Richardson's handbook of projection (1930)

1026 HANDBOOK OF PROJECTION FOR It might here be remarked that up to this time no acceptable substitute for the vacuum tube amplification has been discovered. The vacuum tube may therefore be said to be pretty nearly the "heart" of sound reproduction equipment, which is the reason it has been selected for first consideration. In Fig. 388 we have the diagrammatic representation of a glass bulb from which all air has, so nearly as possible, been exhausted, and a fairly perfect vacuum thus established, and, since the tube is sealed air tight, it is maintained. The connections of such a tube in an amplifying circuit also are indicated. In this tube filament F connects to battery A, as shown. Battery A is a twelve (12) volt storage battery. The tube also contains grid G and Plate P, connected as indicated. NOTE. — It will of course be understood that in actual practice the wires do not connect direct as shown, but through various items of equipment serving various purposes. For the purposes of simplified explanation of vacuum tube action, however, the diagram serves very well, and just now we are concerned only with the action of a vacuum tube when used as an amplifier. Examining Fig. 388, if we send current from battery A through filament F, the filament will of course become heated, in which state it will throw off electrons, as already set forth, each of which is a tiny particle of negatively charged electricity, or electric energy, the action of which will be governed by the well known electric law that positive attracts negative and repels positive. In Fig. 388 in the batteries the long lines represent