US2354718A

US2354718A - Electric system

Info

Publication number: US2354718A
Application number: US418336A
Authority: US
Inventors: Tuttle William Norris
Original assignee: General Radio Co
Current assignee: General Radio Co
Priority date: 1941-11-08
Filing date: 1941-11-08
Publication date: 1944-08-01
Anticipated expiration: 1961-08-01

Description

Aug. 1, 1944.

w. N. TUTTLE 2,354,718

ELECTRONIC SYSTEM Filed Nov. 8, 1941 2 Sheets-Sheet l ELECTRONIC SYSTEM Filed Nov. 8, 1941 2 Sheets-Sheet 2 -from the rectified voltage Patented Aug. -1,' 1944 ELECTRIC SYSTEM William Norris Tuttle, Concord, Mesa, assignor. to General Radio. Company, Cambridge, Mass,

a corporation of Massachusetts Application November 2;, 1941, Serial No. 418,336

47 Claims.

The present invention relates to electric systems. From one aspect, the invention relates more particularly to amplifiers. From another aspect, the invention relates more particularly to vacuum-tube voltmeters.

One type of vacuum-tube meter for the measurement of alternating voltages comprises a rectifier for developing a direct-current voltage from rent amplifier for developing sumcient power to operate an indicating meter. Degenerative coupling may be employed in the amplifier to stabilize the gain and insure permanence of calibration. The use of two-stage degenerative direct-currenmamplifiers in meters of this character, however, has been accompanied by unsatisfactory operation.

It is not easy, for example, to produce a de-' sign such that the opposing currents shall exactly balance, leaving no residual current through the degenerative resistor without, at the same time,

substantially reducing the over-all gain of the system. The difficulties have usually been overcome by providing the amplifier with a further stage or Stages. V

An object of the present invention, however, is to provide a two-stage degenerative direct-current amplifier or voltmeter, in which the residual current through the degenerative resistor balanced out while maintaining maximum gain of the separate stages.

Since the current through the degenerative resistance is zero when the meter reads zero, this resistance can be varied over wide limits without affecting the zero setting. A further object of the present invention, therefore, is to provide a direct-current amplifier the sensitivity of which can be varied over wide limits without simultaneous compensation of the zero adjustment.

Another object of the invention is to provide a novel amplifier.

proposed, although the operating potential can be provided for the screen electrode by means of voltage-dividing resistor circuits or dropping rethe applied alternating voltage, and a direct-cur- Still another object is to provide a simplified degenerative direct-current amplifier.

A further object is to provide a novel voltmeter of which the amplifier may constitute an element.

In prior-art degenerativecircuits, it has been dimcult to provide a constant voltage bias for the screen grid without the aid of separate battery supplies.

In the use of a screen-grid tube in direct-current amplification, high-voltage gain can be obtained in a single stage provided that the screen electrode can be maintained at a'constant potential with respect to the cathode, independent of the applied signal voltage. In circuits previously sistors, the currents through these resistors tend to vary substantially with the applied signal so that a constant screen potential is not obtained and reduction in voltage gain results. y In amplifiers for altematingecurrent voltages, these effects can be corrected by by-pass condensers which, of course, can not be applied to the design of direct-current amplifiers.

ti n, the plate battery of one of the two tubes is utilized as the screen battery forthe other without any resistor circuits being required, thus permitting the maximum possible voltage 'gain which may be'obtained from screen-grid amplifiers.

Other and further objects will be explained hereinafter and will be particularly pointed out in the appended claims.

The invention will now be more fully described -in connection with the accompanying drawings, in which Fig. 1 is a simplified circuit diagram illustrative of the amplifier feature of the invention; Figs. 2 and 3 are similardiagrams, with further complications; and Fig. i is a similar diagram, illustrating -a voltmeter embodying the present invention. c

The illustrated two-stage amplifier comprises two

vacuum tubes

2 and 4. The tube 2 is provided with a cathode 6, shown as a filament, en

ergized, by a cathode battery or other voltage source I, an anode 8, and a control electrode 3.. The tube 4 is provided with a cathode l2, shown as a filament, energized by a cathode battery or other voltage source I 3, an anode l4 and a control electrode IS.

The vacuum tube 2, with its input and output circuits, constitutes the first stage of the twostage amplifier. The external voltage to be amplified may be impressed across input terminals i8 and 28 of the input circuit of the tube 2. Referring first to Fig. 1, this input circuit extends from one input terminal l8, by way of a conductor 20, and through an impedance 22, shown as a resistor, to a junction-point terminal 23; thence, by way of a conductor 26, to the cathode 8; thence, through the space in the vacuum tube 2, to the control electrode l0; and from the control electrode it], by way of, a conductor 26, to the other input terminal 28. For reasons hereinafter stated, the resistor 22 acts as a degenerative resistor. The output circuit of the firstvacuum tube 2 of the two-stage amplifier extends from the cathode B,

through the space in the tube 2, to the anode. 8;

- According to .a ieature of the present inventhence, by way of a conductor 38, through an output impedance 32, shown as a resistor, to the positive pole of a plate or anode or B-battery voltage source 34; from the negative pole of this battery 34, to a Junction-point terminal 35; and, by way of a conductor 38, through an indicating instrument 33 and the impedance 22 and, by way of the conductor 24, back to the cathode 3.

