US2368052A - Electric translating system - Google Patents

Description

Jan. 23, 1945. w. H. UNGER 2,368,052

ELECTRIC TRANSLATING SYSTEM Filed April 29, 1941 2 Sheets-Sheet l INVENTOR w imam 2Q u 7a ATTORNEY Patented Jan. 23, 1945 ELECTRIC TRAN SLATING SYSTEM William H. Unger, New York, N. Y., assignor, by

mesne assignments, to Patents Research Corporation, New York, N. Y., a corporation of New York Application April 29, 1941, Serial No. 390,906

16 Claims.

The present invention relates to electric translating devices more particularly to a simple and efficient circuit arrangement for converting minute changes of electrical reactance, including both inductance and capacitance, into substantially large amplitude changes of current or potential.

An object of the invention is to provide a converting system of this character which is both simple in design as well as stable and eflicient in operation.

A more specific object is the provision of apparatus for converting minute changes of electric capacitance between metallic elements spaced by a dielectric into large amplitude changes of electrical energy.

A further object is to provide a simple and highly efiicient electrostatic pick-up system for faithfully reproducing phonographic sound records.

These and further objects and aspects of the invention will become more apparent from the following detailed description taken with reference to the accompanying drawings forming part of this specification and wherein:

Figure 1 is a basic circuit diagram of a translating system embodying the principles of the invention,

Figures 2 and 3 are theoretical diagrams explanatory of the function and operation of the circuit according to Figure 1,

Figure 3a shows a modification of the circuit according to Figure 1,

Figure 4 illustrates schematically a tone arm and electrostatic pick-up device for reproducing sound records employing a translating system according to the invention,

Figure 5 is an enlarged front view of the pickup head shown in Figure 1,

Figure 6 is a complete circuit diagram of a re producing system embodying features of improvement for use in electrostatic pick-up or translating devices,

Figure 7 is a graph explanatory of the improvements of Figure 6, and

Figures 8 and 9 are illustrative circuit diagrams for modified translating or reproducing systems embodying the principles of the invention.

Like reference characters identify like parts throughout the different views of the drawings.

Referring to the drawings, Figure 1, there is shown an electron discharge tube l0, provided with a cathode I l of any suitable type such as an indirectly heated or equi-potential cathode as grid 13 enclosed by a screen grid [4, a suppressor grid I5 and an anode or plate IS. The suppressor l5 may be omitted or connected to the cathode internally or externally of the tube if a standard tube is used. Control grid [2 is connected to the cathode or ground through a parallel tuned circuit comprising an induction coil I1 shunted by a condenser I8 and control grid I3 is similarly connected to the cathode or ground through a parallel tuned circuit comprising an induction coil [9 shunted by a condenser 20. One or both of the tuned circuits 11-48 or l920 may be replaced by a piezo-electric crystal suitably by-passed for direct current by a high ohmic resistance. The screen grid l4 and plate l6 are connected to suitable high steady potential sources indicated by the plus symbols and bypassed to ground or cathode in a known manner for alternating currents by means of condensers 2| and 22, respectively. The grids I2 and I3 are suitably negatively biased with respect to the cathode by the provision of a condenser shunted {esidstor 23 inserted in the cathode-to-ground In the circuit aforedescribed, if the two tuned circuits fll8 and |9-2U are resonant to the same frequency, the tube will act as an oscillator and generate an alternating current of the same frequency as the resonant frequency of the circuits. For further details of this oscillator which is characterized by the fact that no direct current supply potential is applied to any oscillating electrode and other advantages such as high stashown, a first control grid l2, 2. second control bility, etc., reference is made to U. S. patent application of Hemy M. Bach, Serial No. 353,640, filed August 22, 1940, entitled Discharge tube oscillator, assigned to the same assignee as the present application.

In practice it was found that at a frequency of about three megacycles either of the tuned circuits |1l8 or Ill-20 could be shunted by a resistance such as shown at 24 of as low a value as 10,000 ohms and the circuit would still oscillate, provided that the coils I! and H! were of a fairly high Q and the condenser losses were negligible. If the resistor 24 is omitted and the operation of the circuit considered as an oscillator, it is found that, if the resonant frequency of both tuned circuits is the same, the vectors representin the :voltages c1 and e2 across the tuned circuit are in phase quadrature and the feedback voltage as developed across circuit l'I-l8 by e2 due to space charge coupling between the circuit l920 and H-l8 is in phase with the voltage 61 across the latter as shown in the vector diagram, Figure 2.

