US2426497A

US2426497A - Amplifying system

Info

Publication number: US2426497A
Application number: US506313A
Authority: US
Inventors: William J Field
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1943-10-15
Filing date: 1943-10-15
Publication date: 1947-08-26
Anticipated expiration: 1964-08-26

Description

Aug. 26, 1947'.

W. J. FIELD AMPLIFYING SYSTEM Filed Oct. 15, 1943 2 Sheets-Sheet l .PZW imam ON IOMFZOU INVENTO/Y WILL/19M t]: FIELD Aug. 26,1947. w, HELD 2,426,497

AMPLIFYING SYSTEM Filed Oct. 15, 1945 2 Sheets-Sheet 2 Imncntor WILL/HM J. FIELD attorney Patented Aug. 26, 194.

AMPLIFYING SYSTEM William J. Field, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application October 15, 1943, Serial No. 506,313

Claims. 1

This invention relates to electrical amplifying systems and more particularly to systems for thermionically amplifying signal impulses for the control of other apparatus.

Heretofore, in certain thermionic amplifying systems, it has been common practice to supply the plate potentials of the amplifier tubes from a rectifying system energized by an alternating current source. In the usual rectifying systems, there has been included a filter network for smoothing the rectified output thereby to reduce and substantially eliminate the alternating current component of the rectifier output voltage. To achieve this result, there has been required a relatively heavy and expensive filter network Which has added to the weight and cost of such systems.

According to the present invention, there is provided an amplifying system in which the alternating current component of the rectified plate current supply is advantageously utilized for biasing purposes and as a result, a low weight, low cost, simplified amplifying system is provided, capable of excellent result in control service.

It is an object of the invention to provide such an amplifier, and more particularly, to provide an improved amplifying system for control service capable of being energized from an alternating current.

It is also an object of the invention to provide an amplifying system wherein the plate potential of the amplifier of one stage has an alternating current component which is utilized to produce a desired biasing effect in connection with a succeeding stage.

Other and further objects are those inherent in the invention illustrated, described and claimed.

The invention is illustrated with reference to the drawing in which Figure 1 is a Wiring diagram of the amplifier system; and

Figures 2 and 3 are wave diagrams illustrating the operation of the amplifier apparatus.

Throughout the illustration and description of the invention, the same numerals refer to corresponding parts.

In Figure 1, the amplifier system of the invention is illustrated as controlling an element, generally designated iii, which may be of any mechanism for example a valve, gate or damper, or a speed, direction, acceleration, volume, position or gas analysis control, requiring physical movement throughout a range of positions. The positioning movement of the controlled element in is desired to be made in accordance with the operation of a responsive element, generally designated 30, which is designed so as to be responsive to the condition being controlled and thus as required may be responsive topressure, speed, direction, acceleration, volume, mere position, the analysis of gases or any other factor or derivative function, which in the end is responsive to the manipulation of the controlled element [0. The responsive element 39 is frequently and indeed usually a low energy instrument; hence the need for amplification in utilizing the output of such an element.

In the illustrated environment of the present invention, the reversible movement for positioning the controlled element I0 is furnished to stem ll of the element, by means of a rack and pinion, l2 and 13 respectively, or any other suitable mechanical gear. Pinion i3 is carried upon shaft id and may be driven through reduction gearing I9 from a motor, generally designated by the numeral 20.

Motor 20 includes relatively rotatable rotor and stator elements 2! and 2223. The element 2| may be of the squirrel cage, wound, or other suitable type, depending upon the characteristics of the load of controlled element Hi.

Windings

22 and 23 are connected together at 2 5 and grounded at 25.

Winding 22 is connected so as to be constantly energized from an alternating current supply line 2'! through a phase displacing capacitator 28. The response of the rotor of motor 28 depends upon the energization of Winding 23 and the direction of the response upon whether the current through winding 23 in effect leads or lags the current through winding 22. The amplifier system of the present invention provides the energizing power supply for winding 23.

