US2315042A - Automatic electronic control system - Google Patents

Description

March 30, 1943. H. BQUCKE 2,315,042

AUTOMATIC ELECTRONIC CONTROL SYSTEMS Filed Jan. 11, 1939 a Sheets-Sheet 1 15 SIGNALTF v SIGNAL REGULATION J2 RteuLm-m f zkwvw- SIGNAL J5 enema. 2Z7" REGULATION )2 REGULATION INVENTOR. HeinJ/ -$oucke ATTORNEY.

March 30, 1943. v BQUCKE 2,315,042

AUTOMATIC ELECTRSNIG CONTROL SYSTEMS Filed Jan. 11, 1939 3 Sheets-$heet 2 42 36 70 r Q32 -o I 21 a7 A.F o 45 34 AMPLIFIERG I is o v qll u- F L. 45 4 :35 g

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Fig: 6 L u AMPLIFIER +376 1 INVENTOR. Heinz $011011? ATTORNEY.

March 30, 1943. H. BQUCKE AUTOMATIC ELECTRONIC common SYSTEMS Filed Jan. 11, 1939 3 Shasta-Shet 3 LAMPL'FIER A. F. AMPLIFIER Fig? 8 v INVENTOR. 1H ein aoucle BY ZM/ a ATTORNEY.

Patented Mar. 30, 1943 AUTOMATIC nmcraomc oomor.

' SYSTEM Heinz Boucke, Berlin-Charlottenburg, Germany,

assignor, by mesne assignments, to Patents Research Corporation, New York, N. Y., a corporation of New York Application January 11, 1939, Serial No. 250,315 I In Germany January 6, 1938 9 Claims.

This invention relates to automatic electronic regulator circuits and more particularly relates to novel circuits for insuring undistorted audio frequency signal reproduction with such control circuits.

An important feature of the invention resides in materially simplifying prior circuit arrangements for automatic range control for -neutralizing or compensating impulse shocks due to regulation voltages as to their effect upon the output circuit of the system. High quality volume control was previously obtained with push-pull electronic control stages comprising two opposed regulator or control tubes to. avoid direct current shocks or impulses from appearing in the output circuit. In accordance with the present invention, extraneous impulse neutralization is ob- A further object of the present invention is to provide a volume control system utilizing a balanced output from a single multi-electrode tube employing a grid electrode for the compensation circuit.

Still a further object of the present invention is to provide a dynamic range control system employing a plurality of frequency band groups from the audio frequency spectrum, and applying different time constants in the rectificationthereof to obtain undistorted reproduction.

These and further objects of the present invention will become apparent in the following description taken in connection with the drawtained with a single tube. The principle depends upon the use of a separate grid electrode in a multi-electrode tube for the return or compensation path of the tube output circuit.

A further important feature of the invention resides in novel and useful methods of and circuits for obtaining regulation potentials for antomatic dynamic expansion or range control for an audio frequency system. The regulation potentials are selectively obtained from the audio frequency signals employing different groups of signal frequencies within the audio frequency signal spectrum. Thus. in the preferred embodiment, by eliminating or filtering out the audio frequency band from thirty to one hundred and fifty or two hundred cycles per second from the control system, the prior art was able to avoid low frequency distortion, but impaired the dynamic regulation control. The present invention employs thelow frequency band for a distinct but simultaneously applied regulator potential in conjunction with a control potential obtained from the higher frequencies. A filter having a relatively high time constant is applied for rectifying the low frequency bandbefore. application to the control tube. Undistorted dynamic control is effected in this way as will be more particularly set forth hereinafter.

Accordingly, it is an object of the present invention to provide novel and simplified circuit arrangementsv for a dynamic or volume control system which neutralizes direct current shocks or impulses from the regulation potentials in their effect upon the output circuit of the system.

Another object of the present invention is to provide novel control circuit arrangements for obtaining undistorted dynamic control in an audio frequency system.

ings, in which:

Figure 1 is a circuit diagram of a preferred volume control stage for neutralizing impulses and direct current shock to prevent their reaching the output circuit.

