The high power handling capability of millimeter wave gyro-amplifiers makes these devices attractive for applications such as high resolution radar, long range space communication, and plasma heating. The Vacuum Electronics Branch at NRL is making continuing efforts to develop stable, broadband (> 15 %) millimeter wave gyro-amplifiers operating at low beam voltage (< 100 kV ). Two configurations are being investigated: a two-stage tapered gyrotron-traveling-wave-tube amplifier (gyro- TWT), and a two-stage slow wave cyclotron amplifier (SWCA). The growth mechanism in the two-stage gyro-TWT is based on phase synchronism between the relativistic cyclotron motion of a gyrating beam and a fast guided wave, leading to the azimuthal phase bunching (cyclotron resonance maser instability); whereas wave growth in the SWCA occurs when the gyrating beam is in synchronism with a slow guided wave, resulting in axial bunching (Weibel instability). A two-stage Ka-band gyro-TWT has been assembled and experiments are currently underway to demonstrate stable, high power, broadband amplification. An initial design study on a Ka-band two-stage SWCA with a sever has been completed. A high quality axis-encircling beam (60 kV, 5 amps, Avz/vz 5_ 2 % at vt/vt = 1) is employed in the slow wave circuit. Characteristics of cold-test if components are described.