US2423534A - Control apparatus - Google Patents

Description

July 8, 1947. p UPTON 2,423,534

CONTROL APPARATUS Filed April 3, 1942 2 Sheets-Sheet 1 III III C i 'i I 0 l0 ATTORNEY.

BY 14 M July 8, 1947. P, UPTON 2,42,534

CONTROL; APPARATUS Filed April 3, 1942 2 Sheets-Sheet-2 Y mvsmon. Allocuri- E U I-01L.

ATTORNEY.

Patented July 8, 1947 CONTROL APPARATUS Albert P. Upton. Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application Aprils, 1942, Serial No. 437,561

9 Claims.

The present invention relates to electronic amplifier circuits and particularly to an electronic amplifier circuit adapted for use in a system wherein a reversible motor is operated in accordance with changes in the value of a controlling mechanism, which may respond to changes in a variable condition.

An object of the present invention is to construct an improved and simplified electronic amplifier circuit.

Another object of the present invention is to provide an improved circuit for amplifying alternating electrical signals without shifting the phase of said signals.

Another object of the present invention is to provide an improved amplifier adapted for energization from a source of alternating electrical energy and further adapted to amplify signals of the same frequency as said source. Afurther object is to provide, in such an amplifier circuit means for increasing the stability of the ampliiier, that is, means for substantially preventing the appearance of false signals in the amplifier output due to stray electrical effects from said source.

Another object is to provide an improved amplifier for alternating electrical signals, especially adapted for use in a control system wherein the controlling effect is dependent upon the phase of the signals.

A further object of this invention is to provide an amplifier circuit wherein the number of impedance elements, particularly wound impedance elements, is reduced to a minimum.

Another object of the present invention is to provide, in an amplifier circuit having a plurality of stages, an improved voltage supply circuit such that the output circuits of a plurality of said stages may be connected directly in parallel to the terminals of the voltage supply circuit.

A further object of the present invention is to provide an improved amplifier circuit of the type shown in the copending application of Willi H. Gille and John V. Sigford, Serial No. 408,594, filed August 28, 1941, now Patent No, 2,375,988, dated May 15, 1945, and assigned to the assignee of the present application, and in the copending application of Walter P. Wills. Serial No. 421,173, filed December l, 1941, and assigned to The Brown Instrument Company, a subsidiary of the assignee of the present application.

A further object of the present invention is to provide an improvedamplifier circuit wherein phase distortion is reduced by reducing the number of reactive elements in the input and output 2 circuits of each stage to a minimum, and wherein reactive elements are used only for coupling between stages and for filtering.

Other objects and advantages of the invention will become apparent from a consideration of the appended claims, specification, and drawing, in which:

Figure 1 represents a circuit diagram of a eon trol system embodying certain features of my invention, and

Figure 2 represents a circuit diagram of a control system embodying certain other features of my invention.

Figure 1 Referring to Figure 1, my invention is shown therein, by way of example, as applied to a control system wherein the position of a valve I0 is modulated in accordance with the balance or unbalance of a bridge circuit ll including three temperature responsive resistance elements l2, l3 and it, although of course a larger or smaller number of'such elements could be used; In the system, the unbalanced potential of the bridge circuit H is applied to the input of an amplifier havin three preliminary stages l5, l6 and I1, and an output stage l8. A motor 20, of the split phase type, has one phase supplied directly from a source of power and the other phase supplied from the output; circuit of the amplifier output stage l8. Power is supplied to the system from any suitable source of alternating current, to which is connected the primary winding 23 of a transformer 24. Transformer 24 has a plurality of secondary windings 25, 26, 2'! and 28. Windings 25 and 2B supply power to the amplifier stages, winding 21 supplies power directly to one winding of the split phase motor 20, and winding 28 supplies power to the bridge circuit I l.

Motor 20 is provided with a pair of field windings 30 and 3| and a rotor 32. As stated above, the motor is of the split phase type. wherein, as is well known in the art, the field windings 3| and 30 are displaced in space phase, and wherein the displacement in time phase of the currents flowing through the windings determines the direction of rotation of the rotor 32. Rotor 32 drives a gear train generally indicated at 33. The output shaft of the gear train 33 is connected to a pinion 34 which engages a rack 35 mounted on stem 36 of the valve In. The output shaft of gear train 33 also drives a sliding contact 40 across a potentiometer resistance 4 l The bridge circuit II has a pair of input terminals 42 and 43 and a pair of output terminals 44 and 45. Output terminal'45 is the point of engagement of slider 40 on potentiometer resistance 4I. Input terminals 42 and 43 are.connected to the terminals of transformer secondary winding 28 by means of a pair of conductors 45 and 41.