The rotation of shaft Hi produced by motor 20 effects the desired positioning of the controlled element in and also operates a rebalancing potentiometer of a resistance bridge generally designated by the numeral 46. Bridge 40 includes resistor elements M and 42 which are connected in parallel by leads 43 and M and energized through feeders i5 and 46 from a suitable transformer secondary winding 41. The responsive element 35] mechanically positions a variable tap 33 at selected positions along resistor ll, in accordance with the condition affecting the responsiVe element 30 and so selects the operating potential applied to line 34.

The screw threaded end of shaft l5 works in a threaded block it: to which is secured a blade I! in slidable engagement with resistance 42.

3 Hence, as shaft M rotates in one direction or the other, the blade I1 is moved along resistor 42, and so rebalances the bridge 40 as controlled element I is brought to its next position.

The amplifier system includes a thermionic amplifier tube or tubes and appurtenances, generally designated 60, a discriminator tube section I00, a transformer section I50 and a rectifier section, generally designated I18.

In the illustrated embodiment of the inven tion, the amplifier section 58 includes two stages of amplification, which may be accomplished in separate thermionic tubes or in a double tube, generally designated 6|, as illustrated. Tube 6| consists of a single evacuated envelope 62, and contains two triodes. The first triode constituting the firstamplification stage comprises an indirectly heated cathode 63, and its cooperating grid 64 and plate 55. The second triode which functions as the second amplification stage comprises the indirectly heated cathode 66 together with the latters cooperating grid 61 and plate 68. The cathodes are heated by two filaments 58 and 18 connected in series, one terminal of the series filament circuit being connected to grounded line H and the other terminal supplied by a filament feeder X, which is in turn supplied b a secondary I53 of transformer I50 as hereinafter explained.

The grid 64 is connected to ground wire H by means of a ballast resistor 13, the signal impulse being communicated to the grid by means of Wire 34, which is connected through capacitor to the grid lead 16. The grid element 61 of the second amplifying stage is fed by grid lead 18, the latter being connected to the ground line 1! by means of a resistor 80 and connected through capacitor 82 to junction 83 of the plate circuit 85 of the first amplifying stage- From junction 88, there extends a resistor 85, the lower terminal of which is connected by line 81 to the output terminal I88 of the rectifier section I10.

A second resistor 90 is connected by line 9i to the junction of resistor 85 and line 81, the upper terminal 63 of resistor 00 being connected by line 84 to the plate 68 of the second amplifier stage. Junction 83 of resistor 80 is the output terminal of the second amplifying stage and is connected through blocking capacitor 95 to the rid control line 86 and its branch 86'. The

thermionic tubes, generally designated H0 and I constitute the discriminating tube section I 00 of the amplifier, and each includes an indirectly heated cathode, a control grid, screen grid and plate. Thus, tube IIO includes a cathode II2 which is indirectl heated by filament I I I, a control grid II3, screen grid I I4 and plate II5. Similarly, tube I38 includes a cathode I32, which is indirectly heated by filament I3I, a control grid I33, screen grid I34 and plate I35. The grid II3 of tube H0 and grid I33 of tube I38 are joined by connection 85 and are fed by the same grid lead 96. The grid lead 96 is connected to ground wire I40 by a capacitor MI and a resistor I42. The wire I is grounded at M3. The indirectly heated cathode I I2 and one terminal of the heat-- ed filament III are connected to the ground wire I40, and similarly, the indirectly heated cathode I32 and one terminal of its filament heater I3! are connected together and grounded at I48.

Transformer I58 energizes the system and includes a primary E51, one terminal of which is grounded at I52, the other terminal being fed through an alternating current supply line 21 from a suitable source. The transformer includes a filament heater secondary I53 having one terminal grounded at I54 and the other terminal feeding supply line X, which is in turn joined to the filament terminal X of each of the thermionic tubes, 8!, H8, I36 and Ill.

Another secondary I55 of the transformer has one terminal connected by line II6 to the plate I I5 of discriminator tube I I 0, the screen grid II4 likewise being connected by means of line II8 to a junction II1 of the plate feeder H6. The opposite terminal of the winding I55 is connected by mean of line I35 to the plate I35 of discriminator tube I30, screen grid I34 being likewise connected by means of line I38 to junction I31 on line I36. A center-tap I56 of the winding I55 is connected by means of line I51 to junction I58 and thence by means of line I59 to terminal I60 of the motor winding 23. Junction I58 is connected to cathode I45 through capacitator I82.

