US2166184A - Balanced electron tube amplifier - Google Patents

Description

July 18, 1939. w SOLLER 4 2,166,184

BALANCED ELECTRON TUBE AMPLIFIER Original Filed Sept. 9, 1933 IN VEN TOR.

BY 6 d ATTORNEY.

Patented July 18, 1939 BALANCED ELECTRON TUBE? AMPLIFIER Walter Soller, Tucson, Ariz., assignor of one-half to William H. Woodin, Jr., Tucson, Ariz.

Original application September 9, 1933, Serial No. 688,833. Divided and this application June 23, 1934, Serial No. 732,170

16 Claims. (Cl. 179-171) My invention relates broadly to electron tube circuits and more particularly to electron tube amplification systems.

This application is a division of my application Serial No. 688,833, filed September 9, 1933, for Balanced electron tube circuits, now Patent 2,104,211, issued January 5, 1938.

One of the objects of my invention is to provide a balanced electron tube circuit for the amplification of direct and alternating currents and voltages.

Another object of my invention is to provide a multi-stage electron tube amplification system for signal receiving circuits having means for precisely balancing each of the electron tube stages.

Another object of my invention is to provide a balanced circuit arrangement for multi-tube amplifiers and a method of balancing such circuits in which the simultaneous change in both cathode emission and electrode potentials, including plate potential, may be compensated where such circuits are supplied from a common source of power. 7

Still another object of my invention is to provide a system of balancing a multi-stage amplification system employing screen grid electron tubes, which involves the disposition of resistors of selected value between the output circuit of one electron tube and the input circuit of a succeeding electron tube in such arrangement as to balance the operation of the circuits.

A further object of my invention is. to provide a circuit arrangement for an amplification system employing screen grid electron tubes having resistors in circuit with the screen grid elements for deriving from the power source the required operating potentials for the screen grid elements of the electron tubes.

A still further object of my invention is to provide a circuit arrangement for a multi-tube amplification system operative to amplify either direct or alternating current and in which special arrangements and values of resistors are employed for coupling the output system of one tube with the input system of a succeeding tube while insuring balanced operation thereof.

Still another object of my invention is to provide a circuit arrangement for a screen grid multi-tube amplifier system with a balanced bridge circuit including resistors of selected values in selected arms thereof for effecting a balanced transfer of energy from the output of one screen grid tube to the input of a succeeding screen grid tube.

Other and further objects of my invention reside in the electron tube amplification circuit arrangements as set forth in the specification hereinafter following, by reference to the accompanying drawing, in which:

Figure 1 is a diagram of the circuit of my invention as applied to the amplification of alternating currents or pulsating direct currents and adapted to be energized from an alternating current power supply; Fig. 2 is a diagram of the circuit of my invention as applied to the amplification of steady direct currents and adapted to be energized from an alternating current power supply; and Fig. 3 is a theoretical diagram for the purpose of more clearly explaining the principle of operation of my invention.

Referring to the drawing in detail, Fig, 1 shows an amplification system adapted for connection to an alternating current power source indicated at 3i. An electron tube is provided, as shown at I, having an anode at 2, a cathode at 3, a screen grid at i, and a control grid at 5. as. elementary parts thereof. The anode circuit comprises resistances numbered 6, 1 and 9 connected in series between the anode 2 and the cathode 3. The input circuit in Fig. 1 has been labeled A. C. input and connects with control grid 5 and cathode 3 through resistor Hi. The resistor I6 is in series with resistances 9 and l and together, they constitute a shunt path across the output of the filter 32, as shown. The alternating current power source is connected, as indicated at 3i, to the primary of the power transformer which feeds the full wave rectifier connected with the filter circuit 32. A connection is taken intermediate resistances 9 and l in the output circuit, which connection includes adjustable resistor 28 and fixed resistor 30 disposed in series and connected with the screen grid 4. The values of resistors 30 and 28 are so selected that the required potential is impressed upon the screen grid l. Resistors ii and i may be adjusted to precisely regulate the characteristics of the output circuit. The output system of tube I includes the transformer indicated at 34. The primary winding of transformer 34 is connected with the anode 2 and at a point intermediate resistors 38 and 28. The secondary winding of transformer 34 constitutes the final output of the balanced amplification stage formed by tube 1.