- The upper left arm of bridge circuit II includes a variable resistance 50 and temperature responsive resistance I2. The upper right arm of bridge circuit II includes a fixed resistance ii. The lower left arm of bridge circuit II includes a fixed resistance 52 and a portion of potentiometer resistance 4|, depending upon the position of slider 40. The lower right-hand arm of bridge circuit II includes the temperature responsive resistance elements I3 and I4, fixed resistance 53 and the remaining portion of potentiometer resistance 4i. An adjustable resistance 54 is connected across the terminals of potentiometer resistance H for a purpose to be described later.

Output terminal 44 of bridge II is connected by means of a conductor 55 to control electrode 56 of a triode 52 forming a part of the first preliminary stage I5 of the amplifier. Output terminal 45 is connected by means of conductors 51 and 50 to cathode SI of triode 62. Triode 52 also includes an anode 63.

Triode 52 forms one-half of a twin triode 64 which'may be of the type commercially known as type 7F7. The twin triode 04 also includes a second triode 55 including an anode 66, a control electrode 61. a cathode 00. and a suitable heater element I for heating the cathodes of both triodes 82 and 85.

Conductor 51, which is grounded at I I, forms the negative terminal of the power supply for the three preliminary stages I5, I6 and I1. Conductor I2 forms a positive terminal of the power supply for these three stages.

A unidirectional potential is supplied between conductors 51 and I2 by means of a rectifier circuit connected to transformer secondary winding 25. This rectifier circuit includes a triode 13. which forms one part of a second twin triode I4 which may also be of the type TF7. Triode I3 includes an anode I5. a control electrode I5,

and a cathode I1.

.03, and a suitable heater element 84 for heating the cathodes of both triodes I3 and 80.

The rectifier circuit which supplies power to the preliminar stages I5. I6 and Il may be traced from the upper terminal of transformer secondary winding 25 through a conductor 85, anode i5, cathode ii, a conductor 86. a filter network 81 comprising a resistor 90 and a pair of condensers SI and 92. and conductor 93 to the lower terminal of transformer secondary winding 25. It will be noted that the control electrode and cathode are connected together and are at the same potential so that the triode I3 is always conductive on each operative half cycle of the triode. The filter network 81 also includes ter- .minals 04 and which are hereinafter referred to as the output terminals of this rectifier circuit. Terminal 04 is connected directly to conductor I2, while terminal 05 is connected to conductor 51 through a conductor 06. The eifect oi. the

. rectifier circuit is to maintain conductor I2 at a positive potential with respect to conductor 51.

The input circuit of the first preliminary stage I5 may be traced from cathode GI through conductors 60 and 51, slider 40, bridge circuit output terminal 45, bridge circuit II, bridge circuit output terminal 44, and conductor to control electrode 50. The output circuit of the first preliminary stage I 5 may be traced from positive conductor I2 through a load resistor I00, anode 63, cathode GI. and conductor to negative supply conductor 51.

l The output circuit of preliminary stage I5 is coupled to the input circuit of the second preliminary stage I6 by a condenser IOI, one terminal of which is connected by a conductor I02 to anode 03, and the other terminal of which is connected to a potentiometer resistance I03 forming a part of the input circuit of second preliminary stage It. The condenser IOI serves to transmit any A. C. signal appearing in the output circuit of stage I5 to the input circuit of stage I 6, while blocking the transmission of any 1).- C. signal.

A slider I04 cooperates with potentiometer resistance I03 and is connected to control electrode 51 of triode 65. The slider I04 and potentiometer resistance I03 form a gain control for the amplifier circuit in a manner well known in the art. This gain control may be omitted and a plain resistance used in its stead if adjustment of the amount of amplification is not desired.

The input circuit of the second amplifier stage II; may be traced from cathode" through a resistance I05, grounded conductor 51, a conductor I06, a portion of potentiometer resistance I03 and contact I04 to control electrode 61.