The vacuum tube 4, with its input and output circuits, constitutes the second stage of the twostage amplifier. The input circuit of the tube 4 is connected across the output impedance 32 and the battery 34 in the output circuit of the tube 2. The output impedance 32 of the first tube. 2 thus constitutes the. input impedance of the second tube 4 operating as the customary platecoupling resistor. This input circuit extends from the terminal 35, by way of a conductor 40, to the cathode -l 2; through the space in the vacuum tube 4, to the control electrode l5; and from the control electrode tery 44, by way of a conductor 42, to the cone ductor 33, the anode 3. The input circuit of the tub 4 continues from the conductor 42, through the impedance 32 and the battery 34, back to'the terminal 35. The output circuit ofthe second vacuum tube 4 may be traced from the cathode i2, by way of ,the

conductors

40 and 35, the indicating instrument 33 and the impedance 22, to thetermlnal 23, which is connected to the negative pole of a plate or anode or B-batt'ery voltage source 48; from the positive pole of this battery 48, by way the anode I4; and from the anode l4, through the space in the tube 4, back to the cathode I2.

The B-battery voltage source 341s connected between the anode 8 of the tube 2 and the cathode l2 of the tube 4, with its negative pole connected to the cathode l2 and its positive pole to the anode 3. The connections may be traced from theanode 8, by way of the conductor 30, through the impedance 32 and the battery34, to the terminal 35 and, by way of the conductor 43, to the cathode l2. The B-battery voltage source 46 is similarly connected between the anode of the tube 4 and the cathode i of the tube 2, with its negative pole connected to the cathode 6 and its positive pole to the anode I4. The connections may be traced from the anode l4, byway of the conductor 43, through the battery 43, to the terminal 23 and, by way of the conductor 24, to the cathode 3.

The system, as so far described, resembles what is popularly known as'a direct-current amplifier; for, though the voltage across the impedance 22 is somewhat less than that applied to the

terminals

18 and 23, the power developed across 2,354,718 which includes the indicating instrument 33, is

connected at one end to the junction point 23,

between the negative terminal of the battery 46' and the conductor 24 that leads to the cathode 6.

-It is connected at the other end to the Junction point 35, between the negative terminal of the battery 34 and the conductor 40 that leads to the cathode. The impedance 22 and the indicating instrument in this common portion of the output circuits, between the cathodes G and I2, that the

batteries

34 and 46 send current therethrough in oppoit, through. a biasing batthat. connects the impedance 32 to through of a conductor 43, to

' site directions.

in plate current The operating points of the

tubes

2 and 4, or of one of them, may be so chosen that the opposing currents in this common portion of the output circuits shall balance with extreme accuracy at times when it is preferred that the indicating instrument 33 should read zero.

Since the impedance 22, which is connected in the common portion of the output circuits of the

tubes

2 and 4, is connected also in the input circuit of thefirst tube 2, the amplified current from the tube 4 through this impedance 22, when an external voltage; is impressed across the terminals l8 and 28, is in -a direction opposite to that of the external voltage in the input circuit of the first vacuum tube 2 of the amplis her. It is for this reason that the resistor 22 may be referred to as a degenerative resistor. Although the current through the resistor 22 is derived largely from the tube 4 because of the amplificationof the preceding stage, the change is the result of the action of both tubes, because both tubes operate in such a sense that they both aid in the production of the degenerative voltage across the resistor 22. The currents through the indicating instrument 33 from

the'two tubes

2 and 4 are thus also in the same direction. .To state it otherwise, the incremental changes in the output circuits from both

tubes

2 and 4 resulting from the external voltage applied to the terminals l3 and 28 thus add up to yield a current in the same direction through the impedance 22 and the indicating instrument 33, though producing a voltage opposite in direction to the voltage applied at the terminals l8 and 23 to the input circuit of the the impedance 22 may be very much greater than that taken from the voltage source across the terminals l3 and 23. The voltage across the impedance 22 may build up to a value substantially equal to the applied input voltage, if sufllcient tube 2.

' Three features. among others, may be emphasized: first, the degenerative properties of the impedance 22; secondly, the function of producing balance in the currents through the common portion of the output circuits; and thirdly. the property whereby the incremental output currents from the

tubes

2 and 4 cumulate to produce a current through this impedance 22 in the same direction.

The resistance of the impedance 22 may be considerably less than the resistive impedance of the indicating instrument 33, which latter may be quite high, without adversely affecting the operation of the system. This has a bearing upon the sensitivity of the system. By making the impedance 22 variable, it may be caused to provide a sensitivity control, .as more fully described hereinafter.

Another advantage is that, since the terminal l3 may be at the low voltage of the ground, and as the indicating instrument 33 is subjected to this low voltage, it is possible to use instruments 33, like recording meters, that could not be used in circuits where they would be subjected to high voltages.

The gain of the amplifier without degenera- 33 are thus so connected tle energy gain is available to'provide the overall degeneration that is desired to be used for stabilizing the over-all gain.

According to the present invention, on the other hand, there is no degenerative operation to reduce the gain of the two individual stages of this two-stage amplifier. No degeneration takes place to,reduce the gain 01' the second tube, for

example, because the voltage across the impedance 32 is the only variable voltage in its input circuit: I The degeneration, therefore, can be applied with maximum eifectiveness. It follows that each of the

tubes

2 and 4 contributes its maximum gain to the over-all amplification gain of the system. This, moreover, is accomplished with a minimum number of independent voltage sources, namely, two plate batteries 34 and 43 and one bias battery 44.

