At the University of Maryland, we have been developing high‐power coaxial gyroklystrons. Our present work is focused on the development of a 17.136 GHz four‐cavity frequency‐doubling gyroklystron amplifier. This device will then be used to drive a high gradient linear accelerator structure recently developed by the Haimson Corporation. Our work has been afflicted by many technical challenges, most arising from thermal imperfections in the custom‐made high current emitter of our electron gun. In our latest experimental run, instabilities were detected in the input cavity of our amplifier tube. These instabilities appear when the beam pitch ratio (&agr;) is approximately 1, thus impeding our search of domains with higher &agr; values (note that the circuit was designed to operate at &agr;=1.4). In order to remedy this problem, we have radically redesigned the input cavity, changing both its geometry and Q factor. The new input cavity has been fabricated and cold‐tested. It will soon undergo hot‐test in the next run of experimental studies of the circuit, which will commence after an upgrade of our vacuum system. Here we present the current status of this research. © 2003 American Institute of Physics