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1943 __ Magnetic tape’s development
Comment : BASF replaces cellulose acetate tape with polyvinyl chloride (PVC) tape for magnetic recording. Cooperation between AEG and BASF-then IG Farben, Ludwigshafen works-concerning the Magnetophon sound-recording system began in the fall of 1932. Formulation of the first tapes and their production are described: first carbonyl iron (1933), then iron oxide Fe(3)O(4) (1936), and finally iron oxide Fe(2)O(3) (1939) on a cellulose acetate base, the latter oxide mixed in since 1943 and, since 1945, coated on polyvinyl chloride film.By 1939, BASF researchers had advanced the state of the art of tape quality far beyond its 1936 debut. Probably the most important progress came that summer with the introduction of gamma ferric oxide tape, γ-Fe2O3, with red iron oxide particles, a formula dating back to a 1935 BASF patent that proved so effective that it was not until thirty years later, in 1971 with chromium dioxide tape, that anything fundamentally better would replace it. Tape formulas in Germany, Japan, and the United States in the 1940s, ‘50s, and ‘60s, were evolutionary improvements on this BASF patent. The γ-Fe2O3 magnetic particles were considerably smaller than the original Fe3O4 formulation, which resisted erasing by the permanent magnet erase heads then in use. With DC-bias Magnetophons, the new tape achieved a signal-to-noise ratio of little more than 40 dB and a frequency response remaining 50 Hz to 5 kHz, still unacceptable for “broadcast quality”. Using the same name between 1935 and 1943.the last year of its production., Magnetophon tape Type C contained no fewer than three magnetic formulations: (1) up to the summer of 1936: carbonyl iron (light-gray, metallic pure iron); (2) from the middle of 1936 to the summer of 1939: Fe3O4 (black, cubicular iron oxide); (3) from the autumn of 1939 to 1943: γ-Fe2O3 Gamma-type red, cubicular oxide; needle-shaped variations were developed at the beginning of the 1950s using the same formula. Throughout the development of these magnetic materials, the base film remained the same.cellulose acetate, after which BASF named the product “Magnetophon Tape Type C”. Although polyvinyl chloride (PVC) and later, polyester (Mylar) base films eventually replaced cellulose acetate, the technology lasted well into the 1960s. Type C tape had advantages in manufacturing. Acetone used in the process was cheap and plentiful, and the cellulose acetate was used in all three parts of the tape: base film, magnetic coating, and binder, resulting in a cost-effective and straightforward manufacturing process. One can understand why acetate tape was produced well into the 1950s in Germany and into the 1960s in America. Acetate tape had its weaknesses.it broke easily and was sensitive to humidity. The product had a clear advantage over its plastic successors: it broke cleanly and did not stretch. When acetate broke, the recording engineer could easily splice the tape back together with no audible break in the sound. (Friedrich Engel and Peter Hammar, “A Selected History of Magnetic Recording”)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.
Urls : http://www.richardhess.com/tape/history/Engel_Hammar--Magnetic_Tape_History.pdf (last visited ) http://history.sandiego.edu/gen/recording/mag/p14.html (last visited ) http://history.sandiego.edu/gen/recording/mag/p0.html (last visited )

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