US2032545A - Electron tube - Google Patents

Description

March 3, 1936. H. B. McELRA'n-l ELECTRON TUBE Filed 001,. 26, 1951 2 Sheets-Sheet 1 MHHHHI MMM *my .Y

2 Sheets-Sheet 2 3mm E @ME/mm March 3, 1936. H. B. McELRATl-l ELECTRON TUBE Filed oct. 2e, V1951 ZZ, .a

Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE Claims.

The present invention relates to electron'tubes.

An object of the present invention is to provide a cold radio active cathode for emitting negative electrons in lieu of the conventional hot iilament 5 with its attendant burnouts, current consumption and other well known disadvantages; to provide in the tube a negative radio active grid by use of which may be eliminated the conventional C current and its attending complications and to provide an inherently self-biased grid action to the exclusion of external complicated circuit layouts; and to provide in the tube a radio active anode for emitting positive active charges and assist the B current in drawing to itself the nega- 5 tive charges emitted by the cold cathode.

With the foregoing and other objects in view, the invention will be more fully-described hereinafter, and will be more particularly pointed out in the claims appended hereto.v i

In the drawings, wherein like symbols refer to like or correspondingparts throughout the several views.

Figure 1 is a diagrammatic. view of the improved electron tube employed.

Figure 2 is a diagrammatic view of the improved circuit embodying the potentiometer and the use or a number of the tubes of Figure 1, and

Figure 3 is an enlarged detail sectional view taken through one of the electron tubes.

Referring now to the drawings, III designates the envelope or casing of the tube and in which is placed a cold cathode I I which is shown innermost and connected to a lead I2 which passes to the exterior of the envelope I0 and which may be the cathode circuit lead and is negative. Surrounding the cold cathode I I is the grid I3 which, vn accordance with present usage, is also negative, and which is connected to a lead I4 which constitutes the negative grid circuit lead. Ex-

teriorly about the grid I3 is disposed the anode I5 which is positive and which is connected to a lead I6 extending through the envelope II) and which constitutes the plus plate circuit lead.

In the action of the tube, the "electrons leave the surface of the cold cathode II and pass through the grid I3 which, like the cathode, is negative. The electrons passing through the negative grid I3 strikes the positive anode `I 5, and the anode emits positivev charges of alpha particles and therefore has a tendency to draw the negal tive electrons from the negative cathode II.v

When the positive terminal of a suitable current is connected to the lead I6, there will be a current of electricity flowing when the negative terminal is connected to the lead I2 and the cold cathode I I.v The cold cathode establishes a path for this current across .to the anode I5 and the anode assists the cathode and a direct current crosses the space within the tube from the cathode II to the a'node I5, through the grid I3 in 5 its path. The grid I3, being in the path of this current acts as a valve when an alternating' current or a changing potential is impressed upon it. The negative property of the grid I3, due to its radio active properties is very desirable as it. 10

Y terminal connected to the grid circuit.

Since al1 three of the electrodes II, I3 and I5 are radio active, it follows that each of these electrodes have a charge of an electrical nature; the cathode II and the grid I3 carry negative 25 charges and emit electrons or cathode rays, while the anode or plate I5 carries .a positive charge and emits protons or opposite electrical charges with respect to the cathode and grid. The radio active nature of these electrodes may be accom- 30 plished by any known or suitable method, such as alloying the radioactive material with the respective electrodes, using electrodes composed of materials which give oi radio activity of their own accord, or using metals or substances that 35 have the property -of maintaining induced radio activity or coating the electrodes with suitable radio active substances. The grid I3 and cathode I I must either use a radio active substance which emits electrons or negative electrical charges, or 40 else use a regular radio active substance emitting the alpha, beta and gamma rays and then shielding the less penetrating alpha rays by a thin sheet of suitable material for example aluminum. The shield will thus shut oiI the alpha rays' and 45 allow the penetrating cathode rays or electrons to continue their course.

Since the cathode II and grid`|3 must emit negative electrical charges, they must therefore emit or discharge beta rays and this may be ac- 50 complished by one of two means. The radio active material must emit beta rays and not alpha rays, or else thematerial may emit both alpha and beta rays and in this case the alpha rays will have to be shielded oi or segregated. Ra- 55 (Ra-D) gives off beta rays and no alpha rays. Radium (Ra) and radiothorium (Rd-Th) givesoil alpha and beta ray 'I'hese are the longest life elements in the radio active series;

There are others but ythe above mentioned are considered the best. `These substances may be alloyed with the metallic electrodes o r they may be coated upon the surfaces of the electrodes.

