Flashover in picture tubes and methods of protection

摘要

The aim of this paper is to bring forward and analyse phenomena occurring in a television receiver as a result of a flashover inside a picture tube, and to evolve a systematic approach to a method of protection. The paper first reviews the behaviour of a picture tube under flashover conditions, its effect on receiver circuitry, and a suggestion is made for a possible equivalent circuit. It then establishes a comprehensive method of protection against the large transients generated by a flashover which affect primarily a portion of the receiver directly connected to the base of the picture tube. This protection consists of a separate path for flashover currents, which is switched into circuit for the duration of flashover by means of spark-gaps assisted by series resistors. It is connected in such a way as to provide a minimum disturbance to the rest of the receiver. Further, the paper considers overloads imposed on the e.h.t. generator as a result of discharge of the e.h.t. capacitor by a flashover of the picture tube or other agency. Proposals are made for suitable limiters to protect the output transistor. Finally, a description of some measuring techniques of particular interest in flashover work is given.