Иванов, В. Б., М. Рихтер, and В. И. Ситас. “On the Question of the Comparative Effectiveness of Vacuum Tube and Variable-Frequency Drives”. Eastern-European Journal of Enterprise Technologies, vol. 3, no. 10(57), June 2012, pp. 32-35, doi:10.15587/1729-4061.2012.4180.