This paper describes a very high average power, high peak power, 4 cavity klystron capable of operation in excess of 5 megawatts peak and 300 kilowatts average for pulse lengths greater than 500 microseconds. The tube utilizes a solid beam perveance of

and operates over a 10 per cent tunable bandwidth at power gain in excess of 40 db. The tube employs an insulated collector capable of dissipating in excess of 1 megawatt of average beam power. The window design utilized on this tube has been proven to greater than 15 megawatts peak power and in excess of 300 kilowatts average power. The window is a 6" diameter disc design, fabricated from Beryllium Oxide Ceramic and utilizing peripheral water cooling. The gun design incorporates a modulating anode with unity voltage gain. The phase linearity characteristics of the tube are such that limited pulse compression may be utilized. The tube is designed to tune over 10 per cent bandwidth centered at 1320 megacycles. Gain, efficiency and phase linearity characteristics are included as well as pictures of the critical design areas.