GB762107A - Improvements in or relating to electron guns - Google Patents

Abstract

762,107. Velocity modulated tubes. STANDARD TELEPHONES & CABLES, Ltd. Oct. 14, 1953, No. 28269/53. Class 39(1). An electron gun for a travelling-wave tube or klystron comprises an indirectly heated cathode 5, Fig. 1, focussing electrode 4, and anode 3 secured to cup-shaped magnetic pole piece 1, the cathode 5 and focussing electrode 4 are aligned coaxially with the pole piece and anode by mica washer 16 and are spaced axially from the anode by means of two ceramic washers 13, 17, the upper face of washer 17 being accurately planar and engaging with a seating in the pole piece. The cathode has skirt 6 with holes 7 to reduce heat conduction and carries heater 10 in a closed compartment, emissive surface 9 being concave. In assembly ceramic washer 13 is placed over the cathode and heater to seat on flange 12, focussing electrode support 14 is placed around the cathode on washer 13 and mica washer 16 is placed around support 14 against washer 13. A centring jig is used to make the cathode and support 14 coaxial and a second ceramic washer is placed beneath flange 12 ; tie rods 18 are passed through holes in washers 13, 17 and welded to support 14. The assembly is then clamped together by welding rods 18 to tube 19, after which the centring jig is removed. Focussing electrode 15 is then inserted in support 14 and correctly spaced from the cathode by shims, after which electrode 15 is welded to support 14. The cathode and focussing electrode assembly is then inserted within pole piece 1 holding anode 3 until washer 17 seats against shoulder 22 of the pole piece, so that washers 13, 17 ensure axial spacing, and washer 16, which is a tight fit in the pole piece, co-axial alignment of the electrodes. A resilient washer 24 of mica or metal is secured to the end of the pole piece by metal pins 23 and eyelets 25 welded to the pins, so as to hold the electrodes 6, 15 in correct position. The travelling wave tube has a helix 26 supported in a glass tube 27 between a pair of sleeves at the collector end of the tube and a sleeve and the gun at the other end of the tube, the last four members forming the inner members of chokes, Fig. 2 (not shown). The gun, helix and sleeves are secured together by three ceramic rods 32. In assembly, the gun, helix and sleeve assembly are inserted into the envelope until the most remote sleeve contacts an extension of the collector, and the two parts of metal end cap 35 are sealed together. The collector is sealed through another end cap and has an external heat radiator. The pins 37 and a locating spigot 38 are sealed in a glass base member 39 and the gun and pole piece structure are carried by cylindrical skirt 40, with holes 51 to obstruct heat flow during degassing, welded to metal cup 41 sealed to glass base 39, while cup 41 is sealed to flange 42 of the metal cup 35. The seal between members 41, 42 is a ring weld 44, while the metal cap members 42, 43 are sealed together by a ring of hard solder, using induction heating. The tube is evacuated via a metal exhaust tube secured to an external boss projecting from the collector and the heat radiator is secured to the bras over the exhaust tube. The gun anode 3 has a slotted resilient projection 45 which fits inside helix support tube 27. A U-shaped antenna 46 as described in Specification 755,834 is secured to pole piece 1 and to the end of helix 26 which is brought out through a slot 47 in glass tube 27. Ceramic rods 32 have plated areas at their ends to which flanged sleeves 48 are welded, as described in Specification 762,105. When the electrode assembly has been aligned in a jig, recesses 49 allowing for slight inaccuracies in the lengths of rods 32, the flanges of sleeves 48 are welded to the pole piece at 50. Specification 762,106 also is referred to.