Another secondary winding I55 supplies power to the rectifier section, generally designated I10, The rectifier section includes a full-wave rectifier tube 01' tubes, generally designated I1I, having cathodes I12-I13, which are indirectly heated by filaments I14. Adjacent the cathodes are the anodes I15 and I16.

Anode I15 is connected by line I11 to one terminal of transformer secondary winding I and anode I16 is connected by line I18 to the opposite terminal of winding I65. The mid-point I85 of the winding I65, is grounded at I61. Th'e cathodes I12I13 of the full wave rectifier tube I1I are connected to terminal I80, the latter being connected to ground I8I by capacltator I83. The junction I is also connected through resistor I84 to junction I85, which is in turn connected by line I86 to the output terminal I88 of the rectifier. Junction I is connected through resistor I88 to the ground line I90 and the output terminal I88 is similarly connected through a capacitator I92 to ground.

For clarity in the drawings, the transformer, composed of windings 41 and 49 and core 48, for supplying the rebalancing bridge 40, has been shown as separate from the transformer I50, but the two transformers may, and in most instances are; a unitary structure. Thus secondaryy/inding 41 is merely added to the transformer I50 and is not separate.

Operation When alternating current is supplied to feeders 21 and 5I, the system is energized and winding '22 of the motor 20 is constantly energized. The voltage across winding 22 is displaced in phase with respect to the voltage across primary I5I by about ninety degrees, due to the series condenser 28 in the line feeding the motor winding 22.

The rectifier HI and the center tapped secondary I65 function in the usual manner of a full wave rectifier. Thus, during one half cycle, current tends to flow from the upper end of secondary I85 through conductor I18, anode I16, cathode I13, conductor I82, condenser I83, and

ground connections I8I and I 61 back to the center tap of the secondary winding I65. During the opposite half cycle, current tends to flow from the lower end of secondary I65 through conductor I11, anode I15, cathode I12, conductor I82, condenser I83, and ground connections I8I and I61 back to the center tap of the secondary. Thus, during each half cycle, there is a tendency for current to fiow across condenser I83 in such a direction as to cause a voltage to exist across condenser I83. The polarity of the voltage will be such that the upper terminal oi condenser I83 will be positive with respect to the lower terminal. In other words, a positive voltage will exist between junctions I80 and I8I. The condenser I83 and the condenser I92 cooperate with resistor I84 in the usual manner of the condensers and resistors in a filter system to filter out to a certain extent the alternating current component of the rectified current. Thus, referring to Figure 2, curve I95 represents the voltage across the output terminals of the rectifier before it enters the filter system. The line I91 represents the voltage existing across the output terminals of the filter system. In other words, the curve I91 represents the voltage existing across condenser I92. It will be noted that the voltage represented by line I91 is substantially unidirectional with a slight alternating component. Furthermore, the frequency of this alternating component is twice that of the supply voltage. The curve of the supply voltage would be represented by the curve which would result if the central peak of the three peaks shown in Figure 2 were inverted with respect to the base line. The function of the rectifier in producing the voltage represented by line I95 is simply to invert alternate peaks and to cut off any portion of a voltage curve below the base line. If the second peak of the voltage curve I95 is inverted to represent the original alternating voltage curve, it will be quite obvious that the curve I91 has twice as many alternations the original alternating voltage curve.

The magnitude of this alternating component of the voltage represented by line I51 in Figure 2 will depend upon the degree of filtering. The greater the amount of filtering, the less pronounced will this alternating component be. In the ordinary amplifier circuit it is considered desirable to employ as many sections of filtering as is economically advisable so as to reduce as much as possible the alternating component of the output voltage of the filter system. In the circuit of the present invention, this filter system is so selected as to produce an alternating component of a magnitude just sufficient to give the desired biasing effect.

