. (The) oscillation valve in the transmission and reception of radio messages . ctrons emitted from the filament an equal number of thosein the space are repelled back into the filament.^ THE THREE ELECTRODE VALVE A third electrode may be inserted between thefilament and plate, as the form of a metallic gauge orgrid of fine wires is generally called the grid*. Theaddition of this third electrode makes it possible to in-crease of decrease the current between plate and filamentthrough wide limits. If a voltage is applied to thegridby means of a third battery connected between the filamentand the
. (The) oscillation valve in the transmission and reception of radio messages . ctrons emitted from the filament an equal number of thosein the space are repelled back into the filament.^ THE THREE ELECTRODE VALVE A third electrode may be inserted between thefilament and plate, as the form of a metallic gauge orgrid of fine wires is generally called the grid*. Theaddition of this third electrode makes it possible to in-crease of decrease the current between plate and filamentthrough wide limits. If a voltage is applied to thegridby means of a third battery connected between the filamentand the grid, the space charge effect can be modified. Theelectrons traveling from filament to plate must pass throughthe grid, therefore by varying the potential of the gridbetween positive and negative, we can either retard or speed up the progress of these electrons. By making the grid increasingly negative a point is reached where no flow of electrons will take place between filament and plate. Fig. VII shows the two electrode circuit of Fig. VIwith grid and grid battery PRACTICAL APPLICATIONS OF TKE VALVE While all vacuum valves used at present for thereception of radio messages are of the three electrode type,the old two-electrode rectifier may be used in a circuit suchas Fig. Ill, in place of the crystal rectifier D. Several different groups of curves may be plottedfor the three-electrode valve from which its operating,characteristics may be readily seen. Thus the plate voltage may be plotted against theplate current, giving curves dependent upon the temperatureof the filament, or the grid voltage may be plotted againstthe grid current. The most satisfactory curve, and the onemost commonly used for explaining the operation of the tubeis the grid-voltage, plate current curve, shown in Fig. VIII.
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