This video presentation (I know, it has been a LONG time since I uploaded a YouTube video!!!!!) is of two Minifon Mi-51 pocket sized wire recorders. The Minifon Mi51 first came out in 1951. From 1951 to 1953, they were manufactured by Monske & Co, the original makers of the Minifon. Then from 1953 to 1955, they were manufactured by Protona. The designs are very similar, but different at the same time. The earlier Monske units (later Monske units were not this way) used a mechanically-goverened motor, with mechanically-adjustable speed. The later Monske and all Protona units used a more common electro-mechanical speed regulator, but did not have adjustable speed. However, the electro-mechanically-regulated motor was much more stable in its speed (the drawback being added "governor noise" in the audio). This precision-made Western-German unit was, at the time it was introduced, the smallest recorder in the world. It was popular with the CIA, spies, investigators, and the like. The CIA, spies, investigators, and soforth all had the oppurtunity to use DC-bias for recording their subjects. Yes, this unit is DC-bias. Erasure is with a permanent magnet, mounted AFTER the record/play head. So you have to erase separately BEFORE making a recording, but not WHILE making a recording. You can even erase while playing back, such that a message will be heard only one time, instantly erased after it is played. Here are several weblinks showing interesting websites that showcase Minifon Mi51 units and their history: Crypto museum, which has history about Monske & Co. and Protona. This site also has links to old CIA documents, including an evaluation of the version with the speed control: https://www.cryptomuseum.com/covert/rec/minifon/mi51/index.htm -------------------------------------- Vintage Technics Russian Website. This website features multiple fascinating recorders with detailed information and pictures: https://vintage-technics.ru/Eng-Minifon_Mi51.htm --------------------------------------- PRC68 Website, article on Magnetic Recording. It has not only info on the Minifon but other stuff about the Telegraphone and lots of old patents: http://www.prc68.com/I/MagneticRecording.shtml --------------------------------------- Patent for the Minifon, on the PRC68 site: http://www.prc68.com/I/MagneticRecording.shtml#2866009 --------------------------------------- Red Free Circuit Designs, with the 2W amplifier circuit: https://www.redcircuits.com/Page33.htm --------------------------------------- In 1954 in Australia, the late David Warren invented the Black Box Flight Cockpit Voice Recorder. His inspiration was a Minifon Mi51. Here is a website about his invention: https://www.nma.gov.au/defining-moments/resources/black-box-invented I hope you enjoy this presentation about this fascinating device! And on a different note, I want to mention that Jesus Christ is Lord! ... https://www.youtube.com/watch?v=l7cekeOUVHg

Written before C# class began, with my left hand (I am right-handed) and I that night recorded it on my Califone 70-TF reel tape recorder. The audio is direct to the comptar. ... https://www.youtube.com/watch?v=_5Tx1NRtaWo