Homepage
Crypto
Spy radio
Index
Glossary
USA
USSR
UK
Germany
Poland
Czechoslovakia
Hungary
Yugoslavia
OWVL
Stay-Behind
Receivers
Other
Burst encoders
Intercept
Covert
Radio
PC
Telex
People
Agencies
Manufacturers
• • • Donate • • •
Kits
Shop
News
Events
Wanted
Contact
About
Links
   Click for homepage
AP-5
Polish WWII spy radio set

The AP-5 was a valve-based spy radio transceiver, developed during WWII by Tadeusz Heftman of the Polish Military Wireless Unit (Polski Wojskowy Warsztat Radiowy) 1 in Stanmore (UK) [1]. It was introduced in 1944 and was intended for short-range morse code communications by SOE agents and Resistance Organisations in occupied Poland and in other European countries such as France.

The radio set is very similar to the AP-4 and it is believed that both sets are based on the earlier A-2 2 that was introduced in 1942. The radio is housed in a black wrinkle paint finished metal case with a hinged lid, that measures 28 x 21.5 x 9.5 cm and weights approx. 5 kg. It covers a frequency range of 2-16 MHz – divided over 3 bands – marked in white, yellow and red colours.

The image on the right shows a typical AP-5 set. It is built around five valves (tubes) that can be accessed from the control panel. This was done to prevent overheating and to simplify repairs.
  
AP-3 spy radio set

The radio consists of a crystal-driven transmitter, a tunable receiver and a mains power supply unit that is suitable for 120 and 220V AC networks, all mounted together behind a single front panel that can easily be removed from the case. Inside the top lid are the circuit diagram, and a receiver tuning table. Power sources should be connected to the standard octal socket. Note that the AP-5 doesn't have a send/receive switch like its predecessors, as it features break-in keying.

The case resembles a common toolbox of the era and was though to be more unobtrusive than the fairly large and heavy suitcases in which the regular British spy radio sets were housed during WWII. By using something that resembled a toolbox, it could easily be hidden in, say, a shed.

The transmitter has a buit-in morse key and allows an external one to be connected to the socket marked (K). The AP-5 was introduced around the same time as the BP-5, but has a lower ouput power and a built-in power supply unit. In total, 122 sets were built, but only a few were actually used in occupied Poland. The majority was used by the British Special Operations Executive (SOE).

  1. At the beginning of WWII, a number of Polish soldiers made their way to England, where they were allowed to setup and train their own Army units. Engineers who had escaped to the UK, were generally assigned to the Polish Wireless Unit in Stanmore (near London, UK).  More
  2. The A-2 was introduced in 1942. Like most other Polish A-series radio sets, it is based on the A-1 (Nelka), but has an extra IF-stage in the receiver, as a result of which is was much more sensitive.

Aluminium case with hinged lid Polish AP-3 spy radio set AP-3 spy radio set Top view Internal morse key Antenna tuning Valves (tubes) Receiver
A
×
A
1 / 8
Aluminium case with hinged lid
A
2 / 8
Polish AP-3 spy radio set
A
3 / 8
AP-3 spy radio set
A
4 / 8
Top view
A
5 / 8
Internal morse key
A
6 / 8
Antenna tuning
A
7 / 8
Valves (tubes)
A
8 / 8
Receiver

Controls
The diagram below shows the control panel of the device, which is normally placed horizontally on the table. A suitable AC mains power source should be connected to the octal socket at the rear edge. This socket can also be used to connect an (optional) external power inverter. A wire antenna and suitable counterpoise should be connected to the two terminals at the rear right.

AP-3 controls (top view)

The receiver is located in the front half of the device and has its controls nicely lined up at the front edge. A linear 0-100 scale behind a circular window provides an indication of the received frequency. It should be used in combination with the frequency table in the top lid of the case. The three receiver valves and the PSU's rectifier can be accessed directly from the control panel.

The rear half of the case contains the power supply unit (PSU) and the transmitter. The PSU consists of a large mains transformer (visible at the rear left) that is suitable for 120V and 220V AC, selectable with a screw-in voltage selector. The transmitter is crystal-driven and consists of a single horizontally mounted 6L6 valve that produces an output power between 8 and 12 Watts.

The transmitter is operated with the built-in morse key that is located at the front right edge of the control panel. If necessary, an external morse key can be connected to the socket marked (K) at the right (rear) edge. Note that there is no switch to select between transmit and receive, as the AP-5 features break-in keying. This means that the transmitter is activated by pressing the morse key, and that the receiver is enabled automatically when the morse key is released again.