Referring now to the operation of the control portion of the apparatus, the various elements are shown in the position they assume when the controlled element ID is in the position demanded by the control device 30. With the control elements in this position, the positions of sliders 33 and I1 correspond so that no voltage exists between them. Thus, no signal voltage i applied to grid 64. Let it be assumed now that the condition to which element 33 is responsive changes so as to cause a movement of slider 33 to the right. This will result in an alternating voltage existing between sliders 33 and I1 so as to cause an alternating voltage to be impressed upon grid 64 through'blocking condenser 15. The result of this alternating voltage being applied to the grid 64 is that the current flow through the plate circult of the first triode of tube 6| has an alternating component corresponding in magnitude and phase relation to the alternating signal voltage, this current flowing through the following plate circuit: from junction I88 through conductor 81, coupling resistance 86, junction 83, conductor 85, plate 65, cathode 63, through the ground connections back to terminal IBI. The current flowing through coupling resistance 86 not only has an alternating component due to the signal voltage but also has an alternating component equal in magnitude to the alternating component of the output of the filter system, as discussed above. The alternating component of the voltage across resistor 86 is applied to resistor and hence to grid I51 through the blocking condenser 82, the blocking condenser functioning in the usual manner to block out any unidirectional component of the voltage.

The plate circuit of the second triode of tube GI may be traced as follows: from junction I88 through conductors 81 and SI, coupling resistor 93., junction 93, conductor 94, plate 68, cathode (36, through the ground connections back to terminal IBI. The current flowing through resistor 90 will accordingly be a function of the signal voltage as amplified by the first and second triodes of tube BI and a function of the unbalance voltage appearing across the output terminals of the filter network. The nature of this component due to the unbalance voltage will be dis cussed in more detail later. In any event, the alternating voltage appearing across resistor 93 is impressed through condenser 95 on to grids H3 and I33. This voltage will consist primarily of an alternating voltage representing the amplified unbalance voltage of the bridge as. The magnitude of this voltage will depend upon the extent of displacement of slider 33 with respect to slider I1. The phase of the unbalance voltage will be dependent upon whether slider 33 has moved to the right or to the left of slider I1. Obviously, when slider 33 has moved to the right of slider I1, as in the case being considered, the unbalance voltage is displaced in phase from that existing when the slider 33 assumes a position to the left of slider I1. As was noted in connection with the previously traced circuit connections between the center tapped secondary Hi5 and the two tubes III) and I33, the plates H5 and I35 are so connected to the secondary I55 that the voltages applied to them are 180 displaced with respect to each other. In other words, during any given 'half cycle in which plate I I5 is positive with respect to cathode H2, plate I35 will be negative with respect to cathode I32. The various circuit constants such as condenser MI and resistor I42 are so selected in value that the amplified unbalance voltage of bridge II as it appears on grids H3 and I33 will be in phase either with the voltage applied to the anode H5 or that applied to anode I35. Depending upon which anode voltage it is in phase with, one or the other of the tubes III and I33 will become more conductive.

Let it be assumed that under the conditions described in which the slider 33 has been moved to the right with respect to slider I1, the unbalance voltage as applied to grids I I3 and I33 is in phase with the anode voltage applied to anode I I5. Under these conditions, current will flow through winding 23 of the motor as follows: from the upper terminal of secondary I55 through conductor IIE, plate II5, cathode IIE, conductor I45, ground connections I43 and 25, junction 24, winding 23, junction I59, and conductors I58 and I51 to center tap I56. During the next half cycle, obviously no current fiows through the tube IIU since plate I I5 is negative with respect to cathode IE2. During the same half cycle, anode I35 is positive with respect to cathode I32 but the voltage applied to grids H3 and I33 will be 180 displaced in phase. In other words, the grids H3 and I33 will be negative with respect to the oathode by reason of the signal voltage. Thus, under these conditions, no current will flow through tube I30 and current will flow through tube IIO only tive. As a result, motor 2| will rotate in a direcduring the half cycles in which plate H5 is position opposite to that previously considered to tive with respect to cathode I I2. The result will move valve stem ll downwardly and to move be that a voltage is impressed across winding 23 the threaded block I6 to the left. The movecorresponding to the voltage output of the half ment of threaded block I6 to the left will correwave rectifier. Since it is desired to improve the spondingly move slider IT to the left. Such wave form of the voltage flowing through windmovement will occur until slider II corresponds ing 23 so that it more nearly corresponds to the to the position of slider 33.

