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Cold War
DDR
Stasi
  
DDR Type 2
Short-wave spy transmitter

DDR Type 2 1 was a valve-based short-wave (SW) clandestine (spy) radio transmitter, developed in the early 1960s in the former DDR (East-Germany) by the OTS 2 of the Ministerium für Staats­sicherheit (MfS), better known as the Stasi. It was distributed to field agents in West-European countries – at the other side of the Iron Curtain – and was often hidden in underground caches.

The set consists of a transmitter – suitable for frequencies between 3.15 and 8.5 MHz – a mains power supply unit, a high-speed hand-operated morse burst encoder and several spare parts. 3

The transmitter was intended for use in case of an emergency, by East-German agents operating in West-European countries. The agent generally got his instructions via a One-Way Voice Link (OWVL), also known as a Numbers Station. Any answers would normally be returned via dead drops. If for some reason the agent could not use a dead drop, he would use the transmitter.
  
Transmitter

To avoid the risk of being caught with the transmitter – for example during a house search – it was usually hidden at a predetermined underground hiding place, known as a cache. The agent had coded instructions on where to find the cache. He also had printed instructions on how to use the set, and had several One-Time Figure Pads (OTFP) for the encryption of the messages.

Using a clandestine transmitter from within the host country, is not without risk. If the enemy is able to intercept the transmission, it might be possible to determine the transmitter's location by means of radio direction finding (RDF), which could potentially lead to the arrest of the agent.

For this reason, a so-called burst encoder was included in the set. It allows a coded message to be stored as morse code numbers on a piece of regular audio tape by means of a puncher. Once the message is complete, it can be played back at high speed with a manually operated keyer.
  
Puncher (left) and keyer (right)

In the past, transmitters of this type have reportedly been found by the Bundeskriminalamt (BKA) and by the Bundesamt für Verfassungsschutz (BfV) in forgotten caches throughout Germany [4]. They have also been found in Austria and Switzerland, and perhaps in other countries as well [2]. The one shown here, was found in 2018 in a forgotten cache in a West European country. Based on the manufacturing codes on some of the components, it was probably manufactured in 1962.

  1. The official name of this radio is currently unknown, which is why we use the nickname 'DDR Type 2' coined by Louis Meulstee in 2004 [2].
  2. OTS = Operative Technische Sektor (Operational Technical Division).
  3. A receiver is missing from the set, as the agent generally already had one that was purchased locally, such as the Grundig Transistor Luxus Boy E. The agent used this receiver for listening to the Numbers Stations.

Contents of the two containers, with the transmitter at the center Transmitter PSU Setup for sending a message 30 crystals divided over 3 storage cases Stanze - morse tape puncher East-German Handschnellgeber (manual fast keyer) Two watertight containers in 'Wehrmacht' colour
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Contents of the two containers, with the transmitter at the center
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Transmitter
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PSU
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Setup for sending a message
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30 crystals divided over 3 storage cases
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Stanze - morse tape puncher
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East-German Handschnellgeber (manual fast keyer)
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Two watertight containers in 'Wehrmacht' colour

Features
The transmitter measures 150 x 105 x 50 mm and is housed in a hamerite grey metal enclosure. The diagram below gives an overview of the controls and connections on the body of the device. At the left is a 5-pin 240° DIN socket for connection to the PSU (which has an identical socket). At the front bottom is a 2-pin Kathrein socket for connection of the manually operated burst keyer.


The transmitter has four controls: three recessed knobs for adjusting the frequency, and a push-button at the top left. The latter is used to enable the transmitter whilst tuning the oscillator and PA circuits. The tuning table on the top surface gives a rough pre-set for each frequency. It also specifies which taps on the wire antenna and the counterpoise should be selected for each band.


The image above shows a typical setup for sending a message. At the right is the transmitter, which is powered from the 220V AC mains via the power supply unit (PSU) at the left. A crystal for the desired frequency is installed in the crystal socket at the top left of the transmitter and the tuning knobs have been set to the values given in the table. Antenna and counterpoise wires are connected at the rear (not shown here). At the front is the manually operated tape-based keyer. The PSU has two switches: one for enabling the HT voltage, and one for selecting the desired HT voltage and, hence, the RF power output — 10 or 20W. The 6.3V AC LT voltage is always present.

