US2414636A - Photoelectric apparatus - Google Patents

Description

Jan. 21,1947. CRAIG HAL 2,414,636

PHO TOELECTRIC APPARATUS Filed June 26. 1942 o a 27 L a x33 fvvvvvvy Patented Jan. 21,1947

PHOTOELECTRIC APPARATUS Palmer H. Craig, Gainesville, Fla., and Lester C. Herman, Emporium, Pa., assignors, by mesne assignments, to Invex Inc., a corporation of Florida Application June 26, 1942, Serial No. 448,680

13 Claims.

This invention relates to photo-electric apparatus by which the amperage of the electric current in a work circuit may be controlled by controlling the intensity of the illumination of an electronic tube of the apparatus.

Heretofore the current in a work circuit has been controlled by photo-electric electronic tubes. In one type of such tubes, light sensitive material, that is to say material which when it is exposed to light emits electrons, is provided in an envelope and the flow of these light-emitted electron themselves toward a positive electrode in the tube provides the main current flow through the tube externally available for. use. In another type, the tube is of the general class of space discharge tube, and the electrons emitted from the light-sensitive material start the flow of discharge current through the tube.

In the first type of tube the amperage of th external current is small because of the low lightefi'ected emission of electrons; and in the second type of tube the external current is small because the current flow producing potential on the main electrodes must be kept to a low value to prevent discharge current from flowing when the lightsensitive material is not illuminated.

Because the amount of current made available by such photo-electric tubes when subjected to light is so small, it follow that in most of the practical applications in which light-controlled electric power is wanted, the current output of such tubes must be amplified by auxiliary apparatus.

Also, in the space-discharge type of photo-electric tube, when the discharge current starts to flow responsive to the action of light, the light loses control of it, the light performing merel a trigger action to start the flow.

By means of the present invention an electronic tube of the gaseous discharge type is caused to respond to the action of light and pass current, the amperage of which may be as high as such a tube conducts when used as an ordinary power tube, limited in fact only by the maximum permissible temperature rise thereof; and the present invention comprises means by which the main current flow through such a power tube may be caused to attain its full capacity value or optionally any fractional part thereof by the action of corresponding difierent intensities of light.

The present invention therefore provides an apparatus which is in the true sense a photo-electric power control apparatus.

While the principles of our invention may be variously applied, we have chosen, for illustrativ purposes herein, to describe it as comprising a space-discharge power tube of the rectifier class, having an envelope containing ionizable gas and an anode and a hot cathode; and havin a control electrode or grid the preferred construction and energization of which will be referred to later. In such a gaseous rectifier tube, discharge current flows only from the cathode to the anode and only when the anode is positive with respect to the cathode; and herein reference to the anode as positive is meant in this sense. Also when reference is made herein to energization of the grid with negative potential, it is meant in the sense that the grid energization is negative with respect to the cathode when the anode is positive with respect to the cathode.

Hot cathode rectifier tubes of known construction comprise in various forms metal coated with thermionic material and indirectly heated by an incandescent filament." The electrons emitted by the heated thermionic coatings together with the electrons produced thereby by ionization of the gas in the envelope and fiowing toward the positive anode, constitute the discharge current. Representative of such thermionic coatings are barium oxide and strontium oxide.

In the well known processes of evacuating the envelope of a rectifier tube having such a cathode, the cathode is heated and some of the thermionic material thereof becomes vaporized and condenses on the inner surface of the envelope in a film of thermionic material, so that in an indirectly heated cathode rectifier when finished, the greater part of the thermionic material remains on the cathode but a thin film of the same is in the form of a deposit on the envelope wall.

Also at the end of the evacuating process a socalled getter is employed comprising a metal enclosed pellet of material which, upon inductively heating the enclosing metal, explodes or flashes into vapor having the property of scavenging the envelope interior by absorbing or chemically uniting with the molecules or gas or water vapor still in the envelope. The getter material then condenses upon the inner wall of the envelope in a thin film. The getter may be located at one end of the envelope in which case the getter film will form at the corresponding end portion of the envelope. The film consists of metal and metal oxides, nitrides, carbonates, etc. determined by the getter and the oxygen, nitrogen, carbon dioxide, etc. which may be present in the envelope when the getter is flashed. Representative of such getters is the mixture of 25% barium, 20% aluminum and 5 magnesium in powdered form.

