US2138891A - Electron tube amplification system - Google Patents

Description

Patented Dec. 6, 1938 UNITED STATES PATENT FFICE Walter Soller, Tucson, Ariz., assigner of onehalf to William H. Woodin, Jr., Tucson, Ariz.

Application September 25, 1934, Serial No. 745,460v

2 Claims.

This application is a continuation in part of my application Serial Number` 688,833 filed September 9, 1933 and entitled Balanced electron tube circuits.

One of the objects of my invention is to provide an electron tube amplification system employing multiple electrode electron tubes in which the electrodes are interconnected by balanced circuits for insuring stabilized operation of the ampliiication system.

Another object of my invention is to provide a balanced electron tube ampliiication system employing pentode electron tubes in which. al1 stages are balanced for insuring stabilized operation of the amplification system.

Another object of my invention is to provide a circuit arrangement for insuring balanced operation of a resistance coupled electron tube ampliiication system for eiecting maximum ampliiication per stage without interference from parasitic oscillations.

Still another object of my invention is to provide a resistance coupled electron tube amplification system in which opposing potentials are introduced in selected portions of the resistance coupled amplier circuit for preventing oscillation while allowing maximum amplification.

Another object of my invention is to provide an electron tube amplification system having circuits interconnecting the electrodes of the electron tubes including a resistor carrying current of one electron tube element, the potential drop across which is balanced by the sum of a drop of potential across a resistor carrying part or all of the current of the total supply power, and another voltage either produced by the drop in potential across a resistor carrying the current of' any other element of the same tube or any separately introduced voltage of any kind.

A further object of my invention is to provide an electron tube ampliiication system in which balanced operation is obtained by balancing the potential drops in elements connected with the electrodes of the electron tubes to a substantially balanced condition and then introducing an additional voltage for completely balancing the operation of the amplification system.

A still further object of my invention is to provide a pentode amplification system in which balancing of the entire ampliiier may be eliected in the final ampliiication stage.

Other and further objects of my invention reside in the method and circuit arrangement for balancing the operation of electron tube systems,- as set forth more fully in the specification hereinaiter following by reference to the accompanying drawing, in which Figure 1 is a circuit arrangement of a pentode amplifier system employing my invention; Figure 2 illustrates my invention as applied to a three element electron tube amplifier system and Figure 3 shows the application of my invention to a tetrode circuit wherein balancing is obtained in the iinal amplification stage.

Referring to the drawing in detail, Figure 1 illustrates my invention as applied to a balanced amplifier employing pentode electron tubes. Any of the many multiple plate and grid tubes may be used in circuits similar to the circuit shown in Figure 1. In the arrangement shown in Figure l two stages of amplication have been. illustrated for the purpose of explaining my invention but it will be understood that any number of amplication stages may be employed.

The pentodes are indicated by reference characters I. and 2. Pentode l includes heater element la, cathode lb, grid electrodes lc, ld and le and plate electrode lf. Heater elementy la. is energized from alternating current derived from a suitable power pack connected to terminals HH. Similarly, pentode 2 includes heater element 2a, cathode 2b, grid electrodes 2c, 2d and 2e and plate electrode 2f. The input circuit to the ampliiier system is represented at 3; the output from the amplifier system is shown at 4. The power supply for each of the pentodes is secured by means of a series circuit adapted to be connected to the filter system of a power rectiiier when the tubes are operated from an alternating current source, or to the lter adapted for connection to a direct current line circuit, or to a direct current generator or a battery system.

The power supply circuit for each of. the pentodes comprises a'series path indicated generally at 5 containing resistors 6, l and 8. These resistors are selected in value to produce the desired potential drop for supplying the required biasing potential to control grid Ic, the desired potential to grid ld, the potential for grid le and also the required potential for anode If. Grid le connects with cathode lb at point I3, which is in turn connected to a point intermediate resistors 6 and 'l in the series path 5.

In addition to the resistors 6,1 and 8 in the series circuit I provide separate potential determining resistors 9 and I0, disposed in series between the point II intermediate resistors 1 and 8 and the grid Id. Also I provide a resistor I2 connected at potential point I4 in the series path 5 for determining the potential supplied to anode If. The resistances are selected in such proportions that accurate balanced operation of the amplier circuit is obtained. The succeeding pentode 2 has the input circuit thereof connected with the output of pentode I through connections shown at I5. The connection from control grid 2c is made at a point I6 intermediate resistors 9 and I0 in circuit with grid Id. The connection to the cathode 2b is taken at point Il in the output circuit of pentode I adjacent resistor I2 and adjacent the connection of anode If thereto.

