GB883873A - Travelling-wave tube - Google Patents

Abstract

883,873. Glass to metal seals. MULLARD Ltd. June 24, 1959, No. 21692/59. Class 36. [Also in Group XL (a)] In a travelling wave tube the envelope comprises precision bore glass portions 1, 4 of wide and narrow diameters respectively surrounding the gun and helix 6 respectively and sealed to opposite faces of a metal disc 2, the bores 1, 2 and 4 having precision bores and being accurately coaxial, preferably by the use of jigs in assembly. The object is to make parts 1, 2 and 4 all coaxial so that the tube can be withdrawn and replaced in magnetic focusing means without realignment of the latter and also to make the gun coaxial with the helix 6. In assembly the envelope parts 1, 2 are placed in a jig which engages the precision inner surface of 1 and the outer rim of disc 2, and sealed together and the envelope portion 4 is then inserted into the jig which engages the precision formed inner surface of 4 and sealed to the central boss 3 of disc 2. Disc 2 has precision formed inner and outer surfaces. The outer surface of the helix envelope 4 is preferably ground before putting it into the jig or alternatively after removal from the jig. After the parts have been removed from the jig the helix is inserted in 4 where it is firmly held and located by the inner surface thereof. Next the gun is mounted on its base, the base is located by a jig so as to be coaxial with the bore of helix envelope 4, and the base is sealed to gun envelope 1 so gun and helix are coaxial. The tungsten wire helix has a straight end conductor the end of which is bent in a loop and welded to metal disc 2 so that it can easily be earthed, the gun being operated negative to earth. The helix envelope 4 has small cavities or bubbles in its wall adjacent the inner surface thereof as described in co-pending Specification 851,099, to reduce the dielectric losses in the glass, especially at the gun end. End cap 13 is located by a jig and sealed to helix envelope 4. If helix 6 is not earthed it is not connected to disc 2. The disc 2 and end cap-collector 13 is of Ni-Fe alloy and need not have a central boss.