The ionizable gas in the envelope of such tubes is introduced after evacuation and representative of such gases is argon.

Now we have discovered that if a hot cathode rectifier tube constructed as referred to above, and evacuated and containing argon at suitable pressure to be referred to, and having a film or films on the inner wall of the envelope as referred to, has its grid energized with negative potential to the degree which just prevents current fiow between the anode and cathode for a given potential between the anode and cathode, the tubeis photoelectric. That is to say, if light illuminates either the thermionic coating of the cathode or the condensed thermionic or getter coating on the envelope wall, the grid is thereby rendered ineffective to prevent the current flow, and current flows between the cathode and anode, and furthermore, flows in amperage corresponding to the intensity of the light falling on either of the said coatings; and in correspondence with variations of the intensity of the illumination of the coatings, the current flow varies, from very small amperage up to and includin the maximum amperage capacity of the tube as a rectifier tube and ceases to flow when the light is interrupted.

And We have found furthermore that if the negative potential of the grid be increased still further beyond the degree at which it prevents flow as a rectifier, a degree of super-energization is reached at which the discharge current again flows; and that if then either of the said coatings be exposed to light the grid is thereby rendered ineffective to maintain such flow of current and the current flow'is interrupted, or is reduced commensurably with the intensity of the illumination.

According to this invention the tube responds to light as stated above when the grid is inside the envelope but we prefer to employ an outside band form of grid encircling or embracing the outer wall of the envelope, such band control electrodes being known and being described in patents to Palmer H. Craig representative of which is his Patent No. 2,001,836, issued May 21,

as to the exact nature of the above-described phenomenon or the "full explanation thereof.

Obviously the aforesaid response of the tube to light is not dependent solely upon the use of socalled light-sensitive material, nor in fact upon light sensitive properties as such of the coatings within the envelope, because the amperage flowing through the'tube in response to the action of light is, atiits maximum, equal to the discharge amperage capacity of the tube as a rectifier, and this is many times greater than the electron flow which could possibly be emitted from the said coatings considered as light-sensitive coatings even if such light-sensitive coatings were of the maximum possible area that could be contained within the envelope. The phenomenon seems to depend upon the jointaction (a) of the grid or control electrode in normally preventing electron flow in the cathode and anode (or in causing it to fiow as the case may be); and (b) of the illuminated coating in inhibiting the action of the grid.

The phenomenon may be electro-static in character. When the outside band grid is utilized as described, we believe that it creates an electro-static charge or field within the envelope or on the inner wall thereof, the glass wall of the .envelope functioning in the nature of the 4 dielectric element of a condenser, and that it is this charge or field produced by the grid which controls the amperage flow through the tube; and that electrons or photons are emitted from the said coating when subjected to light, and that they neutralize or drain off or short circuit the said electro-static charge or field thus destroying or reducing it (commensurably with the intensity of the light) and correspondingly change the eiiect of the grid upon the curret flow through the tube. This is evidenced by the fact that the effect of the grid can be similarly changed by diverting or by-passing some of the grid energization by .means of a rheostat disposed externally of the envelope and paralleling the grid as we have found by experiment.

As illustrative of the light-responsiveness of tubes when utilized according to our invention, We have found that a tube having a continuous carrying capacity of 15- amperes, and a capacity of '75 amperes forshort periods of time such as thirty seconds, can "be made .topass the full 7 5 amperes; or cut it .oif,'or passany intermediate amount of current, in accordance with the intensity of the light 'to which the tube is subiected.

