A radiator has an x-ray tube disposed in a coolant-filled housing formed by a tank and an insertable closure for the tank. The x-ray tube is provided with an asymmetrical cooling member disposed in the region of a heat exchanger. Guides are provided which effect circulation of the coolant heated at the cooling member and cooled in the heat exchanger. The coolant circulation is promoted by superimposing thermal convection in the coolant, thermal conduction in the asymmetrical cooling member, and heat flow induced by the electrical fields which are present during the normal operation of the radiator. The result is that the surface temperature of the entire x-ray radiator is substantially the same, independently of the orientation of the radiator.