. The thermionic vacuum tube and its applications . r negative, the total 1 J. M. Miller, Bureau of Standards Bulletin H. Armstrong, Proc. , Vol. 3, p. 220, 1915. VACUUM TUBE AS AN OSCILLATION GENERATOR 291 reactance can only become zero at a frequency F, which is lowerthan the natural oscillation frequency A of the simple parallelcircuit LiCi or L2C2. From the curve it is seen that at frequenciesbelow A the reactance of the simple circuit LiCi is inductive(positive), so that the complex circuit shown in Fig. 165 can berepresented by the simple circuit of Fig. 166. This is a Hart
. The thermionic vacuum tube and its applications . r negative, the total 1 J. M. Miller, Bureau of Standards Bulletin H. Armstrong, Proc. , Vol. 3, p. 220, 1915. VACUUM TUBE AS AN OSCILLATION GENERATOR 291 reactance can only become zero at a frequency F, which is lowerthan the natural oscillation frequency A of the simple parallelcircuit LiCi or L2C2. From the curve it is seen that at frequenciesbelow A the reactance of the simple circuit LiCi is inductive(positive), so that the complex circuit shown in Fig. 165 can berepresented by the simple circuit of Fig. 166. This is a Hartleycircuit. If, on the other hand, the reactance between plate andgrid were inductive, the frequency of oscillation of the circuitwill be such as to make the sum of this inductive reactance andthe reactances of the branch circuits I and II equal to zero. Thiswould require that the reactances of these branch circuits becapacitive and therefore the frequency of oscillation will be higherthan the natural frequency of the circuits I and II Fig. 166. In this case the total circuit reduces to one like that shown inFig. 166, except that instead of the two inductances, we have twocapacities, and instead of the capacity C3, we have an other words, the complex ckcuit is reduced to a simple Colpittscircuit. Coupled circuits can be treated in much the same Meissner circuit shown in Fig. 167 is an example of a coupledcircuit.^ The two oscillation circuits are L1L2C3 and LC. Theeffects that can be obtained with such a circuit by varying theconstants of the oscillation circuits have been discussed byHeising in the paper cited above. The reactance-frequency curvesof such a circuit are shown in Fig. 168, where Xi represents thereactance of the circuit L1L2C3, and X2 the reactance due to1 A. Meissner, Electrician, Vol. 73, p. 702, 1914, 292 THERMIONIC VACUUM TUBE coupling with the oscillation circuit LC. The sum of the tworeactances is indicated by the curve
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