The invention thus provides a simple portable direct-current amplifier employing two tubes 2 and- 4, with only four batteries from which current is drawn, two of which are the anodeor B batteries. 34 and 46, and the other two of which are the cathode batteries 1 and I3. No current, or course, is drawn from the bias battery 44. With battery-

type tubes

2 and 4, single-cell filament-bathode batteries 1, and I3 may be employed. 1

If the resistance of the degenerative resistor "22, moreover, is large compared with the reciprocal of the trans-conductance of the two-stage amplifier, that is, the ratio of the input voltage to the first tube2 to'the output current through the common impedance 22, then the gain is substantially independent of changes in gain in the amplifier. I 1

As is generally true with degenerative directcurrent amplifiers of this character, variations inv the zero reading of the meter 33 due to changes in the plate-battery voltages and in the filament battery ofthe second tube 4 are largely neutralized.

The circuit of Fig. l is reproduced in Fig. 2, but with the tube 2 shown as a pentode, instead of a triode; in addition to the cathode 6, the control electrode Hi and the anode 3, it comprises a screen electrode and a further electrode 52.

In Fig. 2, also, the bias battery M is omitted and the required operating potential for the grid 66 of tube 5 obtained by returning the cathode I2 The further electrode 52 is connected in usual fashion, by a conductor 53, to the cathode 6, and

the further electrode 53, bya conductor 60, to

the cathode l2. The screen electrode 54 of the tube 4 is subjected to the voltage of the battery 34 of the tube 2 by means of a conductor 62 that joins the screen electrode 54 to a junction-point terminal 64 between the impedance 32 and the positive pole of the battery 34. The screen electrode 50 of th tube 2 is similarly subjected to the voltage of the battery 46 of the tube 4 by a conductor 66. The conductor 66, however, 'connects the screen electrode 50 to'a. variable tap 01' a potentiometer resistor 68 that is connected in shunt to the battery 43. The conductor 52, of

, course, may similarly connect variably the screen electrode 54 to. a similar variable resistor (not shown) connected across the battery 34. This may be in addition to, or in substitution for, the variable connection of the screen electrode 50 to the resistor 68 by the conductor 66. g

A voltage bias for the

screen electrodes

50 and 54 is thus provided-without the aid of additional batteries, the plate battery 34 of the tube 4 serving as the screen battery of the tube 2, and the plate battery 46 of the tube 2 serving as the screen battery for'the tube 4.

By adjusting the tap of the screen electrode 50; v as by means of the conductor 86 upon the resistor 68, a zero control adjustment may be provided, independent of the setting of the sensitivity-control impedance '22, for adjusting the voltage from the potentiometer 65 applied to'the screen electrode 50.

In .many prior art circuits, the advantages of 'the screen-grid operation claimed therefor are more apparent than real. This is because variations in the plate current of either of the tubes connected. When the indicating instrument 33 is included in the circuit, however, a sensitive direct-current vacuum-tube voltmeter is provided to an intermediate point 69 on the battery 34,

This arrangement therefore employsonly two teries.

In Figs. 3 and 4, the tube 6 is also shown as a pentcde, the screen electrode being shown at 54 and the further electrode at 56. In these Figs. 3 and 4, furthermore, an additional impedance 63, shown as a resistor, is illustrated as connected in the conductor 24, between the terminal 23 and 'the cathode 8, in the input circuit of the tube 2. This may serve to provide additional bias for the cathode 6. This resistor 59 is omitted from Figs. 1 and 2, because the tube 2 can be operated at the potential of the negative and of the cathode 8;

by the present invention, as the input voltage can be measured interms of .the output current in the impedance 22 with its aid.

In order to reduce the grid or input current in'the tube 2 to a very low value, it is sometimes desired to operate at relatively very low plate and screen voltages. Under these operating conditions, the current through the tube 2 may not be suflicient to balance in the indicating instrument 33 the current from the other tube 4, so as to reduce the reading of the indicating instrument 33 to zero. This difliculty may be overcome, and the first tube 2 may be operated at any de-- sired part of its characteristic, by taking additional current through an auxiliary resistor 10, connected between the positive terminal 64 of the battery 38 and the cathode 6 of the tube 2 as illustrated in Fig. 4. The current through this resistor 10 thus supplements the current through the first tube 2 inbalancing the indicating instrument 33 to zero.-

The two-stage directcurrent amplifier above described may be combined with'a desirable type of rectifier, shown in Fig. 4 as a diode rectifier I2, to produce an extremely sensit ve alternatin energizing its cathode filament l5. Asshown, the

= put terminals ll 'of the, rectifier 12, across a Various taps of the resistors output of the rectifier 12 is and 22, and its input to any desired source of alternatingvoltage by means of input terminals 14 and It. The diode 12 constitutes, with a condenser 11, a half wave diode rectlflercircuit forrectifying alternating voltage impressed at the terminals I4 and IS. The alternating-current components of the rectified voltage are removed by the filtering network consisting of the resistor 80 and the condenser 84.

It is sometimes desirable toemploy a resistance input multiplier between the diode rectifier 12 and the direct-current vacuum-tube voltmeter. A variable shunt impedance 18, shown as a resistor, perating in conjunction with the filtering series resistor 80, connected in the output circuit resistor 88, constitutes apotentiometer for subdividing the direct-current voltage developed by the'diode rectifier 12. Due to the initial space current of the diode l2, variations in the zero voltage will sometimes be produced when varied. These may viding for each setting be compensated for by proof the resistor I8 an adjustable potentiometer across the filament-battery" of the diode 12, so that the zero may be pre-set for each voltage range provided by the potentiometer I8, 80

connected to the inthe shunt resistance 18 is corresponding connected-together contact mem- I required, multi- This adjustable potentiometer may comprise 86 disposed, in parallel series with a resistor 9|. 88 may be connected, by conductors 82, to three contact members 90. Four additional contact members 90 are conaplurality of resistors with the battery I3, in

nected together to the negative end of the fllamentary cathode 13 of the-diode 12. The contact members 90 may be controlled by a deck 84 of a three-deck master switch 92, shown more particularly in Fig. 4. The deck 94 is connectedby a conductor 93 to the conductor 20. Corresponding contact members 85 are connected to the resistor 18 by a second deck 98. .The third deck 96 similarly cooperates with contact members 9|.