In order to send a message, the clear text is first translated into numbers using some kind of conversion scheme. It is then encrypted by means of the so-called One-Time Pad (OTP), also known as a One-Time Figure Pad (OTFP). The hand-puncher is then used to record the numbers onto a regular ¼" magnetic (audio) tape, by punching them out as morse code characters. Once the message is complete, the tape is installed on the keyer and played back at very high speed.

PSU Close-up of the power switches Transmitter seen from the front left Rear view of the transmitter Top view Frontal view Crystal socket Inserting a crystal
Pressing the tuning button Close-up of the tuning knobs Tuning table Power cable and keyer cable Setup for sending a message The number '4' in morse code Manually operated tape puncher Burst keyer
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PSU
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Close-up of the power switches
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Transmitter seen from the front left
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Rear view of the transmitter
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Top view
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Frontal view
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Crystal socket
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Inserting a crystal
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Pressing the tuning button
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Close-up of the tuning knobs
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Tuning table
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Power cable and keyer cable
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Setup for sending a message
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The number '4' in morse code
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Manually operated tape puncher
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Burst keyer





Parts
Transmitter
TX
Mains Power Supply Unit
PSU
Set of quarz crystals Manual code puncher (burst encoder) Manually-operated high-speed keyer (burst keyer) Cables for connection of power and keyer Antenna and counterpoise Magenetic tape for burst encoder
Spare parts Two watertight storage containers Concealment container
Transmitter
The transmitter is the heart of the clandestine radio station. It is suitable for the 3.15 to 8.5 MHz frequency range, and delivers an output power of approx. 20 Watts in CW (morse).

It is crystal operated and has a socket for a HC-6U format crystal at the top left. Suitable crystals were supplied with the set. For each frequency, the three knobs at the front should be adjusted, using the table at the top as a guide. Indicator lamps are present to find the optimal settings.

  
Transmitter

Power supply unit
The PSU shown on the right provides the LT and HT voltages for the transmitter. It is suitable for the 220V AC mains only, which implies that the set was intended for use in Western Europe, e.g. in West-Germany, Austria, Switzerland, etc..

As soon as the PSU is plugged into the mains, it provides the 6.3V LT voltage for the filaments of the valves. The first switch ( ) enables the HT voltage, whilst the second one ( | ●● ) selects between +235V and +415V, which corresponds to an RF output power of 10 or 20W respectively.
  
Power Supply Unit (PSU)

Quarz crystals
The transmitter came with 30 quarz crystals, spread over three metal storage boxes that were basically copies of the crystal boxes supplied with West-German spy radio sets like the SP-15.

The first two boxes contain 24 crystals for the 3.15 to 7 MHz frequency range, but the third box contains 6 crystals from 7.087 to 8.370 MHz, which is above the specified range.

 List of frequencies
  
One of the crystal sets

Puncher
Messages are first converted from letters to numbers, and then encrypted by means of a One-Time Pad (OTP). The encrypted message is then stored onto a regular piece of ¼" audio tape, by means of the puncher shown here.

The knob on the left is used to select a number (0-9) after which a lever at the back is pressed. The number is then punched into the tape as a series of holes that represent the morse code of the number. E.g. '4' is punched as  
 
 
 
 
 


 More information

  
Manually-operated tape puncher

Keyer
Once the message is complete, the tape is wound onto an empty reel that is installed on the left arm of the keyer shown on the right.

The lever is then used to wind the tape from the leftmost reel to the pickup reel at the right, whilst the holes in the tape are read by a switch at the bottom. As this switch is connected to the key input of the transmitter, the numbers on the tape will be transmitted in morse code.

 More information
  
High-speed keyer with cover

Cables
Two short cables were supplied with the kit: a DIN-DIN cable for connection of the transmitter to the PSU, and a 2-wire cable for connection of the keyer to the transmitter.

The pinout of the 3-wire DIN-DIN power cable is specified below. Note that none of the wires is connected to the chassis of the transmitter. The polarity of the 2-wire cable is irrelevant.

 Connections

  
Power cable and keyer cable

Wire antenna
For a proper operation, a wire antenna and a suitable counterpoise should be connected to banana sockets at the rear of the transmitter. The length of each wire depends on the desired transmission frequency.

