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PD-5
Spy radio transmitter - wanted item

PD-5 is a valve-based crystal-operated short wave (HF) spy radio transmitter, developed around 1963 by an unknown country. The device consists of two identically sized units — a mains power supply unit (PSU) and the actual transmitter — and has externally fitted valves (tubes). The device shown here surfaced in China in 2023. Almost all parts are British, which suggests that it might have been built by a country with close ties to the UK, such as Singapore, Hong Kong, or India 1

The two units are interconnected by means of a 14-pin connector at the sides. The transmitter is built around three 6AQ5 valves that are installed into ceramic sockets at the rear of the enclosure. This was likely done to provide efficient cooling. One valve is used for the oscillator, whilst the other two – connected in parallel – are used as a Power Amplifier (PA). Recessed black knobs are present for adjusting the various tuned circuits.

The power supply unit (PSU) is internally wired for use on the Chinese 220V AC mains network, but could internally also be wired for 110V AC.
  
PD5 spy radio set

Both units are housed in a professionally molded black-eloxed aluminium enclosure and have a professionally built interior. It is likely that only a small quantity was made, probably no more than 50 units. The PD-5 was released around the same time as the slightly larger PD-3, which produces a higher output power and has a higher frequency range. It is likely that it used for agent-to-centre communications by a (currently unknown) state actor. The unit shown here was found in China and was obtained by a collector from a former Chinese intelligence warehouse [2]. It was probably confiscated by Chinese authorities in the late 1960s or early 1970s. The device shown here is currently held in the private collection of Reinhard Glogowski in Germany [1].

  1. From 1819 to 1965 (interrupted by WWII), Singapore was part of the British Empire.  Wikipedia
    From 1841 to 1997 (interrupted by WWII), Hong Kong was part of the British Empire.  Wikipedia

PLEASE HELP — The origin of this spy radio transmitter is currently unknown. We are also looking for circuit diagrams and any documentation that is related to this device, including stories of former users. Please help us to expand this page by providing additional information.  Contact us
PD5 power supply (left) and transmitter (right)
PD5 power supply (left) and transmitter (right)
PD5 spy radio set
PD5 spy radio set
Rear view
PD5 transmitter (without valves)
Transmitter - rear view
PD5 power supply
A
×
A
1 / 8
PD5 power supply (left) and transmitter (right)
A
2 / 8
PD5 power supply (left) and transmitter (right)
A
3 / 8
PD5 spy radio set
A
4 / 8
PD5 spy radio set
A
5 / 8
Rear view
A
6 / 8
PD5 transmitter (without valves)
A
7 / 8
Transmitter - rear view
A
8 / 8
PD5 power supply

Features
The image below shows a complete PD-5 transmitter setup. At the left is the power supply unit (PSU), marked PD5-P, with a 6J6 double triode valve installed in a ceramic socket at the top. At the rear is a 2-pin receptacle for connection of the 220V AC mains voltage. The 9-pin socket at the front (SK2) is for connection of a morse key or burst keyer. At the right is a 14-pin male plug (SK1) for connection of the PD5-T transmitter. The set is turned on with the MODE selector.

Click to see more

At the right is the transmitter, marked PD5-T. It is built around three 6AQ5 (EL90) valves that are installed in the ceramic sockets at the rear. At the left is a 14-pin socket (SK1) that mates with SK1 of the PSU. At the rear is a socket for connection of a wire antenna. Strangely, the device has no ground terminal for connection of a counterpoise. At the right is a 2 mm jack socket marked 'J'. The purpose of this socket is currently unknown.

