US2490096A - Cathode anticontamination structure - Google Patents

Description

Dec. 6, 1949 J.'ROTHSTEIN CATHODE ANTICONTAMINATION STRUCTURE Filed May 1, 1946 m m m m JEROME ROTH$TEIN FIG. 2

ATTORNEY cally to a Patented Dec. 6 1949 UNITED STATES ATENT OFFICE CATHODE ANTICONTAMINATION STRUCTURE Jerome Rothstein, Belmar, N. J.

Application May 1, 1946, Serial No. 666,226

4 Claims; (Cl. 250-275) (Granted under the act of March 3, 1883, as amended April 30, 1928; 3'70 0. G. 757) The invention described herein may be manugovernmental purposes, without the payment to me of any royalty thereon.

This invention relates to high power vacuum tubes employing oxide cathodes, and particularly to tubes in which grid emission is suppressed without thereby poisoning the cathodes.

.As is well known grid emission seriously interferes with the efficiency of high power tubes. Heretofore the relatively more efiicient oxide cathodes have not been used as extensively as thoriated cathodes because oxide cathodes contaminate the grid and cause it to emit thermionimuch greater extent than in the case of tungsten or thoriated tungsten. cathodes.

'Gold has been found to alloy with the contamihating barium evaporating from the cathode and has been used to coat grids, thereby suppressing grid emission. Unfortunately during processing and high power operation some gold is evaporated on to the cathode. This gold has a deleterious effect on the oxide cathode emission. Ihe present invention makes use of the fact that gold on the cathode migrates in response to applied thermal gradients, and suitable arrangements are provided by this invention whereby the gold migrates to regions where its deleterious effects are minimized.

One of the objects of this invention is to provide a tube in which poisoning of the cathode from a gold plated grid is almost completely avoided.

Another object is to provide a tube having such an arrangement of parts that poisoning of the cathode due to gold is substantially completely eliminated.

Another object is to provide a tube structure in which any gold migrating to the cathode does not remain on the active cathode region but migrates elsewhere as a result of thermal gradients present in the cathode.

These and other objects will become apparent in the specification and the appended drawing in which:

Figure 1 shows the preferred embodiment of the invention as incorporated in a thermionic tube;

Figure 2 shows a modified form of cathode.

In accordance with the present invention the cathode is so heated that the active region of the cathode is hotter relative to the rest of the cathode than it would ordinarily be. Thus, any gold arriving on the outer surface of the cathode will migrate away from the active regions of the oxide and generally toward the cooler end portions of the cathode thereby not poisoning the active region.

In Figure 1 there is shown by way of example, a triode having a plate H), a grid II, and a cathode I2 provided with an inner heater coil l3 and an outer heater coil M. The coils of the cathode are supported on leads I5 and I6 which connect through the base seal to the usual prongs in the base, not shown. The cathode is held in position by a pair of wire supports I! and IS. The upper end of the tube is sealed with the usual glass cap l9 through which extends the grid lead 28. The grid is suspended from and supported by a connecting member 21 attached to the bottom of lead 20. The anode may be provided with the usual fins 22 for providing plate heat dissipation. Preferably the heater wires constitute tungsten filaments wound spirally as shown and may be covered with aluminum oxide if desired.

The inner heater coil l3 heats substantially the entire length of the cathode. The outer coil I4, however, augments the heat imparted to the cathode possibly raising the temperature of the outer central surface of the cathode to efiicient emitting temperature and most important of all establishes thermal gradients between the center and the ends and alters the normal gradient between the outer and inner surfaces of the oathode which bring about diffusion of the gold to the cooler inactive regions of the gold.

It should be noted that the outer central surface of the cathode by this arrangement of heaters attains a higher temperature than the ends and is not as cool relative to the inner central portion as normally. Any gold evaporated from the grid or otherwise reaching the cathode migrates away from the emitting oxide region to the relatively cool inactive ends of the cathode where it does not interfere appreciably with the functioning of the cathode.

Another arrangement for producing this result is shown in Figure 2. Here the cathode I2 is provided with a single coiled heater wire 30 located within the cathode body and spaced from its walls. A pair of open ended cup-shaped members 3| of heat insulating ceramic material are held against displacement by washers 32 and caps 33, the latter preferabl being metallic and suitably blackened to promote radiation. In addition, caps 33 may be provided with cooling fins if desired. In operation the center zone of the cathode will be heated to a relatively high temperature while the ends, due to the shielding and insulating eiiect of members 3| and the radiating efiect of caps 33, remain relatively c001. Thus there is provided a cold sink at each end of the cathode, the anticontamination function being similar to that of the cathode of Figure 1. Where tube geometry permits the useoi a relat vely long cathode themodification 0f Eig'urez offers the advantage ofsimplicity of heater wire arrangement in comparison with the cathode of Figure 1 as well as a somewhat higher emission efilciency.

I have thus produced a non'poisoning cathode. structure which may be used in vacuum tubes.

where migrant cathode contaminants. or poisons are present.

While I have shown but two..embodiments.of my invention it is obvious that those skilled in the art may produce other arrangements in accordance with this invention and- I therefore do not intend to be limited except within, the scope and extent of the appended claims.

I claim:

1. In a thermionic tube including a cathode element having anemitting surface and at least one other'elementghaving asuriace material part .ofwhich transjerls tosaidemitting surface during zoperationand tends. to causea decrease in emission therefrom, heating means substantially smaller than said cathodedisposed in proximity to one portion of; said cathode emitting surface to, heat said emitting surface, to a substantially higher temperature abs ain one portion than at other, portions, whereby said surface material transferredftosaid; emitting surtace is caused to concentrate,atsaidrotherportions of said emitting surface andemission, from said one portionoi said emitting surface, isglnot substantially decreased.

2. In a thermionic ,tubeincludinga cathodeele- -ment having, an. emitting. surfacesand, at least one other elemen't-havinga Surface. material containing gold, part of which transfers to said emitting surface during operation and tends to cause a decrease in emission therefrom, said cathode having one dimension to be considered as length, heating means substantially shorter in length than a eitmd d .hea ilzem ees, disposed in proximity to one portion of-sa' i d-, cathode emitting surface to heat said emitting surface to a substantially higher temperature at said one portion than at other portions, whereby said gold transferred to said emitting surface is caused .tQcOncentrate at said other portions of said emitting surface, and emission from said one portion of said emitting surface is not substantially dec eased/- 3. In a thermionic tube as in claim 1, said heating means including a heater on the outer surface of said cathode at said one portion of said em t 5 1. 1

4. In a thermionic tube as in claim 1, said heating means including a heater within .said cathode con ntrated relatively nearer said one portion than said other portions.

JE ME 'RQIHSTEI REFERENCES crrnn The following references are of record in the file of this patent:

UNITED STATES PATENT S

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