an x - ray tube having a rotary anode which is supported by a bearing system comprising an axial magnetic bearing and at least one radial sleeve bearing . in operation , mutually cooperating metal supporting faces of the sleeve bearing are separated by a liquid layer wetting the supporting faces . the liquid layer consists of a metal or a metal alloy , such as ga or a ga alloy , whose vapor pressure at 300 ° c . is below 10 - 5 n / m 2 , and which does not attack the supporting faces to any substantial extent . the tube has a long life , produces little noise during operation , and is of relatively simple construction .