POWER VALVES

Radio Record, Volume I, Issue 10, 23 September 1927, Page 6

POWER VALVES

GREATLY IMPROVED ‘TONE. Many New Zealand broadcast listeners are now employing power valves in the last audio stage of their receiving sets. Among the most popular power valves are the 171, 112 and 210 types. It means an incomparably better tone when a power valve is used, and the strained tone when a valve is overloaded is completely eliminated. Former Discrepancies. Older types of radio reccivers reproduced with full intensity only ‘the medium-pitched notes, to which both the loud speaker and the human ear are sensitive. The lower bass notes were not reproduced and the high frequencies were slighted. Under such conditions, tubes of the 201A type were capable of giving satisfactory service. Up-To-Date Requirements, Present day requirements call for full reproduction of a much wider range of frequencies with uniform intensity. ‘Che high frequencies do not carry much energy, and hence impose no additional load on the valve supplying the speaker. The low frequencies, on the other hand, contain most of the energy present in musical selections or speech and, therefore, haye a_ tendency to greatly overload the valves. At the same time, the reproduction of these notes does not give the impression of Joudness, becanse the ear is less sensitive ic them It will be evident, therefore, that quality reproduction requires valves capable of furnishing greater power ontput than can be obtained from 20IA type and similar valves. Emphasis should be placed on this feature of tone quality in reproduction, and not on the volume obtainable from power valves.