The German Magnetophone had advantages over all other magnetic recorders. It was portable (the "K" stood for "Koffer" or portable case in the K1 model of 1935) and was self-contained with its own amplifier and speaker. It was cheaper and more reliable than the steel wire and tape machines. It was financed and manufactured by large and powerful corporations in Germany. The Germany military adopted a field version called the Tonschreiber, or "sound writer," and AEG made a very small spring-driven model C and a model D for war correspondents and a model F dictation machine. The models made for the German Navy were the RE-3 and the R-26. BASF developed a factory to mass-produce the reels of acetate tape, replacing the carbonyl iron coating (light gray in color) with magnetite (black). BASF tested the new tape by recording a concert by Thomas Beecham and the London Philharmonic Orchestra Nov. 19, 1939, at the factory in Ludwigshafen. But the quality of the tape recording that still used dc bias was not good. BASF improved the tape in 1939 with a new formulation of gamma ferric oxide (reddish-brown). The German broadcasting group RRG joined the AEG-BASF partnership and worked to improve its quality. RRG engineer Walter Weber re-discovered ac biasing in April 1940 and the Magnetophone demonstrated to journalists in Berlin June 10, 1941, produced a 60 dB dynamic range and the 50-10,000 kHz frequency response. The model K7 in 1943 had synchronous motors to reduce wow and flutter and could even record in stereo. The tape speed of 30 ips (77 cms) became the standard for future speeds of 15, 7.5, 3.75 and 1.875 ips. Karl Schwarz of the Klangfilm company in Berlin developed a magnetic film stock tape that allowed sound to be recorded on the new color film from Agfa. Although an accidental explosion destroyed the Ludwigshafen tape manufacturing plant in July 1943, the producution was taken over by the Agfa plant in Wolfen. A new plant was built in Aschbach neat Lundwigshave to make theType L tape with a polyvinyl chloride plastic base that increased sensitivity by 10 dB.
