US2068388A - Electron tube in a retarding field circuit - Google Patents

Description

Jan. 19, 1937. SCHRGTER ELECTRON TUBE IN A RETARDING FIELD CIRCUIT Filed Jan. 28, 1933 z gui {IIIII INVENTOR FRITZ SCHROTER BY 7% 4m ATTORNEY Patented Jan. 19, 1937 PATENT OFFICE ELECTRON TUBE IN A RETARDING FIELD CIRCUIT Fritz Schriiter, Berlin,

Telefunken Gesellschaft Germany, assignor to fiir Drahtlose Telegraphic in. b. 11., Berlin, Germany, a corporation of Germany Application January 28, 1933, Serial No. 654,091 In Germany March 23, 1932 2 Claims.

The present invention is concerned with the retarding field circuit arrangement comprising a thermionic tube. It is known that circuit arrangements comprising tubes operating with retarding fields may be carried into. practice in such a way that the sum total of the currents flowing to the grid acting as the plate and to the retarding electrode represent the saturation current of the filament, and that solely the changes in current distribution between these electrodes are utilized. An arrangement of this kind as known in the prior art is shown in Fig. 1.

One difficulty, however, in the attempt to insure full utilization is that even above the saturation potential Eg, the current exhibits a slight additional growth with increase of potential. The situation is illustrated in Fig. 2 graphically in which the voltage Eg acting at the grid (abcissae) is plotted against the sum total of the grid and plate currents (ordinates). The curve there plotted refers to the constant plate potential Ea. The value of the saturation voltage is represented by the point E' In order to be able to fully utilize the current distribution, operation is restricted to the use of cathodes which evidence a saturation defined in the foregoing sense.

A similar current voltage characteristic as the one shown in Fig. 2 is found for tubes which operate with screen grids maintained at a constant positive potential. A characteristic of this sort is shown in Fig. 3. If, while all other potentials are maintained unvaried, the plate potential Ea. of such a tube be raised beyond a certain critical value E'a which lies somewhat above the potential of the screen grid, then the current Ia flowing to the plate will be found to rise only slightly. It is easy to represent for values of several megohms without it being necessary to use the saturation current of the oathode.

In the case of thermionic tubes connected in a retarding-field scheme and which are to be operated in a way as hereinbefore outlined, there is provided between the filament and the grid acting as a plate an arrangement of additional auxiliary grids in such a way that for the quantity a+ a) the same effect is obtained as for the internal resistance of screen grid tubes. In this expression Eg is the potential of the grid nearest the plate, Ig is the value of the current flowing in the aforesaid grid circuit and I9. is the value of the current flowing in the plate circuit. A schematic example of such a tube is shown in Fig. 4. By the 5 use of electron tubes in such an arrangement conditions are no longer dependent upon a cathode having a definite saturation, and this, as is well know from practice, is hard to accomplish. As shown in Figure 4 the inner grid is maintained 0 at a constant negative voltage with respect to the cathode, the second grid at a constant positive voltage while the adjustable battery in the circuit of the third grid indicates broadly any means for applying a high positive potential thereto. As 15 shown, the battery in the plate circuit applies a small negative potential to the plate whereby it repels the electrons passing through the third grid or produces a retarding field. When used as a transmitter tube I have found the following 20 voltages to be satisfactory; third grid 4,500 volts, second grid 250 volts, first grid a few volts negative bias and the plate a negative bias voltage as high as 50 volts, thereby producing the retarding field for the electrons.

I claim:

1. An electron tube circuit arrangement comprising the combination of an electronic tube having a cathode, a retarding field electrode, a grid mounted adjacent said electrode, a source of 30 potential having its negative terminal connected to said cathode and its positive terminal to said grid, means for maintaining said retarding field electrode at a negative potential with reference to said cathode and means for maintaining the 35 sum of the currents to said grid and retarding field electrode substantially constant upon change in potential of said retarding field electrode, said means comprising a second grid located between said cathode and first named grid, 4 a steady source of potential having its negative terminal directly connected to said cathode and its positive terminal directly connected to said second grid, a third grid located between said cathode and second grid and means for maintaining said third grid at a steady negative potential with reference to said cathode.

2. In a. device of the class described, the combination of a vacuum tube having a cathode, a retarding field electrode and a plurality of grids located at different positions in the electron stream between said cathode and retarding field electrode, a source of variable potential having its negative terminal connected to said cathode and its positive terminal to the outer one of said grids, a circuit connecting said retarding field electrode and cathode and including a source of potential having its negative terminal connected to said retarding field electrode, and means comprising the inner of said grids for maintaining the sum of the currents to said outer grid and retarding field electrode substantially constant upon variation of the potential of said outer grid and a source of constant potential having its negative terminal directly connected to said cathode and its positive terminal directly connected to said inner grid.

FRITZ *SCHRGTER.

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