GB1449700A - Cathode-ray tube with variable energy of beam electrons - Google Patents

Abstract

1449700 Cathode-ray tube circuits G D BALANDIN and N G RUMYANTSEV 18 Oct 1974 45190/74 Heading H4T [Also in Division H1] In a C.R.T. 2 operated at variable voltage on luminescent screen 18, e.g. to charge colour, under control of HV supply 27 and switch 26, variation of focus of constant magnetic lens 10 with charge of electron velocity is compensated by bi-potential electrostatic lens 7, 8, the electrodes being connected internally to accelerator electrode 6 and screen 18, so that rise of screen voltage increase the power of the lens. In addition to scanning coils 19 fed by orthogonal deflection unit 25, superimposed electrostatic deflection by plates 20, 21 controlled by character generator 24 draws characters at any point on the screen of size independent of screen voltage. Control unit 21 governs beam current control 23 acting on modulator 5 surrounding earthed cathode 4, the two deflection systems and beam voltage, while the accelerator and magnetic lens have independent supplies 28, 29. In alternative embodiments the electrostatic lens is split, electrodes 7 and 6 being combined with electrode 8 moved beyond lens 10, the field between being maintained by an internal resistive helical stripe (Fig. 2 not shown) or row of resistively connected diaphragms (Fig 3 not shown). In both these cases the character deflection is magnetic, near the accelerator electrode 6. In all embodiments the constant magnetic focusing lens 10 may be a permanent magnet. The first embodiment gives correct focus at two discrete screen potentials, the second and third focus over a range of potentials. The tube may be operated with the screen at fixed potential and the cathode and accelerator at varying potentials.