US2667593A

US2667593A - Electron tube

Info

Publication number: US2667593A
Application number: US197040A
Authority: US
Inventors: Howard D Doolittle
Original assignee: Machlett Laboratories Inc
Current assignee: Machlett Laboratories Inc
Priority date: 1950-11-22
Filing date: 1950-11-22
Publication date: 1954-01-26
Anticipated expiration: 1971-01-26

Description

Jan. 26, 1954 H. D. DOOLITTLE 7 9 ELECTRON TUBE Filed Nov. 22, 1950 H I IO 20 I8 l6 1@ 2| FIG. l

2e 29 25 :2 I I 33 37 as FIG.2

INVENTOR HOWARD D. DOOLITTLE ATTORNE Patented Jan. 26, 1954 ATENT OFFICE ELECTRON TUBE Howard D. Doolittle, Stamford, Conn., assignor to Machlett Laboratories, Incorporated, Springdale, Conn.,

a corporation of Connecticut Application November 22, 1950, Serial No. 197,040

3 Claims. I

This invention concerns an electron tube employing a novel evacuation duct through a solid anode block. More specifically this invention concerns an exhaust duct which emerges at the active anode surface, that surface at which electrons emitted from the cathode impinge, thereby making possible the use of an expansion compensation means which minimizes the change in interelectrode spacing due to heating.

Direct pumping of small tubes, particularly those employed in cavity circuitry, has offered the problem of locating an exhaust duct at some point where its terminating tubulation would not be subject to the constant danger of mechanical breakage. The only part of the tube envelope sufuciently protected to permit location of the exhaust tubulation was found to be on the anode block, and the place usually available on the external portion of the block was found to be on the tubes axis at a point frequently surrounded by cooling apparatus.

Although the problem of mechanical breakage of the exhaust tubulation was solved by axial location, there remained the problem what path through the anode block should be taken by the exhaust duct. When experiments with simple straight exhaust ducts which emerged at the active anode surface were tried, the power loss and upset of tube characteristics encountered were prohibitive. Thus, since ducts terminating at the active anode were unsatisfactory, alternative solutions became necessary. As many anode blocks use essentially all the planar top of the block perpendicular to the axis of the block as the active surface, it became common for ducts to emerge at such anode blocks side walls. Consequently, many designs today employ lateral passages beneath the active anode surface connected to an axial duct.

In tubes of planar geometry, because most passages of present exhaust ducts necessarily terminate in side walls of the anode block, still another problem has recently arisen. It has been found that when tubes heat up, the interelectrode spacing between the anode and its prox1- mate electrode often tends to decrease. Thus a change in capacity occurs causing a resultant change in the frequency of operation. This problem has become especially serious in view of the fact that uses for high frequency tubes in particular are demanding greater and greater frequency stability. The primary cause of this change in spacing has been the differential expansion between the anode terminal, often made of Kovar, and the anode block, usually made of ("ill surface.

copper. Since it was once the practice to join the anode terminal to the anode block at or near the base of the block and remote from the active surface of the anode, there was great opportunity for differential expansion between terminal and block. Recently Kovar shells have been used as a reentrant connection means between the base of the anode terminal and a level on the anode block much nearer the active anode This has helped to reduce the change in spacing by reducing the effective length of the block whose expansion opposes that of the terminal. However, because the exhaust ducts have penetrated the side walls of the anode block, the amount of anode block above the Kovar shell has had to be substantial. Thus even with the improved reentrant Kovar shell, frequency shifts from 6 to 15 me. at a base frequency of 200 me. over a temperature change of 20 to 180 C. have been experienced.

It occurred to me that were it possible to .terminate an exhaust duct at the active surface of the anode, the reentrant Kovar shell could be extended and attached at the active surface of the anode block. Accordingly, ,I conducted ex:- periment which have shown thatif the exhaust opening through the active anode surface is no greater in diameter than one-half the distance between the anode and its nearest adjacent electrode, there will be a minimum of disturbance of the potential field within the tube and. a negligible loss of power. I that it is possible to make where needed providing the area of the opening is small (e. g. in the order of 10 per cent or less) compared with the total cathode area. When exhaust ducts of this description are used it is found that the number of electrons which impinge the anode within the exhaust duct is sulficiently small to be immaterial despite the fact that they are out of phase with the electrons striking the active anode surface.

Accordingly it is the object of my invention to provide an electron tube structure which will maintain essentially uniform spacing between a. planar anode and its adjacent electrode despite severe heating.

Another object of my invention is to provide a simple exhaust duct for use with tubes employing an anode block. If the diameter of the exhaust duct is kept to less than half the interelectrode spacing between the anode and its adjacent electrode, it is possible to terminate this duct at the active anode surface. In some instances this diameter may be exceeded providing have also discovered this opening larger,

anode block emerges at the active anode surface.