The "three-deck switch 02 may assume seven positions in clockwise sequence, corresponding to 0.3, 1, 3, 10, 30, 100 and 300 volts full-scale, as indicated on the dial I00, in Fig. 4. All seven ranges can be obtained by setting thethree-deck switch 92. In each position, it effects an adjustvment of each of the resistors 22 and" and a corresponding adjustment to restore the zero of the multiplier, as will now be explained;

For the first tour voltage ranges correspond ing. as shown, to 0.3, 1, 3 and 10 voltage fullscale. the sensitivity may be varied by means of the degenerative resistor 22. The deck 94, as before stated, controls the zero correction; but since, when changing from one to another of these four ranges, no correction gf the zero is required, the corresponding four -contact members 05 are shown connected together in the manner before described. For the three higher ranges of the instrument, corresponding to 30, 100 and 300 volts full-scale, however, the potentiometer 10. I is employed to increase the range. It is value for the three

highest ranges

30, 100 and 300,

the three corresponding contact members 9! of which are, therefore, shown The third deck 98, for controlling the value of the resistor 18 of the potentiometer I8, 80, leaves this resistor 18 at maximum value for the first four ranges 0.3, 1, 3 and 10, as indicated by the the highest ranges, 30,

bers 95, but operates to give plying action for the three 100 and 300.

A small portable instrument built in accordance with the above design and employing an indicating-meter instrument 33 of 100 microamperes full-scale sensitivity has been made to' yield a fullescale reading on 300 millivolts al- .ternating current covering a frequency range of from 20 cycles to a hundred megacycles.

The following values of the various elements have been found to yield a very satisfactory'instrument:

Battery 44 Vo1ts 7.5 Resistor 32 megohms 10 Resistor 68 1 do- 2 Resistor 49 ohms 15,000 Resistor i0 megohm 1 I i-position resistor 18 -do 0.35, 1 and Resistor 80 do Resistor 88 2do 50 Resistor 8| ohms 800 Resistors 80 rnegohm each; 0.1 Condenser 84 microiarad .02 Condenser I'I do .06

- mately this voltage.

resistance of the resistor 22 should be "about The resistor 22 will have a value depending on the required direct-current sensitivity of the portion of the instrument following the rectifier On the range giving l0 volts alternating current full scale, for example, the rectified voltage-will be approximately 14 volts for full scale. The meterv current of micro-amperes flowing through the resistor Hence, for this range, the

140,000 ohms. The approximate value of the resistor 22' may be similarly determined for the other ranges. In any particular case, it may be adjusted to the exact desired value, during the final calibration of the instrument.

'The

tubes

2 and 4 may be of the type and the tube 12 of the 95'1type. If the tubes 2 and l are pentodes, asillustrated in Fig. 3, the B-

batteries

34 and 46 may, for example, be of 30 volts each. I

Modifications will occur to persons skilled in the art and all such modifications are considered to fallwithin the spirit and scope of the invention, as defined in the appended claims.

What .is claimed is:

1. An electric system having,-in combination. two vacuum tubes each .provided with a cathode, an anode, a control electrode and a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with asource of voltage, means for subjecting the screen electrode of each tube to the voltage of the voltage source of the output circuit of the other tube, a resistor, andmeans for connecting the anode of one tube to the screen electrode of the other tube through the resistor.

2. An electric system having, in combination,

two vacuum tubes each provided with a cathode, w

an anode, a control electrode, a screen electrode,

connected together.

:2 must develop approxltube.

and a further electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are'respectively 5 connected, means connecting the further electrode oi. each tube to the cathode of the same tube, the voutput circuits each being provided with a source of voltage, means for subjecting the screen electrode of each tube to the voltage of the'voltage source of the output circuit of the other tube, a resistor, and means for connecting the anode of one tube to the screen electrode of the other tube through the resistor.

varying the magnitude of the impedance of the common portion to vary the sensitivity. 6. An electric system having, in combination,

two vacuum tubes each provided with a cathode, an anode, a control electrode and a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes or the respective tubes are respectively connected, the

output circuits each being provided with a source oi voltage, means for subjecting the screen electrode of each tube to the voltage of the voltage a. An. electric system having, in combination, )5

two vacuum tubes each provided with a cathode, an anode and a control electrode, one 01- the tubes'having a screen electrode, input circuits in 1 which the cathodes and the control electrodes of the respective tubes are respectively connected,

output circuits in which the cathodes and theanodes of the respective tubes are respectively connected, the output circuits each being provided with asource of voltage, means for subjecting the screen electrode of the said one tube to the voltage of the voltage source of the output circuit of .the other tube, and means connecting the sources of voltage each between .the anode of onetube and the cathode of the other tube source of the. output circuit of the other tube, and means for connecting the sources or voltage each between theianode of one tube and the cathode of the other tube with corresponding poles ofthe voltage sources connected to the 'respective cathodes.

7. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode, a control electrode and a screen electrode, input circuits in which the cathodes and the control electrodes oi the respective tubes are respectively connected, output'circuits in which the cathodes and theanodes Io! the rewith corresponding poles of the voltage sources connected to the respective said cathodes of the said other tubes.

4. An electric system having, in combination, two vacuum tubes each provided with a cathode,

an anode anda control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the i anodes of the respective tubes are respectively spective tubes are respectively connected, the

output circuits each being provided with a source of voltage, means for subjecting the screen elec trode of each tube to the voltage of the voltage source of the output circuit of the other tube, and means for connecting. the sources of voltage each between the anode of one tube and the cathode of the other tube with corresponding poles or the voltage sources connected to the respective cathodes, the, outputcircuits having a common portion connected to the junction connected, the output circuits each being provided with a source of voltage, the output circuit of one of the tubes being coupled to the input circuit of the other tube, and means connecting the sources of-voltage each between the anode of one tube and the cathode of the other tube with corresponding poles of the voltage sources connected substantially directly to the respective said cathodes of the said other tubes, the output circuits having a common portion so connected between the cathodes as to provide a 5 voltage drop suitable to produce degenerative coupling in the input circuit of the said other .5. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodesoi the respective tubes are respece tively connected, the output circuits each being" provided with a source of voltage, the output circuit of one of the tubes being coupled to the input circuit of the other tube, means connectin the sources of voltage each between the anode of one tube and the cathode oi the other tube with corresponding'poles oi the voltage sources connected to the respective said cathodes oi'the said ,other, tubes, the output circuits having a common impedance portion so connected to the Junction .points between the voltage sources and the cathodes to which the voltage sources are respectively. connected as to provide a voltage drop suitable to produce degenerative coupling in the input circuit of the said other tube, and means for 1s points between the voltage sources and the cathodes to which the tively-connected. i

8. An electric system-having, in combination, two vacuum tubes each provided with a cathode, an anode, a control electrode and a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubesare respectively connected, output circuits in which the cathodes and 'the anodes of the respective voltage sources are respectubes are respectively connected, the output circuits each being provided with a source 0! voltage, means for subjecting the screen eleetrode or each tube to the voltage ofthe voltage source 1 of the output circuit of the other tube, and means for connecting the sources of voltage each between the anode of one tube and the cathode of the other tube with corresponding poles of the voltage sources connected to the respective cathodes, the output circuits having a common portionconnected to the Junction points between the voltage sources and the cathodes to which the voltage sources are respectively: connected, and the common portion of the output circuits being provided with a degenerative resistor.

9. An electric system having, in combination,-

.an indicating instrument the control electrodes of the 'tubes are respectively portion or the edance,

i put circuits in odes, the output circuits having a common portion connected to the junction points between the voltage sources and the cathodes to which the voltage sources are respectively connected,

and a resistor connected in the common portion of the output circuits, and means ior effecting balance in the indicating instrument at a predetermined point of a characteristic oi. one of the tubes.-

10. An amplifier having, in combination,

anode, a control electrode and a screen electrode, input circuits in; which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes oi the respective tubes are respectively connected, the output circuits each being provided with an anode battery. and means for subjecting the screen electrode of each tube to the voltage of the anode battery of the other tube.

.11. An amplifier having, in combination, two vacuum tubes each provided with a cathode, an anode, a control electrode and a screen electrode, input circuits in which the cathodes and respective tubes are respectively connected, output circuits in which the cathodes and the. anodes oi the respective connected, the output circuits each being provided with a source 01 volt- '-age, means for subjecting the screen electrode of each tube to thefvoltage of the voltage source of the output circuit'of the other tube, the output circuits having a common portion connected befor applying a volttween the cathodes, means age to the input circuit of one of the tubes, the output circuit of the said one tube having a degenerative impedance connected in the common output circuits and a second imand means connecting the second imthe input circuit 01 the said one tube.

.pedance in 12.1A voltmeter having. in combination, two ,vacuum tubes each provided with a cathode, an

anode and a control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, the control electrode oi-one oi the tubes bein connected to the anode of the other tube, out-'- which the cathodes and the anodesoi the respective tubes are respectively .connected, the output circuits each being pro- .vided with a source of voltage, means connecting the sources of voltage each between the anode oi one tube and thecathode of-the other tube with corresponding poles of the voltage sources connected to the respective cathodes, the output circuits having a common portion connected between the cathodes, an impedance and an inditwo vacuum tubes each provided with a cathode, an

anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means connecting the sources of voltage each between the anode of one tube and the cathode of the other tube with corresponding poles or the voltage sources connected to the respective cathodes, the output circuits having a common portion connected between the cathodes, and an impedance and an indicating instrument connected in the common portion of the output circuits, the impedance having a resistance substantially less than that of the indicating instrument.

14. An alternating-current voltmeter having, in combination, two vacuum tubes each provided with a cathode, an anode, a control electrode and a. screen electrode, input circuits in which the cathodes and the controlelectrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes circuits having a common portion connected to the junction points between the voltage sources and the cathodes to which the voltage sources are respectively connected, animpedance and an indicating instrument connected in the common portion ofthe output circuits, one of the input circuits including the connected to the said one input circuit.

15. A two-stage amplifier having, in combina- 1 .tion, two vacuum tubes,

each provided with a cathode, an anode, a control electrode and a screen electrode, input circuits .in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes oi the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means for subjecting the screen electrode of each tube to the voltage of the voltage source of the output circuit of the other tube, means for applying a voltage to the input circuit of one of the tubes, the output circuit oi the said one tube having a degenerative impedance, the respective tubes with their input and output circuits constituting the two eating instrument connected in the common portion of the output circuits, two terminals by means of which a voltage may be applied to the input circuit of one or the tubes, and means for connecting one of theterminals between the impedanoe and the indicating instrument.

