The nickel base indirectly heated oxide cathode ¿ A review

THE barium oxide indirectly heated oxide cathode came into wide use in 1927 and has since virtually dominated the field of ordinary receiving tubes and many other special types as well. The purpose of this article is to review its present status from the standpoint of the electronics engineer rather than that of the physicist. The role of the cathode alloy as well as some of the possibilities and shortcomings of such a cathode as used in the commercial production of electron tubes will be emphasized. In such a discussion it is necessary, first, to review the possible mechanisms of emission; second, to consider the performance characteristics of oxide cathodes; and third, to offer some comments upon the properties of the various cathode nickel alloys and their effect upon cathode performance.