INDEX TUBE WITH TRACKING STRUCTURES

摘要

The invention is related to a cathode ray tube of the index type (1). Tracking elements (16,18) from a tracking structure flank, preferably above and below each phosphor element (20), being provided on an inner surface of a screen (10). A tracking signal that is derived from response signals from the tracking elements, is used to keep the electron beam (7,8,9) on the right phosphor element. In the index tube according to the invention a part of the tracking lines is provided with gaps (30, 30'). The gaps generate an interruption in the tracking signal. This interruption can inter alia be used to derive the precise position of the electron beam (7,8,9) on the screen (10), especially during the start-up phase of the tube.