A second balanced circuit is coupled to the output of the single amplification stage constituted by tube I for further amplification of the input. Primed reference numbers in the second electron tube circuit denote elements similar to the parts of the first electron tube circuit which are similarly numbered. Alternating or pulsating direct current can be amplified in this arrangement wherein inductive coupling is employed between the stages, as shown at 34, and a single source of anode potential, shown at 32, is connected to the anode of each tube. The screen grid voltage is less than the anode voltage by the drop across resistance shown at 30.

Fig. 2 shows the circuit of Fig. l but employing separate anode supply sources for each tube, as shown at 35 and 36. This permits direct connection of the output of the first stage, to the input of the second stage, as indicated at 4|, and thereby the amplification of steady direct currents as well as alternating currents may be effected. Primed reference numbers in the second electron tube circuit denote elements similar to the parts of the first electron tube circuit which are similarly numbered. The voltage on the screen grid is less than the voltage on the anode by the drop across resistance shown at 30.

Fig. 3 diagrammatically illustrates the electrical bridge circuit embodied in the balanced circuits employed in the multiple stage systems shown in Figs. 1 and 2. The bridge circuit includes a multiplicity of arms or branches wherein the space path resistance between the screen grid or auxiliary electrode 4 and anode 2 constitutes one path or arm; resistance 6 serves as another arm; resistance I, substantially as another; and an additional resistance element 30, as the fourth arm.

In order to effect balance of the bridge circuit, a voltage is introduced in the arm of the bridge comprised substantially by resistance 1, the voltage being produced as a potential drop across resistor 28 due to the screen grid current which is led therethrough by connecting resistor 28 between the screen grid 4 and the resistor 9, the connection including the resistance element 30 constituting one arm of the bridge. Since in balancing the circuit, the currents through resistance elements 6 and 1 are to be particularly considered as I1 and 10, respectively, the resistor 28 is connected in series with these resistance elements and the output circuit. Resistor 28 is a necessary element in effecting balance in the bridge circuit, as will hereinafter be more fully explained.

The condition of balance of the bridge is the condition of zero voltage across the output terminals. Consider the potential drop across resistance 28 as E, the resistances 6 and 1 as R1 and R0, respectively, and the currents in R1 and R0 as I1 and I0, respectively. The factors afiecting the balance of the bridge are the currents I0 and I1. These currents are each dependent on a common factor, which is the source of potential of the system, and the effects thereof may be made to neutralize each other for any variations in the potential source by properly adjusting the resistance of the circuit.

It will be appreciated that the same principles are involved in both a direct heated cathode circuit device and the indirect cathode heating system of Figs. 1 and 2 as long as all power is obtained from the same source. There is a simultaneous change in the heating of the oathode and the plate potential under conditions of changes in the common power supply. Accordingly, variation in cathode emission due to variation of power supply in the circuits of Figs. 1 and 2 will be balanced similar to the direct heated system.

The value of the two resistances R0 and R1 depend upon the characteristics of the tube and circuit. The simplest way to determine this dependence is to regard the output circuit, the voltage E, and the resistances R0 and R1 as a Dowling zero shunt. When a current I0 is passing through R0 and a current I1 through R1, then the requirement for no current through the output circuit is:

Now for the circuit to be balanced for a change A10 in In and a corresponding change A11 in I1, the following equation must hold:

The above is the value of R0 for balanced conditions in terms of E, I1, I0 and the slope of the I1 vs. I0 characteristics. R1 is then determined by Equation (1).

