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← Minifon
  
Protona Minifon Special
Miniature wire recorder

The Minfon Special was a miniature covert wire-recorder developed and built by Protona GmbH in Germany. It was introduced in 1961, at the height of the Cold War, and was intended for use by secret services. The design is a combination of both its predecessors: the Minifon Attaché and the valve-based Minifon P-55. From 1962 onwards it was also sold under the Telefunken brand.

Like the first two Protona recorders, the Mi-51 and the P-55, the Special uses a very thin wire to record audio, which is rather strange considering the fact that with the introduction of the earlier Minifon Attaché Protona had already made the transition from wire to tape-based systems.

The reason for this is simple however: although tape-based systems were gaining popularity, they were limited by their recording capacity. In contrast, the two Minifon Special models offer 2.5 or even 5 hours of uninterrupted recording, which is something a tape-based device can't.
  
Controlling the Minifon Special whilst inside the leather case

Although the Minifon Special uses magnetic wire and is largely based on the design of the P-55, it is an all-transistor device just like the new Minifon Attaché. With its dimensions of 17 x 10 x 4 cm, its a fraction smaller than the P55, but it weights a bit more though: 800g instead of 790g for the P55. The image above shows the Special in a typical Protona leather carrying case. The case also has a small pocket to store some accessories, such as the microphone or an ear piece.

The Special was powered by a single rechargeble 7.2V NiCd battery with an operational voltage range of 6.5 to 8V (7.2V nominally). Like the other Minifon recorders, it could also be powered by an external power supply unit (PSU) with an output voltage of 6 - 12V DC. A wealth of spy-related accessories was available, such as the wrist-watch microphone and the holster. After Telefunken took over Protona GmbH in 1962, the Minifon Special was sold under the Telefunken brand [3].

The leather storage/carrying case Controlling the Minifon Special whilst inside the leather case Taking the Minifon Special out of the leather case Minifon Special The controls and connections of the Minifon Special Close-up of the wire spools. At the back the battery. Close-up of a spool The Minifon Special was powered by a single battery as the machine was fully transistorized.
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The leather storage/carrying case
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Controlling the Minifon Special whilst inside the leather case
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Taking the Minifon Special out of the leather case
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Minifon Special
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The controls and connections of the Minifon Special
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Close-up of the wire spools. At the back the battery.
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Close-up of a spool
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The Minifon Special was powered by a single battery as the machine was fully transistorized.

Controls
All controls of the Minifon Special are located at the front of the device. The battery compartment is located at the rear end of the recorder. The section at the centre holds all mechanical parts and the electronics. They are hidden from sight by a plastic cover. In the image below, a recording wire is installed that runs from right to left, past the recording/playback head at the centre.

Minifon Special. Click for a closer view.

Four large keys are used to operate the recorder: STOP, REWIND, PLAY BACK and RECORD. The volume can be adjusted with the potentiometer at the right. At the left are two indicators: a red signal lamp and and wite/red battery indicator. The accessories are connected to the 9-pin primary accessory socket at the front right, or the 3-pin secundary socket at the front left.

Overview of the controls of the Minifon Special Top view of the Minion Special
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Overview of the controls of the Minifon Special
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Top view of the Minion Special

Accessories
For the Minifon Special, a wide range of add-ons was available, just like for the other models.
The connections at the front of the machine are different though, so that accessories had to be ordered specifically for the Special. Most accessories are connected at the front of the recorder to the 9-pin accessory socket that resembles (but is not identical to) a DIN audio socket.

Covert carrying holster Microphone disguised as a wrist-watch Carr battery adapter (cigarette lighter plug)
Car
Leather carrying case Rechargeable 7.2V NiCd battery
Holster
As the Special was intended for use by law enforcement and intelligence agencies, one of the most desired accessories was a holster for concealing the recorder under the operative's clothing when making covert recordings.

The holster was a simple cloth bag that could be carried under a person's arm, like the holster of a weapon. It was then strapped against the body, and a disguised microphone wwas be used to record a conversation inconspiciously. As a microphone, one would use the standard one, the fountain pen, or the famous wrist-watch.
  