Considering now, in.an attempt to determine the operating conditions of the circuit, that the phase of the voltage er is caused to vary with respect to the voltage e1, it is possible to show mathematically that if the voltag er has a component which is in phase with the voltage e1, then the two voltages will satisfy the conditions of oscillation as long as the losses in the tuned circuits are supplied by the D. C. source, that is the potential of the screen grid supply. A

These conditions are further understood by reference to the vector diagram shown in Figure 2 representing the case of a relative phase angle between the voltage 61 and e'r. The voltage 61 for a given angle 0 will build up to a value such that, if it were to increase further, the added losses would make the total losses greater than could be supplied by the operating current source. Since the operation of the circuit is on the linear portion of the tube operating characteristic, the grids l2 and I3 being at negative potentials with respect to the cathode, this point will be reached when the voltage on grid 12 is great enough to cause a grid current to flow. As a result, the amplitude will be limited by the bias applied to the tube. When the phase shift between er and e'r becomes very great, or if 0 approaches 90, then the amplitude of the component e": in phase with or will become quite small and the direct current source will no longer be able to supply enough power to overcome the losses, inasmuch as the voltage e": is effective in converting the direct current into alternating current. -It might be thought at first that for larger phase angles 0 the amplitude of the oscillations will just become less and therefore the losses decrease to a point where the direct current source can still supply the necessary power. However, 'since the tube is operating on the linear portion of its characteristic, oscillations'if they take place at all will build up to the point where the grid begins to draw "current. Thus, there is found to be a critical phase. shift beyond which oscillations cannot take place wit-h a given coil and condenser combination as has been confirmed by experiments and tests-carried-out by applicant.

As is well known, if two control grids placed at different points of an electron discharge stream are excited by voltages of the same frequency but varying relative phase, the average value of the discharge current will vary as a function of the relative phase departure between .the grid control voltages. It is possible therefore in the circuit aforedescribed by varying the phase angle between the two grid voltages er and eg by detuning one circuit with respect to the other circuit to obtain corresponding amplitude changes of the steady or average plate current flowing through the output circuit of the tube. By using the highest possible Q value for the coils, the oscillations will take place over a wide range of variation of the hase angle 0 and as a result the D. C. or average plate current of the tube will be subjected to substantial variations by controlling the tuning of one of the circuits such as by varying the efiective tuning capacitance or inductance of the circuit in any suitable manner. Experiments have shown that the circuit operates as expected and a typical curve representing average or quiescent plate current i as a function of the capacitance of either condenser l'8 or is shown at 'b in Figure 3. This curve exhibits the discontinuities expected where the circuit suddenly goes out of oscillation if the phase angle variations exceed a given range a: of variation of the capacitance C as shown in the diagram. For the sake of comparison there is shown in dotted lines an operating curve a obtained by the same circuit when operated as a discriminator in nonoscillating condition and with the input grid 12 excited from a separate oscillating source as described in detail in U. S. Patent No. 2,208,091. The present circuit has the advantage over the latter that, without the necessity of a special exciting source, substantially the same or even greater plate current variations are obtained for a given capacitance change thereby making this converter superior and especially suited where bulk and weight are to be reduced to a minimum. It will be evident that instead of varying the capacity of either of the tuned cir cuits 11-18 r Ill-2D variations of the efiective inductance of the circuits may be similarly translated into corresponding plate current changes in substantially the same manner as described hereinbefore. A similar variation as shown in Figure 3 but in the opposite direction is obtained of the average screen current by deelement in either of the tuned circuits l'l-IB or [9-20 so as to form an effective tuning element of the circuit, the invention will now be described in detail as applied to an improved type of electrostatic phonograph or any other pick-up or capacitance translating device characterized both by a greatly simplified design as well as high conversion efllciency and fidelity of the sound reproduction.

In a vibrating system wherein the velocity of the vibratory element varies inversely as the frequency is increased for a constant driving force, the system is said to be mass controlled. Similarly, if the vibratory element has a velocity which is independent of the frequency but dependent only upon the force causing the vibration, the system is referred to as resistance controlled, and finally, if the maximum deflection of the vibratory element from the normal or mean position is proportional to the amplitude of the force causing the vibration then the system is said to be stifiness controlled.