It is among the objects of this invention therefore:

To provide generally an improved ph'ot0 electric apparatus;

To provide a photo-electric apparatus comprising a tube responding to the action of light to pass current through the tube of great amperage limited only by the permissible temperature rise of the tube;

To provide a tube of the rectifier type having a maximum current capacity between the anode and cathode, and apparatus rendering its responsive in an improved manner .to the action of light to causeit to pass current in varying amperage from small current to the said maximum current when illuminated by light in corresponding degrees of intensity;

To provide an apparatus rendering an electronic tube responsive to the action of light .to pass current directly commensurable with the intensity of the illumination of the tubes;

To provide an apparatus rendering an electronic tube responsive to the action of light to pass current inversely commensurable with the intensity of the illumination of the tube.

Other objects will beapparent to those skilled in the art to which our invention appertains.

Our invention is fully disclosed in the following description taken in connection with. the accompanying drawing in which,

Fig. 1 is a front elevational view of a tube with which our invention may bepracticed and with a part .of the tube envelope broken away to disclose internal parts of the tube;

Fig. 2 is a cross sectional View taken from the plane Z'--2 of Fig. 1 with the radial thickness of the parts in section magnified for purposes of illustration;

Fig. 3 is a cross sectional view taken from the plane 3 of Fig. 1 illustrating the internal construction of a cathode which we may employ;

Fig. 4 is a diagrammatic View illustrating an embodiment of our invention, and showing electrical apparatus and circuits associated with a tube such as that of Fig. 1.

Referring to the drawing, we have shown in elevation in Fig. 1 a tube suitable for use in the practice of our invention, and comprising a glass envelope I, having on the lower end thereof a metal plug base 2 of the prong type provided with three insulated prongs 3, 4, and 5 and having above the base a pinch 6, in which are sealed terminal conductors connected to the prongs. The envelope has been evacuated and contains an ionizable gas such as argon therein at a predetermined pressure to be referred to.

In the upper end portion of the envelope l is an anode I electrically connected to an external terminal 8 in the usual manner. The anode may be of graphite or molybdenum, or carbon, or carbonlzed nickel, or may be of other materials such as are commonly used for the anodes of tubes of the hot-cathode rectifier type.

At 9 is shown generally a cathode of the indirectly heated type. It may be variously constructed but we prefer to employ the construction more completely illustrated and described in the patent of Craig and Glauber, No. 2,289,346, issued July 14, 1942. It is believed that it will be sufficient here to illustrate this structure in cross section, and this has been done in Fig. 3. A pair of posts Ill and H mounted in and extending upwardly from the pinch 6, see Fig. 1, support a main outer cathode cylinder l2 of nickel or other suitable metal. Within the cylinder I2 and coaxial therewith is an inner metal tube l3. A plurality of heater tubes [4, l5, I6, I! are disposed between the inner wall of the cylinder I2 and the outer wall of the inner tube l3. Heat insulating tubes or shields I8 and i9 surround the outer' tube 12. Heating filaments 20-20 are provided axially of and within the heater tubes M to H. Their lower ends are all connected to a connector 2| see Fig. 1, and their upper ends are connected to the outer tube 12 in a manner not shown.

By this construction a large sheet metal cathode area is provided, and this area is covered with a coating of thermionic material such as barium or strontium carbonate or a mixture thereof, which, when the cathode surfaces are heated in the process of evacuating the tube as is customary, is converted into strontium or tube l3; and also at 25 on the inner wall of the tube l3.

The electric circuit to heat the filament will be described later.

A getter such as that referred to is shown at 26 in Fig. 1 mounted on a wire 21 connected to one of the posts such as the post H.

The main circuit through the tube is from the prong 5 by post H to the cathode 9, thence through space as a discharge are to the anode 1 and to the external terminal 8.