If a radio activematerial is used on the cathode II and grid I 3 which emits both alpha and beta rays, then a thin metallic` shield will have to be secured to the outside surfaces of these electrodes so as to cut oif the alpha rays and'allow the more penetrating beta rays to continue in theirY path. A metallic covering may be coated or otherwise secured over the radio active material. If the cathode II is in the shape of a cup, the inner surface may be coated with a radio active material emitting both alpha and beta rays, and the metal cup will in itself shut ofi the alpha rays.

As it is desirable that the grid It be porous, it is found desirable to coat or alloy the grid with a radio active preparation which emits beta rays and not the alpha rays, such as radium D as it may interfere with the porosity if a material or substance is used which emits alpha rays which have to be shielded o.

For shielding oil' the alpha rays a thin sheet of aluminum .006 cm. thick will eilectually shut oil' the alpha rays, and the thickness of the materials used is to be determined by their density. Lead, for instance, shields better than aluminum for a given thickness. The plate or anode i5 is preferably alloyed or coated with a radio active preparation which emits alpha rays, such as uranium (U), ionium (Io), protoactinium (Pa), or thorium (Th). No shielding is necessary for the anode i5 or plate as the alpha rays are desired. The cathode ii and the grid i3 will give ofi the beta rays, and the anode or plate Iii will give off the alpha rays.

The amount of radio activity imparted to each electrode will of course be governed by the requirements of the circuits. In some cases the grid bias will be relatively strong necessitating a higher or larger activity of the grid IS while the cathode Il may be only a trie more radio active than usual. In some cases the anode l5 or plate may require a relatively greater radio activity than in others and in each case the radio activity is predetermined by the circuit requirements which may be -controlled by the quantity and quality of the radio active substances employed.

Referring now to Figure 3, the metallic cathode cup II is provided on its inner side with a coating d5 of radio active material having a characteristic as above outlined. The grid i3 is provided upon its inner side, toward the cathode cup II, with a coating of radioactive material d6, and the outer side of the grid i3 is provided with a protecting shield il of aluminum, or the like. In a like manner, the anode plate i5 is provided upon its inner side with a coating of radio active material at. While Figure 3 shows the radio active material in the form oi coating or layers upon the respective electrodes, it is of course understood that this radio active material may be incorporated or embedded in the material or substances of which the various electrodes are formed.

In order to mount the electrodes, the radio active material and the shield of the present invention in a conventional manner within the tube or envelope it, the leads or wires which extend from the respective electrodes. as shown at @cada I2, Il, and I6, may be supplemented by supporting wires 49, or the like, which may have a general configuration corresponding to that of the actual leads so as to produce a symmetrical structure to lend the necessary support to the Various sides of the electrodes. 'I'hese wires and supports may be molded or suitably secured in the anchor stem 50 of the tube which is usually of glass as shown, or leads may be used being carried down through the anchor stem and soldered or otherwise ysuitably secured to the prongs or stems 5I which extend through the cap 52 of the tube in the usual manner. These prongs or stems 5I may be arranged in triangular or any other suitable manner which may be conven- J tional so that the tube may be mounted in an ordinary socket. The envelope I0 is of any practical construction and is shown as secured in the cap 52 by a sealing compound 53 in the ordinary manner. Of course the present invention admits of .various different constructions to adapt the tube for any desired number of electrodes, leads and variations in the shape and construction of the envelope and the cap.

It will of course be understood that when a radioactive material 46 is added to the grid screen I3 and which is capable of emitting beta rays to the exclusion of alpha rays, such as radium D, Ra-D, for instance, the shield l1 around the grid I 3 is unnecessary so that in this case the shield l All would be omitted. In the present illustration of an electron tube 3 electrodes are shown, and of course these operate satisfactorily and constitute the essential elements of a tube. 'I'here are used electron tubes having a greater number of electrodes therein, the essential electrodes, however, comprise the cathode, the grid and the plate. According to this invention three radio active electrodes may be used irrespective of the number of electrodes with which the tube is equipped. 'Ihis adapts the invention to not only the screen \grid tube, but also the pentode and the hi-mu types.

This improved electron tube may be used in radio receiving circuits as a radio frequency amplifier, a detector, a power detector and an audio frequency amplifier or power amplifier. The improved tube eliminates the grid leak and grid condenser used in the detector circuits of some systems as the grid is inherently biased. radio and audio frequency circuits the tube eliminates all biased connections and the C current systems. The improved tube may also be used in radio transmitting circuits where oscillating and amplifying tubes are required as the tube will In the 'I'he secondary winding 2U of the coupling has shunted across its ends a variable condenser 2| which tuning condenser. At 22 is a radio frequency ampliiier tube which is of the above described construction. Within the tube 22 is mounted the negative grid I3, the negative cathode II and the l radio positive plate or anode I5. 23 is a bypass condenser shunted across the plate-cathode circuit of the tube 22. 24 designates the primary winding of the radio frequency transformer and constitutes the first is connected between the plate I5 ofthe tube 22 and the B current supply wire which may be connected to the plus 90 volt terminal thereof.

