US1990974A - Alternating current tube - Google Patents

Description

Feb. 12, 1935. J. R. BEERS ALTERNATING CURRENT TUBE Filed May 24, 1927 g IN V EN TOR.

ATTORNEY Patented Feb. 12, 1935 UNITED STATES PATENT OFFICE ALTERNATING CURRENT TUBE Delaware Application May 24, 1927, Serial No. 193,865

10 Claims.

This invention relates to electron discharge devices, wherein a heated member is disposed to emit electrons in the direction of a colder member. More particularly, it relates to devices which may be heated by the flow of fluctuating electric current wherein the fluctuations do not eiiect the emission of electrons.

This invention has for its object to provide heating and emitting elements for vacuum tubes which may be heated by a fluctuating current and at the same time may be easily manufactured without the difficulties heretofore existing with like devices.

Another object is to arrange a heating element with relation to a member to be heated in such a way as to produce a more concentrated heating effect upon the heated member and yet requiring such a low degree of heat intensity of the heating element that the life of said element during actual normal operation is prolonged practically indefinitely.

A further object is to accomplish the most efficient heating, and therefore, increased life of operation of the heating element by proper proportioning the shape of said element and its space relation to the heated member.

A still further object is to devise a method of sensitizing a vacuum tube from which substantially all of the free gas has been removed but which still retains considerable gas occluded within the material of the electrodes.

A still further object is to provide a method of assembling vacuum tubes having a plurality of elements, one contained within another, and all being carried by supports extending from a common press member.

A further object is to provide a vacuum tube which has a separate heating element from the emitting member and a separate heating circuit, with a socket having base plugs arranged in the standard manner for use in ordinary standard sockets, and still other connections independently located in such a position that the conductors may be arranged some distance from the main circuit conductors; thereby preventing undesirable couplings therewith.

Provision is also made for successful operation of the tube, regardless of the connections of the set in which it is used.

Further and more definite objects will appear in connection with the following specification, claims and drawing, in which,-

Fig. 1 shows an assembled view of the vacuum tube with some of the parts cut away to show the construction of one of the terminals;

Fig. 2 shows a section or the electrodes and the press along the lines 2--2 of Fig. 3;

Fig. 3 shows a section along the line 3-3 of Fig. 2;

Fig. 4 shows a section of the press along the 5 lines 4-4 of Fig. 2;

Fig. 5 shows a detailed view of the heating coil on an enlarged scale; and

t Fig. 6 shows a wiring diagram of the vacuum ube.

Contained within the envelope 1 is arranged the press 2 of the vacuum tube supporting the plate element 3 and the various other electrodes. The base portion 4 is cemented or otherwise attached to the envelope 1 and conductors are arranged between these two elements terminating in the contacts 5, 6, 7 and 8. There are also provided connection terminals 9 and 10 which serve as means for completing the circuit to the heater element 11 within the envelope.

The lower portion of this base 4 is arranged identically with the standard form of vacuum tube base, with the contacts 5 to 8, inclusive, extending from the bottom. The upper portion is provided with a flange 12, with supporting lugs 13 and 14, through which are provided holes for permitting passage of the screws 15 and 16. The wires connecting these screws are brought up from the bottom of the vacuum tube between the tube and the base and soldered, or otherwise connected to the soldering pieces 1'7 and 18, as shown in Fig. 1.

These conductors, indicated at 19 and 20, pass through the press 2 at substantially its middle portion and in order to connect these wires to the soldering plates 1'7 and 18, they must necessarily cross some of the other wires within the stem which supports the press. In order to prevent short-circuiting, and reduce the capacitive relation between these wires and the other wires, sleeves 21 and 22 are slipped over these wires, thereby separating them an appreciable distance from the other wires and preventing a short circuit. The evacuating tube 24 is arranged within the stem and connected to a hole in the press in a standard manner.

The plate 3, as shown in Fig. 2, is arranged on the two supporting pieces 25 and 26, mounted in the press 2, and provided with reverse bends 27 and 28, arranged as near as practicable, to the press 2, thereby providing fairly long parallel portions on which the plate is mounted.

The grid 29 is mounted in a standard manner by welding 30 and 31 and supports 32 and 33. The

support 33 is connected by the lead in wire 34 and the support 25 by the lead in wire 35.

