SELECTING THE TRANSFORMER

Shannon News, 25 November 1927, Page 4

SELECTING THE TRANSFORMER

Apart from their actual powers of amplification, audio transformers offer a fairly easy method of connecting up the two valves, it is dealing with, or, in other words, of handling the signals from' the plate of one valve to the grid of the next, for this cannot be done, for obvious reasons, by a straight connection. More' than two audio transformers are never used (unless of a special type, called “push-pull” transformers), for' the amount of distortion from each, though it may be small, would be so accentuated by the time the third stage was reached that it would be decidedly more than noticeable. So, no matter how good a pair of transform ers may be, the temptation to add more should never be gratified, for distortion . will inevitably result. . Many technical rules and points govern the selection of ft transformer, but, as most of them are hidden from the common gaze, they are of little value in-the choice of a'reliable make. The best criterion .of the.-likelihood of its value is its weight—in other words, the quantity of iron contained in its core. The transformers with the heaviest cores, as a rule, will be found the best. * ,

There are one or two alternative methods of audio-frequency amplification, as resistance-coupling and impedance, both of which, in their freedom from distortion .(resistance coupling can be made absolutely pure) are superior to transformers, but they have several disadvantages which from the popular viewpoint, scarcely appear to be off-set by their > better qualities. Still popular opinion is not always right, and the time may come when this method will receive the support which it undoubtedly deserves. It is at least worthy of further mention.