A mass controlled system is expressed by Newton's law of motion according to the following equation:

F=ma (1) wherein F is the force acting on the system at any moment, m is the mass of the system, and (1 represents the acceleration at the instant under consideration.

Similarly a resistance controlled system is expressed by the following equation:

F=k1v (2) wherein F is again the force, 701 is a constant of proportionality and 1) is the velocity at the instant under consideration.

Finally, a "stiffness controlled system is expressed by the following equation:

wherein F is again the force, k2 a constant of proportionality and :1: the distance that the element has moved from the normal or mean position at the instant under consideration. This latter equation corresponds to Hookes law of springs which says that the force tending the restore a spring to its original shape is proportional to the amount that the spring has been stretched.

In any normal vibratory system the above three terms have to be applied simultaneously although one or more may be small in magnitude relative to the others and may be neglected in a first approximation. Thus, the total force acting on a system is balanced by the three effects stated above which add up to give an equal and opposite reaction on the force causing the motion in accordance with the resultant equation as follows:

F=ma+7c1o+k2w (4) This equation can also be written as follows:

F=m%j+aj +a$ (5 wherein g (it being the second derivative of the distance moved with respect to time represents the acceleration and is the rate of change of distance or instantaneous velocity.

Considering the ordinary phonograph pick-up in which the grooves in a record cause the stylus or needle to vibrate which in turn transmits the vibrations to some elements, usually a crystal or coil serving to convert the vibrations of the mechanical system into corresponding electrical changes, it is seen that the system can be analyzed on the basis of the equation given above if there is substituted for m in all the equations a term representing the moment of inertia of the system with respect to its vibrating axis rather than the actual mass of the vibrational elements. At low frequencies the first two terms on the right-hand side of Equation 5 can be neglected, at least in comparison with the magnitude of the third term and accordingly the system will be stiffness controlled. At very high frequencies the system becomes mass controlled since the velocity and deflection will be very small in comparison to the maximum acceleration so that the first term on the righthand side of Equation 5 will become most important. Over a certain range of medium frequencies the second derivative term will cancel out the term containing only a: and the middle term on the right-hand side of Equation 5 will be most important and accordingly the system will be resistance controlled.

In ordinary practice the response of the pickup and its action on the record are most likely to be unsatisfactory at the high end of the audio spectrum. If the force required to drive the needle is very high, the needle may not follow the exact shape of the groove and distortion will result and the higher frequency may be worn off the record. It is obvious, therefore, that it is desirable to make the vibrating system stiffness or resistance controlled up to as high a frequency as possible. In the recording of voice and music most of the energy in sound is contained in the frequency range of about 250 to 2500 cycles per second, although there may be instantaneous peaks at lower frequencies of very'high energy content. Above 2500 cycles the energy falls off quite rapidly, although these frequencies are essential to the faithful reproduction of speech and music. If the mechanical side of the pickup system can be madesuch that the change or transition to mass control takes place above 2500 cycles, then the force required for a given output will not become excessively higher than the force required for the same output at medium frequencies, until a frequency of say 7500 to 10,000 cycles is reached. At these frequencies the energies will be so small that the forces cannot become too great in any event.

Referring to Figures 4 and 5, there is shown schematically an improved electrostatic pick-up system designed in accordance with the foregoing considerations. The vibrating element takes the simple form of a plate or bar 26 of plastic I or any other suitable elastic material such as Celluloid, cellulose acetate, or even metal integral with or secured to the pick-up head 25' attached to the tone arm 25. The latter is pivoted at 26' in any suitable manner. The vibrating element if consisting of insulating material has a metallic coating or covering 21 applied to one side thereof in any suitable manner such as a foil of aluminum or any other suitable metal. A wire or lead 3| makes contact to the foil by way of a terminal screw 30 and the foil serves as one electrode of an electrical condenser, the other electrode 28 of the condenser being constituted by a substantially stiff metal plate also secured to the pick-up head 25' and whose spacing relative to the average position of the foil 26 is made adjustable by the provision of an adjusting screw 33 engaging the threaded bore of a supporting plate 32 secured to the head 25. A needle or stylus 35 provided with a diamond or sapphire point and held by the bar 26 follows the shape of the grooves in the record 36 ing the distance between the metal foil or layer 21 and plate 28, that is varying the capacitance in accordance with the vibrations of the needie 35.

