US2181366A - Electron tube - Google Patents

Description

Nov. 28, 939. D v, EDWARDS ET AL 2,181,366

ELECTRON TUBE Filed May 17, 1938 wp/mn HFA TEE ya." g v CHTHODE AND HEATER ATTORNEY:

Patented Nov. 28, 1939 UNITED STATES PATENT OFFICE ELECTItON TUBE aware Application May 17, 1938, Serial No. 208,336

2 Claims.

This invention relates to gaseous discharge tubes intended for operation at heavy currents and having a metal vacuum container.

The object is to provide a construction resulting in a small compact tube capable of radiating large, quantities of heat.

In the accompanying drawing,

Fig. 1 is a view mostly in section, of a gaseous discharge tube comprising the invention;

Fig. 2 is a horizontal section on line 2`2 of Fig. 1, partly broken away; and

Fig. 3 is a perspective view of a modication of the tube of Fig. 1.

Like reference characters indicate corresponding parts in the several figures. A

In Fig 1 a gaseous discharge rectier tube I0 has a metal envelope or container II closed by a metal bottom plate I2 which is formed with a trough-shaped sealing ring I3. Sealing material I4 secures the container and bottom plate togeth'er'in sealed insulated relation. A cathode I5 is supported above plate I2, such as by rods I6 Welded thereto, in discharge relation to container II which is also the anode of tube I0. The cathode illustrated is of the internal emissive type having an outer heat shield Il and an inner can I8, each of which has an opening I9 for passage of the gaseous discharge to anode II. The interior surface of can I8 may be electron emissive. It is provided with a heater 25 having multiple current paths between the top of can I8 and a metal plate 2l. The heater itself may or may not be electron emissive depending on whether a directly heated or an indirectly heated cathode is desired. A lead-in conductor 20 for'heater 25 is secured to plate 2I and passes through an insulating bushing 22 in the bottoms of can I8 and shield Il. Conductor 20 also passes through an inverted cup 24 to which it is sealed by welding,

I2 Without touching the latter. The rim of cup 2S is sealed in the trough I3 by the sealing material I4 which may be of glass suitable for making a vacuum tight joint with metal.

Conductor 20 and plate I2 thus form terminals for the cathode and its heater. The heater circuit is from plate I2 through rods I6 to shield II and can I8, thence through heater 25 to plate 2| and back through conductor Y20.

Electrical connections to tube I0 may be made as indicated diagrammatically in Fig. 1, the cathode connection and one heater connection being common. The anode connection to the container-anode II is made through metal members attached thereto as hereinafter described. 1i?

and then through a large center hole 23 in plate (Cl. Z50-27.5)

should be understood that in practice such connections are large enough to carry the maximum current of tube I0, for instance, several hundred amperes for the `cathode and anode connections. In a large rectifier tube rnost of the energy losses in the tube are transmitted to the anode/ by the electron stream and must be dissipated to permit the tube to operate satisfactorily. Heretofore it has been the custom to depend upon radiation to convey substantially all 'of this heat from the anode. Introduction of metal-wall containers permitted removing part of the heat by convection to the air and part by radiation to the surrounding atmosphere. For small tubes, radiation and convection can remove the heat from the area where it is developed rapidly enough to prevent overheating. As the size of the tube is increased -the anode areaover which the energy is dissipated, has, in the past, been increased by lengthening the discharge path and by increasing the cross section. To increase the area heated by the anode losses in large tubes results in a big cumbersome construction and increases the cost of the tube materially as the difficulties of manufacture increase in proportion to the amount of surface that must be evacuated. In addition, the eiciency of the device is impaired because a much larger volume must be maintained in an ionized state resulting in a higher arc drop and therefore greater tube losses.

According to the invention the tube size can be reduced to that giving the optimum discharge path as far as eiciency is concerned and allowing the anode losses to occur in a relatively small area of the ,tube envelope, if the metal envelope is given a spheroid shape and if a radiator composed of material having a high heat conductivity assv is attached on to the outside, for instance, by the I process described herein.

