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Radio PRT-4 has been producing the Electrosvyaz trust since the beginning of 1930. "PRT-4" - (Radio-Transmitting Receiver, 4-tube) is intended for servicing broadcasting devices of wire broadcasting nodes. The receiver wavelength range: 180 ... 2175 m (1667 ... 138 kHz). Reception can be conducted both on the open and on the loop antenna. The receiver has three stages of high-frequency amplification and a regenerative detector cascade. HF radio receiver is a three-stage resonant amplifier with inter-lamp transformer coupling. Each circuit is tuned by changing the capacitance of the variable capacitor, as well as changing the set of high-frequency transformers and switching from one section of the secondary winding to two with a switch. Feedback inductive on the 4th resonant circuit. Detection is done with the help of a grill. Gain adjustment is performed using a potentiometer that changes the bias on the grids of high frequency amplifying lamps. The receiver is designed to work on PT-2 lamps in all cascades, but it can also work on UB-107 or UB-110 lamps. Power supply requires two batteries of 4 and 80 V.