Figures 2 to 5 are modified arrangements for the automatic volume control stage of Figure 1. Figure 6 is a circuit diagram of a system for sound record reproduction providing the shock neutralization principle in the amplification stage thereof in conjunction with dynamic control.

Figure 7 is a circuit diagram of the invention applied to sound reproduction embodying the undistorted dynamic expansion features of the invention.

Figure 8 shows an automatic tone control sys- 12. The control signal is applied to control grid l3 shown adjacent anode It. The invention is' applicable to radio frequency as well as audio frequency as will be understood. The positive or screen grid II is connected to a suitable source of current supply through terminal l6. By-pass condenser I I shunts the grid '15 to the cathode l2.

The output circuit comprising transformer ll and series, condenser 20 is connected between anode H of the tube and a retinn grid electrode 2| located between s'creen electrode l5 and regulator electrode II. A voltage divider or potentiometer 22 is connected between anode It and grid 2|, being in effect in parallel across the output circuit. The anode potential is applied from positive terminal 23 connected to a suitable ice regulation electrode with Figure l. The arrangement of anode ll and return grid 2| on opposite sides of control grid l3 acts as a push-pull scheme, which in the prior art required two individual electron streams.

In place of the voltage divider 22 it is feasible to arrange for shock impulse compensation by connecting the positive source terminal 23 to a midway tap in .the primary-winding 24 of transapplied to control grid |3. This is due to the I shielding effect of positive screen grid l5 interposed between return grid 2| and control grid l3, as shown. In operation, the current through return or compensation grid 2| depends only on the instantaneous value of the regulation or control potential applied to grid ll interposed between it and the cathode. The current flowing through the plate or anode M follows the varying signal potential of the alternating'current signals applied to the control grid l3. However, controls the v average density of theelectron stream between cathode l2 and anode l4. Accordingly, the current flowing through anode I4 is a function both .of the regulation and signal potentials. I

Thus, the signals flowing to the primary of transformer l8 comprise amplified signal frequencies flowing intoanode l4. Theamplified signal frequencies pass through by-pass condenser. 20 and coupling transformer l8. Variations in the regulation potential applied to grid correspondingly affect :the current flow both through, anode [.4 and positive grid 2|. The cur- .rent flow from ,theseelements is in the same former l8. In this case, the voltage divider 22 and condenser 20 is dispensed with and accurate balancing out of the shock potentials may be insured byconnecting variable parallel resistances across each section of the tapped winding of the transformer, or by suitable resistances individually connectedin series with the anode II and grid 2|.

It is tobe understood that as far as the basic idea of the invention is concerned, it is immaterial whether additional grids or electrodes are provided within the amplifier tube l0. Furthermore, it is not essential for the signalsto include the anode I4 of the tube. In Figure 3 I have shown another form of the invention where anode I4 is connected directly to a suitable positive potential '25, and the positive grid electrodes l5 and 2| are connected across voltage divider 22 and the transformer l8. An impedance may be accordance with the variation in potential applied direction towards the primary of transformer I8 and are naturally subtractive in their voltage effect thereon. In accordance with the invention,

the adjustment of thetap on voltage divider 22 is such as to control the respective potentials applied to anode i4 and grid 2| so as to balance or neutralize the current flow effects upon electrodes l4 and 2| due to the regulation by grid II. This procedure causes equal signal effects upon transformer l8 by electrodes l4 and 2| .due to the effects of grid II which cancels out when voltage divider 2| is properly adjusted, as will now be-evident. Y The signal frequencies applied togrid i3 are amplified and pass through transformer l8. for

further application in a conventional manner.

, Direct current potential shocks or impulses origl3. It is to be understood thatvoltage divider '22 shown as variable may, in a practical set, be

to grid II and are passed through grids I5 and 2| with proper neutralization of the shock impulse-excitations in a manner forming the basis of the present invention. V

Figure 4 is a furtherform of the invention em ploying only three intermediate grid electrodes.