The output circuit of second preliminary stage I6 may be traced from positive power supp y line I2 through a load resistance I01. anode 06, cathode 60, and resistance I05 to negative power supply line 51.

The resistance I05 operates to bias the control electrode 01 negatively with respect to the cathode 68, by reason oi. the voltage drop across resistance I05 due to the flow of output current through it.

It has been found that the use of this resistance I 05 in the second stage [0 has the efiect of increasing the stability of the amplifier circuit. That is, it tends to prevent a shift in phase between the amplifier input and output stages and it tends to prevent the appearance of false signals in the output stage when there is no signal applied to the input. It has also been found that the stability of the circuit is better when this biasing resistance is used in the second stage than when it is used in any of the other stages, and that the stability is better when a biasing resistance is used in the second stage only than when such resistances are used in any combination of two or more stages. It has also been iound that the stability is better when no by-passing or filtering condenser is connected in parallel with this resistance.

The exact theoretical reason for the better stability obtained when the resistance I05 is connected in the particular manner described is not known. The existence of such improved stability characteristics has, however, been deflnitely proven by many experiments.

The output circuit of the second preliminary stage I0 is coupled to the input of the third preliminary stage II through a connection which may be traced from anode through a conductor I00. a condenser I00, and a conductor 0 to control electrode 02 of triode 03.

The input circuit of third preliminary stage The rutput circuit of the third preliminarystage I1 may be traced from positive supply line 12 through a resistance I I8, anode 8|. cathode 83, and conductor M5 to negative supply line 51.

' Final output stage I8 includes a pair of triodes and I2I which may be included in a twin triode I22. Triode I20 includes an anode I23, 9. control electrode |24,- and a cathode I25. Triode I2I includes an anode I28, a control electrode I21, and a cathode I28. Twin triode I22 also includes a suitable heater element I for heating both of the cathodes I25 and I28.

The control electrodes I24 and I21 are connected to a common junction I33 by means of conductors I3I and I32, respectively. Likewise, cathodes I25 and I28 are connected to a common junction I34 by means of conductors I35 and I38, respectively.

The output circuit of the third preliminary stage I1 i coupled to the input circuit of the final stage I8 by a connection which may be traced from anode 8| through a conductor I40, a blocking condenser I4I, conductors I42 and I43, to common junction I33 and control electrodes I24 and I21.

The input circuit of the final amplifier stage I8 may be traced from cathodes I 25 and I28 to the common junction I34, resistor I44 and its associated parallel by-pass condenser I45, conductor 51, conductor I48, a resistance I41,-a.nd conductor I43 to junction I33 and control electrodes I24 and I21.

A filter condenser I i connected between junction I33 and conductor 51. The condenser I50 by-passes high-frequency components appearing in the output of stage I1 and passing through the blocking condenser I4I, thereby substantially preventin such components from affecting the control electrodes I24 and I21. Condenser I50 is just as effective in this respect as a condenser connected between anode BI and ground. By connecting the condenser I50 in the manner shown however, it is possible to use a smaller condenser than would be the case if a condenser were connected directly between anode 8| and ground. A condenser connected directly between anode BI and ground would have to withstand the full voltage across the triode 80, while the condenser I50 is connected only in the relatively low voltage input circuit of triodes I20 an I2I. It is, of course, understood that condenser I50 has a relatively high impedance to currents of the supply frequency so as to prevent condenser I50 from efiectively shunting resistor I41.

I have found that, by the use of a filter condenser such as the condenser I50, forming a low impedance path to high frequency currents passing between one of the preliminary stage anodes and ground, it is possible to use the simplified voltage supply circuit shown without undue distortion in wave form of the transmitted signal. The use of non-reactive impedances for loads and for biasing in the preliminary stages reduces distortion in phase of the applied signal.

The simplified rectifier circuit used and the simple type of impedances employed provide a circuit which is small in size and light in weight for the amount of power supplied, as compared with amplifier circuits of the prior art.

The output circuit of triode I20 may be traced from the upper terminal of transformer winding 28 through a conductor I5I, anode I23, cathode I25, conductor I35, Junction I34, resistor I44 and its parallel by-pass condenser I45, grounded conductor 51, a conductor I52, motor winding 30, and a conductor I53 to center tap I54 on transformer secondary winding 28. A bufler condenser I55 and its protective resistor I58 are connected in series between anode I23 and grounded conductor 51.

