FILAMENT TEMPERATURE

Evening Post, Volume CVI, Issue 4, 5 July 1928, Page 23

FILAMENT TEMPERATURE

Few owuors of radio sets realise the importance of correct filament voltage on the vacuum tubes of a radio receiver, according to Bay H. Manson, chief engine or of the Stromberg-Carlson Company. Mr. Manson explains that upon correct voltage depends, not only long life of tubes "but the ■'naturalness of reproduction of the receiver. . "Tlic vacuum tube is.a' soiisitiyo in-r-.triinVoit;" 'ijr snys, "and. it is-essen-tial, that the conditions undur which it

operates are exactly those for which the tube was made. . Operating tubes ou voltage above or below .that for which they were /designed lowers the efficiency of a receiver's operation. Too low voltage prevents them from doing their full work .and causes distortion; too high voltage also causes distortion through overwork and tremendously shortens the lifo of the vacuum tube. Some visual method for assuring correct tube voltage at all times is jiecessaiy, and he recommends that all radio receivers should be provided with voltmeters having a red line to indicate the correct setting, and a control by which the voltage may be adjusted to this correct setting. In this way,'he declares, constantly efficient operation and enchanging naturalness of reproduction are secured. Few receivers are sold in this country with voltmeters ready fitted, and the High price of good-meters usually checks the set-owner's enthusiasm. However, a meter is probably an economical addition to the set, especially when valves taking very small filament currents are used in conjunction with dry "A" batteries. An interesting point in connection with thoriated filaments (such as are used in valves ■of tho 109 and 201 a type) is that they are. not improved but rather the reverse by being run too cool, ov^n though they will operate well, the effect being to make the filament more fragile. Oxide-coated filaments—those which normally run with only a rod glow or less—arc not 'damaged by low. temperature operation. A voltmeter used for testing the accuracy of filament idjustiueiit must have a fairly high resistance.. When its terminals are placed upon the filament terminals of a lighted valve there should be no apparent reduction in the brilliancy of the filament; otherwise the reading will be incorrect and the filament will be working at a higher current than •'■) indicated by the meter..