US3153170A - Electron tube electrode support structures - Google Patents

Description

t- 3, 1964 H. D. DOOLITTLE ELECTRON TUBE ELECTRODE SUPPORT STRUCTURES Filed 001;. 7. 1960 FIG.3

IN VEN TOR.

HOWARD D. DOOLITT LE AGENT United States Patent This invention relates to improvements in electron discharge devices and has particular reference to electron tubes having novel electrode structures.

Still more particularly, the electron tube'of this inven- "tion has an anode structure of novel construction designed to permit controlled thermal expansiomenabling the tube to be operated without substantial shift in resonant capacity or frequency.

In conventional triodes of the character described, expansion of the copper anode toward the grid of the tube when plate voltage was first applied caused a shift in the resonant capacity of the grid-anode structure due to increase in the grid-anode capacitance as the anode became heated. This was improved by replacing the copper with a thin metal shell of a material having low expansion characteristics, such as Kovar, and mounting on the surface of the shell remote from the grid a copper shank which was free to expand outwardly, thus reducing the shift in grid-anode capacitance.

More recently it was found that in using such tubes as amplifiers, frequency drifts would occur, leading to decreased power output. If a tube is optimumly tuned at given plate dissipation, the tuning will generally stay fixed. However, changes in ambient temperature or errors on the part of the person tuning the amplifier may lead to detuning of the circuit, in which case the tuning may be slightly high or slightly low relative to the amplifyingfrequencies. This results in above normal anode dissipation.

Maximum power output is obtained when the device is tuned exactly to the amplifying frequency. Power output goes down and plate dissipation goes up when the device is detuned on either side of resonance. When the circuit is tuned slightly above optimum frequency the resultant increase in anode dissipation tends to retune the circuit. However, if the circuit is tuned slightly below the resonant frequency, the increase in anode dis-- sipa'tion will cause the circuit to be detuned to a still lower frequency, resulting again in decreased power output and a further increase in anode dissipation such that the tube will automatically detune the circuit until the power output is very low.

Applicant has discovered that this detuning is caused by anode expansion due to temperature variations caused by changes in anode dissipation.

Accordingly, it is a primary object of this invention to overcome the foregoing problem by the provision of a novel anode structure wherein variations in anode dissipation will not affect changes in the anode-grid spacing and, therefore, in the tuning of the circuitry. This is accomplished by providing an anode which is in the shape of a relatively thick heavy disc or plate to which is brazed or otherwise sealed the dielectric portion of the envelope which holds the grid and cathode structures. Heat is conducted away from the flat. anode plate by a block of copper or other metal to which fins may be attached for air cooling.

Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawing, wherein FIGURE 1 is a front elevational View partlyin axial section of an electron tube embodying a preferred form of the invention;

Patented Oct. 13, 1964 FIGURE 2 is a fragmentary axial section of a modified form of the invention; and

FIGURE 3 is a fragmentary axial section of a further modification of the invention.

Referring more particularly to the drawings, there is shown in FIGURE 1 a triode which includes a cathode 10, a grid 11, and ananode 12 enclosed within a housing comprised of a plurality of metal and dielectric parts. The cathode 10 is supplied with electric power through a tubular metal terminal structure 13, and the grid 11 is connected to and supplied with a suitable electric potential through a metal annular grid terminal 14. Terminals l3 and 14 are spaced and interconnected by a dielectric member 15, and both the grid and cathode structures internally of the tube are mounted upon and supported by one end portion of a dielectric bulb 16 to which the grid terminal 14 is secured.

The opposite end of the bulb 16 terminates in a substantially plane annular surface against which is located the adjacent surface of an anode plate or disc 17 preferably formed of Kovar or like material having relatively low thermal expansion characteristics. The plate 17 is relatively thick and heavy and is of a size to substantially completely span the end of bulb 16, as shown, and carries at its outer periphery an annular metal terminal 18 which extends from the plate 17, to which it is securely affixed, into closely overlying relation to the adjacent outer surface of the bulb l6. Terminal 18 extends sufficiently f-ar enough along the surface of bulb 16 to permit an eflicient To the outer surface of the heavy plate 17 is secured a block 21-of copper or other material having high thermal conductivity.