The resistance network and the connections to the electrodes in pentode I, as above described, may be considered as a balanced bridge arrangement in which: resistance 8 constitutes one leg; resistance I2, a second leg; the internal resistance between cathode Ib and anode I f of the tube, the third leg; and resistance 1, the fourth leg. This fourth leg is modified to include the internal resistance between the cathode Ib and the grid Id of the tube I and resistance elements S and Iii connected in series, the series circuit being connected in parallel with the resistance 7. The source of potential for the bridge is connected at point I4 between resistances 8 and EZ'and to the cathode Ib. The output is taken from the opposite terminals of the bridge, viz., IS and il. The modication of the fourth leg of the bridge which includes resistance I@ permits the resistance I0 to be included also in the output circuit. The potential drop across resistance Iii, or some equivalent voltage, is a necessary factor in the balancing of the bridge circuit.

The condition of balance of the bridge is the condition of zero Voltage across the output terminals. Consider the voltage of cell 30 or the potential drop across resistance It! as E, the re` sistances I2 and 8 as R1 and R0, respectively, and the currents in R1 and Ro as I1 and Io, respectively. The factors aifecting the balance of the bridge are the currents Io and I1. These currents are each dependent on a common factor, which is the source of potential of the system, and the eiects 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 circuitdevice, as shown in Fig. 2 and the indirect cathode heating system of Figs. 1 and 3 as long as all power is obtained from the same source. There is a simultaneous change in the heating of the cathode andthe 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 3 will be balanced similar to the direct heated system, as illustrated in Fig. 2.

The values of the two resistances R11 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 Io is passing through R0 and the current I1 through R1, then the requirement for no current through the output circuitis:

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

AI (3) -IO-I-IlA-Il 15 The above is the value of R0 for balanced conditions in terms of E, I1, Io and the slope'of the I1 Vs. Io characteristics. R1 is then determined by Equation 1. 20

If E is constant (E is a constant voltage cell 30 in Fig. 2 and in Figs. 1 and 3, it can be considered as a first approximation as constant, because the Equation 5 is the general equation of a straight line. Therefore, if the portion of the characteristics near the operating value of AIo 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 fullled for normal operating conditions. Ihis 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 diiiculty 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 R11, R1, and voltage E; Without voltage E, the circuit wouldV not balance even though it appears the' drop Ro, In 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 willthen cause Roto cancel out of the equation and thereby eliminate the means of adjusting for balance. To have an additional voltage E in the circuit Ru, R1, 0 and the output, is an essential feature of these circuits, and may be provided from a battery, a standard cell or the like, as in Fig. 2, in lieu of the voltage drop across a resistance in the preferred form shown in Figs.. 1 and 3.

The actual values, of the resistances Ro 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 is .placed across the output terminals with R not far from the expected correct value and R1 is adjusted until the meter reads zero. The supply current is then increased by increasing the voltage into the supply circuit and the deilection of the meter noted. Then, with a new Value of R11 (a Value which diers 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 defiectionwill be in the opposite direction to the iirst. Values-of R0 between these two are then taken and the above procedure repeated until a Value of Ro 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 Ro 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 especially in the simplied'circuit of F'ig. 2, and also to sh'ow how closely the other circuits are related to it. Actually, the assumption of E being constant is an unnecessary assumption and can be replaced by the assumption that the resistances I0, 8, and I2 remain constant which can always be accurately fuliilled.

The following discussion will show that the circuits in Figs. l, 2, and 3 will balance, not approximately, but completely for normal operating voltages on the tube and that the conditions are not altered from those just given, I!) being any suitable constant resistance, and R0 and R1V determined experimentally in exactly the same way as before. Call resistance Ill, R2; and the current through it, I2. Then, for balance at some current Io with the corresponding currents I1 and I2, the following equation must hold:

NOW to remain balanced when In changes to Io-l-AID causing I2 to change to Iz-j-Ai'z and I1 to I1+AI1, the following equation must hold also:

11H1- R212 Io Cancelling and rearranging, gives R1(I1.AI0 IgAIl) R2(I2AI0 I0'AI2) 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 In and I1, it was shown that the only requirement was that the I1-Io characteristics must be linear in the operating region, so here in order that the numerator remains constant with change of In and I2, the Iz--Io characteristics must also be linear in the operating region.V These two conditions are practically always met in amplifying tubes.

As it is the ratio RI RI R1: 11o-li; 22 (8) and then it is eliminated in place of Ro, the second condition of balance,

AIO RLIVLKI A12 IVIIAI,

is obtained.