Control grid I3 is dispensed with, and the control signal is applied between ,anode H and cathode |-2. The regulation voltage is applied to grid II as in the previous examples. The output circuit --istaken between positive grid electrodes l5 and 2|, and applied across voltage divider 22 and transformer I8. A further formof the invention is shown in Figure 5 where compensation .grid2l is interposed between regulation grid electrodev H and a fixed voltage divider comprised of a tapped nected in series.

A modified form of the invention is illustrated in Figure 2 where positive screen grid l5 and compensation grid 2| of Figure 1 are interchanged, the return grid 2| being adjacent the control grid l3 and screen grid |5 adjacent regu-' lation grid II. In this form, the current through positive return grid 2| is influencedby the signal potentials applied to the control grid l3 located between grid 2| and anode l4. Direct current shocks in this case will neutralize to the desired degree after voltage divider=22is suitably selected in the manner asalready described in connection resistor, or two resistors of suitable value conplied to grid.

combined, using a split primary windinggof-gthe cathode l2. Anode I4 is connected to one side of'primary 24 of transformer It. The anode direct current potential. from terminal, 22 is applied to anode I through a'shunt resistance 21. A positive screen grid is connected to positive terminal I6 and lies between regulation grid II and control grid l3. A resistance 28 is connected between anode H: and grid 2| and is adjusted to balance the size of the compensation current. The compensation action occurs by the currents from grid 2| and anode l4 merging and balancing out before being applied to the transformer, to

neutralize shock impulses due to potentialsap- These currents could-also be transformer as willbe evident to those skilled in the art. V v u In systems 'where the signal frequencyis at intermediate or radio frequency, means are provided to unite the compensationcurrent with the modulation current, preferably at a positionbe fore the demodulator in such a waythatthe portion of the modulation current due to-the action of the regulator potential is compensated therein. I f

In Flguresfi is illustrated a complete system in which the application is applied to dynamic range control of a phonograph reproducing system. A sound disk 30 cooperates with a tone arm or pick.- up 3| forproducing electrical signal variations across potentiometer control 32, the terminals of which are connected to the input circuit of amplifier stage 33 between cathode 34 and control grid 35 thereof. The output of amplifier 33 is arranged in accordance with the principles of the invention already described to eliminate shock excitation from reaching the output of the coupling transformer 36. The primary 31 thereof is connected between anode 48 and grid electrode 4|. The primary 31 is tapped for the application of the positive voltage from terminal 38. The position of the tap is determined. for proper compensation and neutralization of shock impulses in a manner already described. Shield grid 42 is interposed between compensation grid 4| and anode 48 and receives its proper positive potential from a voltage divider formed by resistances 43 and 44 connected between positive terminal 38 and ground.

The regulation grid 45 is energized by rectified potentials derived from the audio frequency signals in the following manner: The audio signal generated by pick-up 3| is applied to grid 58 of triode through lead 52 and coupling condenser 53. The output of triode 5| is connected to transformer 55 in a conventional manner. The circuits for triode amplifier 5| are also conventional as will be. evident and need not be further described. The output of transformer 55 is connected to a full wave rectifier 56 in a conventional manner. The output of rectifier 56 is supplied fromcathode 51 thereof and center tap 58 ofthe secondary of transformer 55. The rectified output of rectifier 58 is filtered by means -of condenser 60 which is shunted by resistance 6|. Resistance 6| is preferably a potentiometer having a variable tap 62 from which the relative value of the regulation potential is determined and applied directly to regulation grid 45 of tube 33.

A further filtering condenser 63 is connected across the output of potentiometer 6|. The average direct current value of the regulation potential applied to control grid 45 is controlled by potentiometer 65 connected at the opposite terminal to ground potential. A manual level control may thus be effected by the use of potentiometer 65.

The amplification level of the signals applied to control grid 35 of amplifier stage 33 is varied in amplification in accordance with the regulation potential applied to grid 45. as will now be evident. A dynamic volume expansion system is thus-provided as will be understood by those skilled in the art. The output of coupling transformer 36 is applied to a conventional audio frequency amplifier 18, to the'output of which a reproducer 'H' is connected such as aloud speaker unit. The advantage of the present system is the compensation and neutralization of direct current shocks or impulses which may be applied to regulation grid 45, in a manner hereinabove described.

