Sixty-six experimental tubes representing four type constructions were assembled and evaluated. Few of the tubes tested at X-band delivered more than 50 watts at rated heater voltage. The low yield resulted primarily from inadequate pulse cathode emission from the oxide-coated cathode. Grid contamination that was responsible for rapid cathode emission slump was discovered in one group of tubes. The contamination was caused by pick up of impurities during a copper-plating operation. A 26-mc frequency shift was measured on an uncom pensated oscillator when the ambient temperature was changed from -30C to 100C. An improvement in life performance resulted when the cathode temperature of tube was reduced and the modulating pulse voltage was increased. Two tubes are operating well at the 500-hour life point with e sub b 2000 volts.