13. A voltmeter having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, which the cathodes and the control electrodes of the respective tubes are respectively connected, the control electrode of one of the-tubes being connected to theanode oi the other tube, output circuits in which the cathodes and the stages of the amplifier, and means for maintaining the potential of the screen electrode of one of thetubes substantially constant, independent of the output current of the amplifier, to prevent degeneration in the individual two stages of the amplifier.

16. A voltmeter having, in combination, a first vacuum tube and a second vacuum tube each provided with a cathode, an anode and a'control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means connecting the sources 01 voltage each between the anode oi one tube and the cathode of the other tube with corresponding impedance, and a rectifier the control electrode of one or the tubes being connected to the anode of the other tubes, output circuits in which the cathodes and the anodes of the respective tubes are respectively provided with a cathode, an anode and'a' control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means connecting the sources of voltage'each between the anode of one tube and the cathode of the other tube with corresponding poles of the voltage sources connected to the respective cathodes, the control electrode of the second tube being connected to the anode of the first tube, the output circuits having a common portion connected to the cathodes, and an, impedance and an indicating-instrument connected in the common portion of the output circuits with the impedance disposed adjacent to the cathode of the first tube.

18. An electric system having, in combination, a first vacuum tube and a second vacuum tube each provided with a cathode, an anode, a control electrode a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes connected, the output circuits each being pro vided with a source of voltage. means connecting the sources of. voltage each between the anode of one tube and the cathode of the other tube with corresponding poles .of the voltage sources connected to the respective cathodes, the output circuits having a common portion connected to the junction points between the voltage sources and the cathodes to which the -voltage sources are respectively connected, an

impedance and an indicating instrument connected in the common portion of the output circuits, and means for varying the impedance to vary the sensitivity of the voltmeter.

21. An electric system having, in combination, a first vacuum tube, and and a second vacuum tube each provided with a cathode, an anode, a control electrode, and a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means for connecting the screen electrode of one of the tubes to the voltage source of the output circuit and the anodes oi -the .respective tubes are respectively connected, the ouput circuits each being provided with a, source of voltage, means for connecting the screbn electrode of one of the tubes to the voltage source of the output circuit of the other tube, the outputcircuits having a common portion connected between the cathodes, animpedance and an indicating inof the other tube; the output circuits having a common portion connected between the oathodes,'an impedance and an indicating instrument connected in the common portion oi the output circuits, and means for varyin the output current from one 01' the tubes to balance to zero the current through the indicating instrument.

strument connected in. the common portion of v the output circuits, a voltage-divider resistor, and means for varying the voltage-divider resistor to adjust the zero reading of the instru ment.

' 19. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, (input circuits in which the cathodes and the control electrodes of the respective tubes are respectively con-- nected, the control electrode of one of the tubes being connected to the anode of theother tube, output circuits in which the cathodes and the anodes of the respective tubes arerespectively connected, the output circuits each being provided with a source of voltage, means connecting the sources otvoltage each between the anode of one tube and the cathode of the other tube with corresponding poles of the voltage sources connected tothe respective cathodes, the output 1 circuits having a common portion connected to the junction points between the'voltage sources and the cathodes to'which the voltage sources are respectively connected, an impedance connectedin the common portion. of the output circuits, and means for varying the impedance to vary the sensitivity of the' system. 20. A voltmeter having, in combination, tw

22. An amplifier having, in combination, two

vacuum tubes each provided with a cathode, an. anode and a control electrode, input circuits in which the cathodes and the control electrodes. of the respective tubes are respectively connected,

the control electrodeof one of the tubes being connected to ,the anode of the other tube, output circuits in which the cathodes ;and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a. sourceof voltage, meansconnecting the sources of voltage each between the anode of one tube and the cathode of the other tube with corresponding poles of the voltage sources connected to the respective cathodes, the

,output'circuits having a common portion connected .to the junction points between the voltage sources and the cathodes to which the volt age sources are respectively connected, and i an impedance connected in the common portion of the output circuits, the impedance having a resistance large compared to the reciprocal of the transconductance of the amplifier.

23. A rectifier having aninput circuit and an output circuit and having, also, a"cathode and an anode, a voltage-divider connected across; the cathode, an impedance connected in the-output circuit, and means for simultaneously adjusting the voltage-divider and the impedance in such ratio-as to maintain the direct'potential across the impedance in the output circuit substantially constant in the absence or a potential applied to J V the rectifier. vacuum tubes each provided with a cathode, an Y 24. A voltmeter having, in combination, a first anode and a control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected.-

' the respective tubes are .of the respective tubes are ed, output circuits in 8 vacuum tube and a second vacuum tube each provided with a cathode, an anode and a control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of therespective' tubes are respectively connected, the output circuits each being provided with a source of voltage, means connecting the sources of voltage each between the anode of one tube and the pedance and an indicating iinstrument connected in the common portion of the output circuits, 8

rectifier having a cathode, an anode, an input circult and an output circuit, means for connecting the output circuit of the rectifier to the input circuit of the first vacuum tube, an impedance connected in the output circuit of the rectifier, a voltage divider connected across the cathode of the rectifier, and means for simultaneously adassure an anode, and a control electrode, one of the tubes having a screen electrode. input circuits in which the cathodes andthe control electrodes of the respective tubes are respectively connected,

output circuits in which the cathodes and the anodes of. the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means for subjecting justing the second-named impedance and the.

voltage divider to maintain the zero reading of the indicating instrument.

