. Il giornale tecnico Bell System . la curva ingresso-uscita dell'amplificatore. Inoltre, se non vi è alcuna distorsione nei formatori, la deflessione orizzontale sarà proporzionale alla tensione alternata di rete applicata al primo stadio mentre la deflessione verticale sarà proporzionale alla componente alternata della corrente di piastra nell'ultimo stadio. La figura tracciata è quindi la dinamiceEc - Ib caratterizzante di tutti i tubi combinati. Che si tratti DI UNA CAPACITÀ PORTANTE sotto CARICO DEGLI AMPLIFICATORI 581 stalliK il caso può essere visto dall'ispezione delle figure. Nel primo oscillogramma di Fig. 1
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. The Bell System technical journal . the input-outputcurve of the amplifier. Furthermore, if there is no distortion in thetransformers, the horizontal deflection will be proportional to thealternating grid voltage applied to the first stage while the verticaldeflection will be proportional to the alternating component of theplate current in the last stage. The figure drawn is then the dynamicEc — Ib charactertistic of all the tubes combined. That this is sub- LOAD CARRYING CAPACITY OF AMPLIFIERS 581 stanlialK the case may be seen by inspection of the figures. In thefirst oscillogram of Fig. 11 there is shown the characteristic foramplifier No. 1 under 130 volts plate supply and .047 watts outputwhere the amplitude of grid voltage is such that no grid becomespositive with respect to the filament nor is the plate current reducedto zero at any part of the cycle. Under these conditions the tubecharacteristic as shown in the oscillogram has the same nearly para-bolic shape as is found l)y other methods. The analysis made at. Fig. 6—Amplifier Xo. 1—Plate voltage 130-V, 1, 000 c.p.s. input, and distortion with output Variation of gain this point showed 7.3% second harmonic, .8% third and less than.1% fourth and fifth harmonics. The mathematical analysis of theproblem expresses the Ec — h characteristic of the tube by a powerseries and shows that the coefficient of the second power term in theseries is the principal factor in producing second harmonic. Thepercentages of harmonic given therefore are such as would be ob-tained from a tube having a nearly parabolic characteristic. Analyses made at lower outputs showed that the amount of secondharmonic present varies with the power output in a manner de-scribed by a slightly curved line on the logarithmic scale used (Fig. 6).The third and higher harmonics are negligible at low outputs but at 382 BELL SYSTEM TECHNICAL JOURNAL