Cathode Ray Tubes
& Electron Guns
Cathode Ray Tube displays dominated electronic for over 100 years but have now become mostly obsolete. They are still amazing examples of engineering and applied physics with fascinating history and theory of operation. One small and two miniature monochrome CRTs used in camcorders shown in the top right image.
(1) Early monochrome commercial TV set from the 1950s often used simple electron guns with external magnetic focusing. They also used 'ion-traps' to prevent screen 'burn'. Aluminium coating backing the fluorescent screen removed the need for 'ion-traps'. Electrostatic focus added to the gun removed the need for large magnet assemblies on the tube neck. Gun development for B&W CRTs can be seen from the link.
(2) Colour CRT Earlier colour tubes used 3 guns in a 'delta' formation and a 'shadow-masks'. One later development, like the Trinitron shown here, improved the picture brightness with its 'Aperture-Grille' replacing the shadow-mask. Use link (1) for more details on construction.
(3) War-time Tubes Radar was developed during WWII. The tubes used for radar and oscilloscopes use electrostatic deflection many of these found themselves being used in DIY television after the war. This example is probably manufactured by Cosor. The electron gun can be seen at the bottom of the second gun page.
(4) Oscilloscope tubes Similar in construction to the tube above this example is from a Tektronix (154-0682-12) analogue storage scope. A technique using screen coating and flood guns allowed a trace to be maintained on the phosphor screen after it was written by the beam. These remained until digital storage techniques offered a cheaper alternative method of storage. The gun assembly for this tube is shown on the linked page.
(5) Educational CRTs were provided by a number of manufacturers for demonstration in schools and colleges on principles in Physics. They have, unfortunately fallen out of favour with schools mainly due to the high voltages used.
Images link to more information on construction details and to different types of CRT.