The capacitative pick-up in Figure 4 is shown in approximate natural dimension and it is found that the capacitance variations obtained are extremely small and of the order of 1/100 of l mmfd. so as to require a highly sensitive and stable converting system to obtain an output voltage of sufiicient magnitude.

Referring to Figure 6, there is shown a circuit diagram for a pick-up system according to Figures 4 and 5 utilizing a convertor circuit according to Figure 1 which was found to produce satisfactory results in practice. In the arrangement shown, the parallel resonant circuit i1 l8 of Figure 1 is replaced by a series-parallel resonant of coil I1 is no longer connected to ground for direct current. This resistor is made as high as possible without introducing excessive hum and instability into the circuit. A value of .1 to 5 megohms has been found satisfactory in practice. The plate circuit of the tube includes a suitable load impedance such as a resistor which may be replaced by an audio choke or transformer and serves to develop output voltage varying in accordance with the capacity changes of the pickup device and applied to a further amplifier or output device to be connected to output terminals 0-0 by way of coupling condenser 44. The elements I! and 40 are advantageously mounted directly in the pick-up head adjacent to the pickup capacity 4! to form a unit 49 which is connected to the converting unit 48 through a pair of connecting wires 42 passing through the tone arm 25.

The purpose and function of the circuit l'l.|8404l will be explained in the following. Over a certain range of frequencies the circuit |'|-i840-4i has an impedance characteristic somewhat the same as that of a straight parallel resonant circuit as shown in dotted lines, curve -c in Figure '7, the characteristic of the series parallel circuit bein represented by the solid line curve d. The advantage of using a series-parallel circuit in place of a straight parallel resonant circuit is due to the fact that the impedance of coil I! is now replaced by an impedance which isthe difference of two impedances, that is the impedance of coil l1 and the capacitance of condensers 40 and 41 in parallel. In this manner, there is obtained a small impedance which is the difference of two substantiall larger impedances whereby a small percentage change in-one of these impedances will result in a large percentage change in the difference if the other impedance is held constant. The reason for using such an arrangement will be evident when considering the relative magnitudes of the various capacities in the grid circuits. Supposing that the circuit were used as shown in Figure 1 and the variable capacity between elements 2'! and 28 were made i a part of condenser 20 which latter will be .made up entirely or in part of the capacity-of the con necting line 42 in Figure 6 if the tube was placed external of the pick-up. As is understood, this condition of an undesirable capacity of the line 24 in addition to the lumped capacities i8 and 4! exists if the line is of the non-resonant type, that is, if it is short compared with the wave length of the operating frequency used. In this case any capacitance variation in the pick-up element would be swamped by the large capacity of the line. By using a series parallel arrangement as shown in Figure 6, the capacity It can be quite large and it is still possible to resonate the im pedance of the coil with a large shunt capacity. In this manner any small percentage variations of the pick-up capacitance instead of being re: duced or swamped by the shunting effect of a much larger capacity are now magnified by being resonated with a series inductance.

Referring to Figure 8 there is shown an alternative circuitfor an electrostatic pick-upsystern embodying the principles of the invention. According to this modification the pick-up capacity serves to frequency modulate a small oscillator which is advanta geously mounted directly in the pick-up head and tone arm adjacent to the pickup condenser such as indicated in dotted lines in Figure 4. This oscillator in the example shown comprises a three element vacuum tube 60 of the 2,,soaoa2 known miniature or bantam type and a grid tank or oscillating circuit comprised of an induction coil 6| shunted by a variable condenser 62, the latter representing the pick-up condenser. The plate circuit of the tube is regeneratively coupled with the grid circuit through a feedback 'or tickler coil 63 to maintain sustain oscillations at a frequency determined by the resonant frequency of the circuit '6l-li2. Any other type of oscillator circuit may be used for the purpose of the invention as is understood. The oscillations will therefore be frequency modulated in accordance with the variations of the grooves on the record being reproduced. The frequency modulated oscillations are transmitted by way of coupling coil 62' and connecting wires 68 to a fre-' quency discriminator or converter collectively designated by 69 and being of substantially the type as disclosed by U. S. Patent 2,208,091 above mentioned. This discriminator in a known manner comprises an electron discharge tube including a pair of control electrodes 5| and 52 spaced from each other by a positively biased screen grid 53 and 'an output electrode or plate 54. The frequency modulated oscillations produced by the pick-up are impressed upon the grid 5| and cathode by way of a resonant input transformer 55 while a further resonant circuit 56 tuned to the average or center frequency of the oscillations generated by the circuit til-J32 in the absence of modulation is connected to the further control grid 52 and cathode. As described in the above mentioned patent, the tuned. circuit 55 which is substantially exteriorly decoupled from the remaining parts of the system such as b suitable electro-magnetic shielding will be excited by the impressed input potential on the grid 5| by space charge coupling of grid 52 with the electron stream at a varying phase depending on the sense and magnitude of the departure of the impressed frequency from the resonant frequency circuit 56. As a result of the dual control of the electron discharge stream by the grids 5| and 52 thus excited by the same frequency but at varying relative phase, the steady or quiescent plate current will include a component varying substantially in proportion to said phase variations or in turn in proportion to the oscillating frequency. This plate current by the provision of a suitable load impedance such as resistor 58 is utilized to develop an output voltage which varies in accordance with the speech or sounds being reproduced and may be further amplified or applied to any output device to be connected to terminals 0-0 by way of coupling condenser 51.

