GB663838A - Improvements in or relating to electron discharge apparatus - Google Patents

Abstract

663,838. Cathode-ray tubes. WESTERN ELECTRIC CO., Inc. Dec. 12, 1947 [Dec. 13, 1946], No. 32804/47. Addition to 637,820 and 663,837. Class 39 (i). [Also in Groups XXXV and XL (c)] In a signalling system as claimed in the parent Specification in which the amplitude of a complex wave is sampled at recurrent intervals, an electron beam of a cathode-ray tube is deflected in. one direction by plates 20a, Fig. 1, to an extent in accordance with the amplitude of each sample to select a path and is swept along that path by a suitable sweep circuit, and a coding element 26 comprising a plate with rows of apertures formed therein produces pulses at the target 27 representing by a permutation code the sampled signal wave amplitude, a grid electrode 25 with a secondary emission coefficient of greater than unity is arranged in front of the coding element 26, and electrode 24, which collects the secondaries, is connected by a feed-back path comprising an amplifier to the deflecting plates 20a so that as a result of current flowing to grid electrode 25 a feed-back voltage is applied to plates 20a to hold the beam in the selected path. The envelope is in two parts 10A, 10B sealed together at their abutting-edges; the electron gun and two pairs of deflector plates 20a, 21b are mounted in part 10A, and target. 27, coding element 26, grid 25, and collector 24 are mounted on ceramic rods 28, the assembly so formed being supported and spaced from the envelope wall by flexible tungsten wires 30, 37. Gun electrode 14 is provided with one or more metal fingers 18 which engage conductive coating 19 which acts as a shield. One deflector plate 21b has side flanges 22 acting as shields. The target 27 and coding electrode 26 are of nickel or carbonized nickel of secondary emission coefficient less than unity; the coding electrode 26 has seven rows of apertures I .. VII, Fig. 6, of which rows I ... V are formed by punching and rows VI and VII by milling recesses in the electrode and then punching. Grid 25 is a nickel plate 35, Fig. 4, with raised portions 41 along the longer sides of the rectangular aperture 38 across which the grid wires 44 are stretched; the wires 44 fit in transverse V-shaped grooves on either side of the aperture and are tensioned by tungsten rod 45 which is urged into groove 42 by beryllium-copper spring strip 46. The grid wires of coppernickel alloy have a coefficient of expansion equal to or greater than that of nickel plate 35. The grid wires 44 are offset with respect to the coding apertures in such a way that the spaces between the wires and the coding apertures are aligned when viewed from the centre of deflection. The beam position for no signal may be at either end or at the centre of row VII of coding electrode 26. The leftmost apertures of rows II ... VII are larger than the remaining apertures to provide a peak limiting effect; a similar limiting effect obtains at the other end of the rows. The beam is held in its correct path during a sweep despite slight variations in the input signal or misalignment of the grid wires with the direction of the beam sweep or other disturbances in the deflecting system. To avoid coding errors the beam may be blanked and the feed-back circuit closed or the feed-back circuit opened and the beam left on until the plates 20 are energized.