A further feature of the invention resides in equipment. Similarly, sound record reproduc- I tions are also contracted in range and the signals derived therefrom may be advantageously dynamically expanded to more closely represent the original sound ranges. V

In conventional dynamic expanders, a single control or regulation potential is derived by filtering the rectified signal current and applied to a regulationelectrode in an amplifier stage of the system. Inasmuch as good filtering is desirable for undistorted action, increased filtering adds to the inertia or sluggishness of the regulation control. It has not been practical'in single control systems to sufliciently filter the control potentials to a point which is necessary to avoid all distortions due to residues of audio frequency rectification. In practice, the frequencies lying in the band from thirty to about two hundred cycles per second are appreciably distorted as a result of the dynamic regulation using the full band and efficient filtering. Such distortion might be obviated by suppressing frequencies of this band before passing onto the control or filtering circuit. However, this action would impair tion voltages are simultaneously applied to the' the dynamic expansion action since it would then be dependent only upon the volume due to the frequencies above that band.

The feature of the invention designed to overcome this deficiency lies in'supplying a plurality ofregulation potentials acting in the same direction upon the regulator circuit. Thus, for example, one of the potentials is derived solely from the low frequency band, for example,thirty to two hundred cycles, and a second regulation voltagefrom the rectification of frequencies above two hundred cycles. These independent regularegulation electrodes. Independent filtering of these components is thus made possible. The lower frequency bands are filtered" by filters having relatively higher time constants than those of the higher bands. The practical result is that the regulation potentials, in combination, are

substantially free from any traces of residue audio frequencies and cooperate to provide undistorted dynamic expansion. In this way, high fidelity low or bass note reception is assured in conjunction with the dynamic expansion action.

Referring to Figure '7 which is an embodiment of this feature of the invention a disk record 88 is indicated with a pick-up unit 8| generating the sound signals which are applied to the input of the tube 82 between control grid 83.and ground, which communicates to the indirectly heated cathode 84. through the self-biasing filter circuit 8588.

Thesignals are introduced to the tube through the-level control potentiometer 81. A positive screen grid .88 is located beyond the control electrode 83- and is connected to a suitable point in the voltage divider 989l terminating in the source of positive supply 92. The output circuit of tube 82 originates between anode 83 and the providing an undistorted automatic dynamic exing the sound level in translation thereof. In a broadcast transmission, musical and other wide range sound renditions are contracted in their range from the original intensity range to that necessitated by-the capacity of the transmitting cathode'or ground, which includes the primary 34 of the output transformer 95. The output of transformer 951s connected to audio frequencyamplifier 96, in turn connected toreproducer unit 91 which is the loudspeaker.

The novel dynamic control circuit ance with the invention is connected to the output of the triode amplifier I80, the control grid II of which is coupled to the output of pick-up 8| through coupling condenser I02. The output v of triode stage I80 is connected to the primary I03 of transformer I04. The transformer I84 has The cathode is suitably biased in accordondaries I05 and I06 supply the independent channels for the rectification-filter-regulation circuit. The low frequency path in conjunction with winding I 05 is designated, L; the high frequency path with winding I06, H. g

The secondary I05 is shunted by a by-pass condenser IIO. An impedance element III is connected between condenser I I and winding I05. The values of impedance IIO--III are proportionedto by-pass the audio-frequencies, for example above 200 cycles per second. Accordingly, all audio frequencies below 200 cycles per second are introduced to thermionic rectifier unit H2. The unidirectional output of rectifier H2 is filtered by shunt condenser H3 and resistance H4. The adjustable output of the filtered signals is controlled by vtap II5 on potentiometer II4. A further by-pass condenser H6 is shunted across the output of potentiometer II4.

