. The thermionic vacuum tube and its applications . icial line or balancing network having an impedance equal 1 B. Gherardi and F. B. Jewett, Proc. , Nov., 1919, p. reader is referred to this paper for information on the use of repeaters onlong distance telephone lines. 2 W. L. RicH.\RDS, U. S. Patent 542657, 1895. THE THERMIONIC AMPLIFIER 263 to that of the Hne. The purpose of the balancing network can beunderstood from the following: The currents coming from Line W,for example, are branched off at Pi, thus furnishing the input totube E, the amplified output of which is obtai
. The thermionic vacuum tube and its applications . icial line or balancing network having an impedance equal 1 B. Gherardi and F. B. Jewett, Proc. , Nov., 1919, p. reader is referred to this paper for information on the use of repeaters onlong distance telephone lines. 2 W. L. RicH.\RDS, U. S. Patent 542657, 1895. THE THERMIONIC AMPLIFIER 263 to that of the Hne. The purpose of the balancing network can beunderstood from the following: The currents coming from Line W,for example, are branched off at Pi, thus furnishing the input totube E, the amplified output of which is obtained in the outputtransformer Ti. Similarly the amphfied currents from Line Epass through the output transformer T2. Now, if the systeminto which transformer Ti, for example, feeds were not s;yTnmetricalwith respect to the points P2, the amplified current in Ti wouldcause an increased input to be impressed on tube W; this in turnincreases the input on tube E, and the system would produce sus-tained oscillations, or sing. This is prevented by making. FiG. 148. the impedance of the balancing network equal to that of theline to which it is connected, thus making the potentials of thepoints Pi and P2 independent of the currents m the correspondingoutput coils T2 and T\. This, of course, results in a division ofthe amplified output power, one-half becoming available and theother half being wasted in the balancing network. In a system like this the degree of amplification obtainablewithout impairing the quality of transmission depends largelyon the accuracy with which the lines can be balanced. Two-way transmission can also be secured with a singlerepeater, by means of a circuit arrangement such as that shown in 2G4 THERMIONIC VACUUM TUBE Fig. 149. This circuit is known as the 21-type repeater circuit(<(ro-way, one-repeater circuit). Instead of balancing each hnewith an artificial network, as in the 22-circuit, two-way trans-mission, with the 21-circuit, is effected by balancing th
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