After installing a suitable crystal in the XTAL socket of the transmitter, connecting a morse key to socket SK2 on the PSU and setting the MODE selector to TUNE, the indicator to the right of the meter (OSC IND) should light up. If it doesn't, select a different BAND and adjust the oscillator (OSC) for maximum light of the indicator. Next, switch to 'operate' (OPR), hold down the morse key and tune the rightmost two knobs (AMP TUNING and ANT TUNING) for a maximum reading on the meter. The device is now ready for operation. The MODE selector has three settings:

Mode
  • OFF
    Power off
  • TUNE
    Low power transmission (for tuning)
  • OPR
    Full power
Always on
Note that the oscillator is always on, and that the morse key turns the PA valves on and off. Some of the oscillator signal leaks out through the antenna, which means that at short distances from the transmitter, the oscillator signal can be picked up by a receiver, even when the morse key is not held down. This is potentially dangerous for the agent that uses it, as it allowes the device to be located more easily by means of Radio Direction Finding (RDF).

No receiver
No receivers were found with any of the surviving PD-5 units, which indicates that the device was either used for blind transmissions, in which a message was sent and no acknowledgement was needed, or that it was used in combination with a regular domestic short wave receiver that could be purchased freely in the host country without attracting attention.

PD5 transmitter - control panel
PD5 power supply - control panel
Mating connectors
Crystal fitted on the transmitter
Valve sockets
Valves
Mains power connected to the PSU
Antenna connected to the ANT socket
B
×
B
1 / 8
PD5 transmitter - control panel
B
2 / 8
PD5 power supply - control panel
B
3 / 8
Mating connectors
B
4 / 8
Crystal fitted on the transmitter
B
5 / 8
Valve sockets
B
6 / 8
Valves
B
7 / 8
Mains power connected to the PSU
B
8 / 8
Antenna connected to the ANT socket

Origin
The electrolytic capacitors inside the PSU were made by Plessey (UK) in April 1962, which means that the device was probably made in late 1962 or during the course of 1963. Most other parts are from the UK as well. The enclosures are professionally made with manufacturing methods that were commonly used by the USA for devices like RS-6, QRC-222 and CK-8 (GRA-71). The compact and modular construction allows the device to be hidden easily, and tells us that the device was most likely intended for agent-to-centre communication and/or espionage.

According to a former owner, the devices turned up in various places in China, including a city that used to have a large warehouse of the Chinese intelligence agency, some 30 years ago. It is likely that the devices had been captured in the preceeding years, and that after investigation they were stored in the warehouse. They have since landed in the hands of collectors. It is also likely that the Chinese used the design of this transmitter as the base for developing their own spy radio sets [2]. Such sets had a similar circuit, but were built with parts from the Soviet Union.

It is currently unknown by which country or intelligence service the PD-5 was developed, but it is clear that it was produced professionally by a country that had access to first class components, mainly from the UK, and to first class manufacturing methods. As the build style is completely different from the regular British spy radio sets, it seems more likely that it was made by a country near China, which had strong ties with the UK, such as Singapore, Hong Kong or India.


Parts
PD5-T transmitter
PD5-P power supply unit
PSU
Valves (tubes)
Plug-in quartz crystals
Morse key
Wire antenna
Transmitter   PD5-T
The PD5-T is a CW-only transmitter, suitable for sending messages in morse code, either with a morse key or with a medium speed burst keyer.

The device is housed in a black-eloxed molded aluminium enclosure that measures 120 × 67 × 43 mm and weights 430 grams without the valves. It is powered by the PD5-P power supply unit, which should be attached to its left side.

  
Transmitter - rear view

Power supply unit   PD5-P
The PD5-P power supply unit is also housed in a black-eloxed molded enclosure that measures 120 × 67 × 43 mm and weights 860 grams without the valve. A 6J6 valve should be installed into the ceramic socket at the top.

At the rear it has a two-pin receptacle for connection to the mains. It is connected to the transmitter via the 14-pin connector (SK1) at its right side. At the front is a socket (SK2) for connection of a morse key.

  
PSU - front view

Valves   tubes
The PD-5 was supplied with four valves (tubes) that were stowed separately to avoid damage. The smaller valve is a 6J6 double triode, which must be installed in the socket on the PSU.

The other three valves are all 6AQ5 (EL90) penthodes that must be installed in the three sockets at the rear of the transmitter. One of these valves is used in the oscillator, whilst the other two are used in the power amplifier (PA).