The output circuit of triode I2| may be traced from the lower terminal of transformer secondary winding 28 through a conductor I80, anode I28, cathode I28, conductor I38, junction I34, resistor I44 and parallel by-pass condense I45, conductors 51 and |52,-winding 30, and conductor I53 to center tap I54 on transformer secondary winding 28. A buffer condenser I8| and a protective resistor I82 are connected in series between anode I28 and grounded conductor 51.

Motor winding 3| is supplied with energy from transformer winding 21 through a circuit which may be traced from the upper terminal of transformer winding 21 through conductor 51, conductor I52, motor winding 3|, a conductor I83, a condenser I84, and a conductor I85 to the lower terminal of transformer secondary winding 21.

The condenser I84 is chosen so as to form with winding 3| 8. series resonant circuit. Since this circuit is resonant, the current flowing in it, and hence the current in motor winding 3 I, is in time phase with the terminal potential of transformer winding 21. The potential at the terminals of winding 3| leads this current by an angle of approximately ninety electrical degrees, due to the inductance of the winding. Such a condenser is commonly provided in connection with split phase motors, as is well known in the art.

Motor winding 30 may receive electrical ener y in two ways:' (1)- by transmission from output stage I3 through conductors I52 and I53, and (2) by induction through transformer action from motor winding 3|, when the motor is running.

A condenser I88 is connected across the terminals of motor winding 30. This condenser 5 is so chosen with relation to the impedance of winding 30 when the motor is running, that the two together form a parallel circuit resonant at the supply frequency. It will be seen that condenser I88 and winding 30 form a parallel resonant circuit of high impedance with respect to external currents transmitted to winding 30 through conductors +52 and I53. 0n the other hand, condenser I88 and winding 30 form a series resonant circuit of low impedance with respect to internal currents induced in winding 30 by transformer action from winding 3|.

Condenser I88 and winding 30 are so designed that their impedance to external currents matches the internal impedance of triodes I20 and |2|, thereby providing optimum conditions for the transmission of energy in the triode circuits, as is well known in the art.

The fluxes produced by each of the windings 30 and II in the motor do not link the other winding when the motor is standing still. When the motor is rotating, however, the armature reaction distorts the magnetic field in the motor so that winding 30 is linked by a portion of the flux produced by winding 3|. This flux induces a current in winding 30, which is the current previously referred to as being produced by transformer action under running conditions.

The operation of a split phase motor of the type described herein in connection with an amplifier circuit somewhat similar to the present one is analyzed and described in greater detail in the other values may be used without departing from the invention.

Reference Numeral Suggested Values K Megohm. l Megohms. l M ohm.

350 Volts.

350 Volts on each side oi tap 154.

120 Volts.

l0 Volts.

Operation of Figure 1 The temperature responsive resistance elements [2, i3 and it are exposed to temperatures which are individually and collectively indicative of the need for a change in the position of the valve I. The adjustable resistance 50 is provided so that the position of the valve ill to be maintained in response to a given set of temperature conditions adjacent the resistances l2, l3 and It may be manually determined.

When the bridge circuit II is balanced. the output terminals 44 and 45 are at the same potential. and hence no signal is applied to the input circuit of the amplifier. Therefore no signal is produced in the output circuit of the third preliminary stage and no signal is applied to the input circuit of the final stage IB. Triodes I and i2! are therefore equally conductive, and the current appearing in the common portion of their output circuit which includes the motor winding is chiefly unidirectional with a small superimposed alternating component of twice the supply frequency. Under these conditions the twin triode I22 is in effect acting as a full wave rectifier. Such a current does not cause any movement of the rotor 32 and in fact the unidirectional com ponent provides a sort of dynamic braking action on the rotor. Therefore, the valve iii is maintained in the position 'which it has previously reached.

