Abstract <p>A power source has been developed that generates various configurations of alternating current oscillations. The source adds heat to the superconductor in small, controlled portions, which allows studying dynamic processes on alternating current with amplitudes Ia exceeding the average critical values <i>I</i>_<i>c</i>. Analysis of voltages on the sample allows recording the appearance of a narrow normal zone and determining the conditions for stable operation of the superconductor in the critical region. Using video recording, it is possible to study the process of developing thermal instability up to the burnout of the material.</p>