GB534215A - Improvements in or relating to electron discharge devices - Google Patents

Abstract

534,215. Cathode-ray tubes. KLEMPERER, O. July 28, 1939, No. 21913. [Class 39 (i)] In a cathode-ray tube wherein a cross-over in the beam is obtained by a modulating electrode which is biased to zero or negative potential, the change in axial position of the crossover due to the modulation is substantially compensated by an electron lens of the saddle field type which focuses the cross over B on the screen. The first electrode L1 is at a high positive potential to accelerate the beam from the cathode ; the second L2 is at a lower potential to decelerate the beam and form a space charge in the region of the lens ; the third L3 is at a high positive potential. As examples (i) the first and third are maintained at three kilovolts and the middle one at one kilovolt (ii) the first is at three, the second at two and the third at five kilovolts. The modulating electrode at the cathode varies the electron current in the beam and this variation acting through the space charge and the lens varies the focal length of the lens and thus compensates for the shift of the first cross over. The potentials in (i) may overcompensate the shift due to the modulating electrode ; this can be negatived by making the central electrode L2 long. Electrodes of diaphragm form may be used-instead of tubular electrodes-to handle beams of larger diameter. Specifications 470,004 and 505,751 are referred to.