Reliability of TV klystron with multi stage depressed collector

This paper describes the reliability of high power TV Klystrons with multi stage depressed collector. Special features of these klystrons include operating collector stages at different potential to capture electrons arriving at different speeds; carbon coating the stages to reduce secondary emission etc. How these features affect the life expectancy of MSDC Klystrons is a cause of concern. CPI has delivered 150 of these klystrons (VKP-7990) to various TV stations, since 1990. Total operating hours on these klystrons exceeds 7 million hours. These klystrons have saved almost 500 Mega Watt of power and $50 Million for TV stations over last eleven years. Latest data being collected now will show the MTBF to be over 70,000 hours, this compares favorably with other high power standard klystrons.