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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 the container 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 removable batteries. The batteries are held in place by an elastic band at either side of the frame. The complete assembly slides into a grey metal container with a watertight top lid.

The image on the right shows a typical SE-98/3 set inside its metal container with removed top lid, complete with morse key and headphones.
  
SE-98/3 in container with accessories

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 one of the most rare Abwehr sets today.

  1. OKW = Oberkommando der Wehrmacht (Supreme Command of the Armed Forces) in Nazi Germany during the Second World War. Aussenstelle = Outpost.

SE-98/3 in container SE-98/3 in container SE-98/3 outside container, with accessories SE-98/3 in container with accessories Batteries SE-98/3 outside its container 'Mouse' morse key Headphones
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SE-98/3 in container
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SE-98/3 in container
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SE-98/3 outside container, with accessories
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SE-98/3 in container with accessories
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Batteries
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SE-98/3 outside its container
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'Mouse' morse key
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Headphones

Features
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, sitting on a U-shaped sub-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. It is built around three metal 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. It has two antenna inputs, one of which is fed through an attenuating capacitor, and a socket (ground) for connection of the counterpoise.



Front view SE-98/3 outside its container Sub-frame removed from U-shaped outer frame Transmitter (left) and receiver (right) on subframe Power terminal block S-98/3 transmitter E-98 receiver Receiver and transmitter
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Front view
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SE-98/3 outside its container
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Sub-frame removed from U-shaped outer frame
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Transmitter (left) and receiver (right) on subframe
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Power terminal block
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S-98/3 transmitter
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E-98 receiver
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Receiver and transmitter

Parts
The SE-98/3 came pre-installed in a watertight grey metal container which also holds the one year lasting batteries. The container was usually transported inside an unobtrusive suitcase, along with ancillaries like headphones, morse key, crystals, antenna wires, spare parts and tools.

Storage and transport container S-98/3 transmitter
TX
E-98 receiver
RX
Batteries Morse key 'Mouse'
Key
Earphone (Kleinhörer) Wehrmacht headphones Cylindrical quarz crystals
Container
The SE-98/3 came in the grey metal container shown in the image on the right, that also holds the batteries. Transmitter and receiver can be accessed by removed the top lid of the case, which is held in place by two clamp-locks at the short sides. It measures 38.5 x 28 x 10 cm and weights 4000 g (including all parts).

After removing the lid, the radio set can be operated from within the container. Although the case offers space for the ancillaries, such as the morse key and the headphones, those were commonly kept in a separate box.

  
SE-98/3 in container

Transmitter   S-98/3
The transmitter measures just 13 x 10 x 5 cm and weights 750 grams. It is housed in a metal enclosure that was available in several grey tones. It is powered by 270V DC (HT) and 3V DC (LT), which should be supplied via a short fixed cable at one of the corners.

The image on the right shows a typical S-98/3 transmitter with a bright grey front panel. It is shown here with a quarz crystal installed. At the right is a rectangular 4-pin plug by which the device is connected to the battery box.

 Look inside the transmitter

  
S-98/3 transmitter

Receiver   E-98
The receiver is roughly twice the size of the transmitter. It measures 17 x 10 x 8.5 cm and weights ~ 1050 grams. Like the transmitter it was available is several grey tones.

The receiver is powered by 90V DC (HT) and 3V DC (LT), which are supplied via a short fixed cable with a rectangular 4-pin plug. The pinout of this plus is identical to that of the transmitter.

 Look inside the receiver

  
E-98 receiver

Batteries
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.
  
Batteries

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
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 sometimes connected in series to obtain 4000 Ω. The image on the right shows an original Klein­hörer that was made during WWII by Ideal. 1
  
K.Rosinski Kleinhörer in 1937

  1. After WWII, Ideal — based in Berlin (Germany) — became known as Blaupunkt.

Headphones
Alternatively, the SE-98/3 could also be used with a common pair of high-impedance head­phones, that were also used 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.
  
Headphones

Crystals
The SE-98/3 was typically used with a 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
Kleinhörer, made by Rosinski and/or Ideal (Blaupunkt) Kleinhörer 'Maus' morse key and 'Kleinhörer' earphone Original photograph made by Rudolf Staritz in the 1980s [4]. Original advert for the 'Kleinhörer' of 1937
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Batteries
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'Mouse' morse key
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Morse key
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Headphones
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Headphones
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Inserting a crystal
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Crystal
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Crystal
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Kleinhörer, made by Rosinski and/or Ideal (Blaupunkt)
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Kleinhörer
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'Maus' morse key and 'Kleinhörer' earphone
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Original photograph made by Rudolf Staritz in the 1980s [4].
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Original advert for the 'Kleinhörer' of 1937

Interior
Batteries
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

Transmitter without its cover Transmitter interior Transmitter interior - seen from the rear Frame - top side Transmitter detail PA valve Transmitter detail Tuning capacitor
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Transmitter without its cover
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Transmitter interior
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Transmitter interior - seen from the rear
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Frame - top side
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Transmitter detail
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PA valve
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Transmitter detail
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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.
  