  
Valves

Crystals
The PD-5 transmitter must be operated with a suitable quartz crystal that should be installed in the socket marked XTAL. It accepts any crystal with 2.35 mm pins spaced at 12.34 mm, which includes HC-17/U, HC-6/L, CR-5/U, FT241 and FT-243 shapes. Such crystal were available from many WWII surplus stores at the time.

Experiments with the PD5 shown here, have revealed that it can be operated reliably between 3 and 16 MHz.

 Crystal shapes

  
Suitable crystals

Morse key
The transmitter is designed for the transmission of morse code signals, using CW. Basically any type of morse key — big or small — can be used. It is likely though, that the device was used with a small morse key, so that it could be hidden more easily.

The image on the right shows an example of such a key, which in this case was taken from a WWII field telephone.

  
Miniature morse key

Wire antenna
A suitable antenna should be connected to the socket marked ANT at the rear of the trans­mitter. In most cases, a long wire with a mini­mum length of 20 metres should be sufficient.

The image on the right shows an example of a suitable antenna wire. It is important that the antenna is hanging freely in the air and that the remote end is properly isolated from and trees or buildings in its vicinity.

  
Antenna wire with 3 mm plug

Valves
Transmitter with valves - rear view
12.187 MHz crystal
Suitable crystals
Crystal fitted on the transmitter
12.187 MHz crystal installed in the XTAL socket
Miniature morse key
Morse key connection to the PSU
Transmitter - rear view
PD5 transmitter (without valves)
PSU - front view
PSU - rear view
C
×
C
1 / 12
Valves
C
2 / 12
Transmitter with valves - rear view
C
3 / 12
12.187 MHz crystal
C
4 / 12
Suitable crystals
C
5 / 12
Crystal fitted on the transmitter
C
6 / 12
12.187 MHz crystal installed in the XTAL socket
C
7 / 12
Miniature morse key
C
8 / 12
Morse key connection to the PSU
C
9 / 12
Transmitter - rear view
C
10 / 12
PD5 transmitter (without valves)
C
11 / 12
PSU - front view
C
12 / 12
PSU - rear view

Interior
The PD-5 is a professionally manufactured device, with a black-eloxed molded enclosure that consists of two case shells. The shells are held in place by black metric recessed screws around the sides. After removing these screws, the case shells can be taken off, revealing the interior.

Inside the device is an aluminium frame with itegrated threaded nuts and sub-panels, to which all parts are mounted. The image on the right shows the frame as seen from the top. At the right is the antenna coil, which is wound around a rectangular pertinax rod. Behind the coil, the wiring of the two PA-valves is visible.

The left half of the unit contains the oscillator. Its XTAL socket is visible behind the meter. At the bottom side, the other side of the antenna coil is visible, together with the passive parts, the band selector and the tuning capacitors.
  
Transmitter interior - top view

The power supply unit is also housed in a black-eloxed molded aluminium enclosure, and is built in the same style as the transmitter. Inside the device is also an anluminium frame to which all parts are mounted. The transformer was probably purpose-made to fit the small enclosure.

Transmitter with removed case shells
Transmitter interior - top view
Transmitter interior - bottom view
Transmitter interior - top side
Transmitter interior - bottom side
Coil and band selector
Tuning capacitors
Transmitter detail
Transmitter detail
Valve socket wiring
Oscillator tuning knob removed
Manufacturing detail
Power supply with removed case shells
Power supply - top view
Power supply - top view
Power supply - top side
Power supply - bottom side
Plessey capacitors
PSU capacitor and two neon lamps
Transformer wiring
Interconnection detail
Fuse
PSU serial number (stamped into frame)
D
×
D
1 / 23
Transmitter with removed case shells
D
2 / 23
Transmitter interior - top view
D
3 / 23
Transmitter interior - bottom view
D
4 / 23
Transmitter interior - top side
D
5 / 23
Transmitter interior - bottom side
D
6 / 23
Coil and band selector
D
7 / 23
Tuning capacitors
D
8 / 23
Transmitter detail
D
9 / 23
Transmitter detail
D
10 / 23
Valve socket wiring
D
11 / 23
Oscillator tuning knob removed
D
12 / 23
Manufacturing detail
D
13 / 23
Power supply with removed case shells
D
14 / 23
Power supply - top view
D
15 / 23
Power supply - top view
D
16 / 23
Power supply - top side
D
17 / 23
Power supply - bottom side
D
18 / 23
Plessey capacitors
D
19 / 23
PSU capacitor and two neon lamps
D
20 / 23
Transformer wiring
D
21 / 23
Interconnection detail
D
22 / 23
Fuse
D
23 / 23
PSU serial number (stamped into frame)

