US2378797A

US2378797A - Electronic tube circuits

Info

Publication number: US2378797A
Application number: US472950A
Authority: US
Inventors: Otto H Schade
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1943-01-20
Filing date: 1943-01-20
Publication date: 1945-06-19
Anticipated expiration: 1962-06-19

Description

June 19, 1945. Q H SCHADE ELECTRONIC TUBE CIRCUIT Filed Jan. 20, 1945 /VVE l?! aangaf/im FREQa/EA/c y /Los/ ATTORNEY Patented June 19, 1945` ELECTRONIC TUBECIRCUITS Otto H. Schade, West Caldwell, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 20, 1943, Serial No. 472,950

16 Claims. (01.179-171) This invention relates to an improvement in television transmitting systems, and more par-V ticularly, to an improvement in the amplifying system associated with a television pickup tube. For the transmission of high fidelity television images, i-t is` desirable tobe able faithfully t'o transmit a very wide range of picture signals occupying a frequency spectrum of from substantially zero yto frequencies of the order of 12 to 20 megacycles per second. Furthermore, in order that the reproduced images at the receiver may have the proper tonal values and may be of the proper fidelity, it is desirable that all frequency values within this extremely wide range of frequencies be transmit-ted in their proper intensities. The amplification of such a range of frequencies is exceedingly difficult principally by reason of the fact that the circuit elements, which include resistances, condensers and inductances, offerdifferent electrical impedances at different frequencies.

Where a relatively narrow band of frequencies is lto be amplified, a proper choice of the circuit elements may be made in accordance with the different frequencies encountered. However, Where a `Wide frequency spectrum is to be amplified, it is virtually impossible to select the values of the various circuit elements such that attenuation will not`occur in one or another portion of the frequency spectrum,

In virtually all television pickup tubes, some picture signal output load impedance must be employed, and some actual or distributed capacity is always present across this load impedance. If the impedance is in the form of a resistance,

the signal strength available at the output e1ec-' trodes of thetelevision pickup tube Will vary in 'accordance with the frequency of the generated picture signals, with the result that a higher picture signal strength will be present for the stantially linear amplification follows, with the result that all of Ithe picture signals, irrespective relatively lowpicture signals than is present for the higher frequency picture signals. This attenuation with increase in frequency is caused primarily by reason` of the time constant of the output load circuit of the television pickup tube.

In order to compensate for lthis attenuation as a function of frequency, compensating networks must be provided, or' the gain of an amplifier tube must be so controlled as to increase the intensity of the picture signals of relatively high frequency to an extent greater than the increase 'in intensity of the picture signals of low frequency. When the attenuation and phase shift of the higher frequencies of the picture signal series is exactly compensated for, subof Itheir position within the frequency spectrum, represent their proper intensities in accordance 'with the light intensities of the ltelevision image to be transmitted.

The present invention provides a television picture signal amplifier circuit in which the amplification and phase shift of the picture signals is controlled as a function offrequency, in order thereby to compensate for the attenuation and phase shift of the picture signals as a function of frequency caused by the various circuit elements. When complete compensation is accomplished, the picture signal output from the television signal amplifier is substantially linear with the result that the signal strength and phase delay of the picture signals is correct and corresponds to the-particular television image to I be transmitted.

It is, therefore, one purpose of the present invention to provide a television transmitting system in which the picture `signal amplifier associated with the television pickup Itubewill `supply picture signals bearing the phase relationship Ito the transmitted. l

Another purpose of the present invention resides in the provision of a picture signal amplifier in a television transmitter that is so arranged to compensate for frequency attenuation caused by the circuit elements of fthe television system.

Another purpose of the present invention resides in the provision of a television picture signal amplifier 'in which a very Wide band of frequencies may be amplified in a linear manner without attenuation at any portion of the band or spectrum as a function of frequency.

A further purpose of the present invention resides in the provision of an amplifier in a television picture signal amplifier system Vin which the amplification of the amplifier tube is controlled in accordance with a function ofthe frequency of the applied signals.

television image to be resides in vthe'provision of an amplifier tube in a television picture signal amplifier channel in which the effective cathode impedance of the amplifier tube is maintained high, while at the same time the bias potential between the cathode and control electrode of the amplifier tube is not excessive.