E-98 receiver - interior

Receiver outside its enclosure Bottom view showing the three metal valves E-98 receiver - interior Top view showing the passive components E-98 receiver - interior Antenna input transformer Detector/oscillator transformer/coil Top view
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Receiver outside its enclosure
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Bottom view showing the three metal valves
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E-98 receiver - interior
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Top view showing the passive components
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E-98 receiver - interior
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Antenna input transformer
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Detector/oscillator transformer/coil
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Top view

Circuit diagram
Below is the circuit diagram of the S-98/3 transmitter as it was published by Rudolf Staritz many years ago [A]. This circuit diagram is based on the original wartime drawings and is similar to the one that was published in Wireless World in February 1941, which was made after a confiscated S88/5 transmitter. The circuit is built around a single KL2 valve that delivers approx. 3 Watts RF output. Transmission is controlled by a morse key that directly switches the 270V anode voltage.


In this version, the crystal is connected in series between the main coil and the g1 of the valve. By shorting the crystal, the device can be used as a free-running oscillator. It is likely that the design was changed at some point, as in the S-98/3 in our collection (serial number 393) the crystal is connected to ground, and there is no feedback from the tuned circuit, as a result of which it can no longer be used as a free-running oscillator. The circuit diagram of this variant is shown below.


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 (located 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.


DIFFERENCES — The drawing above shows the main oscillator coil, which is different from the initial design. The coil is wound on a 25 mm ceramic cylinder. The primary coil is made of 0.5 mm Cu and has 17 windings. It is connected directly to the 270V, whilst the variable (tuning) capacitor is connected to ground.

The secundary coil also has 17 windings, but is made of slightly thinner 0.4 mm Cu. It has taps at three points, as specified in the circuit diagram above. Also note that one side of the crystal is connected to ground, and that the circuit oscillates by the virtue of the parasitic capacitance between the cathode (k) and the grid (g1). The choke coil (Dr) is connected in series with the cathode of the KL2 rather than in the anode rail.

The later – improved – design is much more stable and puts far less load on te crystal, at the price of loosing the ability to use the transmitter in free-running mode.
Receiver

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 50 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.

DIFFERENCES — Please note that various circuit diagrams of the E-98 receiver are in circulation, all of which are claimed to be 'originals' and all of which are different. For example: the extra antenna input (A/A1) is not always shown and the top half of the oscillator coil (L2) is sometimes drawn at a different location. The E-98 was built if fairly large quantities — the one shown here has serial number 500 — and it is possible that the circuit was modified over time. The diagram above was taken from the original receiver in our collection and closely matches one of the diagrams published by Rudolf Staritz, which were based on wartime drawings [B].

Note that the 20pF capacitor in the anode circuit of the detector valve (DAF11) is actually a trimmer. It is located close to the solder contacts of the DAF11 socket and is just visible in the right half of this image.
E-98 receiver Receiver interior Interior bottom side Receiver interior - seen from the rear Top side Bottom side Receiver detail Receiver detail
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E-98 receiver
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Receiver interior
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Interior bottom side
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Receiver interior - seen from the rear
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Top side
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Bottom side
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Receiver detail
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Receiver detail

Restoration
When we obtained the receiver, it was in non-working condition. After a brief inspection, the main ON/OFF switch was identified as the root cause of the problem. After many years of service and storage, the contacts inside the switch had probably been burned-in or had oxidized.

Although the switch is a non-serviceable part – it is secured with hollow rivets – it was decided to attempt to repair it, as an identical replacement switch was not available. The three hollow rivets were carefully drilled out, so that the upper part could be removed from the bakelite base. It was found that the contacts had indeed burned in.

After cleaning the four fixed base contacts, and the two dumbbell-shaped movable contacts, the switch was reassembled, using three small 2 mm crews to replace the rivets and a drop of locking varnish to prevent them coming out over time.
  
Disassembled power switch with cleaned contacts

The image above shows the disassembled double-pole power switch, with its internal contacts cleaned. After carefully re-fitting the switch and restoring its wiring, the radio could be tested. It worked straight away, but exhibited 'gun shots' when the main tuning capacitor was turned.

Further investigation showed that this effect was caused by four independent problems. The first one was easily fixed. One side of the rightmost trimmer on top of the tuning capacitor had a broken contact. After soldering it back in place, the receiver suddenly became much quieter.

