Thermionic Vacuum Tubes and Their Applications 



By ROBERT W. KING 



Note: The present material was originally prepared for the National 

 Research Council for use in a proposed Manual on "Physical Research 

 Methods and Technique." As the appearance of the Manual has been 

 postponed, the Committee in charge of its preparation has kindly consented 

 to the separate publication of some of the sections in various technical 

 magazines. In order to meet the requirements of the Manual, the form 

 of expression has been made as compact as possible with practically no 

 discussion of theory and no derivation of formulas. Since this style of 

 presentation leaves much to be desired from some points of view, refer- 

 ences have been given to the original literature wherever possible. How- 

 ever, many of the vacuum tube circuits presented have not as yet been 

 treated in the literature. In the preparation of the new material the 

 author has been greatly helped by persons whose contact with these subjects 

 is at first hand. 



Contents: I. Introduction. II. Two-electrode Tubes. III. Three-elec- 

 trode Tubes. IV. Thermionic Amplifiers. V. Amplifier Power Supply. 

 VI. Troubles in Amplifier Circuits. VII. Thermionic Modulators. VIII. 

 Thermionic Detectors. IX. Vacuum Tube Oscillators. X. Miscellaneous 

 Applications of Thermionic Vacuum Tubes. 



I. Introduction 



1. Thermionic Emission. By thermionic vacuum tubes we shall 

 understand those whose operation depends in an essential manner 

 upon thermionic emission. 



The design of the various types of thermionic tubes at present in 

 use requires no knowledge of the exact mechanism of thermionic 

 emission. It may be said, however, that the work of O. W. Richard- 

 son and others leaves little question but that this emission is a physical 

 as distinguished from a chemical process, and occurs from certain 

 substances as the result of the large velocities of thermal agitation 

 acquired by electrons when these substances are raised to a high 

 temperature. 



On the basis of certain plausible assumptions, O. W. Richardson 

 derived 2 the expression, 



I s = Ne = AT^"kf, (1) 



for the thermionic emission per cm. 2 in which 7^ is the saturation 

 current formed by drawing all the emitted electrons to a positively 

 charged electrode placed near the emitting surface, e is the electronic 

 charge and e the Naperian base, A is a constant dependent on the 

 emitting substance but independent of the absolute temperature T, 



2 Richardson, The Electron Theory of Matter, 1916 Edition, page 441. 



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