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PD-3
Spy radio transmitter

PD-3 is a valve-based crystal-operated short wave (HF) spy radio transmitter, developed around 1962 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 Amphenol connector at the sides. The transmitter is built around two 5B/255M (CV391) 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. The other one is used as a Power Amplifier (PA). Recessed black knobs are present for adjusting the various tuned circuits/bands.

The power supply unit (PSU) can be used on the 100, 110 or 220V AC mains network. A later variant was for 190, 205, 220, 230 and 240V.
  
PD3 spy radio set (later version)

Both units are housed in a professionally molded black-eloxed aluminium enclosure and have a professionally built interior. Two batches were probable made: 50 units in 1962 and another 50 in 1966. The PD-3 was released around the same time as the smaller PD-5, which has a less flexible PSU and a lower frequency range. It is likely that these sets were used for agent-to-centre communication by a (currently unknown) state actor. The units shown here were found in China and were obtained by a collector from from a former Chinese intelligence warehouse [2]. It is likely that they were confiscated by Chinese autorities in the late 1960s or early 1970s.

  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
PD3 spy radio set (later version)
PD5 transmitter with valves installed
Transmitter without valves
PD3 power supply unit (later version)
PD3 power supply unit with valve installed
Carton box with 28 crystals
Miniature morse key
Antenna wire with 3 mm plug
A
×
A
1 / 8
PD3 spy radio set (later version)
A
2 / 8
PD5 transmitter with valves installed
A
3 / 8
Transmitter without valves
A
4 / 8
PD3 power supply unit (later version)
A
5 / 8
PD3 power supply unit with valve installed
A
6 / 8
Carton box with 28 crystals
A
7 / 8
Miniature morse key
A
8 / 8
Antenna wire with 3 mm plug

Features
The image below shows a complete PD-3 transmitter setup. At the left is the transmitter as seen from the rear. Two 5B/255M (CV391) valves are sticking out: one for the oscillator and one for the PA. An antenna should be connected at one of the short sides. The frequency is determined by a crystal that must be installed in the XTAL socket on the top surface. At the right is the power supply unit (PSU). It is connected to the transmitter via a 14-pin Amphenol 57-series connector.

PD-3 Mark I, consisting of PD3-T transmitter (left) and PD3-P power supply unit. Probably 50 units made around 1962.

After selecting the desired mains voltage with the rotary switch on the top surface of the PSU, the two-pin receptacle at the rear should be connected to the mains. The Mark I version of the PSU (serial numbers 1 to 50) is suitable for the 100, 110 and 220V AC mains network. Power is enabled with the rotary selector marked OFF/LO/HI at the top surface. It allows the transmitter to be used in LOW or HIGH power mode. Note that the morse key should be connected to the PSU.

PD-3 Mark II, consisting of PD3-T transmitter (left) and PD3-P power supply unit. Probably 50 units made around 1966.

A later version of the PSU – probably serial numbers from 51 onwards – have a slightly different layout. The circular mains voltage selector has been omitted from the top surface, and is repaced by a configurable pin at the short side. This pin can be installed in one of five sockets, allowing a mains voltage of 190, 205, 220, 230 and 240 V AC. Note that the rotary power switch has been replaced by an ON/OFF slide switch. It is unclear whether this is an original factory-installed power switch or an aftermarket repair or modification. It does not have a low power setting.

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-3 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.

14-pin connectors (Amphenol 57-series)
Mains power selector
Configuring the device the 240V AC mains
Crystal installed in the XTAL socket
Antenna
PD3 connected to the mains
B
×
B
1 / 6
14-pin connectors (Amphenol 57-series)
B
2 / 6
Mains power selector
B
3 / 6
Configuring the device the 240V AC mains
B
4 / 6
Crystal installed in the XTAL socket
B
5 / 6
Antenna
B
6 / 6
PD3 connected to the mains

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-3 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
PD3-T transmitter
PD3-P power supply unit
PSU
Valves (tubes)
Plug-in quartz crystals
Morse key
Wire antenna
Transmitter   PD3-T
The PD3-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 152 × 87 × 43 mm mm and weights 630 to 646 grams 1 without the valves. It is powered by the PD3-P power supply unit, which should be attached to its left side.
  
Transmitter without valves

  1. Depending on the version (Mark I or Mark II).

Power supply unit   PD3-P
The PD3-P power supply unit is also housed in a black-eloxed molded enclosure that measures 152 × 87 × 43 mm and weights 1456 or 1418 grams 1 without the valve. A 6J6 valve should be installed into the ceramic socket at the rear.

