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SE 98/3
Abwehr spy radio set

The SE 98/3 was an espionage transmitter/receiver developed during WWII by OKW-Aussenstelle Berlin-Stahnsdorf 1 for use by the German Security Service, the Abwehr, mainly in the Eastern war theatre. The device was introduced in 1941 and was manufactured by OKW Stahnsdorf. From 1942 onwards it was made by OKW-Aussenstelle Wurzen. It was one of the most widely used Abwehr radio sets during WWII and is in fact a miniaturized version of the SE-97/3 suitcase radio.
The radio set consists of a small 3 Watt S-98/3 crystal-operated transmitter and an adjustable E-98 receiver that are mounted on a subframe together with a small power connection block. The subframe slides into a larger frame that also holds the batteries. The batteries are held in place by an elastic band at either side of the frame. The complete SE-98/3 assembly slides into a metal container with a watertight top lid.

The image on the right shows a typical SE-98/3 radio set inside its metal container without top lid, complete with morse key and headphones.
With morse key and headphones connected

The radio is powered by four internal batteries that last one full year when using it 15 minutes each day [2]. Despite the fact that the SE 98/3 was one of the most widely used Abwehr radio sets, only very few have actually survived. Most sets were lost during the war, or were destroyed by its users at the end of WWII. As a result it is arguably the most rare Abwehr set as well.
  1. OKW = Oberkommando der Wehrmacht (Supreme Command of the Armed Forces) in Nazi Germany during the Second World War. Aussenstelle = Outpost.

Storage container Case lock With the lid removed With morse key and headphones connected Removing the radio set from the container SE-98/3 Abwehr spy radio set 'Mouse' morse key Headphones

The diagram below shows the SE-98/3 after it has been removed from its storage container. Although it can be used whilst seated inside the container, we have removed it here to show the various features of the set as it is mounted inside a U-shaped frame. The lower half of the frame is occupied by the batteries that provide the LT voltage (3V) and the HT voltages (90 and 270V).

The upper half of the frame holds a subframe with the receiver (right) and a small transmitter, both of which are connected to the small terminal block in front of the transmitter. The S-98/3 transmitter is the smallest of the two units and is built around a KL2 valve that delivers an RF output power of 3 Watts in CW (A1). It is shown below with a suitable crystal installed at the left.

The E-98 receiver is the largest unit of the set and is mounted at the right half of the subframe. The one shown here is a reproduction that is partly rebuilt from original parts (recovered from the water) and new-old-stock (NOS) parts. The receiver contains three valves (DF11, DAF11 and DL11) and has a frequency coverage of 2.1 to 8.2 MHz, whilst the transmitter covers 3 to 8 MHz.

Seen from the front SE-98/3 Abwehr spy radio set Subframe taken out of the U-shaped frame Transmitter and receiver mounted on a subframe Power terminal block S-98/3 transmitter E-98 receiver Receiver and transmitter

The SE-98/3 was distributed in the grey metal container with watertight top lid, as shown above. The metal container was usually packed inside a leather briefcase of the era, complete with the necessary accessories, such as headphones, morse key, antenna wires, crystals and tools. There was no power supply unit (PSU), as the SE-98/3 is powered by batteries that lasted one full year.
Batteries Morse key 'Mouse'
Earphone (Kleinhörer) Wehrmacht headphones Cylindrical quarz crystals

The exact types of batteries that were used with the SE 89/3 are currently unknown. There are indications that a large 3V battery may have been used in combination with a large 90/270V LT battery, or 3 smaller 90V LT batteries.

There are also indications however, that four equally sized batteries were used as shown in the image on the right. The batteries shown here are reproductions to visualize what they may have looked like. The can be filled with ordinary batteries so that the radio can be demonstrated.

Morse key
Virtually any type of morse key can be connected to the two banana sockets at the bottom left of the transmitter. The SE-98/3 was normally supplied with a small Bakelite® morse key that was nicknamed Maus (mouse).

The image shows a typical Maus with a 2-pin plug at the end of its wire. Note the half-moon button at the front of the key, which was often used for 'spy' equipment. Another type of Maus has a circular button.
Morse key

Earphone   wanted item
Although the receiver is suitable for connection of virtually any type of high-impedant head­phones, it was originally supplied with a small 2000 Ω dynamic earphone, known as Ohrhörer or Kleinhörer, supplied by K. Rosinski in Berlin.

This earphone had a diameter of 34 mm and weighted just 35 grams. To accomodate the user's ear, it was supplied with three different olive-shaped in-ear pieces. Two earphones were often connected in series to obtain 4000 Ω. The image on the right shows a Rosinski Klein­horer aside a Maus morse key [4]. Click for a close-up.
Maus morse key and Rosinski Kleinhörer. Copyright Rudolf F. Staritz [4].

The image above was taken by Rudolf Staritz in the early 1980s. Over the years it has appeared in many of his publications [4]. The Rosinski Kleinhörer was available well before the war. It was advertised, for example, in the August 1937 issue of the DASD amateur magazine CQ-MB. [5][6]
Alternatively, the SE-98/3 could also be used with a common pair of high-impedance head­phones, that are also found with Wehrmacht equipment of the era. The headphones shown here are the Dfh.f. 40.

The headset consists of two speakers with an impedance of 2000 Ω each. Note that the headphones are connected in series with the anode of the DL11 AF amplifier valve, and carry a +90V DC voltage. This means that the wires should be properly isolated.

