The invention describes an X-ray tube for generating X-radiation, wherein the tube comprises a rotary structure, which comprises a rotating anode, a stationary structure for rotatably supporting the rotary structure, a hydrodynamic bearing, which is arranged between the rotary structure and the stationary structure, wherein the bearing comprises a gap between the rotary structure and the stationary structure, means for stabilising the dimensions of the gap with respect to distortions because of thermo-mechanical causes. A further aspect, which is described, is a method for manufacturing the tube according to the invention, wherein means for stabilising the dimensions of the gap are arranged. It is also described an X-ray system for diagnostic use comprising the tube according to the invention, wherein the X-ray system is adapted to stabilise the dimensions of the gap. Another aspect of the specification is a method for manufacturing the X-ray system.