A still further purpose of the present invention resides in the provision of an amplifier tube in a picture signal amplifier channel associated with proper intensity and tube in which the cathode circuit for the amplil fier tube includes an electron path in order that the cathode circuit may have a relatively high impedance without imposing a high bias potential on the control electrode of the amplifier tube.

A further purpose of the present invention resides inthe provision of an amplifier tube in an amplifying channel associated with a television pickup tube in which the cathode circuit of the amplifier tube may have an effective high electrical impedance without the necessity of providing an auxiliary high potential source.

A still further purpose of the present invention is the provision of one or more amplifiers in an amplier circuit for a television pickup tube in which provision is made to generate an inverse feedback voltage on an impedance in the cathode load circuit of one or more ofthe amplifiers for obtaining a predetermined gain versus frequency characteristic of 'the amplifier circuit, the phase and magnitude of the generated feedback voltage being adjustable, and depending on the impedance of the network in the cathode circuit.

Since the impedance of the load circuit of the television pickup tube or the input circuit of the picture signal amplifier tube may be of the order of megohms at low frequencies and only several hundred ohms at high frequencies, a gain variati-on of a range of several thousand times is, therefore, required to compensate for the impedance variation. It is, therefore, another purpose of the present invention to compensate perfectly for variations in the impedance of the output circuit of a television pickup tube or the input circuit of an amplifier stage to permit substantially linear amplification over a wide frequency band ranging from substantially zero to frequencies of the order of from 12 to 20 megacycles per second. l

Still another purpose of the present invention resides inthe provision of a simple and convenient means in a television picture signal amplifler to adjust -the operation of the amplifier to accommodate wide limits of amplifier input impedance or wide limits of television pickup tube. output impedance without altering the over-all gain or frequency characteristics of the amplifier circuit, and without the necessity of changing any of the direct current potentials in the amplifier circuit.

form of the present present invention. Referring now to the drawing, and particularly to Figure 1 thereof, there is shown a television pickup tube I having a target electrode I2 and an output-conductor I4. As is well known to those skilled in the art, when the target electrode I2 is scanned by a focused cathode ray beam, a series of picture signals is generated that may have a wide frequency spectrum ranging from substantially zero frequency to frequencies of the order of 12 or more megacycles per second. The frequency of the produced picture signals is a function of the number of lines scanned per frame, the field repetition rate and other functions,- as is well known to those skilled in the art.

A load circuit including resistance I 6 is connected between the output conductor I4 and ground, and between conductor I4 and ground a certain actual or distributed capacity I8 is also present. A potential is developed across resistance I6 and capacitance I8, and this potential is then applied-to the control electrode of an amplifier tube in order to increase the amplitude of the produced picture signals. The amplifier tube 20 includes at least a cathode, a control electrode and an anode, and in the particular circuit shown, the cathode is connected to ground while the control electrode is connected directly to the output conductor I4 of the television pickup tube I0. The anode of the amplifier tu-'be 20 is maintained positive by con-- necting the anode to a source of positive potential by means of a peaking circuit 22, an inductance 24 and a resistance 26. The tube 20 will then amplify linearly the potentials impressed upon the control electrode thereof, and these potentials in amplified form are generally obtained from point 28 located between the peaking circuit 22 and the inductance 24.

lThese signals are then applied to the control electrode of a further amplifier tube 30 by way of coupling condenser 32. The amplifier tube 3l) includes at least a cathode, a control electrode and an anode, and th`e control electrode is connected to ground by grid resistance 34. The cathode of tube 30 is connected to the negative terminal of a source of potential 36 by means of a relatively large resistance 38 and a parallel condenser 40'. A point along the source of potential 36 (indicated conventionally as a battery in Figure 1) is connected to ground, and the positive terminal of the battery 36 is connected to the anode of tube 30 by Way of load resistance 42, load impedance 44 and peaking circuit 46'. 'Ihe output potentials may then 'be derived between output terminal 48 land ground, the output terminal' being connected to the junction of the peaking circuit 46 and the inductance 44 by way of coupling condenser 50.

