Homepage Crypto Spy sets Burst encoders Intercept Covert Index Cameras Recorders Radio Bugs Radio PC Telex Agencies Manufacturers Donate Kits Shop News Events Wanted Contact Links Protona Minifon Mi-51 Miniature wire recorder   The Minifon Mi 51 was the first of a successful series of portable minature wire recorders built by Monske & Co GmbH (later: Protona) in Germany. It was introduced in 1951 at a time when transistors were not available yet, and all electronics were valve-based.   Using the first generation of minature valves, this marvel of technology measures only 17 x 11 x 3.5 cm, small enough to fit in a pocket or a handbag. It didn't come cheap however. The price of an Mi-51 in 1951 was DM 680! The Mi-51 is battery powered, making it a truely portable device. Bringing the device back to life today is rather difficult, however, as it requires three different voltages: 9V (for the motor), 30V (anode voltage for the valves) and 1.5V (for the filaments). It has a recording capacity of approx. 2.5 hours.    The Mi-51 was invented by Willi Draheim, who started the development in 1948, just a few years after the end of WWII. The Mi-51 was in production from 1951 to 1955, when it was replaced by the P-55. Willi Draheim left the company in 1952, just before the Minifon was taken over by Protona.   Accessories The Mi-51 usually came in a green or brown storage case, such as the one shown above. The case is made of artificial leather, and is not likely to have survived the years. The case shown here has deteriorated somewhat, especially at the edges. After opening the zipper, its contents are revealed. It came with a lot of accessories, such as microphones, earphones, wire spools and a power supply unit.   By far the most eye-catching accessory, is the microphone disguised as a typical wrist watch, shown in the image on the right. It is designed to be worn inconspiciously on the left arm, whilst the wire is hidden in the sleeve. The microphone is very sensitive and the user has to ensure that it is not brushed against his clothing. The recorded audio could be played back over the supplied headphones that had the shape of a stethoscope.      References Roland Schellin, Spion in der Tasche Detailed history of Protona and the Minifon recorders ISBN: 3-936012-00-8 (German) Protona GmbH, Bedienungsanteitung für das kleinste Tonaufnahme- und Wiedergabe-Gerät der Welt... User Manual for the smallest audio recording and play-back device in the world. Two-colour print (German) Protona GmbH, Minifon, Ihr sprechendes Notizbuch Sales brochure and list of accessories. Black print (German) Further information Protona Minifon history and index of machines P-55, the successor to the Mi-51 Main Covert Recorders page Index of covert equipment Other covert equipment Any links shown in red are currently unavailable. If you like this website, why not make a donation? © Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Sunday, 04 May 2014 - 22:46 CET