Patent GB-734771-A (GB)
Title: Improvements in or relating to wave transmission circuits for electron discharge devices
IPC: H01J23/26
Filed: 1952-01-25
Abstract: 734,771. Travelling-wave tubes. WESTERN ELECTRIC CO., Inc. Jan. 25, 1952 [Jan. 27, 1951]. No. 2102/52. Class 39 (1). [Also in Groups XXIII and XL (b)] A helical wave transmission circuit for an electron discharge device; preferably a travelling-wave tube, is carried by insulating support rods which are secured to the helix by a layer of glaze. This is stated to reduce noise as compared with known constructions in which the rods merely lie against the helix. The invention is applicable to the travelling-wave tubes disclosed in Specification 669,473 to the hybrid tubes disclosed in Specification 734,828, and in general' to travelling-wave tubes used as amplifiers,. oscillators or modulators. In manufacture the helix 21, Fig. 2, of steel or preferably of molybdenum is wound on a preferably collapsible mandrel 22 of the same material, and is then normalized. The helix support rods 23 are of low-loss ceramic material, preferably zircon, and the insulating glaze may consist of 6.3 per cent Li 2 O, 5.9 per cent CaO, 16.0 per cent BaO, 21.4 per cent Al 2 O 3 , 50.4 per cent Si0 2 , the helix,- rods and glaze having matching expansion coefficients. The rods are coated along a narrow longitudinal strip with a suspension of the glaze in alcohol projected from a spray gun, the remaining circumference of the rods being masked, Fig. 3 (not shown).. A knife blade can be guided along the surface of the mask to slice the glaze to a uniform thickness. The rods 23 are placed in position around the helix by a jig 24, Fig. 2, with the glaze strips contacting the helix. Amyl acetate dabbed on the rods holds them in place in the jig. The end portions of the rods may be glazed for attachment of the input and output coupling devices which fit over the ends of mandrel 22 and have slots to engage the ends of the rods. After welding the ends of helix 21 to antennµ the jig 24 is closed and the assembly is fired in a hydrogen furnace to melt the glaze. After cooling the jig 24 and mandrel 22 are removed. Loss material, for example colloidal graphite, known under the Registered Trade Mark " Aquadag," is then sprayed over the centre of the entire assembly, preferably through an apertured mask. In a modification the helix 21, Fig. 6, may be connected at one end to a collimating grid 134 as described in Specification 734,828. In this case the ends of the rods 23 adjacent grid 34 extend outside the jig 24 and the end of the helix extends beyond mandrel 22 so it can be deformed at 50. In assembly, grid structure 34 is welded together and fired in a hydrogen furnace to remove oxides and is then fitted on rods 23 by means of slots 39 so that the rods protrude slightly. The helix is welded to grid 34 and to a coupling device at the other end, and the rods are then glazed to all the above members as previously set out. After cooling, the protruding ends of the rods are filed off so that the assembly can fit inside ceramic cup 40. In an alternative construction the helix may be of tantalum, which also acts as a getter and so tends to prevent plasma ion oscillations, in which case the rods are of steatite. The tantalum helix must be vacuum fired since firing in a hydrogen furnace makes it brittle. Specifications 557,811, [Group V], and 669,475 also are referred to.