The central portion 22 of the block 21 extends outwardly as shown and is provided with a longitudinal bore 23 in which is mounted a metal tubulation 24. Bore 23 is in communication with a second bore 25 of smaller diameter extending through the block and plate, whereby the interior of the tube may be evacuated. The outer surface of portion 22 may be threaded to receive a suitable radiator (not shown) or the inner surface of a downwardly extending peripheral flange portion 26 of block 21 may be threaded for this purpose.

Heat from the Kovar plate 17 is readily dissipated through the block 21 which is preferably coextensive with the plate 17. Such efiicient heat dissipation combined with the large size of the plate which lies entirely outside of and is supported upon the bulb 16, and the fact that the plate inherently has low thermal expansion characteristics, results in an anode structure which will resist the tendency to expand toward the grid and thus detune the circuit during changes in anode dissipation.

As a further deterrent to expansion of the anode toward the grid, the plate 17 is provided on its surface nearest the grid with an annular groove 27 which has a diameter at least as large as and preferably somewhat larger than the outer diameter of the effective area of the grid 11 and an inner diameter substantially equal to the outer diameter of the effective portion of the cathode 10. Thus, most of any slight expansion which might occur in the heated central portion of the anode surface opposite the cathode will be in a transverse direction into the groove, thus reducing any tendency of the surface to expand toward the grid.

The annular groove 27 provides a still more important feature of the structure due to the fact it is located in the interelectrode area Where most of the passive capacitance occurs. .Byproviding such a groove, passive capacitance in the interelectrode area is reduced by nearly one-half.

In FIGURE 2 there is shown an anode 28 which is formed as a single unitary structure from a block of selected metal having relatively high thermal conductivity, such as copper. The surface 29 of the anode .28 is substantially planar and extends somewhat beyond the adjacent junctions with the dielectric-bulb 30 and the terminal 31 as shown. The surface 30 is spaced a predetermined distance from the grid 32 and cathode 33, and in such a structure it will .be apparent that the seal with the end of the dielectric bulb 30 will prevent movement of the surface 29 toward the grid 32 under thermal expansion stresses. The surface 29 may also be provided with a groove, as shown at 27 in FIGURE 1, in the area where passive capacitance occurs, if desired to reduce such capacitance.

It has been :found that in the operation of some tubes of the character described, the anode temperature will not only rise, with time, to a selected degree, but the frequency will also shift slightly higher. Such change in frequency has been found to be caused, not by variations in anode-gridspacing caused by expansion of the anode as a result of changes in anode dissipation, but instead by other factors such as, for example, expansion of the dielectric bulb supporting the anode.

If the anode temperature of such a flat anode tube is raised, for example, from about 20 C. to about 80 C., the resonant frequency may rise from about 1600 me. to about 1601 me. Therefore, to compensate for this frequency change in tubes Where this occurs, applicants fiat anode is provided witha substantially fiat raised area 34 as shown in FIGURE 3. The flat annular surface 35 encircling the raised area 34 is sealed to the adjacent end of the dielectric bulb 36 and thus the raised area 34 is located within the bulb. Such raised area is, however, controlledas to its diameter so as to be substantially confined to-the interelectrode space where active capacitance occurs, thus having a diameter substantially equal to the diameter of the effective cathode 37.

It is important that the area 34 be raised only enough to compensate for the change in frequency and, in the foregoing example, would be raised only about .040", depending upon the materials used in the structures and their particular coefficients of expansion, relative sizes, electrical .characteristics, etc. "In any case, the area 35 would be raised only a very small degree. A groove, such as 2 7, may encircle area 35 if desired to reduce passive capacitance as described above.