The voltage developed at the control electrode of tube 20 by the television pickup tube I0 or by any constant current generator having a variable frequency output is proportional to the impedance of the circuit resistance I6 and capacitance I8, and has a frequency characteristic such as that represented by the curve A- in Figure 3. In.

Figure 3 the horizontal or abscissa co-ordinate is graduated as a logarithm scale, and represents the frequency of the produced picture signals. The vertical or ordinate co-ordinate is also logarithymically graduated. It will be noticed by inspecting Figure 3 that the produced picture signals remain substantially constant in intensity throughout a predetermined frequency range, and above this frequency range substantially constant attenuation of signal strength results. It is, therefore, desired that an amplifier or compensating source, which is necessary as cathode circuit of tube 30 is so chosen that the time constant of this cathode impedance is equal to the time constant of the resistance I6 and capacitance I8, with the resistance 38 equal to Zcqm is the input circuit impedance ratio between zero frequency and the cutoff frequency or maximum frequency Fc of the television picturesignal band, and where gm is the mutual conductance of the `ampliiier tube. Under these conditions the relative input voltage at the control electrode of tube 30 (as required for a constant current output of tube 30 as a function of frequency) is represented Where by the curve A with the dotted portion at the higher frequency end of the curve. When these conditions exist, the corresponding gain characteristics of the amplifier tube 30 will be similar to the curve shown at B in` Figure 3, and will result in the plate load circuit of tube 30 havin,r a linear frequency characteristic and the output voltage as represented by curve "C will be substantially constant/up to a frequency of 0.3 Fc, at which frequency it drops to 94% and then decreases to 66% at the maximum frequency Fc of,`

the band.

In` order to satisfy the above conditions, it is apparent that the value of the resistance 38 must be quite high in order to obtain good correction for wide frequency bands, The cathode current of tube 30 causes .a voltage drop Ek across resistance 38, and such a voltage drop would be entirely too great for proper operation of tube 30. In order to oppose the excessive voltage drop, a portion Bk of battery 36 is used so that the cathode of tube 30 is maintained only slightly positive with respect to ground potential (or control electrode potential) in order to provide the proper bias on the control electrode of tube 30. Inasmuch as the value of the resistance 38 must be exceedingly high, naturally the voltage drop will be high, and accordingly the potential of the portion Bk of battery 36 must be quite high. On -test it has actually been found that for a frequency band of 12 megacycles and an input circuit resistance (resistance I6) of one megohm and capacitance (condenser IB) of 25 micro-micro-far- 4ads, the capacity of the condenser 40 should be 100 micro-micro-farads and the resistance of the resistor 38 should be 250,000 ohms for a tube of the type GAC? as tube 30. When these values are used in order-to provide substantially linear ampliiication for a frequency band of the order of 12 megacycles, it is necessary to provide approximately 2,000 volts for the portion Bk of battery 36 when a normal cathode current of 8 milliamperes is permitted to flow through tube 30. Naturally, such a high potential is difficult to provide, and although `the circuit functions completely satisfactorily to accomplish the desired purposes of this invention, it nevertheless is not, from the standpoint of a commercial application, of the usually practiced simplicity. y i

In order to avoid the use of a high potential explained above, it

is possible to use arl electron current path in the cathode circuit of tube 30 to provide an effective high impedance cathode resistance without the necessity of providing a very -high potential source. An embodiment of such an arrangement is shown in Figure 2 of the drawing. In this iigure, all parts identical to corresponding parts in Figure 1 bear similar reference numerals, and in order to avoid repetition, that part of the circuit be considerably higher, a parallel adjustable preceding amplifier tube k will not be again described.

In Figure 2 it will be observed that a pentode 60 is included in the cathode circuit of tube 30. The anode ofthe pentode `6l) is connected directly to the cathode of tube 30, while the cathode '62 of the pentode 60 is connected to the negative terminal of a source of potential 64 (indicated for convention purposes only as a battery in the drawing) by way of an adjustable resistance 66.

