HOWLING AND ITS PREVENTION

Shannon News, 6 December 1927, Page 2

HOWLING AND ITS PREVENTION

What is “howling” and how is it caused? is a question one often hears from amateurs whose neighbours are inconsiderate enough to oscillate over the top of them. For the benefit of these set owners 1 shall try to explain as lucidly as possible just, what howl iug is, and its causes. Whenever the output circuit of an audio-frequency amplifier is coupled to the input circuit instability in the amplifier will very likely be produced and this will result in howling. The output of any audio-frequency amplifier tube has many times the voltage of the input. Suppose, for instance, that the grid of one of the amplifier tubes is set into vibration in one way or another, possibly by someone with big feet walking across the door of the room in which the set is located. As the grid vibrates its relative effectiveness to the value of the plat e current changes in synchronism with the vibrations of the grid. The plate current follows tli e frequency of these vibratons, and, if due to poor wiring, this plate lea.d passes sufficiently close to the grid lead of the tube, there will be a feedback of energy from the output circuit to the input circuit, with the result that the oscillations will be maintained and will manifest themselves in the loud speaker output. The remedy for this is to be sure that none of the wires from the plate circuit is coupled to any of the grid leads.