US2720608A - Cathodes for electron tubes - Google Patents

Description

Oct. 11, 1955 w. WIHTOL CATHODES FOR ELECTRON TUBES Filed March 13, 1951 l/V VEN TOR WEL 7/5 W/HTOL A TTORNEYS United States Patent M CATHODES FOR ELECTRON TUBES Weltis Wihtol, Redwood City, Calif.

Application March 13, 1951, Serial No. 215,240

3 Claims. (Cl. 313332) This invention relates generally to cathodes for electron tubes and more particularly to cathodes having a particular utility in the disc type or lighthouse type electron tubes.

It is a particular object of this invention to provide a self-heated cathode having a utility in disc type and lighthouse type tubes.

It is another object of this invention to provide a cathode which heats very rapidly whereby the cathode heater current may be turned ofl during standby periods without experiencing a long heat-up time.

It is a further object of this invention to provide a selfheated cathode structure having good mechanical strength and the ability to withstand frequent beatings and coolings without substantial change in the positioning of the various tube elements.

These and other objects of the invention will appear from the following description in connection with the accompanying drawings which illustrate one embodiment of the invention and in which:

Fig. 1 is an axial sectional view of an electron tube embodying the invention;

Fig. 2 is a detailed sectional view substantially on the line 22 of Fig. l; and

Fig. 3 is a detailed sectional View substantially on the line 33 of Fig. l.

The invention is illustrated in connection with an electron tube of a type generally known in the art as the disc type tube or the lighthouse tube. In general such tubes are well known to the art and examples appear in such patents as the Drieschman patent, No. 2,446,269, patented August 3, 1948, and the Drieschman and Leonard patent, No. 2,458,693, patented January 11, 1949.

Such tubes are described in said Patent No. 2,458,693, and are usually in the form of a triode structure comprising an anode 10, grid 11 and cathode 12 arranged with active surfaces disposed in parallel planes. These electrodes are mounted in a suitable envelope comprising a body section 13 of vitreous material, such as glass, sealed at one end of an anode supporting member 14 and at the other end to a tubular envelope section 15. Anode supporting member 14 comprises a metal cup having a cylindrical wall 16 and an inturned annular flange 17 to which the body section 13 is sealed.

The anode is preferably made of material having good heat conductivity, such as copper and is provided with a flat anode surface presented interiorly of the body section 13. The anode 10 is provided with an enlarged outwardly and upwardly extending annular portion 18 which is secured to the upper edge of the cylindrical wall 16 of the support 14 in any suitable manner. The cylindrical wall 16 and the annular portion 18 of the anode 10 function as the anode terminal.

A suitable cooler 19 is provided for the anode. This cooler comprises an annular member 20 carrying a series of transverse disc-like heat radiating fins 21. The annular member 20 is secured to the anode 10 by means of 2,720,608 Patented Oct. 11, 1955 an externally threaded sleeve 22, the threads 23 of which mate with internal threads 24 on anode 10 and with internal threads 25 on annular member 20.

The tube is exhausted through a metal tube 26 secured to the anode 10. The tube 26 communicates with the interior of the electron tube through inverted T-shaped passage 27. The upper end of the tube 26 is sealed by means of a glass tubulation 28 by pinching off the tubulation at the tip 29.

The tubular envelope section 15 at the lower end of the envelope is provided with a cylindrical wall 30 and an outwardly extending flange 31 to which the lower edge of the body section 13 is sealed. The tubular envelope section 15 is arranged coaxially with the anode and the cylindrical wall 30 functions as the terminal for grid 11. Grid 11 is supported upon an inverted cup-shaped member 32 provided with a cylindrical portion 33 which contacts the interior surface of the cylindrical wall 30 of the tubular envelope section 15. The upper end of the cylindrical portion 33 is provided with an inwardly extending flange 34 and the latter is provided with an upwardly extending cylindrical portion 35. The grid 11 is secured to an inwardly extending flange 36 at the top of the cylindrical portion 35.