The tube as above described, considered merely as a rectifier tube, has a well-known mode of operation which is, that the filament heats the said tubes and their thermionic coating, causing the latter to emit electrons, and these electrons ionize the gas causing it to emit other electrons, thereby providing a flow of electrons from the cathode to the anode, and when potential is impressed upon the cathode and anode with the anode positive, electric current flows from the cathode to the anode in the nature of a space discharge and the amperage depending upon the impressed potential and the external resistance in the cir- A grid or control electrode 21 is provided in the iii) form of an external metal band upon and out= side of the envelope I, and it may be variously constructed. It may be in the form of a separate wire or band of metal; or it may be a band of metal mesh; but preferably we provide a band which in efiect is sealed into the material of the outer wall of the envelope. The preferred process for applying such a band electrode is that used in ornamenting glassware with bands or the like of platinum or other metal. For example a so-called liquid platinum material of commercial composition and of paintlike consistency is painted in the form of a band on the outer wall of the envelope. The glass and the band are then heated and the band takes on the appearance of platinum metal fused into the glass surface. The band thus made is electrically conductive and metal may be soldered thereto, and accordingly a terminal 28 is connected to the band by solder, and is formed as at 29 for making electrical connection therewith.

The grid is shown as disposed between the cathode and anode which is its preferred position.

The advantages of the present invention are better developed in practice by utilizing alternating electrical potential in its operation, and this will be referred to in some detail for illustrative purposes although those skilled in the art will know how to adapt the same to direct or unidirectional potential.

When alternating current potential is impressed upon the anode and cathode, the flow of discharge current occurs only during those half waves in which the anode is positive; and even without energization of the grid it is automatically interrupted during each half cycle in which the anode is negative; and thus with alternating current such a tube, considered merely as a rectifier tube, admits of control of the efiective amperage flowing by suitable energization of the grid.

If the grid be energized with negative potential to a suitable degree it will prevent flow of discharge current from starting on each successive positive half cycle; or if the grid be energized with a lower degree of negative potential, it will delay the time of starting in each positive half cycle, and by this means, according to the degree of energization of the grid, the current flow can be completely cut oil or its effective value in amperage may be determined or controlled. Again if the grid be energized to a degree beyond that at which it completely cuts ofi or prevents current flow, current will be caused to flow at such super grid energization, and by increasing or decreasing this super-energization of the control electrode, the efiective amperage flow may be respectively increased or decreased, or cut off.

A more stable and otherwise satisfactory control of the amperage blowing through the tube considered as a rectifier tube may be effected if the alternating voltage impressed upon the grid is out of phase with that impressed upon the cathode and anode.

ment. We have found that a suitable phase displacement is approximately 135 degrees lag of band grid potential, behind the anode potential.

In Fig, 4 is .illustrated a representative apparatus for rendering a tube, such as that described above, responsive to light as referred to; and it includes means for effecting the said phase angle of displacement.

In this figure at l is shown the envelope, at l the anode, at 21 the control electrode, at l and II the posts supporting the cathode 9 heated by filaments only one of which is shown. Supply mains and 3! energize the primary 32 of a transformer the secondary 33 of which supplies alternating current at suitable voltage, such for example as five volts, to the above-described heating circuit comprising the filament 2E] and the post Ill. The supply mains also energize the primary 34 of a transformer having a secondary 35 connected in a loop circuit with a resistor 36 and a condenser 31 the said loop circuit being also connected to the cathode 9 by a wire 38. The grid 2! is connected at 39 to the resistor 36 by an adjustable rheostat type of connection to adjust the potential on the grid 21, the circuit for the grid being considered as from the connection 39 to the grid, thence to the cathode 9 through the wire 38 and back to a part of the resistor 36. The condenser 31 may be adjusted to cause the potential on the grid 21 to be out of phase with the potential across the cathode and anode as described, and at this fixed phase displacement, which, as above stated, is preferably of the order of 135 degrees behind the anode potential, the actual potential on the grid 2! may be adjusted by the adjustable connection 35.

For a rectifier tube as described above having a continuous main current capacit of 2 /2 amperes the capacity of the condenser 31 may suitably be .019 microfarad; and the resistance of the resistor 36 may suitably be of the order of 150,000 ohms; and the voltage across the resistor provided by the transformer secondary 35 may suitably be 600 volts for supply mains at 110 volts 60 cycles. As above stated with the fixed phase displacement referred to, the grid connection at 39 may be adjusted for zero grid potential, at which the full 2 /2 amperes will flow in the main load circuit from the cathode to the anode, and if the potential on the grid 21 be adjusted to raise it, the effective amperage in the load circuit will be decreased, and at approximately 450 volts on the grid 21 the main current will be completely out off; and if the potential on the grid 2'! be adjusted to raise it above the cut-off value to a super-potential, the current will again flow and the effective amperage will be greater for higher gridvoltage, and vice versa. It follows that the effective current supplied to the work circuit containing the load of Fig. 4 can be variably adjusted from zero to maximum capacity of the tube by adjusting the connection at 39.

