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Protona Minifon Attaché
Miniature tape recorder
The Minifon Attaché was a minature tape recorder, developed and built by Protona GmbH in Hamburg (Germany) around 1959 as the successor to the valve-based Mi-51 and the P-55. The Attaché is the first all-transistor recorder in the Minifon family and contains a 4-stage amplifier on a printed circuit board (PCB). It is also the first Minifon to use magnetic tape rather than wire.
Rather than open reels with magnetic tape, the Minifon Attaché used a tape cartridge. As the famous Philips Compact Cassette didn't yet exist in 1959, Protona designed their own tape cartridge format. This format would be used for all later tape-based Protona Minifon recorders.

The image on the right shows a typical Minifon Attaché with the tape cartridge removed. The images below also show empty tape cartridges in their original - sealed - packaging. If you look closely, they were supplied by Telefunken and not by Protona, which might appear strange.
The Minifon Attaché with a tape cartridge (cassette)

The reason is that Protona was taken over by Telefunken in 1962, and that the Minifon Attaché was in production right until the end of the Minifon product line in 1967. The same cartridges were used in the Minifon HiFi and the (Telefunken) Minifon Office. The images below give a good impression of how the tape cartridge was loaded.

Clearly visible is the special blue Minifon mini-accu at the rear of the device. Because transistors were used instead of valves, the recorder was powered by a single voltage of 7.2V. The same battery was used with the Minifon Special. The minifon could also be powered by an external power supply unit (PSU). A remarkable detail is that, compared to the earlier P-55 and the later Minifon Special, the position of the power socket and the accessory socket have been swapped.
Minifon Attaché The opened Minifon Attaché without tape cartrdige The Minifon Attaché with a tape cartridge (cassette) Placing a tape cartridge in the Minifon Attaché The Minifon Attaché with open lid, clearly showing the tape cartridge Close-up of the indicator, the accessory-connector and some of the controls An empty tape cartridge in the original sealed storage box Close-up of a corner of the tape cartridge storage box, clearly showing the Telefunken logo.

A wide range of accessories and add-ons were available for the Minifon Attaché, just like for most other models. As the Attaché was mainly aimed at business people, the default range of accessories would include the standard crystal microphone and the stethoscope-style headphones (Stetoset).   
The headphones in the shape of a stethoscope

The headphones in the shape of a stethoscope The single-voltage rechargeable battery

The Minifon Attaché 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 Attaché 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 Attaché 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 below for correct placing of the battery.

Battery labels for the Minifon Attaché 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 Attaché 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

  1. Roland Schellin, Spion in der Tasche
    Detailed history of Protona and the Minifon recorders
    ISBN: 3-936012-00-8 (German)

Further information

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© Crypto Museum. Created: Saturday 24 March 2012. Last changed: Friday, 02 December 2016 - 08:37 CET.
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