US2051179A - Constant control gas discharge tube - Google Patents

Description

Aug. 18, 1936. ROTHE 2,051,179

CONSTANT CONTROL GAS DISCHARGE TUBE Filed May 12, 1933 lNyENTOR H0857 07195 ATTORNEY Patented Aug. 18, 1936 UNETED STATES PATENT OFFICE CONSTANT CONTROL GAS DISCHARGE TUBE Germany Application May 12, 1933, Serial No. 670,723 In Germany May 2, 1932 2 Claims.

It is known to provide a gas filling in electron discharge tubes, for example, three electrode tubes with a thermionic cathode having a surface or coating of high electron emissivity, a grid, and an anode. The ions produced in the tube lessen the space charge and increase the steepness of the discharge characteristic. In the use of these gas filled tubes the serious difficulty was previously encountered that they can be used only with comparatively low anode voltages, because the high velocity ions produced by a higher voltage bombard the electron emitting layer on the cath- =ode and destroy the emission of the tube.

In accordance with this invention this difficulty is overcome in that the ions which are used for lessening the space charge are'not produced directly by the electrical field of the anode voltage, but by the electrical field of an auxiliary electrode which has such a low voltage that the ions produced by this low voltage are not capable of appreciably bombarding the cathode.

As one illustration of an embodiment of the invention a discharge tube with a thermionic cathode, a grid, a screen grid, and an anode will be described.

The cathode is, for example, a usual indirectly heated cathode coated with oxides of barium and strontium, and surrounded by a usual control grid. At a certain distance from the control grid, which is preferably cylindrical in shape, is placed a similar cylindrical screen grid. The distance at which the screen grid is spaced from the cathode and anode, and the gas pressure, are so chosen that a sufficient number of ions is produced by the screen grid to influence the space charge. Behind the screen grid and also surrounding it, is a cylindrical anode which is spaced from the screen grid at a distance as small as possible, and operated with an applied voltage of, for instance, 100 volts with respect to the cathode. The spacing between the screen grid and the anode is made so small that within this space a marked ionization cannot take place; that is, the ionization produced in this space is negligibly small as compared with the ionization produced by the screen grid. Thus the number of ions whose velocity is greater than 40 or volts, and which are the only ions which disintegrate the cathode and exert upon it the detrimental bombardment, is correspondingly and negligibly small. It is obvious that discharge tubes comprising a directly heated cathode or any other desired cathodes and electrodes, can be made in accordance with this arrangement, if only care is always taken that practically all the ions bombarding the cathode are produced by the field of the auxiliary electrode or by the field of electrodes of the same, or of lower voltage, and are below the voltage at which the cathode disintegrates.

The tube just described is shown diagrammatically in the accompanying drawing, in which Fig. l is a diagram of the'tube as connected in circuit, and Fig. 2 is a diagrammatic cross section of the tube.

The partially evacuated envelope l contains gas at low pressure, and encloses the cathode 2, control grid 3, screen grid 4, and anode 5 connected in the usual way to an input circuit 6 and a source of voltage, such as a battery I. The spacing between the screen grid 4 and the anode 5 is dependent on the kind and pressure of the gas in the envelope, and is usually as small as possible, not exceeding the mean free path of the molecules of the gas, and so small that ionization in the space between the screen grid and anode is negligible.

I claim:

1. An electron discharge device comprising a partially evacuated envelope containing sufficient gas to furnish, when ionized during normal operation, a sufiicient number of positive ions to minimize space charge, an oxide coated thermionic cathode, a signal control grid, a cold electrode, and an auxiliary cold electrode interposed between said control grid and said cold electrode, 30 an input circuit connected between the signal control grid and the cathode, means whereby said auxiliary electrode has impressed thereon a constant positive potential suflicient to ionize said gas but insufiicient to produce ions of a velocity greater than about 50 volts, said cold electrode and said auxiliary electrode being spaced a distance less than the mean free path of the ions so that positive ionization of the gas in said space is negligible.

2. An electron discharge device comprising a partially evacuated envelope containing sumcient gas to furnish, when ionized during normal operation, a suflicient number of positive ions to minimize space charge, an oxide coated thermionic cathode, a control grid, a screen grid and means whereby a low constant potential is applied thereto for ionizing the gas, and an anode and means whereby a higher potential is applied thereto, said anode being spaced from said screen grid at a distance no greater than the average mean free path of the ions in said gas whereby no appreciable ionization occurs in the space between said screen grid and said anode.

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