Improvements in or relating to cathode ray tubes

658,287. Cathode-ray tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Aug. 7, 1948, No. 20896. [Class 39 (i)] A cathode-ray tube comprises a cathode 2, grid 6, apertured electrode 7 and anode 9, the voltage required to produce a variation of beam current being reduced by arranging the grid 6 at a distance from the electrode 7, which is between 3/ 2 and 3/ 4 of the diameter of the aperture therein. The lens formed thereby produces a waist in the beam between the grid and anode. In the preferred form, a television receiving tube has a flat or concave grid 6 of 200 apertures per inch and radius of 3 mms., and is secured to a disc 4 which is 0.008 inches thick; it is arranged so that its apex is 0.003-0.006 inches from the emissive surface 2 and 0.030-0.015 inches from the electrode 7. The thickness of electrode 7 may be 0.01 ins. and the anode potential 6 k.v. The grid may be earthed and connected to, or be positively biassed 5 volts with respect to, the electrode 7. A modulating potential of 3 volts between cathode and grid will cause a variation of beam current of 200 m.a.