A device is proposed for producing high-frequency microwaves, having a cathode arrangement with heatable cathodes for emitting electrons, two grating arrangements for controlling and focusing the electrons flow and an anode for recaiving the electrons passing through the grating arrangements. The cathode arrangement and the first grating arrangement and also a blocking or choke element define an output cavity forming a resonance cavity and the anode and the second grating arrangement define an output cavity likeeise forming a resonance cavity. The cathode arrangement has a monuting for the cathode such that deformation of the cathode with reduction of the spacing between the heatable cathode and grating is avoided.