Electron tubes

Chapter Electron tubes

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • 29CHAPTERElectron tubesWHEN YOU THINK OF ELECTRON TUBES, DO YOU IMAGINE THE OLD DAYS OFelectronics? Do you envision radios in racks taller than their operators, with strangelyshaped, glowing, glass globes? Have you heard that “tubes” are totally obsolete?Well, some tubes are still around. The most common example is the cathode-raytube in your TV set. The final amplifier in a TV broadcast transmitter is probably a tube,too.Vacuum versus gas-filledThere are two kinds of tubes: vacuum tubes and gas-filled tubes. Vacuum tubes are byfar more common.Vacuum tubes allow electrons to be accelerated to high speeds, resulting in a largecurrent. This current can be made more or less intense, or focused into a beam andguided in a particular direction. The intensity and/or beam direction can be changedwith extreme rapidity, making possible a variety of different useful effects.Gas-filled tubes have a constant voltage drop, no matter what the current. Thismakes them useful as voltage regulators for high-voltage, high-current power supplies.Gas-filled tubes can withstand conditions that would destroy semiconductor regulatingdevices. Gas-filled tubes also fluoresce, or emit infrared, visible light and/or ultravioletat well-defined wavelengths. This property can be put to use for decorative lighting.“Neon signs” are gas-filled electron tubes.In any electron tube, the charge carriers are free electrons. This means that theelectrons are not bound to atoms, but instead, fly through space in a barrage, somewhatlike photons of visible light, or like the atomic nuclei in a particle accelerator.539Copyright © 2002, 1997, 1993 by The McGraw-Hill Companies. Click here for terms of use.