Connecticut western news., 1922-06-15

grid, determine the value of E. E is the negative potential which must be applied to the grid in order to reduce the plate current to zero. The value of F, which Is the positive grid poten- tial that will cause the maximum or saturatiOn current to flow in the plate circuit, is also determined by the rela- tive position of the grid with respect to the filament and plate. If the grid is of very fine mesh, the value of E Is small because the electrons in pass ing through the small mesh of the grid on their journey from the fila ment to the plate will negatively charge the grid and will be repelled. Similarly a small positive charge ap- piled to a fine mesh will tend to ac- celerate the velocity of the electrons
 In case of a very coarse mesh grid the electrons can pass through the ap- ertureS in the grid without coming In so close to the charge on 1t and relatively high potential will be re- quired on the grid to control the cleo tron stream, or in other words, the current flowing in the plate circuit.
 Referring to Fig. VIII, O-G, is the current that will flow in the plate cir cult when there is no potential ap- piled to the grid. Suppose positive potential as O-I is applied to the grid. The corresponding plate circuit current will be I'D or BID, more than 1t was when the grid had no potential ap- piled to it.
 aF n IT applied to the grid where OH Is Squal in value to O-I, but opposite in sign. The application of the negative po- tential when applied to the grid will cause the plate current to be reduced to a value H-C or 40, less than it was when there was no potential ap- piled to the grid. So 1t is seen that negative potential when applied to the grid does not reduce the plate circuit current as much as the same positive potential increased the plate circuit current. This irregular conductivity of the tube Is made use of when the tube is used as a detector or rectifier of radio signals.
 The incoming radio signal is a high frequency alternating current. Let us apply an alternating difference of po- tential whose maximum positive val ue is equal to O-I and whose maximum negative value Is equal to OH to the grid of the three-electrode tube whose characteristic curve Is the same as that shown in Fig. VIII. In Fig. TX Is shown the alternating difference of potential applied to the grid Through the first quarter Of a cycle, from zero at to a maximum nega- tive value at K, equal to OH, the plate circuit current will vary from O-G, Its value at P when no grid po- tential Is applied to value at O equal to H-CA
 During the next quarter of cycle the grid potential changes from maximum negative value at K to zero at L. The corresponding values of plate circuit current are shown by the portion of the plate current curve OR
 During the next or third quarter of a cycle the applied grid potential increases from zero at L to a maxi mum positive value at NJ, equal to O-l, and causes the plate circuit to in- crease from I-B, its value when the plate potential is zero, to I'D, an in- crease in plate current equal to BID.
 During the remaining fourth quar- ter of a cycle as the applied grid po- tential varies from a maximum posi- tive value at NJ to zero at N, the plate circuit current varies from a value to T.
 Assuming that the characteristic curve as shown in Fig. VIII and Fig. TX was with a potential of 40 volts on the plate, then, If the plate current Is to be reduced to zero by varia- tion of plate voltage-with no poten- tial applied to the grid-the plate voltage must be reduced to zero or a reduction of 40 volts must be made.