Abstract: In a specific illustrated embodiment the upper metal part of the rotating anode which carries the X-ray emitting material at its upper surface is provided with a graphite disc soldered to its lower surface. For accommodating rotational balancing of the anode assembly, the graphite disc is provided with an array of recesses receiving equilibration members of molybdenum. As an example, where the lower heat radiating surface of graphite has a diameter of 100 mm, four discs of molybdenum may be equally spaced about the axis of rotation and have diameters of about 15 mm so as to provide sufficient mass for compensating imbalances and of a size capable of being worked for example by drilling. The equilibration inserts may have flanges at their upper surfaces contacting the anode proper so as to key the inserts into conforming recesses of the graphite disc.