wave form of an alternating current, the con- The operation as described so far, with the exdenser I62 is connected in parallel with winding 10 ception of the presence of the alternating com- 23 through the following circuit: from one terponent due to the filtering system, is substanminal of condenser I62 through conductor I40, tially like that of the motor control system disground connections I43 and 25, terminal 24, windclosed in th copending application of Albert P.

ing 23, terminal I 60, and conductor I59 back to Upton, Serial No. 437,561, filed April 3, 1942. the other terminal of condenser I62. The con- That portion of the operation which is concerned denser I62 by shunting out the higher harmonics with the novel features of the present application tends to cause the curve of the voltage across Will now be described.

winding 23 to be more nearly a sine curve. It will be noted that in the circuit traced The phase relationship of the voltage across through the first triode of tube GI, reference was Winding 23 with respect to that appearing across made to an alternating component of the voltage winding 22 will obviously depend upon Whether due to the alternating component of the voltage tube III} or tube I39 is conductive since these across the output te m n l o the filter y tubes are conductive during opposite half cycles. As previou ly exp ained, this a t rnating ompo- In the case being considered, in which the tube hent i l e a f q e y twice that of the fre- III! is conductive, the voltage across winding 23 25 l y 0f the Supply Voltage Since this alterwill be 180 displaced from that when tube I h ting v l pe s r ss res stor 86, it is is conductive. In one case, the current through p d to g d 6 d Will be a e y the winding 23 will lead by approximately 90 that second triode of tube 6 I. Conseq ly, it will through winding 22 while in the other case, the appear in considerably amplified form across current will lag by approximatel 90 that 30 resistor 90. Since the plate circuit of the second through winding 22. The motor 2I will rotate triode is a so Supplied by the power supply System i one direction or th other depending upon Ila, there likewise will be introduced an alterwhether the current through Winding 23 lags or hating eompehent in the voltage across resistor leads that through winding 22 In the case be- 99 d to s alternating component in the voling considered, it will be assumed that the motor age p d o no 68- In h r wo d the alrotates in such a direction as to so move rod I5 telhatihg component of the Output of the pow r to cause the threaded block I6 to be moved to ly 10 w ll appear in the v e r s rethe right, This ome mov m nt ill cause th sister 90 in two different forms. One of thes is stem II of valve I0 to be moved upwardly so as due to the application of this alternating comto increase the opening of the valve. The moveponent to the anode 68. The second is due to ment f threaded bl k to causes hd [1 t be the application of this alternating component to moved to the right. Such movement will conplate 65 and que tly to grid 61 of the second tinue until the slider I1 corresponds in position triode- This Second component will be d to slider 33, at which time, no voltage will exist placed in phase h r p t o th first and will between sliders 33 and I1. When this happens, -15 be very much greater than the first due to the the voltage impressed upon grids H3 and 133 amplifying eiiect of this second triode. In fact, ill posses no component derived fr bridge due to the voltage gain of the second triode, the 40 and for reasons presently t be described, y portion of the voltage component due to the presthe tube Ho nor tub I30 l be Conductive ence of this alternating component in the volt- Thus winding 23 will b deenergiz d and motor age applied to plate 58 can be disregarded. Due 2I will stop. The apparatus is so designed that to the fact that both grids 64 d 5 a e onthis Wi l occur when the controlled element In nected to

cathodes

63 and 66, current will flow has assumed a position corresponding t th t in the first and second triodes at all times so that therethrough will be 180 displaced in phase from crosses the cathode vo demanded bythe responsiveelement 30 this alternating voltage will be present at all It will be obvious from the above that if slider imes. This alternatin volta e will in urn be 33 is moved to the left, the voltage between applied through bl g Condenser 5 t0 grids sliders as and I! will be 180 displaced from that and v reason f t p ase reversin which existed in the case just considered. As a action between the first and Second S s of result, the voltage impressed upon grids H3 and amplification and by reason of the phase shift- I33 will be similarly 180 displaced in phase. As mg action of condensers 95 and and resistor a result, the Voltage applied