If E is constant (and it can be considered to a first approximation as constant, because the effect on it of a change in electron emission is counteracted by the effect on it of the change in potential drop across resistance 9, affecting the screen grid current therethrough, caused by a simultaneous change in 10) it is evident that the characteristics must be such that the denominator is a constant for all values of Io in order that Rn can be a constant. By putting the denominator in differential form, equating it to a constant and solving the differential equation, we obtain the characteristics of I1 vs. Io necessary to have Re a constant as follows:

Equation (5) is the general equation of a straight line. Therefore, if the portion of the characteristics near the operating value of In is straight, the circuit will balance and remain balanced.

The length of this straight portion determines the range of external fluctuations that can be balanced. This requirement is usually fulfilled for normal operating conditions. This one-tube circuit affords so simple a means of balancing external tube variations that it is as easily set up as an unbalanced circuit, will operate much more satisfactorily, and with refinements, will balance as closely as the two-tube circuit. The advantages over the two-tube circuit are: the elimination of the difficulty in balancing, of extra apparatus, and of the necessity of obtaining exactly similar tubes, which are not readily procurable.

The balancing in these circuits is accomplished by adjusting resistances R0, R1, and voltage E. Without voltage E, the circuit would not balance even though it appears the drop R0 I0 could be made to balance drop R1 I1. This is not possible, as can be seen, by allowing E to equal zero in the first equation after Equation (2), which will then cause R0 to cancel out of the equation and thereby eliminate the means of adjusting for balance. To have an additional voltage E in the circuit R0, R1, and the output, is an essential feature of these circuits, and may be provided from a battery, a standard cell or the like, in

lieu of the voltage drop across a resistance in the preferred form shown.

The actual values of the resistances R0 and R1 need not be calculated from Equations (3) and (l), but can be determined experimentally as follows: A suitable D. C. electric current meter 29 is placed across the output terminals with R0 not far from the expected correct value and R1 is adjusted until the meter reads. Zero. The supply current is then adjusted by increasing the voltage into a primary 3| of Figs. 1 and 2, and the deflection of the meter noted. Then, with a new value of R0 (a value which differs from the expected correct value in the opposite direction from that of the first value taken), R1 is again adjusted for zero reading of the meter, and the deflection of the meter again noted for an increase in supply current. If the correct value of R0 for balance is near the value which was expected, this second deflection will be in the opposite direction to the first. Values of R0 between these two are then taken and the above procedure repeated until a value of R0 and R1 is found for which no deflection is produced in the meter when the supply current is changed. Every tube even of the same type and make differs enough in characteristics to require the values of Ru and R1 to be determined experimentally for balance against supply power changes.

The assumption that E is constant is introduced to simplify the discussion and to show the fundamental idea of balancing against changes in supply power. Actually, the assumption of E being constant is an unnecessary assumption and can be replaced by the assumption that the resistances 2%, l, and it remain constant which can always be accurately fulfilled.

The following discussion will show that the circuits in Figs. 1, 2, will balance, not approximately, but completely for normal operating voltages on the tube and that the conditions. are not altered from those just given, 28 being any suitable constant resistance, and R0 and R1 determined experimentally in exactly the same way as before. Call resistance 28, R2; and the current through it, I2. Then, for balance at some current Io with the corresponding currents I1 and 12, the following equation must hold:

Now to remain balanced when 1'0 changes to I0+AIO causing I2 to change to I2+AI2 and 11 to I1+AI1, the following equation must hold also:

u( 0+ 0) 2 2+ 2' 2 l( l l) substituting R0 in this, gives I R R 1 0 cancelling and rearranging, gives R (I -AI I -AI R (I -AI I -AI This is a similar condition to that of the previous case, the denominator having exactly the same form. Here the numerator also has exactly the same form. In order for the denominator to remain constant with change of I0 and 11, it was shown that the only requirement was that the I1-I0 characteristics must be linear in the operating region, so here in order that the numerator remains constant with change of I0 and I2, the I2I0 characteristics must also be linear in the operating region. These two conditions are practically always met in amplifying tubes.

As it is, the ratio that must fit the requirement of the-characteristics of the tube given by Equation (7), the resistance R2 can be chosen arbitrarily within the operating range and R0 and R1 determined experirnentally in exactly the same way as indicated in the simplified discussion.