The image on the right shows the antenna and counterpose wires, each wound onto a pertinax (paxolin) card. The wires have several taps – each marked with a number – that correspond to the tuning table at the top of the transmitter.

  
Antenna (red) and counterpoise (black) wires

Magnetic tape
To allow the agent to send multiple messages, and re-use the transmitter again in the future, a lot of extra magnetic tape was supplied with the kit. First of all there were three small reels, two of which were filled with regualar ¼" ferro tape.

In addition, a large reel with additional tape was supplied as spare. Assuming that the messages were relatively short, this must have been more than enough for a large number of messages. And even if that was not sufficient, the agent could get a new supply from any regular audio store in the West, without attracting attention.

  
Magnetic tape and spare reels for burst encoder

Spares
In order to allow the operator to repair the PSU and the transmitter in case of a faillure, some spare parts were supplied as part of the kit. This only involves socketet parts, which can easily be swapped by the agent.

The large valve is used in the transmitter's PA stage. The smaller one is used in the oscillator. The items were wrapped in paper and stowed in the cache containers without further protection.
  
Spares

Storage containers
The complete radio station (except for an SW receiver) was stored in the two watertight brass containers shown in the image on the right.

Each container has a rectangular lid that is padded on the inside with rubber. The lid is held in place by a metal bracket with two hex bolts, allowing it to be closed firmly. The colours are painted in traditional Wehrmacht grey.
  
Two watertight containers, marked '1' and '2'

Concealment container
When the radio system was hidden in a secret underground cache, it was usually hidden in some kind of common object that acted as a concealment container. In the case of the radio station featured here, it was hidden inside the regular VARTA 6V car battery shown here.

In fact, the concealment with the complete radio station shown here, was found in a real cache in a West-European country, as late as 2018.

 Read the full story

  
6V varta car battery used as concealment

Antenna wire Antenna wire Counterpoise wire Power cable and keyer cable Power cable Cable for connection of the keyer to the transmitter Magnetic tape and spare reels for burst encoder Spare audio tape for burst encoder
Spare supply reels 30 crystals divided over 3 storage cases Puncher and keyer Puncher (left) and keyer (right) Puncher and keyer
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Antenna wire
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Antenna wire
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Counterpoise wire
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Power cable and keyer cable
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Power cable
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Cable for connection of the keyer to the transmitter
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Magnetic tape and spare reels for burst encoder
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Spare audio tape for burst encoder
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Spare supply reels
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30 crystals divided over 3 storage cases
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Puncher and keyer
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Puncher (left) and keyer (right)
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Puncher and keyer

Forgotten cache
The spy radio set featured on this page, was (re)discovered in 2018 in a West-European country, close to the border of The Netherlands. It was found in a forest, burried approx. 20 cm deep, in a secret underground hiding place, also known as a cache. It had been there for nearly 60 years [1].

The cache was discovered by a fanatic amateur-archeologist by means of a metal detector, and was concealed as a VARTA 6V car battery of the 1960s. At first sight, it seemed to be a regular battery that had been thrown away a long time ago. Apparently undamaged and unmodified, it even had the appropriate weight for a battery.

Curious about why someone would want to burry a regular car battery, and because he heared a rattling sound when he turned the battery over, the archeologist decided to knock out the sides with his pickaxe, and investigate the internals.
  
The concealment container (battery) burried upside down

To his great surprise, there were two rectangular watertight containers inside the battery, padded with sheets of lead to give the battery a more convincing weight. At that point it became clear to him that this was not a regular car battery, but more likely a secret cache from the Cold War era.

The image on the right shows the concealment after the bottom and part of one side of the battery had been cut away. Although the kit had been burried in the ground for nearly 60 years, the two containers showed only minor signs of corrosion, which proves that the concealment (i.e. the battery case) has worked as intended.

After removing the two metal containers from the concealment, it became clear that it might have been better to access it from the top, by removing the tar rig between the top panel and the outer case. The top can then be taken off.
  
Contents of the concealment

The two metal containers are 245 x 125 x 75 mm each. They are made of brass and are painted in the traditional Wehrmacht grey colour. At the top is a lid that has a rubber pad on the inside. The lid is held in place by a metal bracket, which is tightened by means of two large hex bolts.