25. An electric system tube having an output circuit and provided with a cathode, an anode and anauxiliary electrode, an'indicatin'g meter, means connectingthe indicating meter in the output circuit whereby at least a portion of the output current flows through the meter, means for sending a current through the meter in opposition to the output current, and means for varying thepotential on the auxiliary electrode to balance to zero the current through the meter.

26. An amplifier having, in combination, 'a ilrst vacuum tube and a second vacuum tube each provided with a cathode, an anode and a control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of respectively connected, the output circuits each being, provided with a source of voltage, means connecting one of the sources of voltage between the cathode of the first tube and the anode o: the second tube, means connecting a portion of the other source of voltage between the cathode of the second tube and the anode of the first tube, the output circuits having a common portion connected between the cathodes and including the remainder of the said other source of voltage, and an impedance connected in said common portion of the output circuits.

27. An electric system having, in combination,

' two vacuum tubes each provided with a cathode,

an anode, and a control electrode, one of the tubes having a screen electrode, input circuits in which the cathodes and the control electrodes respectively connects which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, a resistor in shunt with the voltage source of the output circuit of the other tube, and means for connecting the screen electrode of the said one tube to the resistor.

. 28. An electric system having, in combination, two vacuum tubes each provided with a cathode,

comprising a vacuum the screen electrode of the said one tube to the voltage of the voltage source of the output circuit of the other tube, and a resistor connected between the positive terminal of the source of voltage of one of the tubes and the cathode oi the other tube. V

29. An electric-system having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode; one of the tubes having a screen which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes (oi the respective tubes are respectively connected, the output circuitswachbeing provided with a source of voltage, theoutput circuit of the said one tube being coupled to the'input circuit of the other the screen electrode of the said one tube to the voltage of the voltage source of the output cirthe cathodes as to provide a voltage drop suitable to produce degenerative coupling in the input circuit of the said other tube.

30. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, input c'rcuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, means for applying a voltage to one of the input circuits, output circuits in which the oath-- odes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, the output circuit of, one of the tubes being coupled to the input circuit of the other tube, means connecting the sources of voltage each between the anode of one tube and the cathode of the other tube with corresponding negative poles of the voltage sources connected to the respective said cathodes of the said other tubes, the difference in potential between the said negative poles and the cathodes to which they are connected being subthe voltage applied to the said one input having a common portion connected between the cathodes, and an impedance connected in the common portion of the output circuits, one of the input circuits including the impedance, the impedancehaving a value such'as to produce a degenerativecoupling in the said one input circuit.

31. An electric system having, in combination. two vacuum tubes each provided with a cathode, an anode, and a control electrode, one of the tubes having a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected. an impedance between said cathodes, output circults in which the cathodes and the anodes of the electrode, input circuits in tube, means for subjecting of direct current, means for subjecting the screen electrode of the said one tube to the voltage of the direct-current source of the output circuit of the other tube, means for supplying the input circuit of the said other tube from the output circuit of the said one tube, and means for applying a varying voltage from an external source to the input circuit of the said one tube.

32. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, an impedance connected between the cathodes, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the and the cathode of the other tube with corresponding poles of the voltage sources connected to the respective cathodes, the output circuits having a common portion connected between the cuit of one of the tubes, and means for connectanodes of the respective tubes are respectively connecting the other end of the said one source of voltage to the anode of the other tube, and means connecting the other source of voltage between the cathode of the said other tube and the anode of the said one tube, the sources of voltage being connected with corresponding poles thereof connected to the respective cathodes, the output circuits having a common portion connected to the said one end of the said one source of voltage and the junction point between the other source of voltage and the cathode to'which it is connected, and the remainder of the impedance being connected between the said one end of the said one source of voltage and the said junction point.

33. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, one of the tubes having an auxiliary electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, and means for connecting the sources of voltage each between the anode of one tube and the cathode ofthe other tube with corresponding poles of the voltage sources connected to the said respective cathodes of the said other tubes. the output circuits having a common portion connected between the voltage sources and the cathodes, an indicating instrument and a degenerative resistor connected in the common portion of the output circuits, whereby a current will flow through the indicating instrument, means for varying the potential on the auxiliary electrode to balance to zero the current through the indicating instrument, and means for varying the degenerative resistor, whereby the variation of the degenerative resistor will not affect substantially the zero balance through the indicating instrument.

34. AvoItmeter having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, input circuits in 'which the cathodes and the control electrodes of the respective-tubes are respectively connected, the control electrode of one of the tubes being connected to the anode of the other tube, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means connecting thesources of voltage each between the anode of one tube ing one of the terminals between the impedance and the indicating instrument in order to produce degenerative coupling in the said input circuit.

35. A two-stage amplifier having, in combination, two vacuum tubes each provided with a cathode, an anode, a control electrode and a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, means for subjecting the screen electrode of each tube to the voltage of the voltage source of the output circuit of the other tube, means for applying a voltage to the input circuit of one of the tubes, the output circuit of the said one tube having a degenerative impedance, and means connecting the sources of voltage each between the anode of one tube and the cathode of the other tube with corresponding poles of the voltage sources connected substantially directly rto the respective said cathodes. of the said other tubes, whereby the potential of one of the screen electrodes is maintained substantially constant,

and the respective tubes with their input and output circuits constituting the two stages of the amplifier.

