pins) 6V DC, right (thin pins) mains AC. AC voltage selector plugs and MAINS/BATTERY selector Power sockets for TX and RX Improvised 6V DC connection

The PSU supplies the following voltages for the receiver:
  • 230V (28mA)
  • 6.3V (1.2A) filaments
  • -12.5V (bias)
The following voltages are supplied to transmitter:
  • 500V (60mA)
  • 230V (18mA)
  • 6.3V (1.1A) filaments
Spares kit
The spares kit, also known as the accessories box, is a high storage box with a removable lid, approx. the same size as the power supply unit. In most cases, the lid has two mounting holes for the Morse key, but with some B2 sets, the lid had a mounting bracket for a slide-on Morse key.
Inside the spares kit are some of the accessories and spare. In most cases, the box is divided into two compartments: a smaller one that contains the spare valves, and a larger one containing all the other parts, such as the band coils, the Morse key (when in storage), spare plugs, spare fuses, mains adapters, etc. (full list below).

Spares kits are often missing from the surviving B2 sets. Luckily, some collectors have been able to make good looking reproduction parts that can hardly be distinguised from the original, greatly increasing the value of an incomplete set.
Spare valves

According to the manual, the following parts should be present:
  • 4 Transmitter coils
  • 1 6L6G valve
  • 1 EL32 valve
  • 1 7Q7 valve
  • 1 7R7 valve
  • 5 Fuses, 10 Amp
  • 5 Fuses, 500 mA (+ 2.1 Amp fuses)
  • 1 Telegraph key
  • 1 Pair headphones
  • 1 Mains lead
  • 1 Battery lead
  • 2 Continental plug pins
  • 1 Adapter 2 pin bayonet cap
  • 1 Adapter Edison screw
  • 1 Aerial wire (100 ft)
  • 1 Earth wire (10 ft)
  • 1 Screwdriver
  • 1 Operating chart (in cover)
Telegraph key
The B2 was supplied with a variety of different Morse keys. The most common one in the small British telegraph key shown in the image on the right. It was usually mounted on top of the metal lid of the accessory box (spares container).

The same one was later used with the Type A Mark III (A3). Other keys, such as the ones in the images below, were also used and/or supplied with the B2 radio. Many operators had their own preference for a specific (external key).
Original morse key

Original morse key Close-up of the original morse key Morse key Close-up of the alternative morse key

Operating instructions
The B2 originally came with a small instruction booklet that was folded to an envelope. The booklet contains 14 extremely thin printed pages that are slightly larger than DIN A4. As the last page contains calibration charts, each B2 spy set came with its own personalized manual.

The image on the right shows the Operating Instructions of the B2 with serial number 42796 that is part of the collection of Museum Jan Corver in Budel (Netherlands). A high-quality scan of this extremely rare booklet is available for download below [2].
B2 instruction booklet

B2 instruction booklet Opening the instruction booklet B2 instruction booklet (open) B2 instruction booklet (page 1) Very thin pages

Technical specifications
  • Receiver frequency range: 3.1-15.2 MHz
  • IF frequency: 470 kHz
  • AF output: 50mW into 120Ω
  • Sensitivity: 1-3 µV @ 10 mW (CW)
  • Transmitter frequency coverage: 3-16 MHz (4 ranges)
  • RF output: 20 W (fundemental and 2nd harmonic), 16-20 W (3rd harmonic)
  • Antenna: 18 meter wire
  • Ground: 3 meter wire
  • AC power supply: 97-140V and 190-250V (40-60Hz)
  • Power consumption: 27W (RX) and 57W (TX)
  • DC power supply: 6V, 4.5A (RX) and 9.5A (TX)
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  2. Type 3 MK.II Operating Instructions
    S/N: 42796. 13 July 1944. Scanned by Crypto Museum. 1

  3. Type 3 Mk.II CIrcuit Diagram
    Part of [2]. Scanned in black & white. 1

  4. Ken Brooks, Special Operations Executive - The B2 spy set
    The VMARS Newsletter, Issue 41, pp. 8-10.

  1. B2 User Manual kindly supplied by Museum Jan Corver.

Further information

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Crypto Museum. Last changed: Wednesday, 05 August 2015 - 11:07 CET.
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