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Wire recorder "PM-39" from 1939 produced the Leningrad plant them. Kazitsky. Rather, he did not release but reworked the C. Lorenz devices purchased in Germany for domestic radio tubes and put up signs with Russian inscriptions. At a time when the Germans were already in 1935, they demonstrated a tape recorder invented by them with recording of phonograms on magnetic tape, in the USSR they continued to develop sound recording equipment on other media. It was developed a lot of things, but it did not fit the industrial production. Therefore, for the needs of various departments (mostly military), a batch of wire recorders was purchased in Germany and transferred to the Kazitsky plant. After the alteration, the device received the name "PMKkt-39", later just "PM-39" (Wire recorder of 1939). The tape recorder was an exhibit at the Moscow Polytechnic Museum. It is unnamed and is marked with the date 1941. A thin steel wire was used in the tape recorder on a reel containing about 4 ... 4.5 kilometers. The wire pulling speed through special, separate heads is variable and regulated from 10 to 60 cm / sec. The operating frequency range of the sound is 300 ... 7000 Hz at maximum speed. Recording time or sound of one reel up to 24 hours.