Fig. 2 shows another electron tube partially in section in which a similar exhaust duct is at a slight angle.

Referring to Fig. l, the drawing depicts in partial section a coaxial diode. The cathode l shown therein is preferably of the oxide coated indirectly heated type. It is supported on a foil collar H which is in turn afiixed within the tube to terminal 12. Another heater terminal (not shown) is commonly used within terminal 12 and forms, together with insulation sealing it to terminal 12, part of the vacuum wall. Ring 13 is joined to terminal l2 by means forming part of the vacuum envelope. A glass ring it joins ring l3 to the tubular anode terminal ring i5.

' A copper anode block [6 is commonly used to conduct away heat generated by electron bombardment of the active anode surface. A reentrant' shell I! made of material having the same coefiicient of expansion as the anode terminal is joined to the anode terminal at its base. As isshown here the reentrant shell may be made of cup shape so that its bottom [8 may serve as the active anode surface. In this case a vacuumtight joint may be conveniently made along'the side walls at the top of the anode block it between it and the reentrant shell H. An axial exhaust duct [9 emerges at the active surface of the anode in an opening 29' having a diameter preferably less than one-half the interelectrode spacing. A metal seal 01f tubulation 2| sealed to anode block H5 at shoulder 22, which may be formed by counterboring, is able to withstand the bombardment of those few electrons which 1 enter the exhaust duct. As the structure becomes heated, the expansion of the anode terminal l5 and glass [4' will tend to compensate that of the reentrant' shell I! so that the interele'ctrode spacing will remain unchanged.

Referring to Fig. 2, a coaxial triode is shown in partial section. Within the tube cathode 25 is afiixed by foil tube 26 to terminal 21. The vacuum wall'may be completed by another heater terminal advantageously sealed coaxially within terminal 21. Cathode terminal 21 is joined to grid terminal 28 by means, including insulation, forming part of the vacuum envelope. Grid terminal 28 supports grid 29 through tubular grid su'D'pOrtw Tubular grid'te'rminal 23 is insulated from tubular anode terminal 3| by glass ring 32.

The top of anode block 33 here serves as the active anode surface. Reentrant tubularmember 34 is afiixed' to thetop of the anode block adjacent the active anode surface. end" of the reentrant member 34'; whose coeflicient of expansion matches that of the anode terminal 3|, is afiixed to this terminal. a glass seal 35 is made at the end of tubulation The other 65 Because 36, the exhaust duct 31 which is again made through the active anode surface is placed at an angle with the axis so that electrons which enter may not cause destruction of the glass which is unable to conduct away heat as readily as metal. The tubulation 36 may be brazed to the anode block at shoulder 38.

My invention is not confined-to the specific embodiments described but may be applied with variations to any vacuum tube construction employing block anodes.

I claim:

1-. In an electron tube having planar anode and cathode electrodes within a vacuum envelope, an anode end portion of coaxial construction for said electron tube comprising an anode terminal ring, a solid anode block, a member forming areentrant'part of the tube envelope and extending. between the anode terminal and the axial level of the active anode surface at which level it is fixed to the anode block, and a duct which passes through the anode block and emerges at the planar active anode surface thereby' reducing the area of said anode surface by an amount which is small compared to the cathode' area, the opposite end of said duct terminating in'seal-off means.

2. In an electron tube having planar anode and cathode electrodes within a vacuum envelope, an anode end portion of coaxial construction for said electron tube comprising an anode terminal ring, a solid anode block, a tubular member forming a reentrant part of the tube en'- velope and extending between the anode termi-' nal and the axial level of the active anode sur-" face at which level it is fixed to-the' anode block in a joint extending along the edge of the gen erally cylindrical surface adjacent the active anode surface, and a' duct which passes through the anode block andemer'g'es at thejplanar anode surface thereby reducing the area of said anode surface by an amount which is small compared to the cathode area, the opposite end of said duct terminating inseal-off means.

3. In' an electron tube having planar anode and cathode electrodes within a vacuum envelope, an anode end portion of coaxial construction for said electron tube'comprisin an anode terminal ring, a' cup member extending" reen trantly into thetubeso that the planar bottom of said 0111) provides the" active'anode surface, a solid anode block fixed to the opposite surface of the bottom of said cup, and'a duct which passes throughthe anode block andthrough the bottom of the'cupto emerge at 'the'active anode surface therebyreducing the area of said anode surface by an amount which is" small compared to the cathode area, the opposite en'd'of said duct t er minating in seal o'ff means;

HOWARD Di DOOLITTLE'.

dormley'et'al oct: 24'; 1950'"