Power sources
The AP-5 can be powered in three different ways:

  1. AC mains
    The AP-5 can be connected directly to the AC mains network in most countries, using the built-in power transformer. The transformer is suitable for either 120 or 220V AC, selectable with a screw-in terminal just below the power socket.

  2. 6V battery
    The AP-5 can be powered from a 6V DC source, such as the battery of a car, by using an external power inverter or vibrator pack between the battery and the AP-5. The vibrator converts the 6V DC source into alternating current (AC), which is then transformed to the desired 450V. The filaments of the valves are connected directly to the 6V DC source.

  3. LT and HT batteries
    In this case a 6V/20Ah battery is used for the filaments (LT), whilst three 120 or 150V batteries are connected in series to provide the 350-450V HT voltage.
Accessories
AC mains power cable
AC
DC power inverter
DC
Large plug-in crystals Headphones External morse key
Key
Instruction manual
AC mains cable
The AP-5 can be connected directly to the AC mains network, by means of the power cable shown in the image on the right. The AC mains is connected directly to two pins (2 and 5) of the octal plug. Note that an extra bridge wire should be present between pins 1 and 6.

 Pinout of the octal socket
  
Mains power cable

DC power inverter
Rather than directly from the mains network, it was also possible to power the AP-5 from a 6V DC source, such as the battery of a car, by using an (optional) external power inverter.

The power inverter should be connected to the same octal sockets as the AC mains cable. Check the pinout of this socket for the correct wiring.

No image available.
  

Crystals
The AP-5's transmitter accepts large crystals with a pin thickness of 2.2 mm and a distance of 19.5 mm. This can be the well-known black rectangular crystals, or (typically) the circular ones shown in the image on the right.

A suitable crystal should be inserted into the socket marked (Q), just below the mains voltage selector. The one shown here can be left installed in the socket when the top lid is closed.
  
Crystal

Headphones
The audio output of the receiver is suitable for connection of a pair of 2000Ω headphones, such as the ones shown in the image on the right.

The same headphones were also supplied with the Polish OP-3 receiver and the British Type A Mark 3 (A3) spy radio set.
  
Headphones

External morse key
For transmissions in morse code, a high quality built-in morse key is available at the front right of the control panel. It can be adjusted for the most comfortable operation.

In addition it is possible to connect an external morse key to the terminals marked (K) towards the rear of the right side of the control panel. Commonly used external keys were the small ones supplied with the British A-3 and B-2 sets (front), and the British Morse Key No. 2 (rear).
  
Morse key No. 2 Mark III (rear) and miniature A3 key (front)

Instruction manual
The AP-5 was usually issued with a brief set of instructions, typed on a set of A5 paper sheets. The instructions were available in several languages, including English, Polish and French.

In addition, a copy of the circuit diagram was commonly present inside the top lid of the case, along with a receiver frequency tuning table.

 Circuit diagram
 Receiver tuning table
 Operating Instructions (French)


  
Page 6 of French operating instructions

Mains power cable Mains power cable Mains transforer, power socket and voltage selector Inserting the power cord Mains power cord fitted Miniature morse key as supplied with the British A3 and B2 Morse key No. 2 Mark III Morse key No. 2 Mark III (rear) and miniature A3 key (front)
Crystal Crystal Crystal socket Placing a crystal 14.141 MHz crystal installed Circuit diagram Receiver frequency table Operating instructions (French)
B
×
B
1 / 16
Mains power cable
B
2 / 16
Mains power cable
B
3 / 16
Mains transforer, power socket and voltage selector
B
4 / 16
Inserting the power cord
B
5 / 16
Mains power cord fitted
B
6 / 16
Miniature morse key as supplied with the British A3 and B2
B
7 / 16
Morse key No. 2 Mark III
B
8 / 16
Morse key No. 2 Mark III (rear) and miniature A3 key (front)
B
9 / 16
Crystal
B
10 / 16
Crystal
B
11 / 16
Crystal socket
B
12 / 16
Placing a crystal
B
13 / 16
14.141 MHz crystal installed
B
14 / 16
Circuit diagram
B
15 / 16
Receiver frequency table
B
16 / 16
Operating instructions (French)

Interior
All parts, including the complete mains power supply unit (PSU), are mounted to the back of the control panel, which is mounted inside a black wrinkle paint finished aluminium case, by means of four recessed 2.5 mm screws. After removing these screws, the control panel can be extracted.

Once the control panel is extracted from the case, it can be turned over to reveal the interior, as shown in the image on the right. The large black mains transformer is clearly visible in one of the corners, whilst the antenna coil and its selector are visible at the front of the image, along with two large adjustable capacitors.

At the center are the solder terminals of the sockets of the four valves that are mounted straight up. The bright aluminium can in the rightmost corner contains a series of capacitors that are used for stabilisation of the HT voltage.
  