Minifon Special in holster for concealed operation

Watch
A wide variety of microphones was available for the Minifon Special, ranging from simple hand­held ones to clip-on microphones and even fully concealed ones, such as the wrist-watch shown in the image on the right.

It should be worn on the left arm and has a fixed cable that runs through the sleeve of the coat to the concealed recorder in the holster under the left shoulder. The wrist-watch mike remained a popular concealment for secret services, long after Protona had stopped trading. The CIA even modified it for use with other recorders.
  
Microphone wrist watch for the Protona Special

Carrying case
For ordinary use, this strong and sturdy leather carrying case was available for the Special. It protect the device during transport but also allowed it to be operated from with the case, as the controls are accessible behind a flap.

At the front of the case is an extra compartment that can be used for storing accessories, like cables, earphone and microphone. A separate carrying strap was supplied to allow the recorder to be carried off the shoulder.
  
The leather storage/carrying case

Car battery adapter
When using the Minifon Special inside a car, it was possible to power it from the 12V car battery by using the cable shown here to connect it to the cigarette lighter socket.

The other end of the cable has a 3-pin plug that mates with the 3-pin power socket at the front panel of the recorder.
  
Car battery adapter

This holster allowed the Minifon to be carried under the clothing Minifon Special in holster for concealed operation Microphone concealed as a wrist watch Microphone wrist watch for the Protona Special Microphone concealed as a wrist watch Connector Car battery adapter
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This holster allowed the Minifon to be carried under the clothing
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Minifon Special in holster for concealed operation
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Microphone concealed as a wrist watch
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Microphone wrist watch for the Protona Special
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Microphone concealed as a wrist watch
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Connector
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Car battery adapter

Battery
The Minifon Special was supplied with a rechargeable 6.5 to 8V battery with a capacity of 500 mAh. It had to be charged at temperatures above freezing point and the charging time was specified at 3 x the time it had previously been used. As the battery will be missing from most of the survinging Minifon Special units, its dimensions are given here, so that it can be reproduced:


The battery consists of two plastic shells with rounded corners. Note that the two corners that are facing the rear of the device have a slightly larger radius (5 mm rather than 3). Each of the sides has a metal contact plate of 10 x 20 mm. The (+) contact is marked on the blue label. The battery has to be placed in the battery compartment of the Minifon Special in such a way that the text 'mini - accu' is visible and readable. The (+) contact should be at the left when viewed from the front of the machine. Check the photographs above for correct placing of the battery.

Battery labels for the Minifon Special in English and German. Click to download.

Glued around the battery is a gold-foil label, printed in blue and white, with instructions on how to use and charge the battery. Depending on the country in which the Minifon Special was sold, these instructions are either in German or in English. For people who want to create their own reproduction battery, we have made them available in PDF format in both languages below.

Inside the battery pack are six DEAC NiCd cells, with a nominal voltage of 1.2V each, producing a total of 7.2V. The batteries are charged with the external battery charger that was available separately. The charger was connected to the charging socket at the front left of the battery.

The charging socket has three holes: the one closest to the bottom is the (+) termial. The one at the centre is the (-) terminal. The slightly smaller hole at the top is for guidance only and ensures that the plug from the battery charger can not be inserted the wrong way around.
  
Inside the battery pack

Connected in series with the (+) terminal from the charging socket, are a diode and a 690 Ohm resistor. These act as a current limiter and are present to protect the batteries against over-charging. The diagram below shows the connection of the batteries and the charging socket.

Battery and charger socket circuit diagram


 Download battery label in PDF format

7.2V NiCd battery Minifon 7.2V mini accu Specifications Charging socket Battery installed in the Minifon Special Inside the battery pack 6 DEAC cells inside the battery pack Front left with the charger socket
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7.2V NiCd battery
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Minifon 7.2V mini accu
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Specifications
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Charging socket
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Battery installed in the Minifon Special
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Inside the battery pack
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6 DEAC cells inside the battery pack
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Front left with the charger socket

Interior
The Minifon Special was one of the smallest recording devices when it was introduced in the early 1960s, with all mechanical and electronic parts cramped into the small space below the two wire spools at the center. The interior can be removed by releasing the only bolt at the bottom.

