GB598540A - Low velocity television transmitting apparatus - Google Patents

Abstract

598,540. Electron image tubes. MARCONI'S WIRELESS TELEGHAPH CO., Ltd. Sept. 13, 1944, No. 17540. Convention date, Aug. 27, 1942. [Class 39 (i)] In a television transmitting tube of the lowvelocity beam scanning type, an electron beam is projected through an apertured secondary emissive electrode 12, Fig. 1, towards a target 2 and is focused by magnetic means 16 and deflected in the scanning operation in two mutually perpendicular directions by wholly magnetic means 17, 18, and the electrons not collected by the target 2 are returned over a slightly displaced path so as to strike the secondary emissive electrode 12, the resulting secondary electrons being collected by a closely adjacent electrode structure 20, 23 symmetrical about the initial beam path. The collecting electrode structure 20, 23, may be cylindrical, as shown, of truncated conical shape, Fig. 2 (not shown), or annular, Fig. 3 (not shown), and it may consist of a single electrode such as 20 or of two electrodes 20, 23, the electrode 20 being secondary emissive and the perforated electrode 23 forming the final collector ; alternatively the electrode 20 is not secondary emissive and is connected to the electrode 23 at 24. A trap electrode 25 prevents secondary electrons from escaping from the field of the collecting electrode structure 20, 23. The beam limiting aperture 13 of the secondary emissive electrode 12 may have a diameter of from two to three thousandths of an inch ; other dimensions are also given. Specifications 526,731, [Group II], 540,034 and 560,904 are referred to.