The above description is directed to the construction and operation of the tube of Fig. 1 considered as a rectifier tube of the indirectly heated thermionic cathode type. As referred to hereinbefore, when the envelope is evacuated by the usual process, which We may employ, some of the heated thermionic coating is evaporated and deposited on the inner surface of the envelope in a .thin film; and the getter when flashed also deposits a film on the tube wall, A film is indicated .in Fig. l by the dotted line 40 and this may be considered as the thermionic film, or the getter rum, or both.

The circuits and apparatus illustrated and described in connection with Fig. 4 are utilized to bring into action the photo-electric property of the tube by one of two modes of adjusting the apparatus. According to the first mode of adjustment the connection at 39 is moved to energize the grid 2! with negative potential (preferably out of phase with the potential impressed upon the anode and cathode as described) just sufficient to prevent the flow of discharge current as described, so that considered as a rectifier tube, the tube is normally rendered in condition to prevent current flow, this being done as stated by moving the adjusting point 39 over the resister 36.

If now light from an outside source is caused to illuminate either the thermionic coating on the cathode, or the film 40 on the inner wall of the envelope, the inhibiting action of the grid is itself inhibited, and the tube passes current between the cathode and anode. The amperage of the current which thus flows is directly commensurable with the degree of intensity of illumination of the thermionic material, or of the film, and if the illumination be sufficiently intense the tube will pass amperage of current up to its full capacity depending of course upon the resistance of the external work circuit, and if the illumination is decreased the amperage flowing through the tube decreases commensurably therewith, and if the illumination is entirely removed the current again ceases to flow. If the grid be normally energized by adjustment to a degree less than suiTicient to prevent current flow, and therefore allows a normal minimum current to flow then similarly light causes the amperage to increase upwardly from this minimum to an amount commensurable With the illumination.

According to the second mode of adjustment, the connection at 39 is moved to energize the grid 21 with a super negative potential, that is, beyond the potential at which current fiow is prevented, and at this super-potential current normally flows through the tube. The greater the super potential the greater the current and vice versa. The grid is therefore. adjusted to a super potential at which the maximum current that is wanted will flow in the load circuit. If now light is caused to illuminate either of the three coatings referred to, the action of the grid in causing current to flow is thereby wholly or partially inhibited and the current flow is out off or allowed to flow at amperage inversely commensurably with the degree of intensity of the illumination.

As will now be apparent, by the aforesaid first means the discharge current amperage increases from zero or a minimum value up to higher values, with increasing intensity of light, and vice versa, the amperage of the current being directly commensurable with the light intensity; and by the aforesaid second means, the discharge current amperage decreases from a high or maxi- .mum value down to lower values or to zero value,

upon the occurrence of increasing intensities of light and vice versa, the amperage of the current flow in this case being inversely commensurable with the light intensity.

So far as we are aware, in no prior photo-electric apparatus does the current amperage of a space-discharge type of tube vary with the intensity of illumination; and in no prior photoelectric apparatus, irrespective .of the type of tube, does the current amperage var inversely with the intensity of illumination.

We have found that the response of the tube to light in such an apparatus is sensitive, and that the light from an ordinary 50 watt commercial lamp at a distance of several feet from the tube and directed at varying intensity upon the tube by a reflector is sufiicient to cause the tube to respond and pass its full capacity of current, or vary it or out it on as the case may be.

In Fig. 1 we have shown at ll a source of light directed by a reflector 42 upon the coating of the cathode 9 through a shutter 43 by which shutter the intensity of the incident illumination may be controlled; and at 44, 45, 46 we have shown a similar arrangement of light source, reflector and shutter, for variably illuminating the film 46.

