Uses of Valves

Radio Record, Volume II, Issue 6, 24 August 1928, Page 10

Uses of Valves

READERS of the "Record" will be familiar with the fundamental principles of the -valve. It will be interesting to mention a few of its many applicatio First, within the set itself, there is: (a) Radio-frequency amplifier valves which amplify the impulses collected by the antenna. . (b) A detector valve, which changes these impulses so that they are audible if applied to earphones or to loudspeaker and if they are loud enough. (c) Audio-frequency amplifier velves. These amplify or make louder the detected signals. (d) Power amplifier. This is always the last valve in the circuit. It is often not included in the smaller sets. The function is to relieve the audiofrequency valves and so purify reception. The essential of a set is a detector; after this valves are added before as radio-frequencies and after as audiofrequencies. Finally a power valve may be added. Secondly, there are valves to rectify the alternating current of the house supply, to give a steady, direct current, Thirdly, valves may be used as 2 measuring device. By a suitable connection, the valve amplifies weak currents and, knowing the amplification factor of the valve, the current can be measured. Then again by "hooking up the apparatus backwards," it can be made to measure higher voltages. A specially-designed valve, one designed to carry more plate current than our valves, has been used to regulate the voltage of direct-current generators. There are certain other applications of the valve. which are very interesting on account of the fact that they permit measurements .f extremely small distances and weights. Used as such, the name ultra-micrometer is given to these arrangements. By a special arrangement of apparatus, it has been possible to measure a weight as small as one thirty-thou-sandth of an ounce, and a distance between two plates of one three-millionth of an inch. In addition to these briefly surveyed, there are multi-grid valves, which have many applications, valves connected with photo-electric cells, eg., neons, and oscillators, speech amplifiers, modulators, and regulators in broadcasting stations.