Radio Broadcast (May-Oct 1926)

516 RADIO BROADCAST OCTOBER, 1926 FIG. 4 A battery balanced amplifier as used in the experiments between New York and wjz of Newark in 1922. It is a resistance-coupled affair wherein only the alternating potential of the plate is supplied to the succeeding grid by means of a balancing battery, which balances the d.c. potential of the plate periphery of the cone was cemented to a ring of canvas which in turn was cemented to a square plywood board. The action of this device, as in the case of the Phonetron cone speaker, is as follows: The armature coil is drawn inward toward the field magnet when the voice current is in one direction, and forced outward from the magnet when the voice current reverses to the opposite direction. In this way, the force is applied between the apex of the cone and the heavy magnet pot without a system of mechanical levers. The loud speaker, being the device which produces the sound, is generally blamed for all the deficiences of the receiving system, including those due to poor receiver, vacuum tubes, batteries, and at times, even the deficiencies of the broadcasting. The better grade of receiver of to-day contains good audio transformers and is capable of producing good quality music with sufficient bass. It is, however, necessary that the batteries have voltage to supply sufficient power to the vacuum tubes. It is also necessary that the vacuum tubes have sufficient power capacity, i. e., sufficient filament emission and normal filament brilliancy. The type uv-201-A and c-301-A tubes, when new and used with a 90-volt B battery, have sufficient emission and, therefore, power ca* pacity, to permit faithful reproduction at only very moderate intensity. However, when the volume is increased with this combination, an accentuation of harmonics occurs, which are evidenced in a faithful speaker by nasal or rattling tones. An unfaithful reproducer will, however, FIG. 5 A large cone speaker built in experimental form. Its mechanism is not unlike that of the Phonetron shown on the previous page. The cone of this model was about four feet in diameter smooth these "rough edges" of the sound and give a more pleasing tone; this deceives the listener into believing that the more faithful speaker is faulty, whereas the facts are that the speaker is faithfully reproducing the voice which has been distorted by the vacuum tubes. This condition can be improved by an increase of plate voltage, which will lower the impedance of the tube and affect a greater transfer of the lower frequencies (when used with a transformer of given inductance), and will also permit the increased amplitude of the lower tones to be passed without distortion. Super-heterodynes and sets of tuned radio frequency type utilizing regeneration have a tendency to change the tonal characteristics of the music or speech, when tuned. As the receiver is tuned to the maximum volume, an accentuation of the bass will be observed. This may cause all tones to become somewhat drumlike in nature with, at times, a complete loss of the treble. The tuning of a receiver should not change the tonal characteristics of the reception excepting that there is, however, a tendency of the human ear to respond more readily to louder sounds. In practically all radio reception of today, the magnitude of the treble is greater than the bass. This must not, however, be confused with the accentuation of bass due to regeneration as referred to above, when a partial or complete loss of treble occurs at the tuning point of maximum volume. A good receiver and speaker will reproduce throughout its tuning range the true relative value of bass and treble, the reduced bass on either side of the peak tuning point being due to the failure of the ear to notice the bass until it is sufficiently loud. The intensity of treble will not lessen at the tuning point of maximum volume, but the bass will sound louder. FIG. 6 Below is shown another view of the balanced amplifier shown at the top of this page, and schematically in Fig. 2 } I 1 ■ <■ ( A FRENCH AMATEUR SHORT WAVE STATION Owned by La T. S. F. Moderne, a Parisian radio magazine. Its call is 8ae and when this station was erected, was using 1764-1499 kc. (180-200 meters). This view shows the antenna and counterpoise