Let it be assumed that the temperature adjacent the temperature responsive resistance i2 decreases. This causes the value of resistance l2 to decrease. This produces an unbalance of bridge circuit II in such a direction that the potential appearing between output terminals 44 and 45 is of the same phase as the potential between terminals 43 and 42, respectively. This potential is, of course, in time phase with the potential occurring at the output terminals of tive. The final stage [8 then supplies to the motor winding 20 an alternating potential which is-in time phase with the potential in the upper half of transformer secondary winding 26. The current through winding 30 lags behind this potential due to the inductance of the winding. Since winding 3! is continuously energized with current in phase with the supply potential, the two windings 30 and II are now energized with currents displaced in phase, and rotation of motor 20 lollows. This rotation is transmitted through gear train 23 so as to drive valve Ill towards open position. The change in position of valve IO- causes the slider to move to the left along potentiometer slide wire 4i so as to restore the balance of the bridge circuit ll. As soon as balance is restored, the signal applied to the amplifier again drops to zero, thereby stopping rotation of the motor 20.

In a corresponding manner. an increase of temperature adjacent the temperature responsive resistance J2 causes an unbalance of the bridge circuit I i in such a direction that the phase of its output potential is shifted in the opposite direction. The potential applied to the input circuit of the final stage it is then in phase with the potential supplied to triode I 2i from the lower half of transformer secondary winding 26. This potential causes the output current of triode Hi to increase and the output current of triode I20 to decrease. The current then supplied to the motor winding 30 is opposite in phase to that supplied during the operation previously described. Motor 20 therefore rotates in the opposite direction. driving the valve ll towards its closed position and moving the slider 40 to the right along slide wire I to rebalance the bridg circuit ii. a

Changes in temperature at points I! and I will similarly result in movement of the valve III.

It should be apparent from the foregoing description that I have provided an amplifier circult which is extremely simple and which prowindings 21 and 28, and with 'the potential supduces an output current variable in phase in accordance with the phase of the input current, and wherein phase distortion-is reduced to a minimum.

The heaters 10, 84 and I30 of the three twin triodes 64, H, and I22 may be connected to any suitable source of electrical energy.

The variable resistance 54 is provided in order to adjust the amount of unbalance of the bridge circuit necessary to cause a movement of slider 40 from one end of slider 41 to the other and, hence, to move the valve l0 from open to closed position, or vice versa. It will be seen that when the resistance 54 connected in parallel with potentiometer slide wire 41 is at a maximum, the change in balance of the bridge circuit due to a given movement of slider 40 will be at a maximum. On the other hand, if the resistance of 5| is reduced to zero, the movement of slider 40 across the potentiometer slide wire ll produces no change in the bridge circuit. Therefore, it will be seen that the resistance 54 may be adjusted to such a value that valve I II will be moved from fully closed to fully open position during a change in the temperature adjacent resistance I 2 over any desired range.

Figure 2 Figure 2 shows a somewhat modified form of my invention. In this figure, a pair of relays 2N and 20! are selectively operated by the amplifier 5 to control the direction of rotation of a reversible 9 motor 223. This motor is of a diflerent type than that shown in Figure 1, and is provided witha pair of windings whose selective energization causes rotation of the motor in one or the other direction.

Circuit elements of Figure 2 which correspond exactly to elements of Figure 1 have been given the identical reference numerals. It will be noted that the only changes are the use of relays, the use of a different type of reversible motor, and some incidental changes in the bridge circuit. Also, in the circuit of Figure 2, the resistance I has been omitted from the output circuit of the second preliminary stage I5. The filtering condenser I50 has been omitted from the input circult of the final stage I8, and its function has been taken over by another filtering condenser 203 connected in the output circuit of the second preliminary stage I6.

In the bridge circuit II of Figure 2, only a single temperature responsive resistance element I2 is used. The variable resistances .I3, I4 of Figure 1 have been replaced by fixed resistors 205 and 205. The variable resistance 50 of Figure 1 has been replaced by a variable resistor 204 in the lower right-hand arm 'of the bridge circuit. The operation of the various elements in the bridge circuit'remains the same.

The output circuit of triode I of Figure 2 may be traced from the upper terminal of transformer secondary winding 20 through a conductor 2I0, winding 2 of relay 200, a. conductor 2I2, anode I23, cathode I25, junction I34, resistor I44 and parallel by-pass condenser I45, and grounded conductor 51 to center tap I54 of transformer secondary winding 26.

correspondingly, the output circuit of triode I2I may be traced from the lower terminal of transformer secondary through a conductor 2I3, winding 2 of relay 20I, a conductor 2I5, anode I25, cathode I28, junction I34, resistor I44 and parallel by-pass condenser I45 and grounded conductor 51 to center tap I54 on secondary winding 25.

