GB840284A - Improvements in high voltage switching tubes - Google Patents

Abstract

840,284. Thermionic valves. MACHLETT LABORATORIES Inc. March 31, 1958 [April 12, 1957], No. 10233/58. Class 39(1). In a tetrode for high voltage switching the cathode and grid electrodes 30, 40, 46 have meniscus-shaped effective surfaces convex towards a planar anode 18, the leads of these electrodes extending through the cathode end of the envelope 10, with re-entrant portions 14, 23 at each end. Anode support 16 is sealed to re-entrant portion 14 and carries a shield 17 to protect seal 15 from undesired electron bombardment. Re-entrant portion 23 is provided with three integral coaxial tubular supports 24, 25, 26. Support 24 ends in a pinch 27 sealing the end of the envelope and carrying support rods 28, 29 and the grid lead. Cathode 30 is a coil of thoriated tungsten wire which is directly heated, one or more turns of which may be individually supported by a fine wire 35 whose ends are fixed to an angled wire 36 held in the stem press to prevent damage to the coil by shock or vibration and to maintain the coil in its convex meniscus shape. The stem 25 supports control grid 40 which is supported on an inwardly turned flange 39 on support 38. The grid may comprise a platinum coated molybdenum mesh to reduce grid omission during the operation of the tube, held between two similar molybdenum rings. The screen grid 46 is similarly constructed and supported. Gettering means 59 are supported on shield 54. The screen grid lead 55 passes through a hole in the control grid support and is screened from the cathode by means of shield 61. Circumferential recesses are provided in the various supporting cylinders to facilitate accurate assembly. Specific electrode displacements being shown by example in the Specification.