Once the bolt is removed, the interior can be carefully lifted out of the metal enclosure. Ensure that the volume adjustment is set to 10 prior to doing this, to prevent it from blocking.

The image on the right shows the interior of the Minifon Special with the 4 large control buttons at the right. The battery contacts are at the left. The grey cylindrical part at the top is the motor which was purpose-built by Protona. Part of the electronics are visible to the right of the motor. At the front (left of the control buttons) are the battery indicator and a small red signal lamp.
  
Minifon Special interior

The electronic circuits are all mounted behind and aside the motor. They are clearly visible when viewing the interoor from the right side of the device. Three of the earliest Germanium-based transistors, such as the AC151, are mounted vertically on the lower Printed Circuit Board (PCB).

Interior of the Minifon Special Minifon Special Interior Minifon Special interior Close-up of the mechanics Close-up of the motor Close-up of the electronic circuits Battery indicator and red signal lamp Close-up of the volume knob and the 9-pin accessory socket
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Interior of the Minifon Special
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Minifon Special Interior
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Minifon Special interior
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Close-up of the mechanics
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Close-up of the motor
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Close-up of the electronic circuits
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Battery indicator and red signal lamp
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Close-up of the volume knob and the 9-pin accessory socket

Models
  • Model S
    Standard model (S) suitable for 2½ hours recording at 34 cm/s. Tape diameter: 0.05 mm. Frequency response: 200-5500 Hz. Time indicator: 90 minutes 2 max. This model was sold in 1962 for approx. DM 925 (EUR 460). The serial number tag 1 is marked with the letters 'S' and 'M'.

  • Model L
    Model with Extended Play or Long Play (L = Langzeit), suitable for up to 5 hours recording at 23 cm/s. Tape diameter: 0.038 mm. Frequency response: 300-3500 Hz. Time indicator: 135 minutes 2 max. Sold in 1962 for approx. DM 985 (EUR 490). The serial number tag 1 is marked with the letter 'L'.
  1. The serial number tag is located in the battery compartment. Early versions of the Minifon Special (serial numbers starting with a '0') are unmarked and are probably all Standard Play versions (S). On later versions, the Standard Play version is marked with the letter 'S' at the bottom left and 'M' and the bottom right of the serial number tag. The Long Play version (L) is marked with the letter 'L' in both corners of the tag.
  2. The time indicator of the 'S' version has a maximum reading of 90 minutes, whereas the time indicator of the 'L' version has a maximum reading of 135 minutes. The time indicator wraps around at the end [2].

Serial number tag in the battery compartment marked 'S' (bottom left) and 'M' (bottom right) Serial number tag in battery compartment marked with 'L' at the bottom left and right Serial number tag in battery compartment. Early version, unmarked with 'S' or 'L'.
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Serial number tag in the battery compartment marked 'S' (bottom left) and 'M' (bottom right)
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Serial number tag in battery compartment marked with 'L' at the bottom left and right
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Serial number tag in battery compartment. Early version, unmarked with 'S' or 'L'.

Related patents
  1. US Patent US2898055, Reversing mechanism for magnetic sound recorders
    22 October 1956, published 4 August 1959.

  2. US Patent US3029034, Break for reversible drive
    24 April 1958, published 10 April 1962.
References
  1. Roland Schellin, Spion in der Tasche
    Detailed history of Protona and the Minifon recorders
    ISBN: 3-936012-00-8 (German)

  2. Protona, Minifon Special, Operating Instructions
    March 1962. 1

  3. Telefunken, Service Information, Telefunken Minifon Special
    November 1966.
  1. Operating instructions kindly supplied by Dwayne Trudelle. February 2015.

Further information
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© Crypto Museum. Created: Saturday 24 March 2012. Last changed: Tuesday, 13 June 2017 - 17:59 CET.
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