From this, it is seen that Ro 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 Ru 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 Ro is arbitrary, a special case of this circuit is when Rezo.

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. l, 2 and 3 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 lament. It is preferable to have the grid to which resistances 9 and Il] 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 AIz and AI1 in I2 and I1 respectively. For these changes, there will be no change in Io; i. e., AIO-:0. For balancing at currents Io, I1 and I2, we have R0I0+R2Ig=I1R1 OI' R0=I`1R1R2I2 Then for balance after a change AIz and A'Ir when I0 does not change,

Equations 8, 9, and 10 are the three conditions that must be fulfilled for this balance` Let the slopes A I0 LIL A11-10' Mini N12-n' 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 fullled. The circuit of Fig. 3 fullflls all the requirements of Fig. 1 in that one. power supply source is used and further allows balancing the entire cascade at the output ofthe nal tube.

A series power supply circuit is provided. for pentode 2 similar tothe power supply. circuit in the rst pentode stage. I have indicated the series power supply circuit for pentode 2 by reference character 5'. In the series circuit 5' there are resistor elements corresponding to those located in the power supply circuit 'of pentode I, that is, the resistors 6', 1' and 8'. Grid 2e connects to cathode 2b at point I3', which in turn connects to a potential point intermediate resistors 6' and 1' in series path/5. The grid electrode 2d is maintained at a pre-determined. potential through a connection which includes resistors 9 and I Il', which connection is taken from point I I intermediate resistors 1 and 8' in the power supply circuit 5'. Anode 2 f is maintained at the required potential by a connection through resistor I2' to I4' in the series path 5'. The output circuit 4 connects between terminal I6 intermediate resistors 9'and IIJ and terminal I1' in the output circuit of pentode 2. The resistors are selected for such value as to obtain accurate balanced operation of the pentode stages.

Referring to Figure 2 of the drawing I have shown the balanced circuit of my invention applied to a three electrode electron tube amplier. In this arrangement the three electrode electron tubes are indicated at I8 and I9. Tube I8. includes cathode. lila, control grid Ib and anode |80. Tube I9 includes cathode lila, control grid I9b and anode |90. The input circuit is shown at 20. The output circuit connects at ZI. A direct current source, such as the output terminals of a filter connected With a direct current generator, the output of the power pack of a rectier unit or a battery source is connected with terminals 22. The series circuit 23 is arranged similarly to the series circuit 5 in Figure l, which circuit includes resistors 24, 25 and 25 connected in series through the cathode I8a.

The potential supplied to anode i8c is determined by resistor 21 connected at the point 28 in the series path 23 and adjacent the resistor 25'. The desired operating potential on grid Ib obtained by connection of the grid circuit to the point 29 in the series path 23. The succeeding three electrode tube I9 has its input circuitconnected with the output circuit of three electrode tube I8 in a very special manner designed to produce the same results which are eiTective when using pentodes as illustrated in the circuit of Figure 1. That is to say, an additional balancing voltage is introduced into the coupling circuit between tube !9 and tube I8. This is accomplished in the circuit of Figure 2 by employing the cell 30, having its positive terminal connected to the point SI intermediate resistors 25 and 25 in series path 23 and having its negative terminal connected to control grid I9b. This additionalcell replaces the drop which is obtained in the resistors 9 and I9 of the circuit of Figure 1 and which connect with grid Id.

In applying the equations above to the circuits in Fig. 2, the voltage of cell 30 is represented by E, and resistances 21 and 26 by R1 and R0, respectively.

The circuit of my invention, either in the form shown in Figure 1 or in Figure 2', provides means for balancing the power current change against the plate current change. Balancing the potential drops due to the power current change and the plate current change is not s'uicient. An additional and separate voltage must VAbe introducedintothe circuit. In Figure 21this additional voltage isV introducedv by means of a cell 31|;` in Figure 1 this additional voltageis introduced by the potential drop across resistors. 9 and. III. in circuit withl grid Id. Balanced operation of the electron tube circuits is thereby. assured. The input circuit of tube I9, connected as aforesaid from control grid I9b to the additional potential source 30, has its input circuit completed by the connection from point 29 tothe terminal 32 intermediate the end of resistor 21 and anode IBc.

The power supply for the` succeeding electron tube I9 is provided in a manner similar tothe power supply for tube I 8inseries path 23", connected with terminals 22', theseries pathY containing resistors 24', 25' and 26' connected` in series through cathode I9a. Resistor 24 provides a drop which is combined withl the drops produced by resistors 21' and 26' andY combined with the potential of source 30 to stabilize the potential on control grid |91). Anode |90 is provided with required potential through the drop across resistor 21'. The output circuit to the next succeeding electron tube, which connects the terminals 2|, is connected through they additional source of potential 30' for introducing the balancing voltage as heretofore explained.