In order to produce an electron discharge between the various elements, a cylinder 36 is mounted upon an insulator 37 carried by the mounting piece 38. This mounting piece is flattened as at 39 in order that the heater element 11 may be more easily attached thereto, as well.

'11 is attached to the short rod 44 and held in place by a cross rod 45 welded to this rod and to the external support 46 mounted in the stem in the press 2. It is important that this support 46 be mounted entirely outside of the enclosure formed by the plate 3, as shown in Fig. 3.

The top end of the cylinder 36 is supported by a second cross piece 48, welded or otherwise attached to the top of the cylinder and to the support piece 49 carried by the press. This additional support also serves for electrically connecting the cylinder to the lead-in wire 50. It is also desirable to arrange this support 49 outside of the enclosure of the plate 3, as shown in Fig. 3. The cylinder 36 can be coated with some material which increases the emission of the electrons and permits operation of the tube at lower temperatures. For this purpose barium or strontium oxides, or a combination of the two might be used.

The support 46, as shown in Fig. 3, might be offset in its arrangement upon the press by providing a small lug 52 whereby it is more rigidly maintained in position. The advantage of so separating this supporting conductor is that it does not interfere with the evacuating tube 24 as much as it would if it.were arranged in the middle of the press, and also the capacitive relation between the other conductors is thereby reduced. This lug is also shownin Fig. 4 with its relation to the other supports and conductors.

The heater element may be composed of any extreme heat resisting and conducting material, but it has been found that substantially pure tungsten is peculiarly adapted for use in such an arrangement, and it is advantageous to arrange the heater in the form of a helical coil having particular dimensions with relation to the size of the conductor. It is also necessary, in order to maintain a sufllcient concentration of heat, to arrange the heater within close proximity to the cylinder 36. The heater element 11 should not be positioned closer than 20/1000 or 25/1000 of an inch, or spaced away further than 80/1000 of an inch from the cylinder 36. If it is spaced closer than 20/1000 or 25/1000, diiliculty is encountered, particularly in use with a coil heater in the forming of short circuits against the inside surface of the cylinder. At distances over 80/ 1000 of an inch, insufficient heating of the cylinder takes place.

It is obvious that every metallic material has its respective melting point, above which it is impossible to heat it by the now of electrical current without fusing. For materials having very high melting points, such spacings between the heater and the cylinder should be maintained,

and these spacings have been determined for such materials where the cylinder is provided with a coating with some emission-aiding materials.

the temperature at which it is necessary to heat the heater. It has been found that a heater in the form of a coil, such as is shown in Fig. 5, provides the most eflicient method of heating the cylinder. This coil is so proportioned that the dimension A, that is the diameter of the wire, which forms the coil, is wound upon a mandrel which is 2% times the diameter of the wire A. In other words, the outside diameter of the coil is 4 times the diameter of the wire. Slight variations from this proportion are possible but in a rough way, these dimensions should be maintained.

This coil is so arranged within the cylinder that it is impossible for any electron which may be emitted by the heater to find its way onto one of the other electrodes. The insulator 37 obstructs the downward path and the end of the sleeve 36 being extended above the top end of the heater thereby prevents interference with the other electrodes by direct emission from the heater. Ordinarily it is unnecessary to heat this heating element above the point at which it will emit electrons, and at such a heat it will raise the temperature of the cylinder or shield suzfllciently high to produce an appreciable emission from the coat on the outside in the direction of the other electrodes.

This cylinder or shield need not be of extreme thickness and it is more desirable to have it as thin as possible,more particularly, in the' neighborhood of 2/ 1000 of an inch. With such a thickness an appreciable flow of electrons therefrom is permitted. within a few seconds after raising the temperature of the heater to a point which is appreciably below the emission temperature of such heater. It is also practicable to extend the heater above the end of the shield, provided the shield itself extends above the other electrodes. However, this is not such a desirable arrangement. This cylinder may be composed of nickel, platinum, or any other metal,

or conducting material which lends itself to such a construction. This shield need not be in the form of a cylinder but might well be in any shape which more particularly adapts it'for use.

It is apparent that with such a construction, the relative positions of the heater, shield, grid and plate elements may readily be inspected from the top. The omission of any obstructing element in the top end of the cylinder or shield permits ready inspection of the heater. It is also desirable to position the ends of the heater so that the ends of the cylinder will not be maintained at such extreme temperatures as the middle portion. Such an arrangement prevents the supporting pieces from becoming overheated I and any damage being done to the welded connections.