In a similarmanner a filter is provided across the output of winding I06 to by-pass the frequencies below 200 cycles in this case. The high pass filter is shown comprising resistance elements I shuntedacross the secondary, and a series condenser I2I. It is to be understood that filter I20'-I 2I is merely shown for schematic purposes and in practice, may comprise different arrangements and different types of impedance elements, such as impedances in place of resistances.

Filter I20--I2I is designed to pass frequencies above 200 cycles in the present case, for example, 200 to 10,000 cycles. Thishigh frequency band is rectified by series rectifier unit I25, the output of which is shunted by afilter composed of condenser I26 and potentiometer I21. The variable tap I28 of potentiometer I21 is used to adjust the value of the signal voltage from the high frequency path. A by-pass condenser I23 is connected across the output of potentiometer I21.

In accordance with the present invention the filter II3-I I4 at-the output of the low pass control section L is designed with a substantially higher than normal time constant. The higher time constant naturally provides a greater filtering action-by the filter, as is well known in the art. The improved filtering action of the hand between and 200 cycles per second prevents harmonics and components thereof from passing on to the regulator electrode.

The filter I26-I21 of the high frequency section H is of the order of the ordinary filters for dynamic regulators with the time constant small enough so that the control action responsivethereto will properly operate the dynamic expansion. The frequencies above 150 or 200 cycles are properly filtered by I26'I21. In a preferred example the filter Ii3-II4 is arranged with a discharge time constant of 1 second, condenser II3 being 2 microfarads and resistance I I4 being 0.5 megohm. The discharge 'time constant of filter I26-I21 of section K, may be arranged for a discharge time constant of the order of .200

milliseconds.

The output from the respective filters is connected in series and forms a unitary direct current potential control for the regulation electrode I30- As shown in Figure 7 the respective outputs of potentiometers H4 and I21 are connected in additive series relationship across the variable tap portions H5 and I28 thereof, the negative terminal of the potentiometer being connected device such as a loud speaker I43.

to ground by lead; and the resultant positive side 78 thereof being connected to electrode I30 through by lead I32.

It is to be understood that the invention is applicable with more than two rectified con- I tiguous bands of the audio frequency spectrum used. A suitable band selection may be 30 to 200 cycles for the low; 200 to 2,000 for the intermediate and 2,000 to 10,000 for the high band. 5 It is to be'understoodthat the described principle of undistorted dynamic volume expansion may be applied equally well to radio frequency or intermediate portions of radio receiver. ever, it is preferable to use it particularly in the audio frequency section in the manner described since it is available for phonograph reproduction as well as radio reception. 8

According to a further modification, the in-.

vention may be applied to amplifying systems for automatic fidelity control such as for needle scratch suppression in phonographic pick-up systems.

An arrangement of this type is shown in Figure 8 comprising a multi-electrode tube having an- (regulation) control grid I31 and an anode or plate I38, The audio frequency Signals impressed upon the grid I34 from a pick-up device or the like are amplified and applied from both the anode grid I36 and the anode I38 to the primary of the output transformer I4I feeding a subsequent amplifier indicated by the rectangle I42 before being impressed upon a translating The output paths from the grid I36 and plate I36 are designed to have different frequency characteristics and to this end the anode grid I36 in the example shown is directly connected to the upper end of the transformer primary I while theanode I38 is connected to the same end of the transformer winding through a high frequency stop or noise suppression filter comprising a series induction coil I38 having its opposite ends bypassed to the cathode through condensers I40. The control potential is obtained by rectifying a portion of the sound output energy by means of rectifier I44 and filtering of the rectified energy by condenser I45 in such a manner as to obtain a control voltage developed across resistor I50 varying in accordance with the average intensity of the sound signals being amplified. This control voltage serves to negatively bias the regulation grid I31 in series with an additional fixed negative biasing source ISI. 0

The operation of this circuit will then be a follows: If the intensity of the sounds increases, the bias on the grid I31 will become more negative with the result that the anode-output path including the noise filter I33, I40 will be more or less blocked thereby opening the output path from the grid I36.' On the other hand. if the sound intensity decreases more output signals will pass through the anode circuit thereby increasing the effectiveness of the noise filter.

