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.
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.
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
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.
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.
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.
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.
The following radio sets in this series, with the same origin,
are currently known:
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 weighs 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.
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 weighs 1456 or 1418 grams 1
without the valve. A 6J6 valve should be
installed into the ceramic socket at the rear.
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).
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.
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.
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.
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.
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.
Below is the circuit diagram of the PD-3, recreated from a very bad photocopy
provided by Louis Meulstee [3]. Please note that this is a preliminary circuit
diagram which may contain errors. The component values have not yet been
deduced. Note the jack socket (J) which sits between the cathode of V2
and the B- rail. Inserting a plug into this socket, disables meter (M) and its
shunt resistor (R4). It is possible that socket (J) was used
for the connection of an external morse key.
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
B1
B1
LT
LT
unused
GND
GND
B2
HT3
HT3
unused
HT2
HT1
HT1
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.
n.c.
n.c.
Morse key (1)
n.c.
n.c.
n.c.
n.c.
Morse key (2)
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.
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:
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
Reinhard Glogowski, PD3-P and PD3-T
Crypto Museum, 15 July 2023.
Anonymous, former owner of a PD3 in China
Correspondence via [1], 26 April 2023.
Louis Meulstee, PD3 circuit diagram
Personal correspondence, August-October 2023.
Any links shown in red are currently unavailable.
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Crypto Museum. Created: Saturday 15 July 2023. Last changed: Wednesday, 05 November 2025 - 12:09 CET.
