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Since 1927, the detector radio P-7 produced the Moscow Telegraph Plant (formerly Morse) and the Nizhny Novgorod Telephone Plant named after Lenin of the Electrosvyaz Trust. In appearance, the receiver resembles the P-6. A feature is the location of the coil so that it serves as walls, this eliminates the need to place the receiver in the box. On the receiver cover, tightened with a bottom through bolt that passes through the center of the coil, 3 terminals and 2 pairs of sockets are placed. The two outer terminals are connected by a jumper, which allows you to turn on the receiver in three ways. With a jumper shorting the terminals with inscription 3 and AK, the condenser is connected in parallel (long waves) with the jumper open and when the antenna is connected to the AK terminal with a free BP terminal, the capacitor is connected in series (short waves), when the antenna is turned on to the AD terminal, grounding terminal 3 and open jumper include only coil (without capacitor). When receiving stations operating on waves from 1000 to 1.800 meters (Comintern station), the capacitor happens in parallel, and when receiving from 800 to 1.100 meters, the capacitor disconnects altogether, and when receiving stations with waves of the order of 300 to 800 m. It is clear that the instructions refer to the reception on a normal amateur outdoor antenna. Tuning the receiver is done by moving the slider of the antenna circuit, thereby enabling one or another number of turns of the coil. The slider to the right of the coil serves to change the detector coupling. Thanks to the slider, it is possible to make a smooth tuning of the antenna circuit, and by moving the slider to select the best detector connection. When several stations operate simultaneously, setting the slider to the middle position moves it up to the receiver panel. This will significantly reduce the interfering effect and will allow to allocate the work of the radio station. The receiver is designed for a range from 300 to 1800 m (according to the instructions 300 ... 1800 m.). It can be used in the absence of powerful radio stations, as it has low selectivity.The price of the receiver is 4 rubles 46 kopecks.