A second problem was caused by one of the blades of the rightmost tuning capacitor. It was slightly deformed – probably as a result from falling down – and touched the adjacent blade after turning the capacitor approx. 130 degrees in. It was fixed with a flat dental modelling knife.
  
Tuning capacitor(s) with trimmers

The last problems showed up intermittently and did not seem to be related to the position of the capacitor. It was partly caused by metal dust which had accumulated between the blades over time, one partly by the main axle which was not always properly connected to ground. Thorough cleaning of the capacitor and applying a drop of cleaning oil to the bearing, fixed both problems.

So far, the following restorations have been carried out:

  • Transmitter: glass of KL2 valve glued in place
  • Circuit diagram taken from real device
  • Receiver: exterior cleaned
  • Power switch repaired and refitted
  • Trimming capacitor soldered in place
  • Tuning capacitor short circuit between the blades fixed
  • Tuning capacitor contact problem fixed
Disassembled power switch with cleaned contacts  Close-up of the refitted power switch Tuning capacitor(s) with trimmers Rightmost trimmer - contact resoldered Tuning capacitors, seen from the side, with two trimmers fitted on top Rightmost blade of the tuning capacitor had been damaged, probably due to a fall Tuning capacitor partly turned-in
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Disassembled power switch with cleaned contacts
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 Close-up of the refitted power switch
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Tuning capacitor(s) with trimmers
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Rightmost trimmer - contact resoldered
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Tuning capacitors, seen from the side, with two trimmers fitted on top
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Rightmost blade of the tuning capacitor had been damaged, probably due to a fall
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Tuning capacitor partly turned-in

Connections
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:


Also note that 90V is only required for the receiver, but that this voltage should be supplied to the transmitter as well, so that its meter can be used to monitor this voltage rail.

Finding a suitable connector for this socket can be very difficult, as they were probably purpose-built at the time. As a gap-fill solution it is possible to use female banana plugs and place them over the pins in the socket. The best solution however, would be to make a replica from era-correct materials. Below are the dimensions of the plug (in mm). The body is made of pertinax.

 Download drawing as PDF

Abwehr 4-pin power plug. Click to download as PDF.

Transmitter valve
Below is the pinout of the socket of the KL2 valve, as seen from the bottom (i.e. the solder side of the socket). Note that the unused pins (here shown in grey) are used as a mounting post for other parts and wires. This valve was manufactured during WWII especially for the German Wehrmacht by companies like Telefunken, Philips and Tungsram. In the latter case, the part number is TKL2.


 KL2 (TKL2) datasheet


Receiver valves
The receiver is built with three different valves — DF11, DAF11 and DL11 — each of which has a metal enclosure (German: Stahlröhre) with a typical 8-pin steel-valve socket (3 + 5 pins). Note that these valves are available in two different heights, both of which are allowed in the E-98 receiver. The diagram below shows the pinout of each valve, as seen from the bottom.



 DF11 datasheet
 DAF11 datasheet
 DL11 datasheet


Technical specifications
General
  • Model
    SE 98/3
  • Case
    Metal container (optionally in leather suitcase)
  • Dimensions
    38.5 x 28 x 10 cm
  • Weight
    4000 grams
  • Dimensions
    13 x 10 x 5 cm
  • Weight
    750 grams
Receiver
  • Model
    E 98
  • Frequency
    2.1 - 8.2 MHz
  • Mode
    AM R/T and CW (morse)
  • Oscillator
    VFO
  • Valves
    DF11, DAF11, DL11
  • Dimensions
    17 x 10 x 8.5 cm
  • Weight
    1050 grams
Transmitter
  • Model
    S 98/3
  • Frequency
    3 - 8 MHz
  • Output
    3 Watt
  • Mode
    CW (A1, morse)
  • Oscillator
    Quartz crystal operated
  • Valve
    KL2
Documentation
  1. S-98/3 tranmitter, - original circuit diagram
    Taken from the original wartime drawings by Rudolf Staritz.

  2. E-98 receiver, original circuit diagram
    Taken from the original wartime drawings by Rudolf Staritz.

  3. KL2 (TKL2) valve datasheet
    Retrieved May 2018 from [7].

  4. DF11, Regelbare HF- und ZF Pentode - datasheet
    Telefunken, December 1941. Retrieved May 2018 from [7].

  5. DAF11, Regelbare NF Pentode mit Diode - datasheet
    Telefunken, December 1941. Retrieved May 2018 from [7].

  6. DL11, Endpentode - datasheet
    Telefunken, December 1941. Retrieved May 2018 from [7].
References
  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

  7. Frank Philipse, Valve datasheets
    Website: Frank's Electron tube Pages.
Further information
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© Crypto Museum. Created: Monday 05 September 2016. Last changed: Monday, 14 May 2018 - 08:06 CET.
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