GB767190A - Improvements in or relating to travelling wave tubes - Google Patents

Abstract

767,190. Travelling wave tubes. MULLARD RADIO VALVE CO., Ltd. Nov. 17, 1953, No. 31863/53. Class 39(1). A travelling wave tube has at one end of the conductive helix a helical conductor forming a continuation thereof and bent at an angle thereto, the helical conductor comprising also a transition portion of progressively increasing pitch and terminating in a straight portion the helix and helical continuation having the same cross dimensions and pitch. The angle may be 85-95 degrees, preferably 90 degrees. The gun can therefore be brought up close to the end of the conductive helix. The transition portion gradually increases in pitch towards the straight portion. In one form a casing is made up of two metal plates 1, 2, Figs. 1, 2 stamped to provide channels 7, 8; 9, 10; 11, 12; 13, 14; 15. 16 which form, when the two plates are assembled in registry, a single continuous passageway of circular cross section. A further communicating passageway 17, 18 houses the electron gun. Curved lugs 4, 5 are secured to the tube envelope (not shown). The first mentioned passageway carries an insulating helix 22, Fig. 7 supporting within it the conductive helix and helical conductors 21. Passageways 7, 8, 15, 16 house the transition portions of the helix, the beam passing along 11, 12. In manufacture, the conductive helix (including the transition portions) and the insulating helix are wound on straight mandrels and the insulating (glass) helix is heated and bent so that its two parts make an angle of 90 degrees. The initially straight conductive helix is then inserted into the insulating helix, using a gentle twisting movement. The straight portions 25 of the helical conductors 21 may be integral therewith or separate members secured thereto. The helix assembly is placed in position, the gun aligned, and plates 1, 2 secured together around the electrodes by soldering or deformation of their edges. Slits 26, 27 prevent electrical interference between the conductors in channels 11, 12, 15, 16 and are sealed up with solder or the edges deformed together. The free ends 31 of the conductive helix are then soldered to or form the inner conductors of two coaxial lines the outer conductors of which are connected to 7, 8, 15a, 16a. To assist the transition, the straight conductor 25 can be gradually increased in cross section, e.g. by electrode position, towards its free end. The connections to the gun, collector and getter are brought out at one end, and to the helix at the other end, of the tube, and the input is connected to 15, 16 which gives a more gradual impedance transition than 7, 8. The insulating and conductive helices may be wound in the same or in opposite senses. The collector may be secured via an insulator to the casing 1, 2. A numerical example is given. Specification 691,399 is referred to. Reference has been directed by the Comptroller to Specification 706,958.