Focus reflex modulation of electron guns

High resolution and low drive features have been successfully combined in a new type of electron gun for cathode-ray tubes. The gun has a spot-defining aperture of 0.007 inch upon which emission from a large cathode area is concentrated by a retarding electron lens. This unit modulates the beam by electron reflection, while focusing it upon the aperture ("Focus Reflex Modulation"). Immediately ahead of the aperture, a modulated virtual cathode is formed with an emission capability of over four amperes per square centimeter. A1000-microa beam with a 6° divergence is controlled by a signal of 12 volts centered at ground potential. Highlight brigntness of 250 foot lamberts was read at 17,500 volts, while more than 500 lines were resolved on a television test pattern. In more recent forms of the FRM gun,1600 microa are measured in the screen return, out of1800-microa cathode current. This is 88 per cent over-all transmission, using the same defining aperture (0.007 inch). 18 volts of drive signal will completely modulate the above current.