The SE-98/3 was typically used with quartz crystal in a cylindrical enclosure, such as the one shown in the image on the right. The crystal should be inserted into the two banana sockets at the bottom of the left side of the transmitter.   
Inserting a crystal

Batteries 'Mouse' morse key Morse key Headphones Headphones Inserting a crystal Crystal Crystal

The SE-98/3 needs four batteries that are installed in the lower section of the U-shaped metal frame, below transmitter and receiver. The batteries are connected to the terminal block in front of the transmitter. One of the batteries (the leftmost one) provides the 3V LT voltage for the filaments of both devices. The 3V rail is protected by a 400mA fuse as shown in this diagram:

The other three batteries each provide 90V and are connected in series to obtain the +270V LT voltage for the transmitter. The +270V rail is protected by a 50mA fuse. A tap after the first 90V battery provides the +90V HT voltage for the receiver. The +90V rail is not protected by a fuse. Although both power sockets are wired identically, the +270V rail is not used by the receiver.
Transmitter   S-98/3
The transmitter consists of a metal frame that holds all components, and a U-shaped metal case shell that is held in place by four recessed screws. It has controls and connections on two of its sides. Sockets are present for connection of the morse key, the crystal and the antenna.

The image on the right shows the interior of the transmitter after the metal case shell has been removed. The big KL2 valve is at the far corner. The meter at the front panel is used for checking the RF output, as well as the battery voltages. It is operated with a small lever below the meter.
Transmitter interior

The circuit diagram of the S-98/3 transmitter is given below. It shows how the transmitter is built around a single KL2 valve that acts as the oscillator as well as the Power Amplifier (PA), delivering approx. 3 Watts RF output. The crystal is inserted into a socket at the left. The transmitter is turned ON by connecting 3V to the filament of the valve via the ON/OFF switch. The actual CW transmission is controlled by the morse key that directly switches the 270V anode voltage.

At the bottom right is the meter. By default it is used for checking the RF output of the device. This is done by picking up a small amount of RF energy with the transformer (K) and rectifying it by means of a Siemens Sirutor, which is in fact an array of diodes connected in series [3]. The voltages of the radio set can be checked by moving the metal lever (hidden behind the PA Tuning knob) away from its default position. From left to right it checks RF Power, +3V, +90V and +270V. Note that +90V is not used by the transmitter. It is only required by the receiver.
Transmitter without its cover Transmitter interior Transmitter interior - seen from the rear Frame - top side Transmitter detail PA valve Transmitter detail Tuning capacitor

Receiver   E-98
The interior of the receiver can be accessed by removing four screws from the sides and taking off the case shell. This reveals a frame with all components that is mounted to the front panel.

The image on the right shows the interior of the receiver after the case shell has been removed, seen from the top rear side. Note that the valves are mounted upside down. The circuit is built around three Telefunken metal valves: a DF11 that is used as RF pre-amplifier, a DAF11 as the oscillator/detector and finally a DL11 as the AF amplifier that delivers audio to the headphones.
Receiver interior - seen from the rear

The circuit diagram of the E-98 receiver is given below, which is actually a miniaturised version of the E-97 receiver. Power is applied to the circuit via the 4-pin connector at the bottom right, of which the +270V terminal is not used. Both the +3V and the +90V rail are passed via the ON/OFF switch. The +3V LT voltage is supplied to the filament of the DF11 via a 10 Ohms resistor. Note that the filaments of the other two valves (the DAF11 and the DL11) are connected in series.

The receive antenna is not shared with the transmitter. Instead a separate wire antenna and a suitable counterpoise should be connected to the ANT and GND terminals at the left. A high-impedant pair of headphones should be connected to the headphones terminals at the top right. Note that the headphones are connected in series with the anode line of the DL11 valve, which means that the wires carry a voltage of +90V. Ensure that these wires are properly insulated.
Receiver outside its case Receiver interior Interior bottom side Receiver interior - seen from the rear Top side Bottom side Receiver detail Receiver detail

The transmitter and receiver are eached powered via the terminal block at the front edge of the radio, just in front of the transmitter. There are two 4-pin male sockets that are wired identically. The sockets provide the +3V LT voltage for the filaments, and the +90V and +270V HT voltages for the anodes of the valves. Note that the receiver does not require +270V. The power sockets are wired as follows, when looking into the male sockets from the front of the device:

Technical specifications
  • Model
    SE 98/3
  • Case
    Suitcase or metal container
  • Model
    E 98
  • Frequency
    2.1 - 8.2 MHz
  • Mode
    AM R/T and CW (morse)
  • Oscillator
  • Valves
    DF11, DAF11, DL11
  • Model
    S 98/3
  • Frequency
    3 - 8 MHz
  • Output
    3 Watt
  • Mode
    CW (A1, morse)
  • Oscillator
    Quartz crystal operated
  • Valve
  1. Louis Meulstee, SE 98/3
    Wireless for the Warrior - Volume 4. Retrieved August 2016.

  2. Arthur Bauer, Some Aspects of the German military Abwehr wireless service...
    ...during the course of World War Two
    15 September 2003. p 10.

  3. Radio Museum and contributors, Siemens Sirutor
    Retrieved September 2016.

  4. Rudolf F. Staritz, Photograph of Maus morse key and Rosinski Kleinhörer
    Reproduced here by kind permission of the author.
    Retrieved October 2016 via Arthur Bauer [2].

  5. CQ-MB, Description of the K. Rosinski Kleinhörer
    DASD club magazine (German). August 1937. Page 125.

  6. CQ-MB, Advert of the K. Rosinski Kleinhörer
    DASD club magazine (German). Date unknown. 2

Further information

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© Crypto Museum. Created: Monday 05 September 2016. Last changed: Tuesday, 11 October 2016 - 19:07 CET.
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