The resistance 66 is provided in the cathode circuit ofthe pentode 60 in order to afford a biasing potential for tube 60, and it will be observed that the control electrode of the tube 60 is connected directly to the negative terminal of the battery A point along the battery is connected to ground potential, and the positive end of the battery or source of potential is connected to the anode load circuit of tube 30. Since it is desirable to operate thescreen electrode of tube 60 positive relative to the cathode, the screen is connected to a point corresponding approximately to the ground point of the source of potential 64.

Inasmuch as the plate impedance of i the pentode 60 may not be theexact value required for producing the desired electrical impedance in the cathode circuit of tube 30, and infact may resistance 68 is provided (corresponding to resistance 38 in Figure `1), one end of the resistance being connected directly to the cathode of tube 30 and an adjustable point along the resistance being connected to ground lby way of a condenser 10, the size of the condenser-1U being chosen such that it offers relatively low impedance to the frequencies to be amplified. A shunt condenser is also connected. between the cathode and groundlto form the proper cathode impedance Ze as explained. The condenser 40 could as well be connected between `the cathode and the negative terminal of the source of potential 64.

The inclusion of the pentode in the cathode circuit of tube 30 overcomes the necessity of providing a high potential source as in Figure 1, since the pentode requires a relatively low direct current energizing potential, yet offers a` relatively high plate impedance which may be of the order of from 300,000 ohms to one megohm in practical tubes. In practice, it has been found that only a voltage of the order of 150 volts is necessary for energizing tube 60, and naturally such a potential is more readily provided than a a potential of the order of 2,000 volts as required in the circuit shown in Figure 1. Should the plate impedance of tube 60 .be excessive to produce the desired results, then the parallel resistance 68 may be included and adjusted to provide the desired cathode resistance corresponding to the resistance 38 in Figure 1. The effective value of the cathode resistance for tube 30 is accordingly the parallelvalue of the plate impedance of the pentode 60 and the value of adjustable resistance 68. The cathode resistance 66 for the pentode 60 may be adjusted to vary the bias of tube 60 in order that the correct amount of direct curcuit arrangement shown and claim as new and desire to wide frequency yband may be accomplished. Furthcrmore, this operation is made possible without the introduction of any complicated circuit arrangement and without the necessity of providn ing an auxiliary high voltage source.

In actual-practice it has been found that the input resistance (i. e., the television pickup tube load resistance I6) may be chosen to have a value ranging from 50,000v ohms to as high as one megohm, and by merely making commensurate adjustments in the value of resistance 68, it is possible to obtain complete correction and constant gain over a frequency band of the order of 12 megacycles per ysecond'or higher regardless of the value of the particular input resistance.

Through the use of the present invention it is, therefore, possible to obtain picture signals of the desired amplitude from the output terminal 48 of the amplifier in order that a wide band of frequencies may be transmitted, and in order that the usual attenuation of the high frequency picture signals will not result.

I t is to ybe appreciated that the particular cirdescribed herein is not necessarily specifically applicable to the use of television pickup tubes, since the circuit arrangement. may ibe used in connection with any source of signals where a very wide frequency band is encountered. v

Although the present invention has been described in its preferred form in considerable detail, it is to beunderstood that various alterations and modifications may be made therein without departing from the spirit and scope thereof, and it isldesired that any and all such alterations and modifications be considered within the purview of the present invention, except as limited by the hereinafter appended claims.

Having now described my invention, what I have protected by Letters Patent is: y

1. A television imageAsignal amplifier for amplifying a wide band of frequencies extending from substantially zero to frequencies of the order of 12 to 20 megacycles per second comprising a signal terminal for supplying a wide frequency :band of image signals, a load impedance connected between the signal terminal and a point of fixed potential comprising parallelly connected resistance and capacitance elementsfa first amplifying means having input and output terminals, means to apply the image signals from the signal terminal to the input terminal of the first amplifying means to produce amplified image signals at the output terminal of said means, a second amplifying means comprising an electron discharge tube having a cathode, a control electrode and an anode, a resistance connected between said control electrode and'the point of fixed potential, means for coupling the output terminal of said vfirst amplifying means to said control electrode, a source of potential having one terminal positive with respect to the point of fixed potential and another terminal negative with respect to the point of fixed poand capacitance elements of the load in parallel with said cathode impedance, said cathode impedance having ra value substantially equal to the ratio of the impedance of the input circuit of the first amplifying means at the low frequency end of the band of image signals to the impedance of said input circuit at the high frequency end of the band of image signals, the product of the cathode impedance and.A its parallel condenser being substantially equal to the product of the resistance impedance, and an output circuit associated with the anode of said second amplifying means.