Figure 8 includes the following further conventional elements; a record disk I48 cooperating with a tone arm or pick-up I46 connected to the input grid I34 by way of an audio frequency transformer I41. As is seen in the system as described, the effectiveness of the needle scratch or noise filter will be automatic'ally'controlled in dependence upon the average sound Howintensity in such a manner as to maintain the most favorable compromise between optimum fidelity and noiseless reception under varying automatic selectivity adjustment, i. e. in other words, combining the advantages of Figures '1 and 8. The tube employed in the example illustrated comprises the following electrodes in the order named: a cathode I55, a first control grid I56 serving for producing dynamic range control, a first anode or output grid I51, a'screen grid I58 maintained in a known manner at a steady positive potential with respect to the cathode, a signal input grid I59, a further output or anode grid I60, a. further control grid II serving for producing automatic fidelity or noise control and a plate or anode I62. A' needle scratch filter comprising series inductance I63' and by-pass condensers I64 is connected between the plate I62 and a first primary winding I56 of the output transformer I65. Anode grid I6II is directly connected to the transformer I66 to obtain fidelity or noise control in the manner substantially similar to Figure 8. The transformer I64 has an additional primary winding I61 and. a secondary I68 connected to amplifier I68 which in turn serves to energize a further output transformer l'lll having three secondary windings I12, I13, I14, one of which (I12) energizes loud speaker "I. Windings I13, I14 serve to derive portions of the audio signal energy'rectified by means of rectifiers I15 and I16 followed by smoothing filters I11 and I18 to produce control potentials varying in proportion to the average sound intensity. One of these control potentlals is impressed upon the dynamic range control grid I58 and the other control potential is impressed upon fidelity control grid I6I. The

grids I56 and I6I are additionally negatively biased by steady biasing sources I19" and I19 in a manner substantially similar to that shown in Figure 8. The output from the positive or anode grid I51 is passed through the primary coil I61 of the transformer I65 arranged in such a manner as to compensate direct currentvimpulses in the primary coil I66 due to sudden potential variations on the control grid I56. To

this end the coils "I66 and I61 are suitably designed and wound in a proper sense to efiect complete neutralization of D. C. shocks or impulses. Item I52 is a record disk-l53, a tone arm or for impressing the audio signals upon grid I59 and cathode I in series with a suitable fixed negative biasing source I19. It is seen, therefore, that an arrangement according to Figure 9 will enable by the aid of a single tube simultaneous dynamic range (compression or expansion) and fidelity (noise or needle scratch) control while at the same time substantially eliminating the disturbing effects of D. C. shocks orimpulses due to sudden or abrupt changes in control potential.

As is understood, in Figures 8 and 9 the anode I38 or I62 may be directly connected to the output transformer and the scratch filter may be inserted in the path from the anode grid I35 or I66, respectively, in which case however the control potential on the grid I31 and I6 I, respectively, should be reversed to secure the same function and results as pointed out.

It will further be evident that arrangements pick-up and I54 the input transformer compensation grids.

,the invention is applicable to various modifications which will suggest themselves to those skilled in'the art and accordingly the specification and drawings presented herein are to be regarded in an illustrative rather than in a lim-' iting sense short of the scope-of the invention as defined in the appended claims What is claimed is: v lQIn combination with an electron discharge device comprising a cathode and an anode, a signal control grid near the anode, an amplification control grid near the cathode and-a compens-ation grid interposed between said signal and amplification control grids, an input circuit connected between the cathode and signal control grid, output impedance means connected between the anode and said compensation grid, a source of space current for said discharge device connected between the cathode and an intermediate point of said impedance means, an amconnected between thetcathode and said signal control grid, output impedance means connected between said anode and said compensation grid,

a source of space current for said discharge device connected between the cathode and an intermediate point of said impedance means, an

amplification control circuit connected between said amplification control grid and said cathode,

