Units of this manufacture were subjected to both temperature cycling and temperature accelerated aging tests, as well as to over voltage tests. The loading was controlled at about 26 kV and a maximum of 1.5 mA Ten units were subjected to temperature-cycle testing over the range of -35 oC to 85 oC. The cycle time was 12 hours. The dwell time at temperature extremes (power up) was 5-1/2 hours and the transition time (power down) was 45 minutes. The units were tested at rated voltage and load. This test continued until 13,870 device hours were accumulated. The test yielded two fail ures. One failure was an external driver; the driver was repaired and the test continued. The second failure was a breakdown in insulation because of a trimmed lead end be- ing inadvertently included in the winding. Neither failure was re- garded as significant in impact on mean time to failure (MTTF)