Interior, seen from the rear right

The transmitter consists of an oscillator with a 6L6 valve (tube), which is mounted horizontally. The 6L6 is keyed by connecting the cathode to ground when the morse key is depressed. An interesting feature of this radio — that is not found on earlier models — is that it uses break-in keying. The receiver consists of four valves: a 6K8 that is used as the oscillator/mixer followed by 6SJ7 IF-amplifier and finally a 6SC7 double-triode that is used as detector and as audio amplifier.

The AP-5 transceiver is extremely well built as can be seen in the images. Despite the fact that the unit shown here is well over 70 years old, it is remarkable good condition.

Interior seen from the right front Interior, seen from the rear right Interior, seen from the rear left Interior, seen from the left front Antenna coil Mains transformer Valve sockets (solder side) Detail
C
×
C
1 / 8
Interior seen from the right front
C
2 / 8
Interior, seen from the rear right
C
3 / 8
Interior, seen from the rear left
C
4 / 8
Interior, seen from the left front
C
5 / 8
Antenna coil
C
6 / 8
Mains transformer
C
7 / 8
Valve sockets (solder side)
C
8 / 8
Detail

Connections
Power socket
The AP-5 can be connected directly to the AC mains, but care has to be taken to ensure that it is configured for the correct voltage. The mains AC voltage should be connected to the 8-pin octal socket at the upper edge of the control panel. The diagram below shows the pin-out of this socket, when looking into the socket from the top of the device. Note that this is different from the circuit diagram (which shows the solder side of the socket). As the socket can also be used for the connection of the DC power inverter (vibrator pack), a wire link has to be installed in the connector (between pin 1 and 6) in order to pass through the LT voltage for the filaments.

  1. LT in 6V
  2. Mains
  3. not connected
  4. HT (+) 350 to 450V
  5. Mains'
  6. LT out 6V (AC)
  7. Ground (LT and HT)
  8. not connected
Mains cable
The diagram below shows the pinout of the power socket when connecting the device to the AC mains. Note that the wire link between pins 1 and 6 is mandatory in order to pass the LT voltage through. Before connecting to the mains, ensure that the correct AC voltage is selected.

  1. Interconnected with 6
  2. Mains
  3. not connected
  4. not connected
  5. Mains'
  6. Interconnected with 1
  7. not connected
  8. not connected
Power inverter
The diagram below shows which pins of the power socket are used when the radio is powered from a 6V DC source, such as the battery of a car, using the (optional) vibrator pack. The 6V from the battery is used directly for the filaments.

  1. (+) LT 6V
  2. not connected
  3. not connected
  4. (+) HT 350 to 450V
  5. not connected
  6. not connected
  7. 0V Ground (common for LT and HT)
  8. not connected
Battery cable
The AP-5 can also be powered entirely from batteries (LT), in which case a 6V/20Ah source should be used for the filaments, whilst the 350-340V HT voltage is provided by three 120 or 150V batteries connected in series.

  1. (+) LT 6V
  2. not connected
  3. not connected
  4. (+) HT 350 to 450V
  5. not connected
  6. not connected
  7. 0V Ground (common for LT and HT)
  8. not connected
Other terminals
  • 1
    Antenna
  • 2
    Counterpoise
  • Q
    Crystal socket (quarz)
  • T
    Headphones (telephone)
  • K
    External morse key
6L6 transmitter valve
  1. Shield
  2. Filament (LT)
  3. Anode
  4. Grid 2
  5. Grid 1
  6. pin missing
  7. Filament (LT)'
  8. Kathode, gate 3
Technical specifications
  • Output power
    8-12W
  • Sensitivity
    2µV
  • Frequency range
    2-16 MHz
  • Bands
    see below
  • IF frequency
    1.5 MHz
Bands
  • 2-4 MHz
  • 4-8 MHz
  • 8-16 MHz (transmitter: 7-16 MHz)
Valves   Tubes
  • 6L6
    Oscillator/transmitter
  • 6K8
    Mixer/oscillator
  • 6SJ7
    IF amplifier
  • 6SC7
    Detector/AF amplifier
  • 5Z4
    Rectifier (PSU)
Documentation
  1. Polski Wojskowy Warsztat Radiowy, Transmetteur Instruction
    AP-5 operating instructions (French). 11 pages (DIN A5-L).
References
  1. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004
Further information
Any links shown in red are currently unavailable. If you like the information on this website, why not make a donation?
Crypto Museum. Created: Sunday 24 September 2017. Last changed: Tuesday, 26 September 2017 - 08:44 CET.
Click for homepage