Minifon
The Minifon by Protona Monske was a battery-operated miniature wire tone , later tape recorder , manufactured in the 1950s , which was developed by the German electrical engineer Willi Draheim from 1948. He was able to win the businessman Nikolaus Monske as financier and set up a laboratory in Faßberg. Together with Ernst Genning, Draheim developed the minifon into a finished product within two years.
history
Originally designed as a dictation machine , the first models (" M51 ", " M53 ", " P55 ") were built with miniature tubes, had up to three batteries (tube heating, tube anode, motor) and recorded on steel wire. Later models ( " attaché ", " hi-fi ") worked with Germanium - transistors , thus had only one battery (12 volts, optionally NiCd battery ) used and reversible half-track tape cartridges (precursor of the cassette tape recorder ). It turned out that the sales of sound wire devices decreased in favor of cassette devices until the end of the minifon production.
The cassettes were offered with recording times of 12, 30 and 60 minutes, but the clay wire models with 2–5 hours of recording time. The cassette was (as with other manufacturers) an in-house development, which experienced considerable competition from the compact cassette from Philips.
Due to their small size, mini phones etc. a. used for espionage purposes. A wide range of accessories was offered for this, such as a wristwatch or a tie pin disguised as microphones or small induction coils that allowed recordings of telephone calls via the stray field of the differential transformer of the telephone sets of that time. The advertising for the minifon focused on this type of use and the accessories.
The different versions of the mini phone were offered by Protona from 1951 to 1962. After bankruptcy in 1953, the Liechtenstein businessman Reinhold Stach and two other investors took over the company. When Stach died after a short illness in 1962, his widow sold the company to Telefunken in August 1962 , so that production continued until 1964/65. After that, devices were only assembled from extensive stocks until 1967.
Clay wire
The clay wire was made of steel with a diameter of 0.05 and later also 0.04 mm. According to the operating instructions, broken clay wire should be repaired with a boatman's knot . The sound wire in the Mi 51 (from 1951) recorded in a frequency band of 200-4000 Hz, with later models 200-3500 Hz or 150-6000 Hz depending on the wire speed. The frequency band also depended on the recording speed, depending on the device a reel can be recorded for 2½ to 5 hours.
The main disadvantage of the sound wire is that, unlike magnetic tape, it cannot record in stereo and is therefore limited to voice recording.
- Minifon special S, built between 1960..62
Inside view of the with control buttons (right), coils for the clay wire (blue), clay head for wire (above, between the coils) and battery compartment (right, without battery)
Pick-up wire that runs into the sound head
Sound head (between the coils) and coils in the side view
Dummy watch with microphone. The housing only the microphone, there was no more space for a clockwork. Therefore, the clock always shows the same time.
Trivia
The Australian aerospace engineer David Warren , inventor of the black box ( "black box"), designed his first prototype by modifying a Minifons after a first totally mysterious crash series of time-art De Havilland DH.106 Comet - jet aircraft in 1953 and the 1954th
literature
- Frank Gnegel: Monskes minifon; in Das Archiv , Ed .: DGPT , Issue 1/2011 , ISSN 1611-0838 , p. 96
- LISTENING DEVICES - microphone under the tie , Der Spiegel , issue 48/1951 of November 28, 1951
- Roland Schellin: minifon - The spy in your pocket (= series of publications on radio history . Volume 12 ). 1st edition. Publishing house Dr. Rüdiger Walz, Idstein 2001, ISBN 3-936012-00-8 .