The longer parallel portions of the supports 25 and 26 are provided so that in assembling the plate 3 may first be slid down to the bends-27 and a halves of the plate, as shown in Fig. 3, to the supports 25 and 26.

In most radio-receiving sets a resistor or varlable rheostat is arranged in the circuit to the filament. It may be connected from either terminal and in order to insure a direct connection whereby such a resistor is short-circuited, the two terminals 5 and 6 which are ordinarily connected to this filament in the standard vacuum tube base, are connected together to form a common return from the cylinder or shield 36. This insures that when this vacuum tube is inserted in the standard socket provided in a radio-receiving apparatus, that no loss of emciency will take place due to the inclusion of the rheostat in the circuit. As shown in Fig. 6, the terminals 9 and 10 are directly connected to the heater element 11; the contact 7 to the grid 29; and the contact 8 to the plate 3. With this arrangement the tube may be used with any of the present-existing type of radio-receiving sets with a minimum of change and a maximum of efficiency. The heating connections may be readily connected to the terminals 9 and 10 by conductors which are spaced an appreciable distance away from the radio and audio frequency circuits. This construction overcomes most difficulties encountered when attempting to operate radioreceiving apparatus by the direct application of alternating current.

In the manufacture and process of evacuation of vacuum tubes constructed along the lines of the one shown, certain methods and arrangements are necessary which are peculiar to the construction used. It has been found that where a cathode member of such large area as is presented by the shield is used, often times considerable difliculty is encountered due to the fact that a large amount of gas is occluded in the coating which covers the outside. This coating, which may be of oxide or other material, will absorb a large amount of gas and therefore unusual means are necessary to remove it. It has been found advantageous in this type of construction to apply a voltage of 400 volts or more for a brief period of time in order to remove this occluded gas. As soon as the effective resistance offered by this gas is removed by the application of this higher voltage the requisite seasoning at the lower voltage has been found sufficient to sensitize the tube.

While particular relative dimensions have been stated in regard to the heater element and the shield, slight deviations, in either greater or smaller amount, are permissible in producing an effective vacuum tube. If a coil of wire is used in which the mandrel is greater than 2 times the diameter of the wire the opposite sides of the turns will ordinarily be separated too far apart to have any appreciable heating effect in an accumulative way across the diameter of the central hole. The main purpose of the coiling of the wire is to intensify and concentrate the heat. It also aids in the resilience of the heater so that it will be maintained in a more nearly rigid position. Such a construction also permits a much shorter over-all length of the heater unit than would be possible with a single straight wire. It is also preferable to have the spacings between consecutive turns as close as possible without actual contact. With proper arrangement of parts, these spacings can be reduced to a matter of four or five-thousandths of an inch.

From the construction described it is evident that with the cylinder positioned as shown, the distance from the heated portion of the heater to any adjacent electrode within the tube is greater than the distance through which the electrons are thrown out, and therefore any variations of current in the heater element will produce no effect upon the current in these electrodes. The cause of the heat transfer between the heater and the shield is not known exactly but it is believed to be due to pure heat radiation and possibly partly from heating of the shield due to electron impact.

With the construction thus set forth, the shield will produce a substantial emission of electrons within three to ten seconds after the application of normal voltage across the heater. This is sufficient to overcome any difficulties when alternating current is applied to the heater of twenty five cycles or more. The construction indicated is more particularly adapted for use with sixty cycle alternating current. This construction will therefore cause the shields to be heated at a substantially constant temperature when such a fluctuating or pulsating current is applied to the heater.

In the foregoing description the electron-emitting element 36 has generally been referred to as a shield and sometimes as a cylinder, but in the use of these terms it is wished to be understood that this element functions as a source of electrons and in practice, as well as in the prior art, it is usually termed the cathode. The exact term applied to this element is not so important as the fact that it is metallic in nature, has the smallest practical wall thickness in order to heat up rapidly, and is coated with oxides of barium, strontium or the like to produce emission of electrons and permit operation of the tube at lower temperatures.

It is therefore apparent that a simple and easily manufactured vacuum tube, adapted to be operated by pulsating, fluctuating, or alternating current, has been described, the alternating current being applied to the heater element to cause the shield to emit electrons in the ordinary manner of the incandescent type filament. The filament, with proper spacings, as indicated, from the shield, may be operated at a temperature below that which will emit electrons and the diameter of the shield will be raised above that point at which the shield will emit electrons. It has been explained that the device will function more efficiently if the inner surface is treated in the proper manner. This treatment may consist of applying blackening or darkening substance to the surface, or by merely roughening it, as might be accomplished by simple abrasion. Care must be taken in the abrasion of the surfaces of such thin material as is indicated for this element.