t grids

3 and 3 I42, this voltage will be so related to the voltages will no longer be in phase with the anode voltage applied to anodes I and that it tends to applied to plate II5, but, on the other hand, will drive grids 3 and I33 e ative durin t ose he in phase with that applied to anode I35. As portions of the anode voltage cycles in which e a result, only tube I38 will be conductive so that 65 anode s most Positive h respect 0 the c current will flow through winding 23 as follows: In othel Words, referring o F ure 3, the from the lower terminal of secondary I55 through Voltage due to the a p d alternating Voltage conductor I36, plat I35, cathode I32, ground existing across the output terminals of the filter connections I48 and 2-5, terminal 24, field windystem is represented in co siderab y exagger ing 23, terminal I an, and conductor I59 and I5! ed form by the curve 2M. The voltage applied to the center tap of secondary I55. As a result of to plate H5 is represented by the curve 202 and current flowing through this circuit, winding 23 that applied to plate I35 b the curve 203, It will again be energized, but the current flowing will be noted that at the point a, the curve 20I ltage line so that the efthat just considered when tube II 0 was conducfoot of this voltage from point a to point I) while anode I35 is positive, is to drive the grids I I3 and I33 negatively. Similarly, the voltage curve 2M is below the cathode voltage line between points and d so that when anode H5 is positive the eifect of this voltage is likewise to bias the grid negative with respect to the cathode. Due to the fact that th voltage is of twice the frequency of the voltage applied to the anodes H5 and I35, it is thus possible to have an alternating voltage function so as to bias the grids negative with respect to the cathodes during both half cycles. Quite obviously, if the grid voltage were of the same frequency as the anode voltage, it could be elfective to bias the grid negatively only during one of each two half cycles. With the present arrangement, however, it so functions during both half cycles. It is true that between points I) and c, for example, the effect of this voltage is to drive the grid positive with respect to the cathode. During this portion of the anode voltage cycle, however, the anod voltage is relatively low so that there is very little tendency for the tube to pass current even though the grid may be at a higher potential than the cathode. Furthermore, due to the tendency of the anodes and screen grids to emit when hot and thus cause current to fiow through condenser MI during the half cycles in which the anodes are negative, there is a considerable tendency for a charge to be built up on condenser I4I of such polarity as to cause the grids to be biased negatively. Because of this, any current flow that takes place through tubes I I0 and I30 in the absence of a signal from the bridge 40 is negligible.

It will be thus seen that I have devised an arrangement in which it is possible to reduce the amount of filtering that is necessary in the D. C. power supply and to utilize the resulting ripple in an advantageous manner to bias the grids of the final output tubes. The constants of the filtered network are so selected that the unfiltered alternating ripple is of such a value and phase as to give the correct amount of bias. Obviously, if it is too great, it will tend to counteract the effect of a small unbalance voltage from bridge 4|. By properly selecting the constants of the filter circuit, however, it is possible to obtain the exact amount of bias that is necessary and at the same time to reduce the cost of the filter circuit.

While I have shown a specific embodiment of my invention, it is to be understood that this is for purposes of illustration only and that my invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. An electronic discriminator circuit comprising a plurality of electronic discharge devices each comprising an anode, a cathode, and a control element, means for applying alternating Voltages of the same predetermined frequency but of opposite phase relationship to the anodes of said devices, means for so applying signal voltages to the control elements of both devices that one or the other of said devices becomes conductive, the device that is conductive depending upon the characteristics of the signal voltages, and further means for applying to the control elements of both devices an alternating biasing voltage of twice the predetermined frequency, of a magnitude independent of the anode current, and of such phase relationship with respect to the alternating voltages applied to the anodes of said devices that said biasing voltage is effective over the intermediate portions of the positive 10 half cycles of the anode voltages applied to both anodes to bias the control elements negatively with respect to the cathodes.