`2. A signal amplifier for amplifying a wide frequency band of signals extending from substantially zero to frequencies of the order of many megacycles per second comprising a source of signals having an output terminal for supplying such signals, a load impedance connected between the Signal output terminal and a point of fixed potential comprising a resistance and effectively parallelly'connected distributed capacitance elements, a signal amplifying'means includingan electron discharge tube having a cathode, a control electrode and an anode, a resistance connected between said control electrode and the point of fixed potential, means for coupling the source of signals to said control electrode, a source of potential having one terminal positive with respect to the point of fixed potential and another terminal negative with respect to the point of fixed potential, a load impedance connected between the positive terminal of the source of potential and said anode, a cathode impedance connected between the negative terminal of the source of potential and said cathode, a condenser effectively connected in parallel with said cathode impedance, said cathode impedance having a value substantially equal to the ratio of the effective impedance of the signal output terminal load impedance at the low frequency end of the band of signals to t/he effective impedance of the signal output terminal load impedance at the high frequency end of the band of signals, the product of the cathode impedance and its parallel condenser being substantially equal to the product of the load resistance and capacitance at the signal source output terminal, and an output circuit associated with the anode of said second amplifying means.

3. A television signal amplifier for amplifying a Wide frequency band of signals comprising a signal output terminal, for supplying the wide frequency band of signals, a first amplifying means having an input circuit andan output circuit, said input circuit including parallelly connected resistance and capacitance elements connected between the signal output terminal and a point of fixed potential, means to apply the signals from the signal output terminal to the input circuit of the first amplifying means to produce amplied signals in the output circuit of said means, a second amplifying means comprising an electron discharge tube having a cathode, a control electrode Vand an anode, a resistance connected between said control electrode and the point of fixed potential, means for coupling the output circuit of said first amplifying means to said control potential having positive and negative terminals electrode, a source of v means for connecting `a point along said source of potential to the point of fixed potential, a load impedance connected between the positive terminal of the source of potential and said anode, a cathode impedance including an electron discharge path having an electron emitter and an electron collector connected between the negative terminal of the source of potential and said cathode withthe negative terminal of `the source of potential connected Ato sa'id electron emitter, a condenser effectively connected in parallel with said cathode impedance, said electron emitter and electron collector constituting the only electron conducting path between the negative terminal of the source of potential and said cathode of the said second amplifying means, the product of the cathode impedance and its parallel condenser being substantially equal 4to the product of the input circuit resistance and capacitance elements, and an output circuit associated with the anode of said second amplifying means.

4. A television signal amplifier for amplifying a Wide frequency band of signals comprising an output terminal for supplying the wide frequency band of signals, an amplifying means having an input circuit, said input circuit including a resistance and an effectively parallelly connected capacitance, means to apply the signals from the output terminal to the input circuit of the amplifying means, said amplifying means including an electron discharge tube having a cathode, a control electrode and an anode, a resistance connected between said control electrode and a point of Xed potential, means for coupling the input circuit of said amplifying means to said control electrode, a source of potential having positive and negative terminals, means for connecting a point along said source of potential to the point of xed potential, a load impedance connected between the positive terminal of the source ol potential and said anode, a cathode impedance including an electron discharge path having an electron emitter and an electron collector connected between the negative `terminal of the source of potential and said cathode with the negative terminal of the source of potential connected to said electron emitter, a condenser effectively7 connected in parallel with said cathode impedance, the product of the cathode impedance and its parallel condenser being substantially equal to the product of the input circuit resistance and capacitance, and an output circuit associated with the anode of said tube. f