If, in place of solving first for R0 in Equation is obtained.

From this, it is. seen that R0 can just as well be chosen arbitrarily in place of R2 and then R2 and R1 adjusted for the balanced condition experimentally in exactly the same way as R0 and R1 were. This is a more convenient method of adjusting, as during adjustment, the tube can be held closer to its operating voltages. As R0 is arbitrary, a special case of this circuit is when R0=0.

So far, it has been shown that these circuits will completely balance out changes in the supply power sources. It will be shown now that a further adjustment of the circuits in Figs. 1, 2, is possible, whereby they will balance both changes in the power source, and changes in cathode emission due not only to variations in the power supply, but to any cause, as for example, the deterioration of the cathode or filament. It is preferable to have the grid to which resistances 3i} and 28 are connected, between the cathode and the control grid for this type of balancing.

Let changes in the electron emission not due to power supply variations produce changes of A'I2 and AI1 in E2 and I1 respectively. For these changes, there will be no change in Io; i. e.,

AIu=0. For balancing at currents I0, I and 12, we have R0I0+RZI2:I1R1 01- R0= R1I;R2I2

Then by substituting these values in Equations (8), (9), and (10) and eliminating the Rs we obtain the condition between the currents. and slopes that must be fulfilled.

The circuits of my invention show methods of taking the output of an electron tube circuit from between the anode and a grid, which is useful not only for balancing and stabilizing the tube circuit, but as a form of amplifier circuit to be used for any purpose where direct or alternating currents or voltages are to be amplified. The circuits of my invention comprise a network of resistances and the balancing is accomplished by the network itself, permitting amplification of a given input independent of its frequency or phase.

The method of taking the output from anode and a grid results in a higher degree of amplification than heretofore obtained besides balancing the circuit.

Wherever in the specification and claims I have referred to the screen grid of the electron tube, I desire that it be understood that any grid element additional to the control grid may be employed and is intended to be included by the said term screen grid. Either grid of a pentode may be employed in the circuit arrangement set forth herein. The circuits will operate with any tube employing a grid between the filament or cathode and the control grid.

The circuit of my invention may be used in line wire systems and circuits as a repeater or booster and in many other uses which require substantial and undistorted increase of the energy impressed on the input of the amplifying system.

Although I have described my invention in certain of its preferred embodiments, I desire that it be understood that my invention is not to be limited thereby but may be modified in arrangement and no limitations are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. An amplification system comprising a multiplicity of electron tubes each including a cathode, a control grid, an anode and a screen grid, a source of anode potential, 2. connection extending from the cathode in a first of said tubes to said potential source and a circuit extending from said cathode to said anode, said circuit including a multiplicity of variable resistor elements electrically connected in series, a connection from a point between the two of said resistor elements adjacent said anode to the other side of said potential source, a connection from a point between two other resistor elements in said series circuit to said screen grid, a variable resistor included in said last mentioned connection, and a connection between the anode of the first tube and the cathode of the succeeding tube, and a connection between the grid terminus of the resistor connected with the screen grid of the first tube and the control grid of the second electron tube, the said multiplicity of resistor elements and said variable resistor adapted to effect a balance of potential across said last mentioned connections.

2. An amplification system comprising multiplicity of electron tubes each including a cathode, a control grid, an anode and a screen grid, a series circuit interconnecting the anode and cathode electrodes of a first of said tubes, the screen grid electrode thereof being connected through an impedance to a point in said series circuit, a connection between the anode of the first electron tube and the cathode of the succeeding electron tube; a connection between the grid terminus of the impedance connected with the screen grid of the first electron tube and the control grid of the second electron tube, and means including said impedance for maintaining a balance of potential across said connections.

3. A balanced electron tube amplification system comprising an electron tube device having anode, cathode and auxiliary electrodes, a bridge circuit connected with said electron tube device and having the auxiliary electrode to anode interelectrode path as one arm thereof, and resistance elements comprising the other three arms thereof; a source of potential connected with said bridge circuit through the cathode to auxiliary electrode interelectrode path and at the opposite point in said bridge from said auxiliary electrode, output terminals connected with said bridge at said anode and the opposite point in said bridge from said anode, a connection from the resistance element in the arm of said bridge opposite from said interelectrode arm to said cathode, and a resistor in the last said connection.

