2 Page 27 COMPARISON WITH A PENTODE a triode has both strong and weak points If in mathematical analyses the triode be considered as an infinite impedance pentode with negative feedback certain of its advantages ID: 27877
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AN 23.2 - Page 27 ¨ COMPARISONWITHAPENTODE,a triode has bothstrong and weak points. If, in mathematicalanalyses, the triode be considered as an infinite-impedance pentode with negative feedback, certainof its advantages appear as direct and expectedresults of negative-feedback theory and in someof particular interest for control circuits and outputtriodes, since the back actionfrom the anode on the emission-controlling Þeld atthe cathode is then appreciable. Fundamentally, Fig. 1a shows a conventional pentode represen-tative of any screen-grid, multi-electrode valve. Fig.1b shows a conventional triode. The dynamicIt is seen that Eqn. 1 becomes identical with +m gm=ce gr gm= ggm= cathode. (If is positive, Eqn. 2 represents a form of the EquivalentAnode Circuit theorem. This theorem also applies tothe circuit in Fig. 1c where a Þctitious screen gridhas been inserted between the anode and cathode tojustify the transfer of the voltage from the anodecircuit to the grid circuit where it appears as the Þc-titious voltage (c)B+0BA +Ð +Ð B++Ð +Ð +Ð +Ð Ð+ Shield