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Since 1945, the PGR-3 subscriber loudspeaker has been producing the Leningrad Union Telephone Plant No. 3 (afterwards, NPO Signal). There is not much information on this subscriber speaker. The photographs show that the loudspeaker is applied piezoelectric. Since 1951, the Tula plant `` Octave '' produced the same AG, it was on the company's website in the product list. More information in the instructions glued to the back of the case. Perhaps one of the varieties of the loudspeaker, and possibly the product of the Octave plant in the last three photographs.