4. In an electron tube amplifier, a method of balancing an amplifier circuit employing a single electron tube device having at least three electrodes a source of power for energizing said electrodes, at least two of the electrodes being cold electrodes, which method consists in deriving a voltage from the current flowing through one of the cold electrodes of said tube, deriving a second voltage from said source of power, deriving a third voltage from the current flowing through another cold electrode of said tube, and combining said voltages in such manner and proportion as to effect a balance of potential in the combination.

5. An electron tube amplification system comprising an electron tube device having at least three electrodes, at least two of said electrodes being cold electrodes, a source of potential for energizing all said electrodes, means for deriving a potential drop proportional to the current through one of said cold electrodes, means for deriving a potential drop proportional to the current through another of said cold electrodes, and means for deriving a potential drop from said source of potential, said means being connected in open series relation and relatively so proportioned and arranged as to produce Zero potential difierence across the terminals of said series relation, said terminals constituting output terminals for said amplifier.

6. An electron tube amplification system comprising a plurality of electron tube devices having input and output circuit connections with the output of one of said devices connected with the input of a second of said devices, a source of potential, electrodes in each of said electron tube devices including at least two cold electrodes, means for energizing the electrodes of the second of said devices from said source of potential; means for deriving a potential drop proportional to the current through one of the cold electrodes of the last said device, means for deriving a potential drop proportional to the current through another of the cold electrodes of the last said device, and means for deriving a potential drop from said source of potential; said means for deriving potential drops being connected in open series relation and relatively so proportioned and arranged as to produce zero potential difference across the terminals of said series relation, said terminals constituting output terminals for said amplifier.

'7. An electron tube amplification system including a plurality of electron tube devices, each having an anode, a cathode, and a plurality of grid electrodes, a source of power individual to each of said electron tube devices, circuits interconnecting the electrodes in each electron tube device and the corresponding source of power comprising a connection from one terminal of said source of power to the anode electrode, a re.- sistance element in said connection, a series circuit including a plurality of resistance elements connected to said source of power, a connection from said cathode electrode to a point in said series circuit intermediate two of said plurality of resistance elements, one of said grid electrodes connected to a point in said series circuit thence through another of said plurality of resistance elements to the terminal of said power source connected to said anode, a separate resistance element in the connection to said grid, and output terminals connected to said anode and said grid electrode, the potentials of said output terminals being balanced by the algebraic sum of the potential drops across the said resistance elements connected between said anode and said source of power and between said grid electrode and said source of power, the anode output terminal of a preceding electron tube device being connected through another of the plurality of resistance elements in the series circuit connected with the succeeding electron tube device to the cathode of said succeeding electron tube device, and the grid output terminal being connected with a second grid of g the succeeding electron tube device.

8. The method of balancing the output circuit of an electron tube amplification system, which comprises producing a potential drop proportional to the anode current, producnig a potential drop proportional to the power supply current, introducing an auxiliary voltage of substantially constant magnitude, and combining the said potential drops and said auxiliary voltage in a series relation, the algebraic sum of the instantanecus voltage values being zero in the balanced condition of the circuit.

9. Means for balancing the effects of variations in the anode current of an electron tube amplifier due to unstable operating conditions, which comprise a resistor carrying the anode current subject to said variations, a second resistor connected with the first said resistor and carrying current having the same variations but in the opposite sense with respect to the variations in said anode current, and means connected with second resistor for introducing a substantially constant voltage in addition to the potential drop across the said second resistor for balancing the potential drop across the first said resistor whereby the effects of the variations in the anode current are substantially compensated.

