This paper describes a 280‐kV constant‐gradient positive‐ion acceleration tube in which the interelectrode voltage is established with a voltage divider chain of resistors that is mounted inside the vacuum of the tube. A single glass pipe serves as the vacuum envelope, flat aluminum disks are used for the tube electrodes, and resistance‐paint‐coated plastic cylinders compose the voltage divider chain. These construction features simplify tube construction and keep manufacturing costs low. During high‐voltage tests, interelectrode voltage was estimated to deviate less than ±6% from uniformity, heat was adequately dissipated from the vacuum‐mounted resistors, and the maximum design acceleration voltage of 280 kV was held. Furthermore, preliminary ion acceleration trials yielded from 0.7 &mgr;A of N+2at 50 kV to 1.5 &mgr;A at 280 kV. The accelerated‐beam cross section, as viewed on a ground quartz screen, remained stationary during those trials, indicating that the tube configuration provided adequate shielding of the beam from asymmetric charges on the interior insulating walls of the tube.