5. A television signal amplifier for amplifying a wide frequency band of signals comprising a source of signals having an output terminal, an amplifying means having an input circuit, said input circuit including a resistance and an effectively parallelly connected capacitance,means to apply the signals from the output terminal to the input circuit of the amplifying means, said amplifying means including an electron discharge tube having a cathode, a control elctrode and an anode, means for coupling the input circuit to said control electrode, a source of potential having positive and negative terminals, a load imelectron discharge pedance connected between the positive terminal of the source of potential and said anode, a cathode impedance including an electron discharge path having an electron emitter and an electron collector connected between the negativeterminal of the source of potential and said cathode, a condenser effectively connected in parallel with said cathode impedance, the prodcondenser being substantially equal to the product of the input circuit resistance and capacitance, and'an output circuit associated with the tube having a cathode, a control electrode andV an anode, an input circuit for said amplifying means including a resistance and effectively parallelly connected distributed capacitance elements, means for applying the signals: to the input circuit of said amplifying means, a source of potential having positive and negative terminals, a load impedance connected between the positive terminal of the source of potential and said anode, a4 cathode impedance connected between the negative terminal of the source of po-A tential and said cathode, said caiode impedance having a value substantially equal to the ratio of the effective impedance of the input circuit at the low frequency end of the band of signals to the effective 4impedance of the input circuit at the high frequency end of the band of signals, .a condenser effectively connected in parallel with said cathode impedance, the-product of the cathode impedance and its parallel condenser being substantially equal to the product of the input circuit resistance and capacitance elements, and an output circuit associated with the anode of said electron discharge tube.

7. A television picture signal amplifier for amplifying a wide frequency band of signals comprising an amplifying means including an electron discharge tube having acathode, a control electrode and an anode, an input circuit for said amplifying means including parallelly connected resistance and capacitance elements, means for applying the signals to the input circuit of said amplifying means, a source of potential having Vpositive and negative terminals, a load impedance cbnnected between the positive terminal of the source of potential and said anode, a cathode impedance including an electron emitter and an electron collector connected between the negative terminal of the source of potential and said cathode with the electron emitter connected to the negative terminal of the source of potential, a condenser effectively connected in parallel with said cathode impedance, said electron emitter and collector constituting the only electron conducting path between the negative terminal of the source of potential and said cathode, the product of the cathode impedance and its parallelly connected condenser being substantially equal to the product of the input circuit resistance and capacitance elements, and an output circuit associated with the anode of said electron discharge tube.

8.- A television picture signal amplifier for amplifying a wide frequency band of signals comprising an amplifying means including an electron discharge tube having a cathode, a control electrode. and an anode, an input circuit for said amplifying means including a resistance and an effectively parallelly connected capacitance, meansfor applying the signals tothe input circuit of said amplifying means, a source of potential having positive and negative terminals, a load impedance connected between the positive terminal of the source of potential and said anode, a cathode impedance including an electron emitter and an electron collector connected between the negative terminal of the source of pouct of the cathode impedance and its parallel u tential and said cathode with the electron emitter connected to the negative terminal of the source of potential, a condenser eifectively connected in parallel with said cathode impedance, the product of the cathode impedanceand its parallelly connected condenser being substantially equal to the product of the input circuit resistance and its parallelly connected capacitance, and an output circuit associated with the anode of said electron discharge tube.

9. `A television signal amplifier for amplifying a wide-frequency band of signals comprising an amplifying means including an electron discharge tube having a cathode, a control electrode and an anode, an input circuit for said amplifying means including a resistance and an effectively parallelly connected distributed capacitance, means for applying the signals to the input circuit of said amplifying means, a source of potential having positive and negative terminals, a load impedance connected between the positive terminal of the source of potential and said anode, a cathode impedance including an elecv second including an amplifying means having a,

tron emitter and an electron collector connected between the negative terminal of the source of potential and said cathode,V a condenser effectively connected in parallel with said cathode impedance, the product of the cathode impedance and its parallel condenser being substantially equal to the product of the input circuit resistance and its parallel capacitance, and an output circuit associated with the anode of said electron discharge tube.