10. In an electron tube amplifier circuit employing at least one electron tube device having a cathode and a plurality of cold electrodes, a resistor carrying the current to one of said cold electrodes, a source of power for said amplifier circuit, a separate resistor directly connected with both terminals of said source of power and carrying current therefrom, said resistors being connected in series between said cold electrode and said cathode with the polarity of the potential differences thereacross in opposite relation for approximately balancing said potential differences, and means for introducing an additional potential diiierence in series with the said potential differences and of such polarity in relation thereto as to eiiectively and completely balance the potential difierences.

11. In a multi-stage amplification system, a balanced electron tube circuit comp-rising an electron tube device including anode and cathode electrodes, a source of power, a connection including a resistance element from said source of power to said anode, a voltage divider connected across said source, a connection from said cathode to said voltage divider, means for supplying a separate voltage connected with said voltage divider at a higher potential than said cathode connection, and output terminals connected with the last said means and said anode, the polarity and the magnitude of the potential differences between the output terminals being such that the potentials of the said output terminals are balanced.

12. In a multi-stage amplification system, a balanced electron tube circuit comprising an electron tube device including anode and cathode electrodes, a source of power, a connection including a resistance element from said source of power to said anode, a voltage divider connected across said source, a connection from said cathode to said voltage divider, means for supplying a separate voltage connected with said Voltage divider at a higher potential than said cathode connection, and output terminals connected with the last said means and said anode, the algebraic sum of the potential differences in the series circuit between said output terminals, i. e., in the first said resistance, in the portion of the voltage divider between the anode connection and the connection of the last said means, and in the last said means, is zero.

13. In a multi-stage amplification system, a balanced electron tube circuit comprising an electron tube device having anode, cathode and grid electrodes, a source of power, a connection from said source of power to said anode eleca trode, a resistance element in said connection, a voltage divider connected across said source of power, a connection from said cathode electrode to said voltage divider, means for supplying an additional voltage connected with said voltage divider at a higher potential than said cathode connection for balancing the drop in potential across the resistance element in the connection to said anode by the algebraic sum of the drop in potential across the voltage divider from the connection of said resistance element at the source of power to the connection of said means and the additional voltage supplied by said means, said additional voltage being of a magnitude for effecting said balance, and an output circuit connected with said anode electrode and said means.

14. An electron tube amplification system including a plurality of electron tube devices, anode, cathode and grid electrodes in each of said electron tube devices, and balanced circuits interconnecting the electrodes in each of said electron tube devices, said balanced circuits each comprising a source of power, a connection from said source of power to the anode electrode, a resistance element in said connection, a voltage divider connected said source power, a connection from said cathode electrode to said voltage divider, means for supplying an additional voltage connected with said voltage divider at a higher potential than said cathode connection for balancing the drop in potential across the resistance element in the connection to said anode by the algebraic sum of the drop in potential across the voltage divider from the connection of said resistance element at the source of power to the connection of said means and the additional voltage supplied by said means, said additional voltage being of a magnitude for effecting said balance, an output circuit connected with said anode electrode and said means, and an input circuit interconnecting the grid and cathode in each of said electron tube devices and connected with the output circuit of the preceding electron tube device.

15. The method of directly coupling stages of electron discharge devices in an amplifying system which consists in balancing the output circuit of a preceding device by producing a potential drop proportional to the anode current, producing a potential drop proportional to the power supply current, introducing an auxiliary voltage of substantially constant magnitude and combining the said potential drops and said auxiliary voltage in a series relation, the algebraic sum of the instantaneous voltage values being zero in the balanced condition of the circuit; and impressing potential from the points of balanced potential in said output circuit upon the input circuit of the next succeeding device in said amplifying system.

16. The method of directly coupling stages of electron discharge devices in an amplifying system which consists in balancing the output circuit of a preceding device by producing a potential drop proportional to the power supply current, producing separate potential drops proportional to the currents of two different elements of said preceding device, and combining all said potential drops in a series relation, the algebraic sum of the instantaneous voltage values being zero in the balanced condition of the circuit; and impressing potential from points of balanced potential in said output circuit upon the input circuit of the next succeeding device in the amplifying system.

WALTER SOLLER.

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