My invention is applicable to circuits employing electron tubes of various. constructions, such as screen grid tubes, pentodes and multi-electrode tubes employing a plurality of grid and plate electrodes, and according to the type of tube employed I may provide a` cell to` introduce the desired potential drop for balancing or I may derive the balancing potential from the drop across resistors in circuit with a grid electrode as heretofore described in connection with- Figure 1. Where structural conditions permit I may combine the power supply circuits ofv ay multiplicity of electron tubes, as shown in Figure 3.

In this arrangement tubes 33 and 34 are shown with the output circuit of one tube coupled with the input circuit ofthe succeeding tube and having an input circuit and an output circuit 36. The power supply of direct current characteristic is connected at, 31 and traversesY the series path 38, which path contains resistors 39, 40,- 4I, 42, 43 and 44. Tube 33 includes heater element 33a, cathode 33b, grid 33e, grid 33d and plate 33e. Similarly, electron tube 3 4 contains heater element 34a, cathode 34h, grid 34e, grid 34d and plate 34e.

The grid bias potential for tube 33 is determinedr by theV drop across. resistor 39v which is disposed in the grid cathode circuit. The potenv tial on grid 33d is determined by the drop across resistor 4D. The anode potential for-anodev 33e is determined by the drop across resistors 40 and 4I. The output circuit olftube 33 is coupled with the input circuit of tube 34 through resistor 45. The bias on control grid 34o is determined by the drop across resistor 42. The potential on grid 34d is derived` from the drop across resistor 43. The balancing potential on grid 34d is determined by the drop4 across resistors 46 and 41 connected in series with tap 48 intermediate resistors 43 and 44. The potential on anode 34e is determined by resistor 49 connected with point 50 in the series power supply circuit 38. The output circuit of the amplier at 35 connects at point 5I intermediate resistors 46 and 41 in circuit with grid 34d and the point 52 in the Output circuit of tube 34. In applying the equation above to the balancing circuit in Fig. 3, the voltage drop across resistance 41 is represented byv E,

and resistances 49 and 44, by R1 and Ro, respectively.

All of the stages of the amplifier illustrated in Fig. 3 are balanced in the last stage. This is possible because a common power supply circuit is provided for all of the stages. It will be noted that in the circuits of Figs. 1 and 2 separate power supply paths are provided for each stage.

My invention is directed to any method of changing the characteristics of a tube, as for example, by placing a resistance across the tube, so that it can be balanced. My invention is not confined to electron tubes, but is applicable to any form of cathode ray tubes.

My invention contemplates any amplification system of one or more electron tubes having three or more elements in which all elements of each tube are supplied by one source of electric power and in which the drop in potential across a resistor carrying the current of one element can be balanced by the sum of a drop of potential across a resistor carrying part or all of the total supply power current and another voltage either produced by the drop in potential across a resistor carrying the current of any other element of the same tube or any separately introduced voltage of any kind.

I have described my invention in certain preferred embodiments but I desire that it be understood that modications may be made without departing from the spirit of my invention. For example, I have mentioned the arrangement of resistors in the power supply paths. I may employ impedances in the power supply paths in lieu of resistors. Other changes may be made in the circuits of my invention and I intend no limitations upon my invention other than imposed by the scope of the appended claims.

What I claim 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 and an anode, a separate series circuit containing a source of potential for energizing said cathode and anode in each of said electron tubes, a connection including a resistor from one terminal of said source of potential to said anode, a connection from the series circuit connected with the succeeding electron tube to the anode of the preceding electron tube, a connection from the control grid of the succeeding electron tube to a point in the series circuit connected with the preceding electron tube thence through a resistor in said series circuit to the terminal of said source of potential connected with said anode, and a source of compensating potential included in said last mentioned con nection for balancing the potential across the connections to the succeeding electron tube circuits.

2. An electron tube amplification system including a plurality of electron tube devices each having anode, cathode and 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 resistance 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, output terminals, one of said output terminals connected to said anode, and a separate source of potential, the other of said output terminals connected through said separate source of potential to a point in said series circuit thence through another of said plurality of resistance elements to the terminal of said source of power connected to said anode, the potentials of said output terminals being balanced by the algebraic sum of the voltage across said separate source of potential and the potential drops across the resistance element connected between said separate source of potential and said source of power, and across the resistance element connected between said anode 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 other of the output terminals being connected with the grid electrode in said succeeding electron tube device.

WALTER SOLLER.

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