Restoration
As the device featured here is not part of our collection — it was given on loan for a short period of time [1] — we have only tested it functionally, and have made no attempt to restore it. Power was applied with a VARIAC and was gradually raised over the course of 15 minues from 50V to 200V, in order to allow the electrolytic capacitors in the PSU to reform themselves somewhat.

It should be noted that the device was designed for use on 220V AC and that the mains voltage in continental Europe is now 240V AC. For this reason, we have set the VARIAC to a maximum of 200V for our tests. With a mains voltage below 180V, the oscillator became unstable.

The device was first tested with a 12.187 MHz crystal. After the valves had warmed up, appropriate settings of the BAND selector and the oscillator tuning (OSC) were sought and found. Note that the oscillator is always on, and that it can be picked up on a nearby receiver.
  
12.187 MHz crystal installed in the XTAL socket

For the experiment, we connected an improvised antenna — a 20 metre long wire — to the ANT terminal at the rear of the transmitter. The oscillator signal could easily be picked up by our general coverage communications receiver, even when a 30dB attenuator was inserted in the antenna path. A 100 Hz hum was noticable in the signal, indicating that the electrolytic capacitors inside the PSU have lost most of their capacity. It is up to the owner to replace them (or not).

For the next experiment, we connected an improvised morse key to the SK2 socket at the front of the PSU. Only two pins of this socket are used for the morse key (C and H). They connect the kathode of the PA valves to ground. When pressing down the morse key, the meter gives an indication of the antenna current. The rightmost two knobs (AMP TUNING and ANT TUNING) were then adjusted for a maximum meter reading.

The fact that the hum in the signal increases when the key is held down, is another indication that the electrolytic capacitors are worn out.
  
Morse key connection to the PSU

Apart from this, the transmitter works perfectly, some 60 years after it was made. We tested it with various crystals and it could be made to operate reliably between 3 and 16 MHz. A crystal at a frequency of 18.074 MHz worked, but produced an unstable signal. This probably means that this frequency it outside the transmitter's specified range. At the lower end of the spectrum, a frequency of 3 MHz appeared to be the lowest on which a stable signal could be obtained.

Test setip with crystal, morse key, antenna and mains connection
Mains power connected to the PSU
Antenna connected to the ANT socket
12.187 MHz crystal installed in the XTAL socket
Morse key connection to the PSU
Plessey capacitors
PSU capacitor and two neon lamps
E
×
E
1 / 7
Test setip with crystal, morse key, antenna and mains connection
E
2 / 7
Mains power connected to the PSU
E
3 / 7
Antenna connected to the ANT socket
E
4 / 7
12.187 MHz crystal installed in the XTAL socket
E
5 / 7
Morse key connection to the PSU
E
6 / 7
Plessey capacitors
E
7 / 7
PSU capacitor and two neon lamps

Connections
Inter-module connector   SK1
A set of 14-pin male/female connectors, both marked SK1, are used to connect the PSU and the transmitter. The male part at the right side of the PSU, mates with the female part at the left side of the transmitter. The image below show the pinout when looking into the male part on the PSU. The pinout of this connector is currently unknown.

