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Since 1933, the low-frequency amplifier VUP-30N has manufactured plant No. 2 of the NKPT. The amplifier is a modernization of the previous model "VUP-30". The end stage of the amplifier is fenced off on radio tubes of the M-127 type, and the rectifier on B-128 lamps, respectively, transformers and rheostats are changed in the amplifier to support these new radio tubes. The lamp pinout in both amplifiers is the same, so they are interchangeable with a corresponding change in the output power up to 30 watts on old lamps and up to 50 watts on new ones.