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.
  
PD3 power supply unit (later version)

  1. Depending on the version (Mark I or Mark II).

Valves   tubes
The PD-3 was supplied with three 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 two valves are both 5B/255M (CV391) that must be installed in the two sockets at the rear of the transmitter. One of these valves is used in the oscillator, whilst the other one is used as a power amplifier (PA).

  
PD3 valves

Crystals
The PD-3 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 crystals were available from many WWII surplus stores at the time.

The PD-3 shown here came with the 28 crystals shown in the image on the right, each of which could be used for three different frequencies.

 Crystals supplied with PD-3
 Crystal shapes

  
Click to see more

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 side 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. Note that the PD-3 does not have a counterpoise connection.

  
Antenna wire with 3 mm plug

PD3 valves
Carton box with 28 crystals
Quarz crystal
Miniature morse key
Morse key connection to the PSU
C
×
C
1 / 6
PD3 valves
C
2 / 6
Carton box with 28 crystals
C
3 / 6
3 / 6
C
4 / 6
Quarz crystal
C
5 / 6
Miniature morse key
C
6 / 6
Morse key connection to the PSU

Interior
The PD-3 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 front right is the antenna coil, which is wound around a ceramic cylinder. Towards the rear panel is the wiring of the two valves.

The left half of the unit contains the oscillator. Its XTAL socket is visible at the top left. At the bottom side, the other side of the antenna coil is visible, together with the passive parts, the band selector and the two large tuning capacitors.
  
PS3 transmitter (early version) interior

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 aluminium frame to which all parts are mounted. The transformer was probably purpose-made to fit the small enclosure.

PS3 transmitter (early version) interior
PS3 transmitter (early version) interior
PS3 transmitter (early version) interior
PS3 transmitter (early version) interior
PS3 transmitter (early version) interior
PS3 transmitter (early version) interior - top view
PS3 transmitter (early version) interior - wiring
PS3 transmitter (early version) interior - bottom view
PD3 power supply unit (early version) interior
PD3 power supply unit (early version) interior
PD3 power supply unit (early version) interior
PD3 power supply unit (early version) interior - top view
PD3 power supply unit (early version) interior - bottom view
Electrolytic capacitors
Transformer detail
Internal morse key and external morse key socket
PD3 (later version) interior
PD3 (later version) interior
PD3 (later version) interior
PD3 (later version) interior
PD3 (later version) interior
PD3 (later version) interior - top view
PD3 (later version) interior - bottom view
PD3 (later version) wiring
PD3 power supply unit (later version) interior
PD3 power supply unit (later version) interior
PD3 power supply unit (later version) interior
PD3 power supply unit (later version) interior
PD3 power supply unit (later version) interior
PD3 power supply unit (later version) interior - top view
PD3 power supply unit (later version) interior - bottom view
Configuring the voltage
D
×
D
1 / 32
PS3 transmitter (early version) interior
D
2 / 32
PS3 transmitter (early version) interior
D
3 / 32
PS3 transmitter (early version) interior
D
4 / 32
PS3 transmitter (early version) interior
D
5 / 32
PS3 transmitter (early version) interior
D
6 / 32
PS3 transmitter (early version) interior - top view
D
7 / 32
PS3 transmitter (early version) interior - wiring
D
8 / 32
PS3 transmitter (early version) interior - bottom view
D
9 / 32
PD3 power supply unit (early version) interior
D
10 / 32
PD3 power supply unit (early version) interior
D
11 / 32
PD3 power supply unit (early version) interior
D
12 / 32
PD3 power supply unit (early version) interior - top view
D
13 / 32
PD3 power supply unit (early version) interior - bottom view
D
14 / 32
Electrolytic capacitors
D
15 / 32
Transformer detail
D
16 / 32
Internal morse key and external morse key socket
D
17 / 32
PD3 (later version) interior
D
18 / 32
PD3 (later version) interior
D
19 / 32
PD3 (later version) interior
D
20 / 32
PD3 (later version) interior
D
21 / 32
PD3 (later version) interior
D
22 / 32
PD3 (later version) interior - top view
D
23 / 32
PD3 (later version) interior - bottom view
D
24 / 32
PD3 (later version) wiring
D
25 / 32
PD3 power supply unit (later version) interior
D
26 / 32
PD3 power supply unit (later version) interior
D
27 / 32
PD3 power supply unit (later version) interior
D
28 / 32
PD3 power supply unit (later version) interior
D
29 / 32
PD3 power supply unit (later version) interior
D
30 / 32
PD3 power supply unit (later version) interior - top view
D
31 / 32
PD3 power supply unit (later version) interior - bottom view
D
32 / 32
Configuring the voltage

