THE three-element vacuum tube is becoming a fairly common tool to the physicist, electrical engineer and experimenter, and the literature on the subject has grown rapidly, so that at the present time it is really voluminous .
Its theory of operation is quite widely known and is found in most modern textbooks on physics and radio communication . Radio literature is usually generously sprinkled with vacuum-tube circuit diagrams .
It is not the purpose of this paper to take up any of the fundamental theories of operation of the tube or its circuits, but to furnish information and give help to those who professionally, or for pleasure, experiment with these devices .
It is also not the intention to attempt to cover the field of tube operation, but merely to call attention to certain phases of the subject not widely known or appreciated .
It is a rather usual occurrence to those working with vacuum tubes in an experimental way to encounter unlooked-for difficulties and obtain unexpected results .
A number of these more unusual effects will be discussed ; first those of a general nature, next those occurring when the tube is used as an oscillator, and finally a few when the tube is used for a number of other purposes .
A tungsten filament type of tube is assumed in the paragraphs to follow, and most of the discussion relates to power tubes .
Certain properties of a tungsten filament as an electron emitting source will first be mentioned, for although these are simple and probably well known, they will hear repetition because of their importance in obtaining satisfactory results with such a type of tube . * Presented at the Stated Meeting of the Institute held Wednesday, December 15, 1920 .