a screen grid at cathode signal potential interposedbetween said amplification control and 3. In an automatically controlled amplifier for electric signals, an electron discharge device comprising a cathode, an anode, a signal control grid near said anode, a regulation grid for controlling the amplification near said cathode and a compensation grid between said signal control and-reguiation'grids, an input circuit connected to said signal control grid and said cathode, output impedance means connected between said anode and said compensation grid, a source of space current for said discharge device connected between the cathode and an intermediate point of said impedance means, means for averaging a portion of the signal energy-being amplified to derive a direct control potential varying in proportion to the average signal amplitude, means for. applying said control potential to said regulationv grid, a screen grid at cathode signal potential interposed between said signal control grid and said compensation grid, the intermediate point of said impedance means being chosen so that current through said impedance means due to potential on said regulation grid is compensated.

6 v a tube comprising acathode and an anode, a signal control grid near said anode, an amplification control grid near said cathode and an anode grid interposed between said signal and amplification control' grids, an input circuit connected to said signal control grid and said cathode, output impedance means-connected between said anode and said anode grid, a source of space current for said 'tube connected to an intermediate point of said impedance means and said cathode, an amplification control circuit connected'to said amplification control grid and said signal control grid, and means for balancing'the currentsdeveloped in the branches of said impedance means at opposite sides of said intermediate point due to varying potential on said amplification control grid.

5. In combination with an electron discharge tube, comprising a cathode and an anode, a signal control grid near said anode, an amplification control grid near said cathode and an anode grid interposed between said signal and amplification control grids, an input circuit connected to said signal control grid and cathode, output impedance means connected between said anode cathode, a screen gridat cathode signal pot'ential' interposed between said anode grid and said and said anode grid, a source of space current for said tube connected to an intermediate point of said impedance means and said cathode, an amplification control circuit connected to said amplification control grid and said cathode, a

screen grid at cathode potential located between said amplification control grid and said anode grid, and means for substantially balancing the currents developed in the branches of said impedance means at opposite sides from said intermediate point due to varying potential on said amplification control grid.

6. In an amplifier including an electron discharge tube provided with a cathode, a main anode, a compensation anode, a signal control grid and an amplification control grid, an input circuit connected between said signal control grid and said cathode, a common output circuit for saidmain and compensation anodes, means Ion.

anode, a signal input grid near said anode, an amplification control grid near said cathode and a ioraminous auxiliary anode located between said signal and amplification control grids, an inputcircuit; connected between said signal control grid and cathode, means for applying control potential to said amplification control grid, a common output circuit for said main and auxiliary anodes, means including circuit connec- ,fl

tions from said anodes to said output circuit ,to balance the output currents due to potential variations on said amplification control grid, and means for substantially preventing said signal control grid from affecting the current to said auxiliary anode.

8. In an amplifier including an electron discharge tube provided with a cathode, a main anode, a signal input grid near said anode, an amplification-control grid near said cathode and a foraminous auxiliary anode located between said signal and amplification control grids, an

input circuit connected between said signal control grid and said cathode, means for applying control potential to said amplification control grid, a common output circuit for said main and auxiliary anodes, means including circuit connections from said anodes to said output circuit to balance the output currents due to potential variations on said amplification control grid, and a positively biased screen grid at cathode signal potential arranged between said signal control r grid and said auxiliary anode.

9. In an amplifier including an electron discharge tube provided with a cathode, a main anode. a signal input grid near said anode, an amplification control grid near said cathode and a foraminous-auxiliary anode located between said signal control and amplification control grids, an input circuit connected between said signal control gridand said cathode, means including rectifying and filter means for averaging a portion of the signal energy being amplified to derive a direct current control potential vary- I ing in proportion to the average signal strength,

means for applying said control potential to said amplification control grid, a common output circult for said main and auxiliary anodes, means including circuit connections from said anodes to said output circuit to balance the output currents due to potential variations on said amplification control grid, and a positively biased screen grid at cathode signal potential arranged between said signal control grid and said auxiliary anode.

, HEINZ BOUCKE.

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