Improvements in or relating to display arrangements for cathode ray tubes

659,097. Cathode-ray oscillographs. STANDARD TELEPHONES & CABLES, Ltd. Oct. 12, 1948, No. 26545. [Class 37] [Also in Group XL (a)] In order to ensure sharp focus of beams of cathode-ray tubes employing electrostatic deflection when the mean potential of the deflecting plates varies, particularly when used in the arrangements disclosed in Specification 590,260, the potentials of one or more of the beam producing electrodes are derived from a circuit including a source which generates a potential which at any instant is proportional to the mean potential of the deflecting plates. A tube 1 has its electrodes 2 ... 7 supplied in the usual way from a resistance chain 11 ... 13 connected across a H.T. supply, and the deflecting plates 8 are connected to sources such that their mean potential varies by an amount v. To maintain focus of the beam a generator 16 applies to terminal 9 a potential variation of the same form and magnitude as the variation v and of the same sign, de-coupling condensers 17 ... 21 having negligible reactance at the lowest frequency of the variation v. Depending upon the characteristics of the variation v the generator 16 may take different forms which are described in detail. In Fig. 2 (not shown), the generator is connected in parallel across a certain proportion of the resistance chain such that the potentials of the tube electrodes and the deflecting plates with respect to the most - ve tube electrode 4, vary in the same proportion; the theory underlying this arrangement being given. In this arrangement the decoupling condensers are omitted. In a further arrangement, Fig. 3 (not shown), embodying the principle of Fig. 2, the generator affects only electrodes 6, 7 and the condensers 17 ... 21 and additional resistances are employed.