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valdemar poulsen magnetic recording, Tape Recorder; Valdemar Poulsen's Telegraphone; magnetic tape recorder using thin steel 1907 Stock Photo Alamy, TELEGRAPHONE: magnetic recording tele phone invented by Valdemar Poulsen (1869-1942). He applied for a patent on 1 December 1898; and the instrument aroused interest at the Paris Exposition of 1900. RIBBON