The containers are marked 1 and 2 respectively and contain half the radio set each. Some items are wrapped in paper, but the crucial parts – the transmitter and the PSU – are each packed in a hermetically sealed plastic bag. Note that the semi-transparent plastic bags feel sticky, which suggests that the plasticizer used in the PVC base material has meanwhile become volatile.

The PSU has been well protected by the plastic bag, as no corrosion is found on the exterior. Inside the PSU, the mains transformer exhibits minor traces of rust that eare easily brushed off.
  
Transmitter in hermetically sealed bag

This proves that even though the items are packed in a hermetically sealed bag, which is stored in a watertight container, which in turn is packed in a watertight concealment, some air molecules will still be able to penetrate the packaging and cause corrosion, especially after nearly 60 years.

In order to protect the delicate parts of the transmitter, its chassis is made of zinc-plated metal. Furthermore a large moisure eater is packed with it inside the plastic bag. This way, the zinc on the chassis is used as a sacrificial electrode, similar to a ship's sacrificial anodes.

The image on the right shows the corrosion at the bottom side of the transmitter. As the parts inside the transmitter are still 'as new' – even the silver-plated variable capacitors – this method seems to have worked well. With that in mind, it should be clear that the items of this particular cache find are in exceptionally good condition.
  
Corrosion at the bottom of the transmitter

Although there is some rust on the crystal boxes and their lids, the crystals themselves are still in immaculate condition. Surprisingly, the rubber bands that keep the antenna wires on the paxolin cards, are still fully elastic and have not become brittle over time. More under Restoration below.

Looking at the remains of the concealment container, it becomes clear how it was made. The Stasi had taken an off-the-shelf 6V 1 car battery from the West-German manufactuer VARTA, which would not raise any suspicion when found in a free West-European country.

After removing the tar seem at the top of the battery, the interior (i.e. the lead plates) was removed. The walls between the three battery cells were removed, and the lead plates were cut-off. Only the parts of the interior directly below the three filling points, were left intact.
  
Bottom view of the opened Varta 6V car battery concealment

This way, it would still seem like a regular battery when someone would remove one of the yellow caps and look inside. The two metal containers – which were probably purpose-made – were then stowed in the hollowed-out base, padded with some of the original lead plates to give it a more convincing weight. The top was then re-installed and the seem was sealed again with black tar.

As an aside note, it is interesting to realise how every effort was made to hide the fact that the transmitter was made in the DDR. Although the DDR had its own electronics industry (e.g. RFT), only parts from Western manufacturers (mainly German and British) was used. The main valve in the transmitter was supplied by Haltron (UK), the selenium rectifiers in the PSU are from Siemens, and the antenna current lamp is made by Osram.

The plugs and sockets are all made by Kathrein and Hirschmann, and most of the resistors and capacitors are made by British manufacturers.
  
British manufactured capacitors

The transmitter and the PSU are extremely well-built, with is emphasized by the fact that it still works after nearly 60 years of underground storage under uncontrolled conditions. In the section Restoration, it is described how the device was brought back to life at Crypto Museum in 2018.

  1. Unlike today, where most cars have a 12V battery, many cars in the early 1960s still had a 6V battery. VARTA was one of the main suppliers of car batteries in Western Europe.

