GB1293596A - Improvements in electron tubes comprising an evacuated envelope enclosing at least three cylindrical electrodes - Google Patents

Abstract

1293596 Thermionic cathode tubes VARIAN ASSOCIATES 21 Nov 1969 [21 Nov 1968] 57089/69 Heading H1D In an electron tube having at least three cylindrical electrodes including a filamentary cathode, an anode and a grid, the cathode 10 is supported by a hollow metallic cylinder 20 which coaxially surrounds at least a portion of a cylindrical metal stem 16 and two axially spaced apart dielectric annuli 22, 24 are interposed between the stem 16 and cylinder 20, one annulus being in fixed abutment with both the cylinder and stem and the other being in abutment with the cylinder and stem such that relative axial movement therebetween is permitted. Fixed annulus 22 rests upon seats 45 and 41 in the cylinder and stem and is secured thereto by applying a force W to each of two annular rings 47, 48, heating the arrangement and allowing movement between the annulus and cylinder, brazing the metallic rings 47, 48 to the cylinder and stem, cooling the arrangement and finally removing the mechanical forces W. The other annulus 24 engages a groove 43 in the stem. Preferably both annuli are segmented and comprise spaced ceramic arcs. Copper cylinder 20 is fixed at its lower,end to flexible copper collar 26 and at its upper end to molybdenum cup 19 supporting the cathode 10. The cathode comprises two sets of parallel thoriated tungsten filaments wound into helices, which are welded together at some of the crossover points such that rows of unwelded crossovers are separated by two or some other even number of rows of welded cross-overs, Fig. 10 (not shown). The ends of the filaments are welded at each end of the cathode to thin molybdenum bands (52), Fig. 7a (not shown), which have a number of flexible integral tabs (53) that are individually welded to respective top and bottom support cups 18, 19.