Abstract: The glass envelope of a rotating anode x-ray tube has a tubular stem sealed into it. A rotor shaft which supports the x-ray target and induction rotor is coaxial with the tubular stem. The front ball bearing for the shaft has its outer race fixed in the end of the tubular stem and its inner race fixed on the shaft. The rear bearing has its inner race fixed on the shaft and its outer race fixed in a bearing retainer sleeve which is axially yieldable in the tubular stem. A coil spring is interposed between one end of the stem and the bearing retainer sleeve to force the outer race, balls and inner race of the bearings into good electric current exchange contact during rotor operation and to accommodate thermal expansion.