In case of A. C. operation tube 50 is preferably of the indirectly heated type as shown and a suitable rectifying system 56 and smoothing filter 61 connected to the heating circuit through a potential divider 65 is provided to produce the necessary direct heating current for the oscillator tube 50. The plate supply is preferably provided bya common source such as a battery or rectifier inwhich case four connecting wires will be required between the oscillator and the converter 69 in the manner shown. The mounting of the oscillator in the pickup head and/or tone arm has the advantage of reducing the effect of the stray capacities across the pick-up condenser 62 to a minimum and making the percentage variationin the tuning capacity as high as possibler According to practical tests made the resonant frequency of the arm or bar holding the -needle was approximately 2000 cycles, .that is well above the usual resonant frequencies of ordinary pickups. A small amount of damping was used to reduce the resonant peak. This damping may be of the usual damping materials. A vinyl resin used as damping material and applied in various Ways was found to give satisfactory results. The amount of damping to be applied is so small that practically any small amount of damping material applied to some part of the bar 26 will very effectively dampen out any small eaks in the resonant characteristic. In practice, the resonant frequency of the vibrating arm could be raised to at least 4000 cycles by the use of suitable materials. The most suitable material can easily be determined by knowing the elastic limit of the material, the modulus of elasticity and its density. The best material would have the highest modulus of elasticity and elastic limit for a given density. For instance, nylon or other recently developed plastics such as Lucite, Tenite, or the like will give good results for this purpose. However, ordinary Celluloid or resilient metal has been found entirely satisfactory for ordinary use.

If the average gap of the variable pick-up capac ty is made very small then the sensitivity will become relatively high but the distortion will be excessive. Using the circuit of Figure 8, the sensitivity can be made comparable to that of ordinary pick-ups, that is the deflection of .001" will give an output of approximately one volt and the second harmonic distortion will be approximately 2% at this output voltage. This is only the distortion inherent in the pick-up that is the distortion in the output voltage assuming a sine wave deflection of the needle point. In practice the needle will not follow the groove shape exactly which is a source of distortion existing in all pick-ups and can only be eliminated by using a groove and needle point of microscopic dimensions. The complete oscillator when using a miniature or bantam size tube and variable capacitor assembly can easily be made to fit into a space of square and about 1 /2 to 2" lon as indicated in dotted lines in Figure 4. A four wire cable is brought out through the tone arm 25 but since the maximum plate voltage for miniature tubes is 45 volts and the losses in the high frequency lead can be quite high without impairing the operation, the cable can be made quite thin and flexible. It is advisable to provide a bypass condenser for the plate of the oscillator as large as possible and to mount it in the arm just back of the pick-up head.

\ Referring to Figure 9 there is shown an alternative circuit arrangement for an electrostatic pick-up system according to the invention. According to this embodiment an oscillator of fixed or constant frequency is utilized combined with a discriminator tube 50 and serves to excite one of the control grids, in the example shown the grid 5| near the cathode. Thevariable pickup capacitance is associated with the phase discriminating circuit connected between the other control grid and cathode whereby in turn due to the combined efiect of the gridipotentials on the electron stream the capacitance variations are transformed into corresponding amplitude changes as described in the above mentioned U. S. patent.