Such a radiator is shown at 26 in Figs. 1 and 2. It provides' heat dissipation directly and radially by metallic conduction from every part of container-anode II that'is subject to overheating. The radiator is made of metal having a high heat conductivity and high coeihcient of thermal expansion, such as aluminum or copper. The body 21 of the radiator has a fairly thick and uniform wall surrounding the substantially cylindrical portion of container II but is much thicker at the top. A thick web 28 formed integrally with body 21 may be provided and may have metal inserts 29 in the form of supporting brackets, the ends 30 of which are adapted to be secured to a support 34. Either bracket may function as the anode terminal for the tube.

Radially disposed cooling ns 3I may be cast integrally with body 2'I or be attachedI thereto.

The radiator may have, in addition, a surrounding stack 35 to increase the circulation of air through the fins by natural convection.

Before attaching radiator 26 to tube I0 the latter should be degassed, filled with the desired ionizable medium, and permanently sealed, because degassing processes employ high temperatures (up to 1000 C.) which would injure 'or destroy the radiator, and in any event, prior attachment of thev radiator would interfere with the tube-making processes.

In the embodiment illustrated in Fig. l the radiator is' made separate from the tube and is attached thereto by pouring in a molten metal lling 32 having a higher coefficient of thermal expansion than the metal composing the evacuated container Il. Zinc and tin are suitable lling metals when chamber Il is made of steel. For good heat conductivity it is essential that no part of the surface of envelope I I at which substantial anode losses occur be fiat or concave outwards. In Fig. l it will be noticed that al1 surfaces on which anode losses occur are convex outward. In a discharge tube of this sort the area over which the anode losses will be distributed depends on the pressure `of the gas filling. It would probably cover the area above the top of cathode I5 with the intensity increasing toward the axis of the tube. For this reason the radius of curvature is decreased as the axs is approached. This radius of curvature taken in conjunction with the difference in thermal expansion of the material of the radiator filling and envelope results in intense casting strains when the lling material solidies tending to collapse the dome of envelope II. The intimate contact thus obtained by radial stress is essential to satisfactory operation, because any area of low local pressure results in severe gassing.

or even melting of the envelope I I under load. Due to the lower heat conductivity of the zinc or tin filling 32 compared to copper or aluminum the thickness of the space to be iilledA isas small as is consistent with good casting practice.

Modications rof the Fig. 1 construction are possible; for instance, 'if desired the entire radiator may be cast on to the envelope IIr provided the latter is treated Vto withstand the temperature attained in casting without seriously affecting the properties of the tube. At the present time, plain steels are not available which can adequately resist the diffusion of hydrogen at the casting temperature of aluminum. To increase the life of the tube the steel may have a thin vitreous enamel coating on the outside. By the use of severe casting strains set up in the manner described it is possible to cast zinc or tin in such close contact with the enamel that heat is removed to the radiator during heavy load without damage to the tube, and good electrical contact is obtained with the steel.

To increase the temperature strains as much as possible the method of casting may be as follows: Radiator 26 is turned upside down and heated to about 400 C. Zinc or tin, in a separate crucible, is heated to melting temperature. The envelope II is warmed to C. or so. Such molten metal in excess is quickly poured into the cup formed by the radiator and then tube I0 is forced down into the molten metal and heldl metal during the casting process to insure the solidication of the molten metal around the nose of envelope II first and to prevent hidden voids in the filling metal. A groove 33 may be provided in the wall of container II to interlock the solidified metal with tube I0.

By this process it is believed the pressure set up causes plastic flow of the filling metal on cooling thus causing it to iill in minute crevices or roughness in the radiator casting and in the enamel coatingon the tube. It is, of course, apparent -that enamel is a poor conductor of heat and .for this reason the coating must be made extremely thin so that the temperature drop across it will not be severe. Such large quantities of heat are involved that the conductivity of the container II tending to carry heat around any point of poor contact is negligible. So much heat must be transmitted that even in a thin layer of steel a very appreciable temperature drop will occur across this metal. Needless to say, the radiator must have a large thickness of aluminum or copper directly opposite the anode surface to provide suii'icient cross section to conduct the heat away from the flow is more or less radial at all points and results in a very rapid increase in the cross section of the heat conducting path as the heat is carried away from the anode surface. The cross section of radiator 26 is increased so much within 3 or 4 centimeters of heat travel from the surface of anode Il that temperature drops are not serious. It is then only necessary to provide adequate cross section of attachment for the radiating fins 3|'. It is preferable to dispose the ns vertically relative to the mounting position of the tube in order toV make all of them eifective for cooling.

