GB402781A - Improvements in or relating to cathode-ray tubes - Google Patents

Abstract

402,781. Cathode-ray tubes. SIEMENSSCHUCKERTWERKE AKT.-GES., Siemensstadt, Berlin. May 30, 1932, No. 15328. Convention date, May 30, 1931. [Class 39 (i).] Cathode-ray beams are caused to converge to a point or to be divergent or parallel, without changing the central axis of the beam, by means of electrostatically charged diaphragms in the form of flat rings symmetrically surrounding the axis of the beam and having an orifice of diameter greater than that of the beam, the diaphragms not taking part in the production of the beam and acting on the beam after it has passed the anode. The diaphragms are apertured discs or circular rings or combinations of these as in Figs. 8 and 9, in which the disc 1 and ring 2 are differently or oppositely charged. In Fig. 9, two discs 1, 3 are connected together to enclose the ring 2. The aperture in the diaphragm may be twice as large as the crosssectional area of the beam, the field increasing with the distance from the axis so that the rays are deflected to a greater extent at a distance from the axis. Negatively and positively charged diaphragms produce convergence and divergence respectively and correspond to convex and concave lenses for light rays. An image-magnifying device corresponding to the microscope can be produced by combinations of diaphragms. The acceleration of the rays by the field of the diaphragm on one side counteracts the retardation on the other side. In Fig. 5, rays drawn from the cathode k by an anode not shown are formed into a parallel beam by a diaphragm b<1> and made convergent by a diaphragm b<2>. As the deflection of a ray depends on its velocity, the rays passing through the aperture in the screen b<3> connected to the cathode are of uniform velocity. The homogeneous beam is made again convergent by a diaphragm b<4> the potential of which is varied to vary the number of electrons passing through the aperture in a screen b<5> and so to modulate the intensity of the beam made convergent or parallel by a diaphragm b<6>. The beam is deflected to scan the screen s by plates a<1>, a<2> and is focussed on to the screen to produce a sharp spot of light. The diaphragm b<4>, b<6> may be at the same potential and equidistant from the screen b<5>.