As mentioned hereinbefore, rectifier tubes of the gaseous discharge type are known containing a gas such as argon in the envelope. In the above described tube, we also prefer to employ, as stated, a gas such as argon, but we have found that the pressure of the gas within the envelope when the tube is to be used for its light responsive properties described, may to advantage be taken into account. For any pressure utilized, the grid energization will correspond if the optimum photoelectric efiect is wanted. If a low gas pressure is used, the grid voltage used to normally prevent current flow may be lower and vice versa. At the higher gas pressures and corresponding higher grid voltage as well as at the lower pressures and corresponding lower grid voltage, the above described photo-electric action is present, but for a given maximum light intensity, the maximum flow of current decreases as the pressure and grid voltage increase and also as they decrease. It follows that there is an intermediate optimum pressure (and corresponding grid voltage) and we have found that for argon gas, which we prefer to use, this optimum pressure is of the order of 10 to 200 microns of mercury.

While the connection at 39 has been illustrated and described as adjustable, it will be understood that in cases in which the quantitative elements of the apparatus are predetermined and the light responsive operating characteristics are preselected, this connection may be a fixed connection.

Also, as is believed to be obvious, while the tube is passing current responsive to the action of light the amperage of the current may be varied, if desired, by shifting the connection at 39.

We have referred hereinbefore to shutters to control the intensity of the illumination of the tube, and such shutters are representative of objects of any kind which may be moved to intercept or change the intensity of the illumination, whereby the main current flow through the tube will be controlled by such moving objects, or by the presence or absence of any light intercepting object.

. Also, while we have described the control of variation of the current amperage through the tube in response to variations of light intensity by utilizing a negative grid energized out of phase with the positive anode and having the grid potential adjusted by a rheostat, it is to be understood that our invention may likewise be practiced by a system which adjusts the phase displacement of the grid energization with respect to the anode potential.

In alternating current installations, in which accurate variation in the flow of current through the tube in response to variations of light intensity is not wanted, and all that is wanted is initiation and interruption of current responsive to light, a satisfactory operation of the appait) ratus may be had if the negative grid be energized in phase with the positive anode.

It is believed that these alternative means for practicing our invention will be understood from the more complete description of the preferred means without further illustration or description herein.

As referred to hereinbefore, the tube illustrated and described herein, apart from its photo-electric property when used with its associated apparatus, is a tube of the rectifier class, the amperage of the discharge through which may be controlled and varied by controlling the'grid voltage (or its phase relation to the anode voltage). Such a tube considered merely as a rectifier tube constitutes the subject matter of the patent of Palmer H. Craig and John J. Glauber, No. 2,289,346, issued July 14, 1942, and the pending application of Palmer H. Craig, filed May 20, 1942, Serial Number 443,717 both assigned to the same assignee as the present application.

Our invention is not limited to the exact details of construction nor to the exact means of rendering the tube responsive to the action of light illustrated and described. Changes and modifications may be made within the spirit of our invention without sacrificing its advantages and within the scope of the appended claims. For example, two tubes may be used in multiple back-to-back arrangement to pass a full wave of alternating current.

We claim:

1. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sumcient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value to which it responds to normally prevent the anode-cathode-impressed potential from causing current flow in the Work circuit in the absence of illumination of the light responsive material; means to cause source light to illuminate the light responsive material to thereby cause anode cathode current to fiow in the Work circuit at amperage determined by the intensity of the illumination.

2. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufficient to cause gaseous space discharged current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value to which it responds to normally prevent the anode-cathode-impressed potential from causing current flow in the work circuit in the absence of illumination of the light responsive material; means to cause source light to illuminate the light responsive material to a selected intensity of illumination to thereby cause anode cathode current to flow at amperage predetermined thereby.

3. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufiicient to cause gaseous space discharge current to flow between the anode and cathode when the control electrodeis unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value to which it responds to nrmally prevent the anode-cathode-impressed potential from causing current flow in the work circuit in the absence of illumination of the light responsive material; means to cause source light to illuminate the light responsive material to thereby cause anode-cathode current to flow in the work circuit at amperage determined by the intensity of the illumination; and means to vary the intensity of the illumination to correspondingly vary the current amperage.

4. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the Work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufficient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value at which it responds to cause current to flow in the work circuit of lesser amperage than when the control electrode is unenergized; means to cause source light to illuminate the light responsive material to thereby cause the amperage of the anode-cathode current in the work circuit to change.

5. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the Work circuit being energized by alternating potential which impresses on the anode and cathode a potential suflicient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to thereby cause it to have a value at which it responds to cause current to flow in the work circuit of lesser amperage than when the control electrode is unenergized; means to cause source light to illuminate the light responsive material to thereby cause the amperage of the anode-cathode current in the work circuit to increase.

6. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the Work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufiicient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling thesaid energization of the control electrode to thereby cause it to have a value at which it responds to cause current to flow in the work circuit of lesser amperage than when the control electrode is unenergized means to cause source light to illuminate the light-responsive material to a selected intensity of illumination to thereby cause the amperage of the current in the work circuit to increase to a value corresponding to the intensity of the illumination.

'7. An apparatus for photo-electrically control.- ling the current amperage in a work circuit comprising: an electronic tube having an envelope:

containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode l3 energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufificient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit vfor the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to thereby cause it to have a value at which it responds to cause current to flow in the work circuit of lesser amperage than when the control electrode is unenergized; means to cause source light to illuminate the light responsive material and means to vary the intensity of the illumination, to thereby cause the amperage of the current in the work circuit to vary.

8. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sulficient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the oathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value greater than that which would pre- ,vent anode-cathode current flow, to cause current to flow in the work circuit; means to cause source light to illuminate the light responsive material to thereby cause the anode-cathode current in the work circuit to decrease.

9. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufficient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value greater than that which would prevent anode-cathode current flow, to cause ourrent to flow in the work circuit; means to cause source light to illuminate the light responsive material to thereby cause the anode-cathode current in the work circuit to decrease to zero value.

10. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-re sponsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential suificient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value greater than that which would prevent anode-cathode current flow, to cause current to flow in the work circuit; means to cause source light to illuminate the light responsive material to a selected intensity of illumination to thereby cause the anode-cathode current amperage in the work circuit to decrease to a value corresponding to the intensity of illumination.

11. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential suificient to cause gaseous space discharge current to flow between the anode and cathode when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value greater than that which would prevent anode-cathode current flow, to cause current to flow in the work circuit; means to cause source light to illuminate the light-responsive material to thereby cause the amperage of the anode-cathode current in the work circuit to decrease; and means to vary the intensity of the illumination to cause the decreased amperage to vary.

12. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-re sponsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the Work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufficient to cause gaseous space discharge current to flow in the work circuit when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value to which it responds to cause current to flow in the work circuit of lesser amperage than when the control electrode is unenergized; and means to cause source light to illuminate the light responsive material to thereby cause the amperage in the work circuit to change directly commensurably with the intensity of the illumination.

13. An apparatus for photo-electrically controlling the current amperage in a work circuit comprising: an electronic tube having an envelope containing gas and an anode and a thermionic electron emissive cathode and light-responsive material and provided with a control electrode; a circuit for maintaining the thermionic cathode energized the anode and cathode being connected in the work circuit; the work circuit being energized by alternating potential which impresses on the anode and cathode a potential sufficient to cause gaseous space discharge current to flow in the work circuit when the control electrode is unenergized; the envelope being disposed with respect to an external source of light for illumination of the light-responsive material thereby; an energizing circuit for the control electrode for energizing it with alternating potential which is negative with respect to the cathode when the anode is positive with respect to the cathode; means for controlling the said energization of the control electrode to cause it to have a value greater than that which would prevent anode-cathode current flow, to

cause current to flow in the work circuit; andmeans to cause source light to illuminate the light responsive material to thereby cause the amperage in the work circuit to change inversely commensurably with the intensity of the illumination.

PALMER H. CRAIG. LESTER C. HERMAN.

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