GB766640A - Improvements in or relating to travelling wave tubes - Google Patents

Abstract

766,640. Travelling wave tubes. STANDARD TELEPHONES & CABLES, Ltd. July 24, 1953, No. 20596/53. Class 39(1). The glass envelope of a travelling wave tube comprises a cylindrical portion 2 formed with accurately dimensioned pimples 20 coaxial with the inner cylindrical surface of the envelope to serve as locating means for mounting annular flange 21 also coaxial with said inner surface and cementing the flange to the envelope. In manufacture envelope portions 2, 6 are held accurately coaxial by an internal closely fitting stepped mandrel and sealed together. Without removing the mandrel the envelope portions are inserted in a lathe and the surfaces of the pimples are ground to make them coaxial with the internal walls of the glass envelope portions. Alternatively the pimples can be formed at this or an earlier stage by using a mandrel with air jet passages, heat softening the glass, and blowing out the pimples against a mould. The gun, helix 3 and three accurately ground glass rods 4, 5 for supporting the helix are then assembled as a complete unit sealed to press 8. Finally this unit is inserted into envelope 2, 6 until sleeve 17 abuts against ridge 18 of the envelope, the press 8 is sealed to the envelope, and the valve processed and based with phenolic base 9 in normal manner. The mounting flange 21 is then cemented to base 9. To ensure that flange 21 is accurately coaxial with the helix and gun axis the tube is mounted, before the cementing, in a jig comprising platform 24 holding bush 26 fitting accurately around pimples 20, and carried by pillars 25 from base plate 22, and platform 27 carried by studs 28 and having an accurately formed recess for holding flange 21. To ensure that chokes 16, 17 and probes 14, 15 are in the correct axial position in the tube the distance h (between choke 16 and flange 21) is accurately determined by rotating knurled nut 33 to raise or lower the travelling wave tube until the top of choke 16 is flush with the upper surface 31 of bush 30, carried by platform 29. To assist in this adjustment part of surface 31 is ground a few thousandths of an inch lower than the remainder of the surface. The cementing can now take place, a small heating unit (not shown) being used to set the cement. If the flange 21 is to be used to locate the tube in its associated apparatus in a given angular position it has a groove, shown in the drawing as engaged by tongue 34. The gun is located within envelope 2 by mica washers 7. The final gun anode 11 is connected to side cap terminal 12, and is conductively joined to sleeve 16 by metal tube 19. The helix support rods 4, 5 are secured at their ends to choke sleeves 16, 17.