EXHAUSTED VALVES

Radio Record, Volume I, Issue 24, 30 December 1927, Page 5

EXHAUSTED VALVES

HOW TO REVIVE THEM, A common cause of failure in modern wireless receivers, and one which the average listener seldom suspects, is the failure of the valves (writes "8BD" in the Melbourne ‘‘Argus’’). A few davs ago a friend asked me to look at his set to see why it was not working. After making an extensive examination of all the equipment, and testing all the batteries, I subjected the valves to a test and found that the filaments of several of them were exhausted. Although the dull emitter types of valves have practically revolutionised wireless reception in the last few years, they are subject to the insidious trouble of filament exhaustion without the filmament actually breaking or "burning out."? The operation of the dull-emitter valve depends on the inclusion in the filament of some substance-usually the element thorium-which possesses, to a minor degree, the essential properties of adium, The presence of this substance in the filament will cause it to emit a dense cloud of electrons, which are the electrical units conveying the current through the valve between the plate and the filament at a much lower temperature than that at which an ordinary untreated filament will prorg an electron cloud of equal density.