The secondary winding 26 of the transformer is provided with a variable condenser 2'I shunted across its leads. This condenser comprises another tuning condenser. A detector tube 28, of the same construction as above set forth, is connected to the radio frequency transformer. A bypass condenser 29 is shunted across the platecathode circuit of theV tube 28 and has one side connected to the primary winding 30 of an audio frequency transformer having a laminated core 3I, and the other side connected to common return 38. 'I'he other end of the primary winding 30 is connected to the plus 45 lead wire 32 connected to the terminal of the B current circuit. Connected in parallel with the secondary winding 33 is a high resistance element 35 shunted across the secondary winding 33andwhich has a movable contact 36 for varying th volume of current or voltage of the grid I3 of' an audio frequency amplifier tube 3l having the grid thereof connected directly to the movable contact 36. 'I'he resistance 35 andthe movable contact 36 provide what is commercially known as a potentiometer and the mounting of this resistance control element in its operation of the circuit is deemed to be an important feature of the present invention. The cathode I I `of the tube 31 is connected to the common return B minus wire 38 and to the adjacent branch Wires leading from the resistance35, and the secondary winding 33 nf the audio frequency transformer. The anode or plate I5 is connected to one of the output wires 39, the other wire or side of the output isreturnedto the plus 135 volt terminal 44 of the B current through the wire 40.

'Ihe B current has its negative terminal 4I connected to all of the cathodes in the circuit through the wire 38, and all of the secondary windings and all of the condensers are also connected to the wire 38. The detector tube 28 uses the plus volt terminal 42 and the radio frequency arnf plifier tube 22 use's the plus 90 volt terminal 43 while the audio frequency amplifier tube uses the maximum voltage or plus 135 volts through the output wire 39.

Though not shown in the drawings, it is clear and understood that these electrodes or systems may be enclosed in vacuum tubes or envelopes or in tubes or envelopes containing a rareed gaseous atmosphere, as is done in certain electronA tubes.

It is obvious that various changes and modlfications may be lmade in the details of construction and design of the above specifically described embodiment of this invention without departing from the spirit thereof, such changes and modications being restricted only by the scope of the o following claims.

I claim as my inventioniv 1. An electron tube comprising a partially evacuated envelope, a multiplicity of electrodes in the envelope, at least one of said electrodes having a porous shield substantially providing a supplemental electrode in said envelope, one of said iirst electrodes comprising a cathode, a secondof said electrodes comprising a grid, said porous shield mounted in the path of the electron stream and having electrical connection with said grid, a third electrode comprising an anode, said cathode and grid cooperating to establish a diierence of potential with respect tosaid porous supplemental shield, said anode .adapted to augment the process of ionization to produce a conductive path for the current flow.

2. An electron tube comprising an envelope adapted to contain a rareed gas, a plurality of electrodes mounted in the envelope, a porous shield mounted in the envelope, one of said elec- -trodes comprising a cathode including a radio active substance, another electrode comprising a grid including a radio active substance, another electrode comprising an anode including a radio.

active substance, said shield being mounted to absorb a preponderance of one kind of radio active emission and utilize said absorbed emission to assist the functioning of the radio active grid.

3. An electrical device comprising an envelope containing a low pressure gas and a cold radio active cathode emitting beta rays mounted in said envelope and a radio active grid emitting beta rays mounted in said envelope, said grid having a porous shield providing an auxiliary electrode mounted in said envelope and having an electrical connection with said radio active grid, and a radioactive anode mounted in said envelope and the said radio active cathode, radio active grid and radio active anode having leads emerging from said low pressure envelope for connection to an external circuit.

4. An electron tube comprising an envelope, a plurality of radio active electrodes mounted in said envelope at least one of the electrodes having a porous shield providing a supplementary electrode mounted in said envelope and having electrical connection with the said radio active electrode, and said porous supplementary electrode functioning to assist one of the said radio active electrodes, at least two of the said radio active electrodes emitting beta rays and at least one of the said radio active electrodes emitting alpha rays.

5. An electron tube comprising an envelope, an electrode having a porous supplementary shield mounted in said envelope, a cold radio active cathode mounted in` said envelope, a radio active grid mounted in said envelope and a radio active anodev mounted in said envelope, othe said cold CII radio active cathode and radio active grid establ

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