The forgotten cache as found in a West-European country in 2018 6V varta car battery used as concealment Common Varta 6V car battery Contents of the concealment Looking into the battery Concealment device Bottom view of the opened Varta 6V car battery concealment Original lead sheets removed from the battery and re-inserted to weight up the concealment
Two watertight containers in 'Wehrmacht' colour Rubber padded lid with locking bar Rubber-padded container lid Two watertight containers, marked '1' and '2' Contents of the two containers PSU in hermetically sealed plastic bag Transmitter in hermetically sealed bag Moisture eater packed with the transmitter
Corrosion at the bottom of the transmitter 30 crystals divided over 3 storage cases Antenna wire British manufactured capacitors Rear view of the transmitter's interior Kathrein 2-pin female socket Spare Haltron 2E26 valve Siemens selenium rectifiers in the PSU
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The forgotten cache as found in a West-European country in 2018
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6V varta car battery used as concealment
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Common Varta 6V car battery
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Contents of the concealment
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Looking into the battery
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Concealment device
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Bottom view of the opened Varta 6V car battery concealment
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Original lead sheets removed from the battery and re-inserted to weight up the concealment
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Two watertight containers in 'Wehrmacht' colour
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Rubber padded lid with locking bar
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Rubber-padded container lid
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Two watertight containers, marked '1' and '2'
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Contents of the two containers
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PSU in hermetically sealed plastic bag
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Transmitter in hermetically sealed bag
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Moisture eater packed with the transmitter
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Corrosion at the bottom of the transmitter
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30 crystals divided over 3 storage cases
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Antenna wire
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British manufactured capacitors
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Rear view of the transmitter's interior
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Kathrein 2-pin female socket
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Spare Haltron 2E26 valve
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Siemens selenium rectifiers in the PSU

Interior
The transmitter measures 150 x 105 x 50 mm and weights 914 grams. It is housed in a metal grey hamerite enclosure, that consists of a zinc-plated frame and a hamerite top section that is held in place by four screws. The top panel is fitted with four recessed screws at the corners.

It is possible to remove just the top panel, or the entire case shell. The image on the right shows the transmitter after removing the case shell. At the front are the three circular tuning knobs.

The transmitter is divided into three sections. At the left is the oscillator, which is built around a 6AG5 valve. Just behind the valve socket, is the crystal socket. At the right is the power amplifier (PA), which is built around a 20W 2E26 valve. At the centre is the antenna tuning circuit, in which a seven-position rotary switch selects one of the seven taps of a large antenna coil just behind it.
  
Transmitter interior seen from the front

Together with the large adjustable capacitor to its right, the coil is part of the tuned circuit of the PA. Both should be adjusted for the highest output power at the desired frequency. The left­most knob is for tuning the oscillator. A table on the top surface of the case, provides some presets.

There is no additional filtering, so the emission of unwanted harmonic frequencies has to be taken for granted. Although it is possible to adjust the tuning controls in such a way that the harmonics are reduced, the agent had no way to check this, and could only rely on the table(s).

The two voltages for the transmitter – 6.3V AC for the filaments and a variable HT voltage for the anodes of the valves, are supplied by the power supply unit (PSU). The PSU consists of a metal base frame that holds all components, and a removable metal grey hamerite case shell.
  
PSU interior

The interior of the PSU – as shown in the image above – can be exposed by removing the four screws from the lower edges of the sides, and lifting off the case shell. At one side is the fixed mains cable. At the other side is the 5-pin power output socket that should be connected to the transmitter. The PSU consists of a transformer, two selenium rectifier bridges (made by Siemens), and two capacitors. The output power of the transmitter is controlled with one of the switches on the metal bridge at the left. It allows selection between 235 and 415V, equivalent to 10 and 20W.

PSU Bottom view PSU removed from its enclosure PSU interior PSU interior Close-up of mains transformer with fuse and neon lamp Transmitter interior seen from the front Transmitter - interior
Top view Rear view Oscillator PA stage with Haltron 2E26 valve Crystal socket and tuning push-button Antenna current lamp Detail British manufactured capacitors
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PSU
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Bottom view
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PSU removed from its enclosure
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PSU interior
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PSU interior
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Close-up of mains transformer with fuse and neon lamp
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Transmitter interior seen from the front
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Transmitter - interior
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Top view
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Rear view
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Oscillator
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PA stage with Haltron 2E26 valve
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Crystal socket and tuning push-button
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Antenna current lamp
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Detail
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British manufactured capacitors

Restoration
When we obtained the radio station featured here, it was in a well-preserved state, especially when considering the fact that it had been burried in the ground for neary 60 years. After a first rough inspection, it was thought that it would be possible to bring the set back to life again.

The first item to be checked was, of course, the PSU. An intitial inspection of the interior showed some minor rust on the mains transformer, but that was easily brushed off. We also discovered that the fuse holder no longer provided a good contact, and cleaned it with a small dental mill.

After checking the other components, a VARIAC was used to raise the mains voltage gradually from 50V to 200V over a period of several hours, to give the capacitors time to reform themselves. After a few hours, the PSU produced stable LT and HT output voltages, without running hot.
  
