. The thermionic vacuum tube and its applications . 46 XIO 48 XIO^ 50 XIO^ 55 XIO* 60 XIO* 65 X106 70 75 80 XlO^ 85 X10« 90 X10« 95 X10« 100 XIO 220 THERMIONIC VACUUM TUBE Fig. 112 shows the relation between power amplification andthe ratio of external impedance Zo to the plate resistance curves were computed from equation (35) with the followingvalues: m = 5, rp = 5XlO^ ohms, rs = 6XlO ohms, and the imped-ance
. The thermionic vacuum tube and its applications . 46 XIO 48 XIO^ 50 XIO^ 55 XIO* 60 XIO* 65 X106 70 75 80 XlO^ 85 X10« 90 X10« 95 X10« 100 XIO 220 THERMIONIC VACUUM TUBE Fig. 112 shows the relation between power amplification andthe ratio of external impedance Zo to the plate resistance curves were computed from equation (35) with the followingvalues: m = 5, rp = 5XlO^ ohms, rs = 6XlO ohms, and the imped-ance Zo was assumed to have an angle of 45°. The lower curvegives the amplification expressed in ratio of output to input power,while the upper curve gives the power amplification expressed inmiles of standard No. 19 gauge cable. It is seen that while thejiower ratio varies considerably from the maximum value when the ratio —? deviates from unity, yet the change in the efTect produced on the ear, which is more in accordance Avith the upper curve. Fig. 112. expressed on the logarithmic scale, is quite small. A changein amplification of one standard cable mile is not serious. Theexternal impedance mto which the tube works can therefore havevalues ranging from about one-half to two and one-half times theplate resistance without producing any marked change in effect asheard in the telephone receiver. Now, it was stated above that the condition to be satisfied bythe receiver shunt is that its insertion in the circuit must not changethe total impedance of that circuit, and this must be true for alladjustments of its shunt and series resistances. The receivershunt is, of course, so arranged that the shunt and series resist-ances are only inserted in definite paire, the object being that thechange in the total impedance, due to the insertion of a shunt THE THERMIONIC AMPLIFIER 221 resistance must be compensated for by the addition of a corre-sponding series resistance. Referring to Fi
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