Wikipedia
Magnetophon was the brand or model name of the pioneering reel-to-reel tape recorder developed by engineers of the German electronics company AEG in the 1930s, based on the magnetic tape invention by Fritz Pfleumer. AEG created the world's first practical tape recorder, the K1, first demonstrated in Germany in 1935 at the Berlin Radio Show.
Later models introduced the concept of AC tape bias, and thereby improved the sound quality by largely eliminating background hiss. The resulting reproduction was so great an advance on any existing recording method that even those well acquainted with the industry could not tell the recordings from live play. Adolf Hitler used these machines to perform what appeared to be live broadcasts from one city while he was safely away in another. A cache of 350 of these tapes was released years later when they were found in Koblenz.
Two later model Magnetophons were returned to the United States after the war, having been found in Frankfurt. These included both the newer oxide coated PVC tape developed by I.G. Farben ( BASF division) as well as the AC bias system. The Army officer who tracked them down, Jack Mullin, would use these machines as the basis of his own designs, which he first demonstrated to the San Francisco chapter of the Institute of Radio Engineers in May 1946, and later at the MGM Studios in Hollywood in October of that year. Attending the SF demo were Ampex engineers Harold Lindsey and Myron Stolaroff, who were inspired to design their own reel-to-reel recorder based on Mullin's modified Magnetophon. Mullin's friend, Richard Ranger, had also designed his own take on the Mullinized Magnetophon called the Rangertone; however, a demonstration of that machine to Bing Crosby didn't go well. Mullin then arranged for Crosby to experience a demonstration of the machine designed by Lindsey and Stolaroff: the Ampex Model 200A. Although an initial showcase of the Ampex machine was unable to demonstrate recording, the audio quality of its playback was good enough to get Crosby to agree to work with them. With Bing Crosby arranging financial support for start-up manufacturing, the Ampex 200A went into production and within three years most major recording studios had purchased one.