Relay 200 controls the operation ofa switch arm .220 into and out of engagement with a fixed contact 22I. When switch arm 220 engages contact 22I, an energizing circuit is completed for winding 222 of motor 223. This circuit may be traced from the upper terminal of transformer winding 21 through conductors 224 and 225, switch arm 220, contact 22I, a conductor 225, motor winding 222, and a conductor 221 to the lower terminal of transformer secondary winding 21.

Relay 20I controls the operation of a switch arm 230 into and out of engagement with a fixed contact 23I. When switch arm 230 engages contact 23I, an energizing circuit is completed for winding 220 of motor 223. This circuit may be traced from the upper terminal of transformer secondary winding 21 through conductor 224, switch arm 230, contact 23I, a conductor 232, motor winding 228 and conductor 221 to the lower terminal of transformer secondary winding 21.

When the bridge circuit is balanced. no potential is present at the bridge output terminals 44 and 45. Therefore, no signal is transmitted to the input circuit of the final stage I0, and the triodes I20 and I2I are equally conductive.

The impedance of relay windings 2H and 2 is so designed that the relays do not move their associated switch arms to their attracted position unless the conductivity of one of the triodes I20 and HI has been increased substantially above its normal value by the application of an alternating current signal of proper phase relationship to the input circuit of the final stage I8.

If the temperature adjacent resistance I2 decreases, its resistance decreases, and a potential appears between output terminals 44 and 45 which is in phase with the potential between terminals 42 and 43, respectively. This potential at the terminals 44 and 45 is amplified by the three preliminary stages and applied to the input circuit of the final stage I8 without any substantial shift in phase. Since it is in phase with the terminal voltage of secondary winding 28, it is also inphase with the voltage supplied from the upper half of secondary winding 20 to the triode I20, and out of phase with the voltage supplied to triode I2I. Triode I20 therefore becomes more conductive, energizing relay 200 and thereby causing motor 223 to drive slider 40 to the left so as to rebalance the bridge II, and simultaneously to open valve I0 so that more heat is supplied to the space adjacent resistance I2.

When a rise in the temperature adjacent resistance I2 takes place, the potential appearing at terminals 44 and 45 is in the opposite phase from the case previously considered, and accordingly causes the energization of relay 20 I, thereby energizing motor winding 228. Motor 223 then 4 drives slider '40 to the right to rebalance bridge II, and simultaneously moves valve I0 towards closed position, thereby reducing the supply of heat to the space adjacent resistor I2.

If desired, the impedance of relay windings 2i I and 2 may be so designed that both relays attract their armatures when the bridge circuit is balanced. If used in this way, the two motor windings 222 and 228 oppose each other under balanced conditions, resulting in a stalled motor with a sort of braking action, which may aid in preventing overrunning of the motor.

The operation of the circuits'shown in Figure 2 is analogous to the operation of the circuits of Figure 1, and it is believed that further description of its operation is unnecessary.

' While I have shown and described certain preferred embodiments of my invention, modifications will readily occur to those who are skilled in the art, and I therefore wish my invention to be limited only by the scope of the appended claims.

I claim as my invention:

1. In an electronic amplifier circuit including a plurality of stages, each stage having an input circuit and an output circuit, means for supplying said stages with rectified alternating electrical energy, means including a blocking condenser for coupling the output circuit of each stage with the input circuit of the succeeding stage, and filter means for one of said output circuits comprising a condenser connected directly to said blocking condenser and directly across the input circuit of the succeeding stage.

2. An electronic amplifier circuit, comprising in combination, three stages of amplification, each stage having an electronic discharge device and an input and an output. circuit, the discharge devices of said three stages having substantially the same electrical characteristics, means for supplying a signal voltage to the input circuit of the first stage, and means in only the intermediate of said three stages for producing a degenerative feed-back effect to suppress any tendency of any two adjacent stages to cooperate in the generation of oscillatory voltages, said last named means consisting of an unbypassed resistor com- 1 1 mon to the input and output circuits of said intermediate stage.