It will be apparent that a radiator of the type described dissipatesmost of its energy by convection rather than by radiation and that the velocity of the air through the fins can be increased if the stack 35 is provided to constrain the ow of heated air above the tube. This results in an increase in radiation but is often omitted because of space limitations.

Fig. 3 illustrates a. modification wherein the web 28 and brackets 29 of Fig. 1 are omitted and outer edges of some of the fins 3I by small screws 38, or in some other manner, so that the stack supports the entire structure.

The steel used for container II may be cold rolled or stainless steel. In some cases other metals may be used if they have the requisite strength and resistance to hydrogen diffusion at the temperatures employed.

For the radiator body the aluminum or copper may be alloyed with other metals. Alloys containing magnesium, nickel, zinc or cadmium also may be used if they have high heat conductivity and high coeicient of expansion. The melting point may be high for a precast radiator but it should be fairly low if cast directly on the container. The ns 3l may be cast as part of the radiator body or they may be of sheet copper having good heat conductive connection to a central metal body or die-casting.

For the illling metal, tin is preferred for its 10W melting point (234 C.) whereas zinc is presweating.

The attachment of a radiator on a gaseous discharge tube as above described results in a tenfold increasein the capacity of the tube to rectify current. For instance, a tube of the type shown in Fig. 1 in which the container is about 31/2 inches in diameter and '6 inches long can supply a load of 15 kilowatts at 110 volts when it is equipped with a radiator but without the radiator it cannot supply more than 1% kilowatts load.

A practical advantage of a precast radiator with a lling metal is that, when the electron tube fails or is worn out it may be removed by melting the fllling metal and then theradiator casting may be used-with a new tube.

While the invention is particularly advantageous in connection with gaseous discharge tubes it may also be used to advantage with high power high vacuum tubes and in general with electron tubes having metal or partly metal containers irrespective of the number or kind of contained electrodes, type of discharge, degree of vacuum, or the natureof the gas or vapor lling.

The invention also is applicable generally to sealed metal containers having a source of heat therein and requiring faster cooling than is obtained by natural radiation from the container itself.

A The terms spheroid and spheroidal as used in the specification and claims include ellipsoid or ellipsoidal or conoid or conoida While two specific embodiments of the invention have been shown and described it should be understood that further modications may be made such as to meet different conditions or uses, and therefore the appended claims are intended to cover all modiilcations within the true spirit and scope of the invention.

We claim:

l. An electron tube comprising a cathode, an anode enclosing the cathode and being wholly spheroidal in shape over that part of the anode surface which receives the electron discharge, and a radiator having a heat conducting portion of higher co-eiiicient of expansion than that of the metal anode and having a spheroidal recess complementary to and fitted over the spheroidal anode and at the normal operating temperature of the tube being stressed in tension in all directions tangential to the recess surface to exert high inward pressure against all parts of the spheroidal surface of the anode over which it is tted, which stress can be relieved only by temperature above the normal operating temperature of the tube.

2. An electron tube comprising a cathode, an anode enclosing the cathode and being wholly spheroidal in shape over that part of the anode surface which receives the electron discharge,. a radiator having a heat conducting portion oi' higher co-emcient of expansion than that of the metal anode and having a spheroidal recess complementary to and iltted over the spheroidal anode and at the normal operating temperature of thetube being stressed in tension in all directions tangential to the recess surface to exert high inward pressure against all parts of the spheroidal surface of 'the anode over which it is fitted, which stress can be relieved only by temperature above the normal operating temperature ofthev tube, and a spheroidal'liner interposed between the anode and the radiator, said liner being of metal relatively soft comparable to the anode and the radiator and having a melting point lower than that of the anode and the radiator and higher than that of the operating temperature ot the tube.

DONALD V. EDWARDS.

EDWARD B. VAN NOTE.

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