The Proto‐II accelerator has been used to implode krypton and xenon annular gas puffs. A significant fraction of the machine electrical energy was converted first to plasma kinetic energy and then to x rays when the plasma pinched on axis. Quantitative measurements using time‐resolved bolometers have shown as much as 10% of the total radiation yield near 1 keV in Xe and 2 keV in Kr. We have compared this radiation yield to the predictions from one‐dimensional magnetohydrodynamic code calculations. The implosions were also observed with both time‐integrated pinhole cameras and spectrographs. No hard x‐ray (E>10 keV) output was observed.