A high energy x-ray tube includes an evacuated chamber (12) containing a rotor (34) which rotates an anode (10) through a stream of electrons (A) in order to generate an x-ray beam (B). The rotor includes an outer cylindrical armature (38) made from a thermally and electrically conductive material. An intermediate cylindrical member (40) circumferentially engages the inside diameter of the armature. The rotor also includes a bearing assembly (C) having a bearing shaft (52) centrally aligned with a longitudinal axis (Z) of the rotor. An inner bearing member (42) is concentrically spaced from the bearing shaft and defines forward and rearward bearing grooves (46F, 46R). Forward and rearward bearing races (70F, 70R) are positioned between the inner bearing member and the bearing shaft. A plurality of forward and rearward bearings (48F, 48R) are dimensioned to be received between the forward and rearward bearing races and bearing grooves, respectively. Forward and rearward biasing spring washers (74F, 74R) apply a continuous, opposite biasing force to the forward and rearward bearing races, respectfully, so that the bearing races urge their respective ball bearings into an optimal operating position.