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The Thermionic Valve and Its Developments in Badiotelegraphy and Telephony

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The Thermionic Valve and Its Developments in Badiotelegraphy and Telephony THE THERMIONIC VALVE AND ITS DEVELOPMENTS IN BADIOTELEGRAPHY AND TELEPHONY THERMIONIC VALVE- AND ITS DEVELOPMENTS IN EADIOTELEGEAPHY AND TELEPHONY BY J. A. FLEMING, M.A., D.Sc., F.E.S., University Professor of Electrical Engineering in the University of London, Member of the Institution of Electrical Engineers, Member of the Royal Institution of Great Britain, etc., etc. AUTHOR OF " "THE PRINCIPLES OF EI.ECTBIC WAVE TELEGRAPHY AND TELEPHONY," AN ELEMENTARY MANUAL OF RADIOTELEGRAPHY AND BADIOTELEPHONY," "THE WIRELESS TELEGRAPHIST'S POCKET BOOK OF NOTES, FORMULA AND CALCINATIONS," ' THE WONDERS OF WIRELESS TELEGRAPHY," ETC., ETC. LONDON THE WIRELESS PRESS, LTD. 12 & 13 HENRIETTA STREET, STRAND, W.C.2 SYDNEY, N.S.W. : 97 CLARENCE STREET MELBOURNE: 422/4 LITTLE COLLINS STREET NEW YORK ROME WIRELESS PRESS INC. AGENZIA RADIOTELEGRAFICA ITALIANA 25 ELM STREET VIA GREGORIANA 36 MADRID ROTTERDAM LA PRENSA RADIOTELEGRAFICA NEDERLANDSCH PERSBUREAU RADIO 43 CALLE DE ALCALA , BOOMPJE 23A '' 1919 ERRATUM. Footnote on p. 139 should read, Figs. 75, 76, 77. ALL RIGHTS RESERVED. PREFACE THE present extensive use of appliances in modern radio- telegraphy and radiotelephony based on the thermionic emission from an incandescent cathode in a vacuous bulb, of which the Fleming oscillation valve was the first repre- sentative, has given rise to much published information on the subject in technical journals as well as to numerous patent specifications. Since most of the recent great advances in wireless telegraphy and telephony are dependent on the employment of these inventions it seemed desirable to collect together in a single volume some of this literature for the assistance of radio-engineers. The author, there- fore, accepted the invitation of The Wireless Press, Limited, to write a small book on the practical side of the subject. It has not been deemed necessary to enter very fully into the purely scientific researches on thermionic emission from incandescent substances, because it has already been treated very fully by Prof. 0. W. Kichardson in his excellent mono- graph, The Emission of Electricity from Hot Bodies (Long- mans, Green & Co., London). The introductory chapter of the present volume, never- theless, provides a brief sketch of the researches which led up to the practical applications described in subsequent chapters. The author has, however, felt it necessary to explain in rather full detail the history of this practical application by himself and others, and of the patent litiga- tion which has taken place in the United States and in Great Britain in connection with it, on account of the efforts which have been made to depreciate the Author's work on this subject. The legal judgments in these actions are printed as an appendix, and will enable the reader to view the ques- tions of priority of invention from the standpoint of unbiassed and competent judges. One other matter calls for remark, and that is the question of nomenclature. The essential structure of all the devices described in the following pages is a bulb of glass or other vii 4 161 SO THE THERMIONIC VALVE im- material more or less perfectly evacuated, and containing a filament of carbon or metal which can be rendered incan- descent, and also used as a cathode for an electric discharge, the bulb also containing one or more cold metal anode plates or grids. To various forms of this instrument a very large number of names have been applied. The single anode bulb was originally named by the author an oscillation valve, and it has generally in Great Britain been since called a valve detector, Fleming valve, or Thermionic valve, but in the United States varieties of the two anode form of it have been christened Audion, Oscillion, Kenotron, Pliotron, Dynatron. Pliodynatron, Ultraaudion, Tungar, and by other trade names. Such plenitude of appellation is puzzling to the uninitiated, and the names are not very self-explanatory. All the instru- ments depend entirely for their radio use on the same physical fact viz., the emission from an incandescent cathode of ions of some kind. Prof. 0. W. Eichardson has called these bodies thermions. For the most part, and at high tempera- tures, the thermions are the so-called electrons or ultimate negative corpuscles or atoms of negative electricity. Since these thermions are not different in nature from the ions liberated by other agencies, such as ultra-violet light, radio-active substances or X-rays, it is permissible to raise the question whether a special name is really required for the ions liberated from incandescent bodies. Appliances depending upon this emission have, however, been rightly named thermionic appliances. The author has accordingly ventured to borrow Prof. Eichardson' s term and to use the word thermion occasionally as an abbreviated name for any radiotelegraphic instrument depending upon this