In the example shown, a crystal controlled oscillator is provided comprising a triode H, a re sistance shunted crystal l2 connected to the grid and cathode thereof and a parallel resonant circuit 13 inserted in the platecircuit of the tube in a manner well known and being in coupling relation with a grid coupling coil 14. The phase discriminating circuit connected to the other control grid 52 comprises a condenser 15 shunted by a series tuned circuit comprised of an induction coil 16, the variable capacitance element 11 of the pick-up being shunted by a fixed condenser 18 to eliminate the effect of the capacity of connect ing leads 80 between the pick-up head and con verter in substantially the same manner a described in connection with Figure 6. The high frequency circuits are carefully decoupled by means of shields BI and 82 to prevent interaction and spurious phase shifts liable to affect the accuracy and stability of the converter. The plate circuit of tube 50 includes a load resistance 58 and coupling condenser 51 for developing output voltage.

It will be evident from the foregoing that the invention is not limited to the specific circuits. arrangement of parts and details shown and disclosed herein for illustration, but that the underlying thought and principle of the invention will be susceptible of numerous variations and modifications coming within the broader scope and spirit of the invention as defined in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a limiting sense.

I claim:

1. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid, and a second control electrode arranged substantially in the order named, a source of high steady potential con nected to said accelerating grid and cathode, first resonant impedance means connected to said first control electode and cathode, second resonant impedance means connected to said second control electrode and cathode toproduce sustained self excited oscillations,- having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode,

' the resonating frequency of one of said impedance means being variable with respect to the resonating frequency of the other impedance means, an output circuit to return the electron space current to said cathode, and means operatively associated with said output circuit for developing energy having an amplitude varying in proportion to the relative departure of the resonating frequency of one of said impedance means from the resonating frequency of the other impedance means.

2. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid, and a second control electrode substantially arranged in the order named, a source of high steady potential connected to said accelenating grid and cathode, first and second resonant impedance means connected to said first and second control electrods respectively, and said cathode to produce self-excited sustained oscillations having a frequency determined by the resonating'frequencies of said'iin pedance means superimposed upon the steady electron space current emitted from said cathode, the resonating frequency of one of said impedance means being variable with respect to the resonat ing frequency of theother impedancemeans, an output circuit to return the electron space current to said cathode, and load impedance means in said output circuit adapted to develop output energy having an amplitude varying proportionately to therelative departure of the resonating frequency of. one of said impedance means from the resonating frequency of the other impedance means.

3'. In a translating circuit, an electron. discharge tube provided with a cathode-,a first control electrode, an accelerating grid. and. a second control electrode arranged substantially in. the order named, a source of high steady potential. connected, to said accelerating grid and, cathode, a parallel tuned circuit comprising capacitative and inductive reactance elements connected to one of said control electrodes and said cathode, further resonant impedance means-connected to the other control electrode and. cathode, the resonant frequency of said impedancemeans being related to the. resonant frequency of said parallel tuned circuit to cause self-excited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposedv upon. the steady electron space current a emitted from said cathode, at least one of. the elements of. said tuned circuit being, subject to variations of its reactance thereby relatively de tuning said circuit with. respect. to said impedance means, an output circuit to, return the. electron space current to said cathode, and. means operatively associated with said output circuit to develop energy having an: amplitude varying substantially in proportion to said reactance variations.

4. In a. translating circuit, an electron discharge tube provided with a cathode, afirst control electrode, an accelerating grid and a second control electrode arranged substantially in the order named, a source of high steady potential connected to said accelerating grid and cathode, means for substantially negatively biasing both said control electrodes with respect to said accelerating grid, to produce a concentrated space charge adjacent to said grid, a parallel tuned resonant circuit comprising capacitative and inductive reactance elements connected to one of said control electrodes and said. cathode, further resonant impedance means connected to the other control electrode and cathode, the resonant frequency of said impedance means being related to the tuning frequency of said circuit to cause self-excited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode, the resonant frequency of said circuit being variable relative to the resonant frequency of said impedance means, an output circuit to return the electron space current to said cathode, and means operatively associated with said output circuit to develop energy having an amplitude varying as a function of the tuning variations of said resonant circuit.

