Abstract: In order to operate high-frequency heating equipment such as, for example, plasma torches, it is desirable to provide a power generator which will generate a high-frequency high voltage providing a large amount of power. If an oscillator circuit includes an electron tube (1), a control circuit (7) and a frequency-determining circuit that is formed by a coaxial waveguide (11) which is biased in the neighborhood of its short-circuited end a high-frequency high voltage will be obtained at the open end of the waveguide. The power supplied by the electron tube is stepped up to the permissible maximum value for given maximum supply voltage by having the electron tube generate the corresponding current, which is determined by the choice of the point (14) at which the coaxial waveguide (11) is biased.