In 1900, the Berlin company Mix & Genest began manufacturing magnetic sound recorders. The further development of Pulsen's Telegraphon did not take place until tube amplifiers became available in the early 1920s. Typical Berlin recorders, all of them with information carriers made of steel, were the Vox dictating machine, the Stille SEPMAG transport, the Echophone Dailygraph, and the Lorenz Stahlton-Bandmaschine (Steeltone-Tapemachine). In 1935 the AEG Magnetophon K1 started the magnetic tape era and by introducing ac biasing in 1940 and two-channel stereophonic technology in 1943, a previously unknown reproduction quality was obtained.
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