5. In a translating circuit; an electron discharge tube provided with a cathode, a first control electrode, an. accelerating grid and a second control electrode arranged substantially in the: ordernamed, a.v source of high steady potential connected to said accelerating grid and cathode, means for maintaining both said control electrodes at a substantially negative potential with respect to said accelerating grid to produce a concentrated electron space charge adjacent to said grid, a parallel tuned circuit comprising an inductance andcondenser subject to capacity variations connected to one of said control electrodes and said cathode, further resonating impedance means connected to the other control electrode and cathode, the resonant frequency of saidtuned circuitand theresonant frequency of said impedance means being related to cause selfexcited sustained oscillations having afrequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted fromsaid cathode, an output circuit to returnthe electron space current to said cathode, and means operatively associated with said output circuit to develop energy having an amplitude varying substantially in proportion to the capacity variations of said condenser.

6. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid and a second control electrode arranged substantially in the order named, a source of high steady potential connected to said accelerating grid and said cathode, a parallel tuned circuit comprising an inductance and a condenser connected to one of said control electrodes and said cathode, a resistance shunting said circuit, further resonating, impedance means connected to the other control electrode and cathode, the resonating frequency of said circuit beingv related to the resonating frequency of said impedance means to cause self-excited; sustained oscillations havingv a frequency determined by the resonatin frequencies of said impedance means superimposed upon the steady electron space current emitted from saidv cathode, an output circuit to return the electron space current to said cathode, and means operatively associated with said output circuit. to develop energy having anamplitude varyingas a function of the relative tuning departure of said circuit from the resonating frequency of said impedance means.

7. In a translating circuit, an electron discharge tube provided with a cathode, a. first control electrode, an accelerating grid and a second control electrode arranged substantially in the order named, a source of high steady potential connected to said accelerating grid and cathode, means for substantially negatively biasing both said control electrodes with respect tosaid accelerating grid toproduce a concentrated space charge adjacent to said accelerating grid, aseriesparallel resonant circuit comprising, a first condenser shunted by aninductance in series with a variable condenser connected to one of said controlelectrodes and said cathode, an impedance permeable to direct current shunting said resonant circuit, further resonating impedance means connected to said other control electrode and cathode, the resonant frequency of said circuit and the resonating frequency of said impedance means being related to cause self-excited sustained oscillations. having a frequency detennined by the resonating frequencies of said impedance means superimposed upon the steadyelectron space current emitted fromsaid cathode, an output circuit to return the electron space current to said cathode, and, means operatively associated with said output circuit to develop. energy having an amplitude varying; substantially in proportion to capacity variations of said va-xiablecondenser.

8. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid and a second control electrode arranged substantially in the order named, a source of high steady potential connected to said accelerating grid and cathode. means for substantially negatively biasing both said control electrodes with respect to said accelerating grid to bring about a concentrated electron space charge adjacent to said accelerating grid, a series-parallel resonant circuit comprising a firstrelatively large condenser shunted by an inductance in series with a relatively small variable condenser", said resonant circuit being connected to one of said control electrodes and said cathode, an impedance permeable to direct current shunting said resonant circuit, further resonating impedance means connected to said other control electrode and cathode, the resonating frequencies of said resonant circuit and said impedance being related to cause self-excited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode, an output circuit to return the electron space current to said cathode, and means operatively associated With said output circuit to develop en ergy having an amplitude varying substantially in proportion to the capacity variations of said variable condenser.

9. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid, 2. second control electrode and an anode arranged substantially in the order named, means for applyin high steady operating potentials to said accelerating grid and anode, further means for substantially negatively biasing said control electrodes with respect tosaid accelerating grid to bring about a concentrated electron space charge adjacent to said accelerating grid, first and second resonant impedance means connected to said first and second control electrode, respectively, and said cathode to cause self-excited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode, the relative resonating frequency between said first and second impedance means being variable, an output circuit connected to said anode, and means operatively associated with said output circuit to develop energy having an amplitude varying substantially in proportion to the relative frequency departure of said first from said second impedance means.

10. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid, a second control electrode and an anode arranged substantially in the order named, means for applyin high steady operating potentials to said accelerating grid and anode, further means for substantially negatively biasing both said control electrodes with respect to said accelerating grid to bring about a concentrated electron space charge adjacent to said accelerating grid, a parallel tuned circuit comprising capacitative and inductive reactance elements connected to one of said control electrodes and said cathode, further resonating impedance means connected to said other control electrode and cathode, the tuning frequency of said circuit being related to the resonating frequency of said impedance means to produce selfexcited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode, the reactance of at least one of the elements of said tuned circuit being variable thereby relatively detuning said circuit with respect to said impedance means, an output circuit connected to said anode and cathode, and load means in said output circuit adapted to develop energy having an amplitude varying substantially in proportion to the variations of said variable reactance element.

11. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid, a second control electrode and an anode arranged substantially in the order named, means for applying high steady operating potentials to said accelerating grid and said anode, further means for substantially negatively biasing both said control electrodes with respect to said accelerating grid to bring about a concentrated electron space charge adjacent to said accelerating grid, a parallel tuned circuit comprising a condenser subject to capacity variations and an inductance connected to one of said control electrodes and said cathode, resonating impedance means connected to the other control electrode and cathode, the tuning frequency of said circuit being related to the resonating frequency of said impedance means to produce self-excited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode, an output circuit connected to said anode, and load impedance means in said output circuit adapted to develop energy having an amplitude varying proportionately to the capacity variations of said condenser.

12. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid, a second control electrode and an anode arranged substantially in the order named, means for applying high steady operatin potentials to said accelerating grid and anode, further means for substantially negatively biasing both said control electrodes with respect to said accelerating grid to bring about a concentrated electron space charge adjacent to said accelerating grid, 2, series-parallel resonant circuit comprising a first condenser shunted by an inductance in series with a condenser subject to capacity variations, said resonant circuit being connected to one of said control electrodes and said cathode, an impedance permeable to direct current, shunting said resonant circuit, further resonant impedance means connected to the other control electrode and said cathode, the tuning frequency of said circuit being related to the resonating frequency of said impedance means to produce self-excited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode, an output circuit connected to said anode, and load impedance means in said output circuit adapted to develop energy having an amplitude varying substantially in proportion to the capacity variations of said variable condenser.

13. In a translating circuit, an electron discharge tube provided with a cathode, a first control electrode, an accelerating grid, a second control electrode and an anode arranged substantially in the order named, means for applying high steady operating potentials to 'said accelerating grid and anode, further means for substantially negatively biasing both said control electrodes with respect to said accelerating grid to bring about a concentrated electron space charge adjacent to said accelerating grid, a series-parallel tuned resonant circuit comprising a comparatively large condenser shunted by an inductance in series with a comparatively small condenser subject to capacity variations, said resonant circuit being connected to one of said control electrodes and said cathode, an imped'- ance permeable to direct current shunting said resonant circuit, further resonant impedance means connected to said other control electrode and said cathode, the tuning frequency of said resonant circuit being related to the resonating frequency of said impedance means to cause selfexcited sustained oscillations having a frequency determined by the resonating frequencies of said impedance means superimposed upon the steady electron space current emitted from said cathode, an output circuit connected to said anode and cathode, and load impedance means in said output circuit adapted to develop output energy having an amplitude varying substantially in prportion to the capacity variations of said condenser.-

14. A resonant circuit comprising a non-resonant two-wire transmission line .having a selfcapacity forming at least part of the capacitive reactance of said circuit, an induction coil and varying capacitance in series and connected across one end of said line to form a combined inductive reactance in parallel to and resonating with said capacitive reactance to result in a desired resonating frequency of said circuit, and a utilization circuit connected to the opposite end of said line.

15. A resonant circuit comprising a non-ream nant two-wire transmission line having a selfcapacity forming at least part of the capacitive reactance of said circuit, an induction coil and condenser in series and connected across one end of said line to form a combined inductive react: ance in parallel to said capacitive reactance,'a relatively small varying tuning capacitance in parallel to said first condenser for controlling the resonating frequency of said circuit, and a utiliza: tion circuit connected to the opposite end of said line.

16. A parallel-tuned resonant circuit comprls ing a non-resonant two-wire transmission line, a condenser connected across one end of said line and forming the capacitive branch of said circuit together with the self-capacity of said line, an inductive reactance branch for said circuit connected across the opposite end of said line and comprising an induction coil in series with a varying capacitance to form a resultant inductive reactance resonating with said first condenser and said line to obtain a desired resonating frequency of said circuit, and a utilization circuit connected to said first mentioned end of said line.

WILLIAM H. UNGER.

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