From the foregoing .it will be apparent that applicant has provided a novel anode structure which overcomes previously existing problems caused by thermal expansion. However, it is to be understood that various changes may be made without departing from the spirit of .the invention as expressed in the appended claims.

I claim:

1. An electron discharge device comprising an evacuated housing which includes a tubular member of dielectric material of given diameter having an annular planar end surface, a cathode mounted within said tubular member and supported adjacent the end thereof opposite said surface, a grid structure positioned within said tubular member and freely spaced therefrom and supported adjacent the same end thereof at which the cathode is supported, and an anode structure positioned adjacent the grid on the side thereof opposite the cathode and comprising a disclike metal member of substantial thickness having a substantially planar surface abutting said end surface and spanning the entire diameter of said end surface, said metal member being vacuum sealed at said surface to the tubular member and supported only at said seal and movable under thermal expansion stresses only in directions away from the anode whereby interelectrode spacing is unaffected by thermal expansion of the member.

2. An electron discharge device as set forth in claim 1 wherein interelectrode spacing is unaffected by thermal expansion of said metal member, said metal member is provided with means for dissipation of heat comprising a block of metal having relatively high thermal conductivity aflixed to the side of the metal member remote from the tubular member.

3. An electron discharge device as set forth in claim 1 wherein said block is substantially coextensive with the surface of the metal member to which it is afiixed.

4. In an evacuated electron tube embodying a tubular housing portion of dielectric material of given diameter having a substantially planar annular end surface and containing parallel cathode and grid electrode structures having substantially circular effective surfaces, said electrode structures being freely spaced from the housing portion in the area of said end surface and supported adjacent the opposite end of the housing portion, an anode for said tube comprising a disc of rigid and relatively thick metal having relatively low thermal expansion characteristics, said disc being substantially entirely outside the housing portion and having a substantially planar surface coplanar with said end surface of the housing portion and spanning the entire diameter thereof and sealed thereto, the member being supported only at said seal and movable under thermal expansion stresses only in directions away from the anode whereby interelectrode spacing is unaffected by thermal expansion of the member.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,119 Beggs June 18, 1946 2,819,421 Ringland et al. Jan. 7, 1958 3,109,119 Spurck Oct. 29, 1963

Claims (1)

1. AN ELECTRON DISCHARGE DEVICE COMPRISING AN EVACUATED HOUSING WHICH INCLUDES A TUBULAR MEMBER OF DIELECTRIC MATERIAL OF GIVEN DIAMETER HAVING AN ANNULAR PLANAR END SURFACE, A CATHODE MOUNTED WITHIN SAID TUBULAR MEMBER AND SUPPORTED ADJACENT THE END THEREOF OPPOSITE SAID SURFACE, A GRID STRUCTURE POSITIONED WITHIN SAID TUBULAR MEMBER AND FREELY SPACED THEREFROM AND SUPPORTED ADJACENT THE SAME END THEREOF AT WHICH THE CATHODE IS SUPPORTED, AND AN ANODE STRUCTURE POSITIONED ADJACENT THE GRID ON THE SIDE THEREOF OPPOSITE THE CATHODE AND COMPRISING A DISCLIKE METAL MEMBER OF SUBSTANTIAL THICKNESS HAVING A SUBSTANTIALLY PLANAR SURFACE ABUTTING SAID END SURFACE AND SPANNING THE ENTIRE DIAMETER OF SAID END SURFACE, SAID METAL MEMBER BEING VACUUM SEALED AT SAID SURFACE TO THE TUBULAR MEMBER AND SUPPORTED ONLY AT SAID SEAL AND MOVABLE UNDER THERMAL EXPANSION STRESSES ONLY IN DIRECTIONS AWAY FROM THE ANODE WHEREBY INTERELECTRODE SPACING IS UNAFFECTED BY THERMAL EXPANSION OF THE MEMBER.

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