Cathode-ray tubes

Chapter Cathode-ray tubes

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • Cathode-ray tubesEveryone encounters TV picture tubes. You’ve almost certainly looked at a computermonitor (even cash registers have them now), and you’ve probably seen an oscilloscopein some form. These video displays all use cathode-ray tubes (CRTs).The electron beamIn any CRT, an electron gun emits a high-intensity stream of electrons. This beam is fo-cused and accelerated as it passes through anodes that carry positive charge. The an-odes of a CRT work differently than the anode of a radio-frequency vacuum tube.Rather than hitting the anode, the electrons pass on until they strike a screen whose in-ner surface is coated with phosphor. The phosphor glows visibly as seen from the faceof the CRT.Unless deflection is used to move the electron beam around the screen of the CRT,you’ll only get a brilliant spot in the center of the screen. Deflection of the beam makesvarious displays possible. The beam can be deflected by electrostatic fields or by mag-netic fields.Electrostatic deflectionA simplified cross-sectional drawing of an electrostatic CRT is shown in Fig. 29-7. Theelectron beam is pulled toward the positive deflecting plates and is repelled away fromthe negative plates. There are two sets of deflecting plates, one for the horizontal planeand the other for the vertical plane. The higher the voltage between the plates, the greaterthe intensity of the electrostatic field, and the more the electron beam is deflected.546 Electron tubes29-6A grounded-grid RF power amplifier.