2. An electronic phase discriminator comprising a plurality of electronic discharge devices each comprising an anode, a cathode, and a control element, means for applying alternating voltages of the same predetermined frequency but of 0pposite phase relationship to the anodes of said devices, means for applying signal voltages of the same frequency and the same phase relationship to the control elements of both devices so that one or the other of said devices becomes conductive depending upon the phase relation of the signal voltage to the anode voltage of that device, and further means for applying to the control elements of both devices an alternating biasing voltage of twice the predetermined frequency, of a magnitude independent of the anode current, and of such phase relationship with respect to the alternating voltages applied to the anodes of said devices that said biasing voltage is effective over the intermediate portions of the positive half cycles of the anode voltages applied to both anodes to bias the control elements negatively with respect to the cathodes.

3. An electronic discriminator comprising a plurality of electronic discharge devices each comprising an anode, a cathode, and a control element, means including a source of alternating voltage for applying alternating voltages of the same predetermined frequency but of opposite phase relationship to the anodes of said devices, means for so applying signal voltages to the control elements of both devices that one or the other of said devices becomes conductive, the device that is conductive depending upon the characteristics of the signal voltages, and further means including a full wave rectifier energized by said source of alternating voltage for applying to the control elements of both devices an alternating biasing voltage of twice the predetermined frequency and of such phase relationship with respect to the alternating voltages applied to the anodes of said devices that said biasing voltage is effective over the intermediate portions of the positive half cycles of the anode voltages applied to both anodes to bias the control elements negatively with respect to the cathodes.

4. In a multi-stage amplifier, first and second electronic discharge devices, each having an anode, a cathode, and a controlelement, a source of alternating voltage, means comprising a rectifier and a filter system operatively connected to said source for obtaining therefrom a unidirectional voltage having a small component of alternating voltage, means for applying a signal voltage to the control element of said first electronic discharge device, means for connecting said rectifier and filter system to the anode of said first discharge device so as to form an anode circuit, means for applying voltage derived from said last named anode circuit to the control element of said second electronic discharge device, whereby the voltage applied to said control element of said second electronic discharge device has a component due to the signal voltage and an alternating component derived from said rectifier and filter system, means for applying an alternating potential derived from said alternating source of power to the anode of said second electronic discharge device, and means for maintaining a phase relationship between the alternating component of the voltage applied to the control element of said second discharge device and derived from the rectifier and filter network and the alternating potential applied to the anode such that said alternating component is effective to apply sufficient biasing voltage to said control element of said second device that in the absence of a signal voltage said second discharge device is substantially non-conductive during the entire cycle.

5. In a multi-stage amplifier, first and second electronic discharge devices, each having an anode, aoathode, and a control element, a source of alternating voltage, means comprising a full wave rectifier and a partial filter system operatively connected to said source for obtaining therefrom a unidirectional voltage having a small component of alternating voltage of twice the frequency of said source, means for applying a signal voltage to the control element of said first electronic discharge device, means for connecting said rectifier and filter system to the anode of said first triode so as to form an anode circuit, means for applying voltage derived from said previously named anode circuit to the control element of said second electronic discharge device, whereby the voltage applied to said control element of said second electronic discharge device has a component due to the signal voltage and an alternating component derived from said rectifier and filter system, means for applyin an alternating potential derived from said alternating source of power to the anode of said second electronic discharge device, and means for maintaining a phase relationship between the alternating component of the voltage applied to the control element of said second discharge device and derived from the rectifier and filter network and the alternating potential applied to the anode such that the alternating voltage applied to the control element of said second discharge device is effective to bias the grid negatively during that portion of the conductive half cycle in which the anode potential is greatest.

6. In a multi-stage amplifier, first, second, and third electronic discharge devices, each having an anode, a cathode, and a control element, a source of alternating voltage, means comprising a full wave rectifier and a partial filter system operatively connected to said source for obtaining therefrom a unidirectional voltage having a small component of alternating voltage of twice the frequency of said source, means for applying a signal voltage to the control element of said first electronic discharge device, means for connecting said rectifier and filter system to the anode of said first and second triodes so as to form anode circuits therefor, means for applying a voltage derived from the anode circuit of said first device to the control element of said second electronic discharge device whereby the voltage applied to said control element of said second electronic discharge device has a component due to the signal voltage and an alternating component derived from said rectifier and filter system, means for applying a voltage derived from the output circuit of said second discharge device to the control element of said third discharge device, means for applying an alternating potential derived from said alternating source of power to the anode of said third electronic discharge device, and means for maintaining a phase relationship between the alternating component of the voltage applied to the control element of said third. discharge device and derived from the rectifier and filter network and th alternating voltage applied to the anode such that the alternating voltage applied to the control 12 element is efiective to bias the control element negatively with respect to the cathode.