  1. ?
  2. ?
  3. ?
  4. ?
  5. ?
  6. ?
  7. ?
  8. ?
  9. ?
  10. ?
  11. ?
  12. ?
  13. ?
  14. ?
Morse key   SK2
At the front of the power supply unit is a hexagonal socket for connection of a morse key or medium speed burst keyer (up to 300 WPM). It is a 9-pin Winchester M9-series socket, made by Electro Methods Ltd in the UK, of which only two pins are used (C and H). Shorting these two pins, enables the transmitter's PA stage. Below is the layout when looking into the socket.

  1. n.c.
  2. n.c.
  3. Morse key (1)
  4. n.c.
  5. n.c.
  6. n.c.
  7. n.c.
  8. Morse key (2)
  9. n.c.
Antenna   ANT
At the rear of the transmitter (PD5-T) is a 2 mm socket for connection of a wire antenna. In practice, a 20 m long wire would probably be sufficient. Strangely there is no connection for a counterpoise or ground wire. It is possible though that the capacitive coupling to the mains wiring provides a sufficient counterpoise in this case.

2 mm jack socket   J
At the right side of the transmitter is a socket for a 2 mm jack, similar to the ones that are commonly used with earphones. This socket is fully isolated from the chassis and has two connections, known as ring and tip. The function of this socket is currently unknown.

Mains
At the rear of the PSU is a two-pin receptacle for connection to the mains AC network. In this case, the PSU is wired for use on 220V AC, but the transformer can internally also be wired for use on 110V AC networks. Note that there is no ground connection (earth}. As a result, due to capacitive leakage inside the PSU, part of the mains voltage can be felt on the metal body of the PSU and the transmitter. It is therefore strongly discouraged to place one hand on the body of the transmitter, whilst operating the morse key with the other hand.


Specifications
  • Device
    Spy radio transmitter
  • Purpose
    Agent-to-centre communication
  • Model
    PD-5
  • Manufacturer
    unknown
  • Country
    unknown 2
  • Year
    ~ 1963
  • Valves
    3 × 6AQ5 (TX), 1 × 6J6 (PSU)
  • Frequency
    3 - 16 MHz
  • Bands
    5
  • Operation
    Crystal
  • Modulation
    CW (morse)
  • Output
    10W (est.)
  • Mains
    220V AC
  • Dimensions
    120 × 67 × 43 mm (each)
  • Weight
    430 g (Transmitter) 1
    860 g (PSU) 1
  • Quantity
    50 (est.)
  1. Without the valves (tubes).
  2. Probably Singapore, Hong Kong or India.

Parts origin
Parts from the following countries have been identified:

  • Valves
    3 × 6AQ5 (EL90), 1 × 6J6 (Mullard, UK)
  • Valve sockets
    ?
  • Meter
    ?
  • Capacitors
    Plessey (UK)
    Murata (Japan)
    Lemco (UK)
  • Resistors
    E-SIL Components (UK)
  • SK1
    14-pin male/female, SMRE 14S, Electro Methods Ltd. (UK)
  • SK2
    9-pin female connector M9S, Electro Methods Ltd. (UK)
Known serial numbers
Below are the surviving PD-5 units that have surfaced so far.

  • PD5-T-15 (10)
    Transmitter
    Reinhard Glogowski
  • PD5-P-26 (17)
    Power supply
    Reinhard Glogowski
It is believed that the designator consists of the model number (PD5), followed by the device type (T = transmitter, P = PSU), followed by the serial number. Given the low serial numbers found, and the absence of leading zeros, it seems likely that around 50 units were made. The number in brackets is the serial number that was found inside the device, engraved in the chassis.


References
  1. Reinhard Glogowski, PD5-P and PD5-T
    Crypto Museum, 25 April 2023.

  2. Anonymous, former owner of a PD5 in China
    Correspondence via [1], 26 April 2023.
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Crypto Museum. Created: Tuesday 25 April 2023. Last changed: Friday, 01 September 2023 - 08:59 CET.
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