Patent GB-798622-A (GB)
Title: Improvements in or relating to travelling wave tubes
IPC: H01J23/02
Filed: 1956-05-14
Abstract: 798,622. Travelling wave tubes. TELEFUNKEN, GES. MAY 14, 1956 [May 12, 1955], No. 14877/56. Class 39(1). The helix of a travelling wave tube is supported by three external ceramic rods 13, Fig. 2, which are'fixed directly to a metal base member 15 forming the last electrode of the gun assembly preceding the helix, the helix rods and gun forming one unitary structure which is supported from the glass base of the tube by spring means. In the preferred form the ceramic rods 13 are fixed in recesses in the end face of accelerating anode 15 by solder such as silver solder. In assembly member 15, Fig. 3 is put over boss 42 of a soldering gauge 41, a rod gauge 44 is placed in a bore in the boss 42, the ceramic rods, precision ground to the required diameter, are inserted in the recesses in the end face of 15 together with a ring of solder and gauge 47 is pushed on to three guide rods 43. The gauge 47 has central apertures for the ceramic rods 13 to prevent the assembly from twisting and to press the rods 13 against 15, the latter being also locked against twisting by a key and slot 48. Solder is now placed in the recesses, flexible clamps 45 are applied to press the rods 13 against two regions of the rod gauge. The parts of the rod gauge in the region of the clamps 45 have radial fitting portions equal in diameter to the helix. The solder is now melted in a protective gas atmosphere by high frequency inductive heating by loop 49 to join the rods 13 to metal base 15. After this the rod gauge 47 and clamps 45 are removed, and the helical delay line and coupling sleeves 6, Fig. 1, are assembled and adjusted outside the tube envelope. The central aperture in metal envelope cup portion 1 enables the helix and rod assembly attached to metal cup 15 to be inserted into glass or ceramic envelope portion 2. The free ends of rods are held by the collector. The helix is slid between the ceramic rods 13 and held in position by one or more clamps 50. Lossy material such as carbon is provided in the vicinity of the clamp or clamps as shown the loss is a helical graphite strip resting on at least one rod. The clamp(s) can be replaced by ceramic discs. If the ceramic rods are on a smaller circle than the helix the latter forces the rods apart so that clamps 50 are not necessary or there can be one clamp 50 only. The helix end is spot welded or soldered to member 26 which also serves as a choke, and 26 is pressed against surface 30 by spring 27 a ring of insulation 31 being interposed. The gun electrodes are insulated from one another by spacers 18, 19 carried in a metal cup 20. A ceramic rod 32 is locked in disc 28 and cup 20 to prevent transverse movements of the gun, and the gun leads have flexible parts 22. The tube has a metal cylinder 1<SP>1</SP> carrying glass base 23 and soldered to metal cup 1 at 25. A further socket such as a " Pico " socket with 7, 8 or 9 fins can be glazed to 1<SP>1</SP>. Focusing of the beam may be by a solenoid, permanent magnet or may be electrostatic. The waveguide feeders have spring contacts 5, 8. At the collector end, Fig. 4, the helix end is welded or soldered to member 40 and the ceramic rods fit in holes in metal member 34 to allow axial play but so that the rods cannot touch the collector 35. The pump tube 39 is sealed to metal envelope portion 34 by two metal cylinders 36, 37 and glass seal 38 and glass or ceramic envelope part 2 is glazed to part 34. The above helix supporting arrangements are suitable for tubes with large cathodes (i.e. large compared with the beam diameter). The gun and rods are secured by clamps, cement or metal ceramic soldering. The envelope must have freedom axially with respect to the gun and helix system so that flexible gun leads are necessary. If magnetic screening of the gun is required, the metal member 1 and/or 15 is of iron or hovar. The diameter of the ceramic rods and of the helix is approximately equal to give substantially no dispersion. The soldering is butt soldering. Cement may replace the solder. A prior art arrangement is referred to in which to obtain alignment between gun and helix a second system of ceramic rods is provided into which the gun and the first rod system is built.