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From the beginning of 1929 until December 1930, the low-frequency amplifier UP-3 produced the factory No. 2 of the NUPP NKPT (formerly Profradio). The amplifier is designed for radio broadcasting stationary nodes. The amplifier has 3 pre-amplification stages and a push-pull output stage with 6 lamps, 3 in each arm. From December 1930, the plant produced an upgraded amplifier "UP-3N".