10. An amplifier for amplifying a wide band of frequencies extending from substantially zero to frequencies of the order of many megacycles per second comprising an amplifying means including an electron discharge tube having a cathode, a control electrode and an anode, an input circuit for said amplifying means including parallelly connected resistance and capacitance elements, a source of potential having positive and negative terminals, a load impedance connected between the positive terminal of the source of p0- tential and said anode, a cathode impedance including an electron path having an electron emitter and an electron collector, means for connecting the electron collector to said cathode,

means for connecting the electron emitter to the negative terminal of the source of potential, a condenser effectively connected in parallel with said cathode impedance, the product of the cathode limpedance and its parallel condenser being substantially equal to the product of the input circuit resistance and capacitance elements, and an output circuit associated with said anode.

11. An amplifier for amplifying a wide band of 4frequencies extending from substantially rzero to frequencies of the order of many megacycles per second including an amplifying means having a cathode, a control electrode and an anode,` an input circuit for amplifying means including effectively parallelly connected resistance and capacitance elements, a source of potential having positive and negative terminals, a load impedance connected between the positive terminal of the source of potential and said anode, a cathode impedance including an electron discharge path having an electron emitter and an electron collector, means for connecting the electron collector to said cathode, means for connecting the electron emitter to the negative terminal of the source of potential, a condenser effectively connected in parallel with said cathode impedance, the product ofthe cathode impedance and parallel concathode, a control electrode and an anode, an input circuit for said amplifying means including effectively parallelly connected resistance and capacitance elements, a source of potential having positive and negative terminals, a load impedance connected between the positive terminal of the source of potential and said anode, a cathode impedance including an electron discharge path having an electron emitter and an electron collector, means for connecting the electron collector to said cathode, means for connecting the electron emitter to the negative terminal of the source of potential, a condenser effectively connected in parallel with said cathode impedance, said electron discharge path constituting the only electron conducting path beween the negative terminal of the source of potential and said cathode, and anoutput circuit associated with said anode. K

13. An amplier circuit including an electron discharge tube having a cathode, a control electrode and an anode, means including a resistance for connecting the control electrode to a point of fixed potential, an input circuit associated with said control electrode, a source of potential having positive and negative terminals, means for connecting a point along said source of potential to the point of fixed potential, a load impedance connected between said positive terminal of the source of potential and said anode, an eifectively high impedance cathode element comprising an electron emitter and an electron collector, means fo-r connecting the electron collector to said cathode, means for connecting the electron emitter to the negative terminal of the source of potential, and an output circuit associated with said anode.

14. An amplifier circuit including a tube having a cathode, a control electrode and an anode, an input circuit associated with said control electrode, a source of potential having positive and negative terminals, means including a resistance for connecting said control electrode to a point along said source of potential, a load impedance connected between said positive terminal of the source of potential and said anode, an effectively Y high impedance cathode circuit including an electron emitter and an electron collector, means for connecting the electron collector to said cathode, means for connecting the electron emitter to the negative terminal of the source of potential, and an output circuit associated with said anode.

15. An amplifier circuit including an amplifying tube having a cathode, a control electrode and an anode, an input circuit connected to said control electrode, a source of potential having positive and negative terminals, a, load impedance connected between the positive terminal of the source of potential and said anode, an electron discharge tube having a cathode, a control electrode and an anode, means for connecting the anode of the electron discharge .tube to the cathode of the amplifying tube, means for connecting the cathode of said electron discharge tube to the negative terminal of the source of potential, means to maintain a predetermined bias potential between the control electrode and cathode of said electron discharge tube, and an output circuit associated with the anode of said amplifying tube.

l 16.- An amplier circuit including an amplifying tube having a cathode, a control electrode and an anode, an input circuit connected to said control electrode, a source of potential having positive and negative terminals, a load impedance connected between the positive terminal of the source of potential and said anode, an electron discharge path including a cathode, a. control electrode and 10 an anode, means for connecting the anode of the electron discharge path -to the cathode of the amplifying tube, means for connecting the cathode of said electron discharge path to the negative terminal of the source of potential, means to vary the bias potential between the control. electrode and cathode of said electron discharge path, and an output circuit associated with said load impedance.

O'I'TO H. SCHADE.