thermi- onic emission, in place of the longer words thermionic valve, amplifier or oscillator. It is easy and self-explanatory then to speak of a high vacuum or low vacuum thermion, or of a two-electrode or three-electrode thermion, and such phrases are, perhaps, more descriptive than artificial words like Kenotron, Pliotron, Dynatron, etc. Some agreement on this question of nomenclature seems desirable if only to prevent the too exuberant growth of strange words which are merely trade names for modifications of generically similar devices. The author submits, there- fore, this suggestion tentatively to the radio-engineering fraternity. viii KADIOTELEORAPHY AND TELEPHONY As considerations of the present cost of paper and printing in time of war have imposed severe limitations upon the size of the present book, it has not been found necessary to include detailed descriptions of every so-far devised circuit or scheme for using thermionic instruments as detectors or generators in radio work, nor mention of every patent specification taken out in connection therewith. Sufficient information has, perhaps, been given to enable the practical or incipient radiotelegraphist to understand the principles involved in the various stages of invention. The recent advances in radiotelephony are entirely based on the utility of the thermion as detector, amplifier, and generator of electric oscillations, and are due to the large number of inventive and scientific minds which have been brought to bear on the subject since the author made the pioneer invention (see Appendix). It is hoped that justice has been done to all contributors as well as to those authors on the subject from whom the present writer has drawn information. The author is indebted for the use of diagrams and blocks to The Wireless Press, Limited, for illustrations taken from articles in The Wireless World and in The Year Book of Wireless Telegraphy and Telephony, of them being many" from an article by Dr. W. H. Eccles on Ionic Valves," and many others from excellent articles by Mr. J. Scott- Taggart which have appeared in The Wireless World recently. Also to the Editor and Proprietors of the Proceedings of the Institute of Radio Engineers of New York for many diagrams taken from papers in this journal, and to the Council of The Institution of Electrical Engineers, London. The author desires to record his obligations to the editorial staff of The Wireless Press, Ltd., and especially to Lieut. G. M. Wright, of the Marconi Company's engineering staff for assistance in collecting information, particularly that on the thermionic apparatus made by Marconi's Wireless Telegraph Company, Ltd. London, June, 1919. J. A. F. IX CONTENTS CHAPTER I. PAGK HISTORICAL INTRODUCTION 1 1. The Development of Radiotelegraphic Detectors. 2. Various Types of Detector. Coherers, Magnetic, Electro- and Thermionic. 3. The Evolution of the lytic, Crystal " Electric Glow Edison, Swan and Steam. Mole- Lamp," by " cular Shadows in Glow Lamps. The Edison Effect." Investigations of it by Preece and the Author. Scattering of Carbon Molecules and Emission of Negative Electricity from the Glow Lamp Filament. The Author's Discovery of a Similar Effect in the Arc Lamp and in Air at Ordinary Pressure. 4. Relations of Heat and Electricity. Guthrie's Discovery. Work of Elster and Geitel. 5. Investigations of J. J. Thomson on Electric Discharge in Vacuum Tubes. Conveyance of Electricity by Ions. Laws of Electrolysis. The Electron. 6. J. J. Thomson's Work on the Con- duction of Electricity Through Gases. Measurement of Ratio e/m. C. T. R. Wilson's Discovery of Condensing Power of Ions on Water Vapour. 7. Use of this Fact by J. J. Thomson to Determine the Value of the Electron Charge e. Ions Emitted by Incandescent Bodies. Thom- son's Measurement of e/m for Thermionic Emission. Mass and Size of the Electron. 8. The Unit of Positive Electricity. Structure of the Atom. Electric Conduction. Electronic Theory of Electricity. 9. Experimental Study of Ther- mionic Emission by Richardson and others. Nature of the Ions Emitted. Thermionic Emission from Incandescent Tungsten. Richardson's Law Connecting Absolute Temperature and Thermionic Saturation Current. 10. Origin of the Ions Emitted from an Incandescent Wire. Wehnelt's Cathode. Emission of Negative Ions from a Nernst Glower. Emission of Positive Ions from Incandescent Wires. CHAPTER II. THE FLEMING OSCILLATION VALVE 46 " 1. Edison's of the Edison Effect." "Discovery " Appli- cation of the Edison Effect by the Author to the Con- struction of an Oscillation Valve or Rectifier of High Frequency Currents. The U.S. Court of Appeals Judg- ment that this was not an Obvious Application. The Fleming Valve. Mode of Using it to Rectify Electric Oscillations. Measurement of the Rectifying Power or Efficiency. 2. Use of the Fleming Valve in Radiotelegraphy in 1905 as a Detector. Senatore Marconi's Mode of Use with a Tele- phone and Oscillation Transformer. Marconi -Fleming Valve Receiver Sets. Valves with Oxide-coated Cathodes. Experiments of Willows and Hill. 3.
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