A high-frequency power oscillator comprises a multi-­grid electron tube (5), a current source (3) and a voltage-limiting circuit (4).
The current source (3) is connected to the screen grid of an electron tube (5) arranged as a tetrode. This limits the screen grid current when the voltage on the anode of the tetrode (5) is momentary lower than the screen grid voltage.
Between the screen grid and the cathode of the tetrode a voltage-limiting circuit (4) is inserted which starts being conductive above a predetermined threshold value. This forms a limit to the screen grid voltage so that it is possible to operate the tetrode (5) in a pulsating manner. A suitable embodiment of the voltage-limiting circuit (4) comprises a triode (4). The voltage between the grid and the cathode of the triode (4) is set to a constant value by means of a voltage source (2).