3. An electronic amplifier circuit, comprising in combination, three stages 01' amplification, each stage having an input circuit and an output circuit, a resistor common to the input and output circuits of the intermediate one of said three stages for biasing said input circuit negatively, said other two stages having unbiased input circuits, power supply means comprising a rectifier and filter network adapted for connection to a source of alternating electrical energy and having a pair of output terminals, and direct conductive connections between said output terminals and the output circuits of each of said stages.

4. An electronic amplifier circuit, comprising in combination, at least three stages of amplification, each stage having an input circuit and-an output circuit, a resistor common to the input and output circuits of the intermediate one of said three stages for biasing said input circuit negatively, said other two stages having unbiased input circuits, power supply means comprising a rectifier and filter network adapted for connection to a source of alternating electrical energy and having a pair of output terminals, direct conductive connections between said output terminals and the output circuits of each of said stages, and filter condenser means connected directly across a portion of one of said output circuits.

5. An electronic amplifier circuit, comprising in combination, three stages of amplification, each stage having an input circuit and an output circuit, a resistor common to the input and output circuits of the intermediate one of said three stages for biasing said input circuit negatively, said other two stages having unbiased input circuits, power supply means comprising a rectifier and filter network adapted for connection to a source of alternating electrical energy and having a pair of output terminals, direct conductive connections between said output terminals and the output circuits of each of said stages, filter condenser means connected across a portion of one of said output circuits and in series with said filter network, a pair of input terminals adapted for direct conductive connection to a source of alternating electrical signals, non-inductive means for coupling said input terminals and the input circuit of the first stage, and further noninductive coupling means between each output circuit and the input circuit of the next succeeding'stage.

6. An electronic amplifier circuit, comprising in combination, at least three stages of amplification, each stage having an input circuit and an output circuit, a resistor common tothe input and output circuits of the intermediate one of said three stages for biasing said input circuit negatively, said other two stages having unbiased input circuits, power supply means comprising a rectifier and filter network adapted for connection to a source of alternating electrical energy and having a pair of output terminals, direct conductive connections between said output terminals and the ouput circuits of each of said stages, filter means for one of said output circuits comprising a condenser connected across the input circuit of the succeeding stage, a pair of input terminals adapted for direct conductive connection to a source of alternating electrical signals, non-inductive means for coupling said input terminals and the input circuit of the first stage,

and further non-inductive coupling means between each output circuit and the input circuit of the next succeeding stage.

7. In a multi-stage amplifier, a plurality of electronic discharge devices, each of which comprises a container and a group of. electrodes within said container including an anode, a cathode, and a control electrode, at least one of said devices containing two such groups, a filter network, connections between said filter network and the anode and cathode of only one of the two groups of electrodes of said one discharge device such that said anode and cathode function as a half wave rectifier to supply a pulsating unidirectional voltage to said filter network, connections between the anodes, cathodes, and control electrodes of the remaining groups of electrodes forming a plurality of amplification stages, each having an input and an output circuit, said filter network having a pair of output terminals, and direct connections between said pair of output terminals and the output circuit of each amplification stage.

8. In an electronic amplifier circuit for amplifying an alternating signal voltage, said amplifier circuit including a plurality of stages, each stage having an input circuit and an output circuit,

means for supplying said stages with rectified alternating electrical energy, means including a blocking condenser for coupling the output circuit of each stage with the input circuit of the succeeding stage, and filter means for one of said output circuits comprising a condenser connected directly to said blocking condenser and directly across the input circuit of the succeeding stage, said last named condenser having a high impedance to current of the frequency of said signal voltage but of low impedance to current of relatively high frequency.

9. In an electronic amplifier circuit for amplifying an alternating signal voltage, said amplifier circuit including a plurality of stages, each stage having an input circuit and an output circuit, means for supplying said stages with rectified alternating electrical energy of the same frequency as said signal voltage, comprising a rectifier and a filter including condenser means, coupling condenser means for coupling the output circuit of each stage with the input circuit of the succeeding stage, and filter means for one of said output circuits comprising a condenser connected directly across the input circuit of the succeeding stage, said last named condenser having a capacity which is relatively small as compared with that of said first named filter.

ALBERT P. UPTON.

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

UNITED STATES PATENTS

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