The cathode 12 in tubes of this type is generally mounted on a stem 37 arranged coaxially with the envelope and arranged to project into the envelope through tubular envelope section 15. The cathode stem 37 comprises a pair of concentric stem members including an outer tubular part 38 and an inner rod like part 39. These stem members are joined together by a glass seal 40 between the outer tubular part 38 and the rod 39. The stem 37 in turn is secured to the tubular envelope section 15 by a glass seal 41 between the lower end of tubular envelope section 15 and approximately the middle of stem 37. A cup-shaped terminal 42 is fixed to the outer end of rod 39.

The above mentioned structure, in general, is well known in the art and is recited merely to describe the preferred environment for this invention. The invention itself comprises an improved cathode construction having a utility in connection with the above mentioned environment.

The cathode disclosed in this application comprises a disc 43 provided with a downwardly turned cylindrical edge 44. The disc 43 is supported on the upper end of the outer tubular part 38 of the stem 37 with the cylindrical edge 44 of the disc 43 embracing the outer circumference of the tubular part 38. The lower surface of the disc 43 is secured to the upper end of the rod 39 by means of an eyelet 45. The eyelet 45 comprises a cylindrical wall 46 which embraces the upper end of rod 39 and an outwardly extending flange 47 which embraces the lower surface of the disc 43.

Breather openings 48 are provided in the cylindrical wall 46 of the eyelet 45 and breather openings 49 are provided in the upper portion of the outer tubular part 38 of the stem 37 to prevent rupture of the disc 43 when the tube is exhausted.

The upper surface of the disc 43 is provided with an emissive coating 59 selected from materials such as barium or strontium.

The disc 43 is made from very thin foil such as, for example, tantalum having a thickness of .0005. In operation the thickness and conductivity of the foil should be so selected that the cathode will be heated to approximately 1000 Kelvin and not quite to incandescence.

The outer tubular part 38 acts as the cathode connector and also acts as one connector for the heater. The cup-shaped member 42 acts as the other connector for the heater.

The cathode construction described above is self-heated.

, r 3 It will be observed that the use of two circumferentially arranged connectors to the cathode, to-Wit the upper end of the outer; tubular part 38 which is one connector and the outwardly extending flange 41 which is the other connector tendsto produce even heating of the cathode disc 43.

In actual practice it has been found that the cathode of thisinvention will reach operating temperature in approximately /2 of a second instead of the usual minute or two. This greatly reduces'standby problems and tends to lengthen the tube life,

This application describes the preferred embodiment of this invention and is merely illustrative and this application contemplatessuch changes as fairly fall within the scope of the following claims.

The invention is claimed as follows:

- 1. An improved rapid heating flat cathode for an ultra high frequency electron tube including an outer cylindrical support, an inner cylindrical support, said first cylindrical support and said second cylindrical support being mounted coaxially with respect to one another, the upper ends 'of said first and second cylindrical supports being formed displaced downwardly into circumferential contact with the upper end "of the outer cylindrical support, said tubular support and said cylindrical support adapted to conduct heating current to and from said thin disc.

2. An improved uniformly heated flat cathode for an ultra high frequency electron tube including a first cylindrical support, a second cylindrical support, said first cylindrical support and said second cylindrical support being coaxial with respect to one another, an eyelet secured to and extending beyond one end of said second cylindrical support, the upper ends of said first support and said eyelet being formed with concentric annular surultra high frequency electron tube including an outer cylindrical support constituting a cathode connector, an inner cylindrical support, said outer cylindrical support and said inner cylindrical support being coaxial with respect to one another, said supports having high electrical conductivity, the upper ends of said cylindricalsupports being formed with concentric annular surfaces, and a thin selfheating conducting disc of tantalum having a thicknessof the order of .0005 inch and secured to said annular surfaces, said disc having a lower electrical conductivity compared to said supports.

References Cited in the file of this patent UNITED STATES PATENT S' Spencer June 21, 1949 McKay June 3, 1919 v y -m1

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