An inexpensive, expandable, continuously pumped, all‐metal flash x‐ray tube (FXT) was developed. It was coaxialy integrated at the end of a 70‐&OHgr; flexible coaxial transmission line. The tube, which has a small, 0.5‐mm, x‐ray source size when operated at 200 kV, produces a dose rate of 5×107R/s (at exit port). The produced x‐ray pulse has a duration of 20 ns, thus permitting the radiography of high‐speed transient phenomena.