36. An amplifier having, in combination, two vacuum tubes each provided with a cathode, an

anode, and a control electrode, one of the tubes having a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected. the control electrode of one of the tubes being connected to the anode of the other tube, output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, and means for subjecting the screen electrode of the said one tube to the voltage of the voltage source of the output circuits of the other tube.

37. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode, and a control electrode, one of the tubes having a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes of the respective tubes are respec cuits having a common portion connected between the cathodes. 38. An electric system having, in combination,

two vacuum tubes each provided with a cathode,v

an anode; and a control electrode, one of the tubes having a screen electrode, input circuits in which the cathodes and the control electrodes the output circuit oi. the other tube, the output 10 circuits having a common portion connected between the cathodes so as to provide a voltage drop suitable to produce degenerative couplin in the input circuit "of the said other tube.

39. An electric system having, in combination, s

- an anode and a control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected.

two vacuum tubes each provided with a cathode, an anode and a control electrode, input circuits in which the cathodes and the control electrodes of the, respective tubes are respectively connected, output circuits in which the cathodes and go the anodes-of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, the output circuit of one of the tubes being coupled to the input circuit of the other tube, the output circults having a common portion connected between the, cathodes, and an impedance connected in the common portion of the output cirasoame cults in which the cathodes and the control electrodes of the respective tubes are respectively connected, output circuits in which the cathodes and the anodes o! the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, the output circuits having a common portion connected between the cathodes, the outpnit circuit of one of the tubes having a degenerative impedance connected in the common portion of the output circuits and a second impedance. and means connecting the second impedance in the input circult of the said one tube.

43. An electric system having, in combination, two vacuum tubes each provided with a cathode,

output circuits in which the cathodes and the anodes of the respective tubes are respectively connected, the output circuits each being provided with a source of voltage, the output circuits having a common portion connected between the cathodes, an impedance and an indicating instrument connected in the common portion of the output circuits, two terminals by means of which a voltage may be applied tothe 7 input circuit of one oithe tubes, and means for cults, one of the input circuits including the impedance, the impedance having a value such as to produce a degenerative coupling in the said one input circuit.

I 40. An electric system having, in combination,

two vacuum tubes each provided with a cathode, an anode, and a control electrode, one otthe 5 tubes having a screen electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected; output circuits in which the cathodes and the anodes of the respective tubes are respectively 40 connected, the output circuits each being provided with a source of voltage, means for sub- Jecting the screen electrode of'the said one tube to the voltage of the voltage source of the output circuit oiv the other tube, and means for u connectingthe sources of voltage each between the anode of one tube and the cathode of the other tube with corresponding poles of the voltage'sources connected tothe respective cathodes.

41. An electric system having, in combination,

two vacuum tubes each provided with a cathode, an anode and a control electrode, input circuits in which the cathodes and the control electrodes lot the respective tubes are respectively connected, output circuits in which the cathodes 55 and the anodes of the respective tubes are respectively connected, theoutput circuits each being provided with a source of voltage, and means for connecting the sources of voltage each between the anode of onetube and the cathode of the other tube with corresponding poles oi the voltage sources connected to the said respective cathodes of the :said other tubes, the output circuits having a common portion connected'between the voltage sources and the as means for balancing to zero the current through the indicating instrument, and means for varying the degenerative resistor.

42. An electric system having, in combination, two vacuum tubes each provided with a cathode,

arilanode, and a control electrode, input cir- 7 being provided with a source of connecting one of the terminals between the im-, pedance and the indicating instrument in order to produce degenerative coupling in the said input circuit.

.44. An electricsystem having, in combination,

two'vacuum tubes each provided with a cam ode, an'anode, and a control electr one of the tubes having a cults in trodes of the respective tubes are respectively connected, output circuits in which the cathodes tubes are reand the anodes of the'respective spectively connected, the output circuits each voltage, means for subjecting the screen'electrode of the said one tube to the voltage of the voltage source of the-output circuit'of the other tube, the output. circuits having a common portion connected between the cathodes, and an impedance and an indicating instrument connected hr the common portion of the output circuits.

45. An electric system having, two vacuum tubes each provided with a cathode, an anodeand a control electrode, input circuits in which the cathodes and the control elec-.=

trodes of the respective tubes ar respectively connected, output circuits in which the cathodes and' the anodes or the respective tubes are respectively connected, the output circuits each being provided witha source of voltage, the output circuits between the cathodes, an impedance and an in-, dicating instrument connected in the common portion oi the output circuits, and means for varying the output current from one of the tubes to balance to zero the current through the indicating instrument.

46'. An electric system having, in combination, two vacuum tubes each provided with a cathode, an anode and a control electrode, input circuits in which the cathodes and the control electrodes of the respective tubes are respectively connected. output circuits in which the cathodes and the anodes oi the respective tubes are respectively connected, the output circuits each being provided with a source oi voltage, the output circuits having a common portion'connected between the screen electrodefinput cir- V which the cathodes and thecontrcl elecin combination,

having a common portion connected" ,means for varying the voltage-divider resistor to adjust the zero reading of the instrument.

4?. An electric system having, in combination,

vacuum-tube apparatus having an impedance and an indicating instrument, a rectifier having a cathode, an anode, an input circuit and an output circuit, means for connecting the output circuit to the vacuum-tube apparatus, an impedance connected in the output circuit, a voltage divider connected across the cathode. and means for simultaneously adjusting the voltage divider and the impedance to maintain the zero reading of the indicating instrument. u

WILLIAM NORRIS TUTTLE.