The generator of relaxation oscillations on the unijunction transistor is investigated. On its basis the generator of rectangular impulses is designed and manufactured, which is used in this work for fast charging of the capacitor when studying free oscillations in RLC-circuit. Measurements of all parameters of a contour are carried out. By means of an additional high-frequency detector and of devices of the generator AHP1003 and the oscilloscope TDS2012B quality amplitude-frequency characteristics are measured. Technical results of the conducted researches are the new laboratory installation for study of oscillatory processes in electrical circuits and the generator of rectangular impulses on the unijunction transistor.