PSU interior

It was decided not to raise the mains voltage above 200V AC, to prevent the mains transformer from going into saturation, and to increase the life span of the valves. Next, it was time to try the transmitter. The interior was inspected thoroughly, but all components were free from corrosion.

Although the zinc-plated bottom panel of the receiver showed some signs of corrosion, the crystal socket was clean, as were the contact pins of the valves. Even the two silver-plated adjustable capacitors were clean, as if they had been installed yesterday. Apparently, the zinc chassis has worked as a sacrificial anode.

As the transmitter has no electrolytic capacitors, there was no need to run a reform cycle. When we were certain that everthing was OK, it was deemed safe to power it up. A 4.230 MHz crystal was installed in the transmitter's crystal socket.
  
Transmitter - interior

The power cable was installed between the PSU and the transmitter, and the PSU was connected to the mains (via the VARIAC, set to 200V). The neon lamp on the PSU came to life immediately, and after a short while, the filiments of the valves also lighted up. The RF power selector was set to 10 Watt (RF power switch set to ) and the HT voltage was enabled (HT power switch set to ).

This caused the leftmost neon lamp on the top surface of the transmitter to light up. A suitable dummy load was connected to the antenna and counterpoise sockets at the rear, and the tune button (in front of the crystal) was pressed. The transmitter came to life immediately, and with the knobs at the front, the optimum was found.

The transmitter produces a strong and stable signal at the fundamental frequency, but also produces strong unwanted harmonics, with the f2 being only 3dB down. Furthermore, the f3 is only 10dB down and the f5 is just 20 dB down.
  
One of the crystal sets

The inside of the lids of the crystal boxes, was padded with a thin bright green foam, which had almost fully desintegrated. As it affects the metal crystal enclosures, it was decided to remove it, and replace it with a thin layer of felt with the same colour. Any rust on the body of the crystal boxes was removed superficially, but was otherwise left intact. Only a small spot on the top surface of the transmitter was restored, in order to prevent the existing paint from coming off.

The following restorations have so far been carried out:

  • PSU fuse holder repaired
  • Minor rust removed from mains transformer
  • Regeneration of the PSU capacitors
  • Foam in lid of crystal boxes replaced by felt
  • Minor paint repairs
  • Cleaning and oiling of the puncher
  • Plastic bags removed and stored elsewhere
PSU interior Transmitter - interior One of the crystal sets
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PSU interior
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Transmitter - interior
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One of the crystal sets

Connections
Power
  1. +HT +235V or +415V DC
  2. not connected
  3. Common
  4. LT 6.3V AC
  5. not connected
Specifications
  • Frequency
    3.15 — 7 MHz (in reality: 3.15 — 8.5 MHz)
  • Output
    10 or 20 Watts (selectable on PSU)
  • Modulation
    CW (keyed)
Valves
Crystals
The following 30 quarz crystals were supplied with the kit (frequency in kHz):

  • 3152
  • 3318
  • 3498
  • 3670
  • 3783
  • 3878
  • 4047
  • 4187
  • 4230
  • 4323
  • 4555
  • 4743
  • 5158
  • 5202
  • 5410
  • 5530
  • 5548
  • 5715
  • 6250
  • 6310
  • 6363
  • 6570
  • 6657
  • 6807
  • 7085
  • 7493
  • 7610
  • 7705
  • 8190
  • 8370
Spare parts
Documentation
  1. 2E26 valve datasheet
    RCA, 20 June 1947.

  2. 6AG5 valve datasheet
    General Electric, date unknown but later than September 1946.
References
  1. Anonymous, DDR 'Type 2' transmitter in cache concealment
    Crypto Museum, December 2018.

  2. Louis Meulstee, Wireless for the Warrior, volume 4
    ISBN 0952063-36-0, September 2004

  3. Louis Meulstee, 'Type 1-4' GDR
    Supplement Chapter 57, July 2016.

  4. Detlev Vreisleben, personal correspondence
    June — December 2018.
Further information
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© Crypto Museum. Created: Sunday 02 December 2018. Last changed: Tuesday, 11 December 2018 - 08:12 CET.
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