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BELL SYSTEM TECHNICAL JOURNAL 



izes the field due to its positive companion so that the latter becomes 

 ineffective in drawing electrons avv^ay from the cathode. As the 

 negative grid approaches zero potential it uncovers the positive grid 

 electrically so that the latter becomes highly effective in drawing a 

 large space current from the cathode at the moment when the peak 

 current is drawn to the plate. This would not be so effectively ac- 

 complished if the lateral wires were symmetrically arranged. 



POSITIVE 

 GRID (net) 



(e: 



D 



CONTROL GRID 

 POSITIVE GRID (net) 



Fig. 17 — Schematic diagram showing the arrangement of electrodes in a co-planar- 

 grid tube. 



In Fig. 18, characteristic curves are shown for a co-planar-grid tube 

 designed to operate at a plate potential of 130 volts and at a plate 

 current of 35 milliamperes. Each of the three groups of curves shows 

 the plate current as a function of the control-grid voltage for plate 

 voltages of 100, 130 and 160 volts, and with the positive-grid voltage 

 maintained constant at the indicated value. It is evident from these 

 curves that the primary effect of increasing the potential of the 

 positive grid, or net, is to translate the group of plate-current curves to 

 the left. By so doing it is obvious that larger control-grid swings are 

 possible, at any given operating plate current, without the potential of 

 the control-grid becoming positive at any time. This results in a 

 comparatively large power output, to obtain which large grid swings 

 are essential. 



The lower curve in Fig. 18 shows that a nearly linear relation exists 

 between the positive and negative increments in voltage that must be 

 applied to the positive and negative grids, respectively, to maintain a 

 constant operating current, in this case 35 milliamperes. 



