362 BELL SYSTEM TECHNICAL JOURNAL 



usually applied to the tube, its operation as an amplifier, and a simple 

 approximate method for computing the power output and percentage 

 of distortion are explained. 



No new material is presented in the paper although some of it is 

 presented from a somewhat different point of view from that usually 

 found in the literature. An effort has been made to present in reason- 

 ably compact form the essential features of the subject most useful to 

 engineers interested in vacuum-tube applications. 



The subjects discussed include: the portion of electron theory upon 

 which the fundamental principles of vacuum-tube operation are based; 

 space charge, the three-halves power law, temperature and voltage 

 saturation; characteristics of the three-element tube; definition and 

 physical significance of the terms plate resistance, transconductance, 

 and amplification factor; dynamic characteristics, power output, and 

 distortion ; various means of coupling the vacuum tube to its associated 

 circuits; and means for testing vacuum tubes for adequate thermionic 

 emission. 



Coaxial Communication Transmission Lines.^ S. A. Schelkunoff. 

 A non-mathematical discussion of the mechanism whereby energy 

 may be transmitted over long distances at high frequencies by the use 

 of "coaxial conductors" is presented in this paper. A coaxial system 

 consists of a cylindrical conducting tube within which a smaller con- 

 ductor is coaxially placed. Such conductors, which reduce interference 

 and crosstalk, are applicable for the transmission of telephone, tele- 

 graph, and television signals over a very wide range of frequencies. 



Some Aspects of Quality Control.'' W. A. Shewhart. The object 

 of this paper is to make clear what is meant by quality in a practical 

 objective way that is subject to experimental verification and to con- 

 sider some aspects of the problem of control. As a basis for judging 

 the quality of current product it is necessary to obtain first of all 

 adequate information, in the most efficient manner, on which to 

 render a judgment. This can be accomplished by providing an 

 inspection specification which is distinct from the design specification. 

 One specifies the quantity and kind of evidence that is required as a 

 basis for judging whether or not the quality of the product will attain 

 its goal; the other specifies the goal. Certain elements of uncertainty 

 must be allowed for in setting the goal. The discussion closes by 

 pointing out the necessity of keeping a running report or record of the 



^ Elec. Engg., December, 1934. 

 ' Mech. Engg., December. 1934. 



