Radio Broadcast (Nov 1923-Apr 1924)

298 Radio Broadcast great, broad-minded country of ours which early recognized his genius, took him lovingly in her arms, and carried him steadily to the pinnacle of his fame." As we recollect the many talks by Steinmetz which it was our good fortune to hear, it seems that his life and work assuredly bore out the thesis which President Nicholas Murray Butler of Columbia University recently submitted to a group of engineering students, to whom he was giving an informal talk. Although he was "not an engineer and didn't pretend to understand the great problems which engineers undertake," yet his observations, those of a layman, had convinced him "that only those engineers really succeed and accomplish things who have imagination. " Steinmetz was gifted with a wonderful imagination, and the products of this imagination he brought to concrete and useful forms by the workings of his well trained mind. Furthermore, he could really think — an activity in which few of us seriously indulge. How the C Battery Prevents Distortion Your Amplifier Need Not Distort Signals If You Know How to Apply the Proper C Battery Voltage to the Grid By JOHN F. RIDER TRAN S FO R M E R coupled audiofrequency amplification is almost as old as the three-element vacuum tube, yet its refinements are just appearing before the public. Before broadcasting became popular, when spark and CW signals dominated the ether, distortion in an audio-frequency amplifier was a rare complaint. The character of the signal did not require distortionless amplification. Very little attention was paid to the design of amplifiers, if the desired amount of volume amplification was obtained. Since broadcasting came in, the requirements for audiofrequency amplifiers have been much more exacting. To-day, amplifiers are required which shall increase the intensity of the signal, yet retain all the fine variations of the voice impulse, so that the music emitted from the loud speaker is an exact reproduction of that picked up by the microphone in the studio. Even if the transmission is perfect, entirely without distortion, and if the detection is perfect, nevertheless the signal is distorted after passing through a two-stage amplifier. What has caused the distortion? The C battery eliminates distortion, increases the life of the B battery, and makes the audio amplifier more economical to operate. Fig. 1 is a schematic diagram of a standard two-stage audio-frequency amplifier. One can readily see that there are only two parts of the amplifier which can cause distortion: the coupling transformers and the vacuum tubes. In which of these two does the trouble lie? Extensive experiments have been made and are continually being made by the manufacturers of audio-frequency transformers, in an endeavor to produce a transformer that operates perfectly on all frequencies encountered in the broadcasting of voice and music. Their experiments have proved successful, and transformers that function admirably in that respect are now on the market. Therefore, let us also assume that the transformers in the amplifier have been matched for the tubes and are perfect. The entire unit operates excellently on weak signals, but the distortion persists when strong signals are being amplified. So, by the process of elimination, we have arrived at the vacuum tube as the source of our troubles. We find by experience that, by reducing the brilliancy of the filament, we can minimize the distortion to a certain degree, but this method is unsatisfactory, as it results in a decrease of signal intensity.