Connections
Inter-module connector   SK1
A set of 14-pin male/female connectors, marked SK1 and PL1 respectively, 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.  Datasheet

  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. 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 {side of the transmitter (PD3-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 top surface 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-3
  • Manufacturer
    unknown
  • Country
    unknown 1
  • Year
    ~ 1962, 1966
  • Valves
    2 × 5B/255M (CV391), 1 × 6J6 (PSU)
  • Frequency
    6 - 27 MHz
  • Bands
    5
  • Operation
    Crystal
  • Crystals
    28 (see below)
  • Modulation
    CW (morse)
  • Output
    30 W (est.)
  • Dimensions
    152 × 87 × 43 mm (each)
  • Quantity
    100 (est.): 50 in 1962, 50 in 1966
  1. Probably Singapore, Hong Kong or India.

Mark I
  • Mains
    100, 110, 220V AC
  • Weight 1
    Transmitter: 630 g
    PSU: 1456 g
  • S/N
    01-50
  • Quantity
    50 in 1962 (est.)
  1. Without the valves (tubes).

Mark II
  • Mains
    190, 205, 220, 230, 240V AC
  • Weight 1
    Transmitter: 646 g
    PSU: 1418 g
  • S/N
    51-99
  • Quantity
    50 in 1966 (est.)
  1. Without the valves (tubes).

Crystals
The PD-3 set was supplied with 28 crystals, each of which can be used on the fundamental frequency (f1), the second overtone (f2) or the third overtone (f3). All crystals are of the FT-243 (CR-6B/U) type and come from US Army surplus. They are labelled with a sequential number (1-28) on the top, and with the three possible frequencies (f1, f2 and f3) at the rear.

Nr. f1 (MHz) f2 (MHz) f3 (MHz)   Nr. f1 (MHz) f2 (MHz) f3 (MHz)
1 6.175 12.350 18.525   15 7.425 14.850 22.275
2 6.2733 12.5466 18.8199   16 7.5733 15.1466 22.7199
3 6.340 12.680 19.020   17 7.675 15.350 23.025
4 6.4733 12.9466 19.4199   18 7.710 15.480 23.220
5 6.525 13.050 19.575   19 7.875 15.750 23.625
6 6.6066 13.2133 19.8200   20 7.975 15.950 23.925
7 6.700 13.400 20.100   21 8.0733 16.1466 24.2199
8 6.775 13.550 20.325   22 8.175 16.350 24.525
9 6.8733 13.7466 20.6199   23 8.2066 16.4133 24.6200
10 6.940 13.880 20.820   24 8.325 16.650 24.975
11 7.0733 14.1466 21.2199   25 8.475 16.950 25.425
12 7.175 14.350 21.525   26 8.575 17.150 25.725
13 7.250 14.500 21.750   27 8.625 17.250 25.875
14 7.3733 14.7466 22.119   28 8.750 17.500 26.250
Parts origin
Parts from the following countries have been identified:

  • Valves
    2 × 5B/255M (CV391), STC (UK)
    1 × 6J6, Mullard (UK)
  • Valve sockets
    ?
  • Meter
    ?
  • Capacitors
    Plessey (UK)
    Murata (Japan)
    Lemco (UK)
  • Resistors
    E-SIL Components (UK)
  • SK1
    14-pin male/female 57-10140, Amphenol (UK)
  • SK2
    9-pin female connector M9S, Electro Methods Ltd. (UK)
  • Crystals
    Cold War army surplus, (USA)
Known serial numbers
Below are the surviving PD-3 units that have surfaced so far.

  • PD3-T-32
    Transmitter
    1962
    Crypto Museum
  • PD3-P-32
    Power supply
    1962
    Crypto Museum
  • PD3-T-55
    Transmitter
    1966
    Reinhard Glogowski
  • PD3-P-55
    Power supply
    1966
    Reinhard Glogowski
It is believed that the designator consists of the model number (PD3), 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 between 50 and 100 units were made. The manufacturing year is estimated, based on the manufacturing dates of the electrolytic capacitors.


References
  1. Reinhard Glogowski, PD3-P and PD3-T
    Crypto Museum, 15 July 2023.

  2. Anonymous, former owner of a PD3 in China
    Correspondence via [1], 26 April 2023.
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Crypto Museum. Created: Saturday 15 July 2023. Last changed: Friday, 01 September 2023 - 08:59 CET.
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