Battery radio `` PRT-4 ''.
Amplifying and broadcasting equipmentThe battery radio "PRT-4" has been produced by the Electrosvyaz trust since the beginning of 1930. "PRT-4" - (Radio-Broadcasting Receiver, 4-tube) is intended for servicing the broadcasting devices of wire broadcasting nodes. Receiver wavelength range: 180 ... 2175 m (1667 ... 138 kHz). Reception can be carried out both to open and loop antennas. The receiver has three high-frequency amplification stages and a regenerative detector stage. The RF radio receiver is a three-stage resonant amplifier with transformer inter-tube connections. The adjustment of each circuit is carried out by changing the capacitance of the variable capacitor, as well as changing the set of high-frequency transformers and changing from one section of the secondary winding to two using a switch. Inductive feedback to the 4th resonant circuit. Detection is carried out using a gridlick. Gain control is performed using a bias potentiometer on the grids of high frequency amplifying tubes. The receiver is designed to operate on PT-2 lamps in all cascades, but it can also operate on UB-107 or UB-110 lamps. Two batteries, 4 and 80 V are required for power supply.