7. In a multistage electronic amplifier, a source of alternating voltage, a final stage comprising two electronic discharge devices each comprising an anode, a cathode, and a control element, said anodes being oppositely connected to said source of alternating voltage, said control elements of said discharge devices being connected together into a common input circuit, means including a voltage amplification stage for applying a control voltage to said common input circult and for causing one or the other of said electronic units to be rendered conductive depending upon a characteristic of said control voltage, means including a source of pulsating unidirectional voltage for energizing said voltage amplification stage, said last named means being effective to introduce into said control voltage an alternating component due to the pulsations in said unidirectional voltage, and means for maintaining a phase relationship between said alternating component and said source of alternating voltage such that said alternating component is effective to bias the control elements of said electronic discharge devices negatively with respect to their cathodes durin the intermediate portions of both half cycles of the anode voltage.

8. In a multistage electronic amplifier, a source of alternating voltage, a final stage comprising two electronic discharge devices each comprising an anode, a cathode, and a control element, said anodes being oppositely connected to said source of alternating voltage, said control elements of said discharge devices being connected together into a common input circuit, means including a voltage amplification stage for applying a control voltage to said common input circuit and for causing one or the other of said electronic units to be rendered conductive depending upon a characteristic of said control voltage, means including a full wave rectifier and a partial filter system connected to said source of alternating voltage for energizing said lt amplification stage, said last named means being effective to introduce into said control voltage an alternating component due to the ripple in the output of said partial filter system, and means for maintaining a phase relationship between said a1- ternating component and said source of alternating voltage such that said alternating component is effective to bias the control elements of said electronic discharge devices negatively with respect to their cathodes during the intermediate portions of both half cycles of the anode voltage.

9. In a multistage electronic amplifier, a source of alternating voltage, a final stage comprising two electronic discharge devices each comprising an anode, a cathode, and a control element, said anodes being oppositely connected to said source of alternating voltage, said control elements of said discharge devices being connected together into a common input circuit, means including a voltage amplification stage for applying a control voltage to said common input circuit and for causing one or the other of said electronic units to be rendered conductive depending upon a characteristic of said control voltage, means including a full wave rectifier and a partial filter system connected to said source of alternating voltage for energizing said voltage amplification stage, said last named means being efiective to introduce into said control voltage an alternating component due to the ripple in the output of said partial filter system, and means for maintaining a, phase relationship between said alternating component and said source of alternating voltage such that said alternating component is effective to bias the control elements of said electronic discharge devices negatively with respect to their cathodes during the intermediate portions of both half cycles of the anode voltage, the filter system being so designed that said ripple is of such magnitude as to produce the desired amount of bias.

10. In a multistage electronic amplifier, a source of alternating voltage, a final stage comprising two electronic discharge devices each comprising an anode, a cathode, and a control element, said anodes being oppositely connected to said source of alternating voltage, said control elements of said discharge devices being connected together into a common input circuit, means including a voltage amplification stage for applying an alternating control voltage to said common input circuit, said control Voltage being reversible in phase for causing one or the other of said electronic units to be rendered conductive depending upon the phase of said control voltage, means including a full wave rectifier and a partial filter system connected to said source of alternating volt- 14 age for energizing said Voltage amplification stage, said last named means being efiective to introduce into said control voltage an alternating component due to the ripple in the output of said partial filter system, and means for maintainin a phase relationship between said alternating component and said source of alternating voltage such that said alternating component is effective to bias the control elements of said electronic discharge devices negatively with respect to their cathodes during the intermediate portions of both half cycles of the anode voltage.

WILLIAM J. FIELD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,297,836 Levy Oct. 6, 1942 2,330,377 Phair Sept. 28, 1943 2,121,987 Rosenberg June 28, 1938 2,128,070 Bahls Aug. 23, 1938 2,376,513 Shafier May 22, 1945 2,375,599 Jones May 22, 1945