GB754727A - Electron tube - Google Patents

Abstract

754,727. Thermionic valves. STANDARD TELEPHONES & CABLES, Ltd. Jan. 26, 1954 [Jan. 29, 1953], No. 2321/54. Class 39 (1). To reduce the current to the screen grid 3 by improving the focusing effect of the control grid, the pitch of the latter is made a multiple of the screen grids and its portions which are aligned with the screen grid are nearer to the screen grid than its other portions. Thus the control grid may be made of two interleaved helices 2a, 2b, Fig. 2, the helix 2a which is aligned with the screen grid turns being of larger diameter; a third helix of the same diameter as 2b may be wound inside, and aligned with, helix 2a, Fig. 3 (not shown). In another form a single helix 2a, Fig. 4, may have its turns or half-turns facing the screen grid bent out towards the screen grid as shown. Another way of obtaining the same effect is simply to make the aligned portion of the control grid of larger diameter wire, Fig. 1 (not shown).