Cathode ray tube eliminating enlarging of focused beam spot near display edges - supplies dynamic modulated signals to two electrodes to form beam, pre-focussing lens, four pole lens and main lens

The cathode ray tube includes a display screen. An electron gun generates three electron beams and directs them onto the screen. The gun contains a number of electrodes (36,38,40,42,43,44,46) which are spaced apart from three cathodes (34). The electrodes form a beam forming range. A pre-focussing lens, quadruple-pole lens and a main focussing lens are located in the path of the electron beams. The CRT conveys a dynamic, modulated signal (V subscript (F2 + MODULATION)) to one of the electrodes, which forms both the quadruple-pole lens and also the main focussing lens, and to another electrode (40) which is both near the beam forming range and also forms the pre-focussing lens. ADVANTAGE - Has combined dynamic focussing correction and dynamic astigmatism correction.