Having thus described my apparatus, I do not wish to be limited to the exact modifications shown, but desire to include a full range of equivalents as has been developed by the prior art, to the extent indicated in the following claims.

What I wish to claim is:

1. An alternating current quick heating thermionic tube comprising an electron-emitting element and a heater therefor consisting of a conductor wound in the form of a single helix, the outside diameter of said helix being approximately four and one-half times the diameter of said conductor.

2. An alternating current quick heating thermionic tube comprising, an emitting shield having the form of a complete enclosing circuit, a heater enclosed therein, a support for said heater and an opening provided at one end of said shield and an insulating spacer at the other end of the shield between said shield and support.

3. An alternating current quick heating thermionic tube comprising, a tube-shaped emitting element of smallest practical wall thickness surrounding a heater composed of a coil of substantially pure tungsten, the outside diameter of said coil being approximately four and one-half times the diameter of the heater wire and spaced more than twenty-thousandths of an inch and less than eighty-thousandths of an inch from said emitting element.

4. An alternating current quick heating thermionic tube comprising, a plurality of electrodes, including a cathode and a heater therefor, a base attached thereto having bottom and side terminals, said side terminals being connected to said cathode heater and conductively independent of said bottom terminals.

5. An alternating current quick heating vacuum tube comprising a press having a plurality of upstanding supports, a heater element supported by two of said supports in substantially parallel relation therewith, one of said supports being longer than the other and supporting the outer end of said heater, a cathode in close spaced relation to and surrounding said heater but prevented from electrically contacting therewith at one end by an insulating spacer between said heater support and cathode and said cathode supported at the other end by another of said supports from said press and a plurality of other electrodes surrounding said cathode.

6. An alternating current quick heating thermionic tube comprising, a press having a plurality of upstanding supports, a heater element supported by two of said supports, a cathode in close spaced relation to and surrounding said heater but prevented from electrically contacting therewith at one end by an insulating spacer between said heater support and cathode, and said cathode supported at the other end by another of said supports from said press and a plurality of other electrodes surrounding said cathode.

7. An alternating current quick heating thermionic tube, comprising a hollow cathode coated with a material for producing emission at low temperatures, a heater enclosed therein composed of material which does not emit at operating temperatures, said heater comprising a wire wound in the form of a helix, the outside diameter or which is approximately four and one-half times the diameter of the heater wire, the spacing of said heater with respect to said cathode being not less than twenty-thousandths of an inch nor more than eighty-thousandths of an inch therefrom.

8. An alternating current quick heating thermionic tube comprising, a cathode consisting of an emitting shield having the form of a complete enclosing circuit, a heater enclosed therein, said shield having the smallest practical wall thickness and coated with a material for producing emission at low temperatures, said heater consisting of a single self-supporting coil of tungsten wire having the turns thereof closely spaced and wound on a mandrel approximately two and one-half times the diameter of the wire, the ends 01' the coil terminating in straight sections and the spacing of the coil with respect to the shield being not less than twenty-thousandths of an inch nor more than eighty-thousandths of an inch therefrom.

9. An alternating current quick heating thermionic tube comprising, a hollow cathode, a heater enclosed therein, said heater consisting oi a single self-supporting coil of tungsten wire wound on a mandrel approximately two and one-half times the diameter of the wire, the ends of the coil terminating in straight sections and the spacing of the coil with respect to the cathode being not less than twenty-thousandthsof an inch nor more than eighty-thousandths of an inch from said cathode. 3

10. An alternating current quick heating thermionic tube comprising, a press having a plurality of upstanding supports, a heater consisting of a single self-supporting coil of tungsten wire having the turns thereof closely spaced, the ends of 4 the coil terminating in straight sections secured to two of said supports, a tube-shaped cathode coated with a material for producing emission at low temperatures, the cathode being in close spaced relation to and surrounding said heater 4 but prevented from electrically contacting therewith, said cathode being supported on both ends from'said press and having its ends extend beyond said coil, whereby the passage of electrons irom the heater element to the other elements is pre- 5 vented.

JOHN R. BEERS.

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