462,530

PATENT SPECIFICATION

Application Date: July, 8, 1935. No. 19480/35.

" " " Sept. 9, 1935. No. 25070/35.

" " " Dec. 5, 1935. No. 33805/35.

Complete Specification Left: July 6, 1936.

(Under Section 16 of the Patents and Designs Acts, 1907 to 1932.)

Specification Accepted: March 8, 1937.

------------------------

PROVISIONAL SPECIFICATION

No. 19480 A.D. 1935.

Improvements in or relating to Electric Circuits for Reducing the Effective Shunt Capacity introduced by Circuit Elements such as, for example, Electric Batteries

I, ALAN DOWER BLUMLEIN, of 32, Audley Road, Ealing, London, W.5, a British Subject, do hereby declare the nature of this invention to be as follows:-

The present invention relates to electric circuits for reducing the effective shunt capacity introduced by circuit elements such as for example, electric batteries and relates more particularly but no exclusively to circuits which are required to handle signals covering a wide range of frequencies.

In many resistances coupled devices, especially amplifiers used in television trouble is experienced owing to the stray capacity introduced by certain circuit elements. For example, if a D.C. coupling is required between two valves and it is effected by introducing a source of D.C. between the output of one valve and the input of the next, the stay capacity to ground of this source may be too great to allow the circuit to be operated in the normal manner. Similarly, the capacity of a cathode heating battery to ground may be excessive when the load is put in the cathode circuit of a valve. Finally, in valves where the coupling resistance is required to dissipate much energy, it may be found difficult to provide a resistance which will dissipate the power and a the same time have a reasonably low self capacity. These stay capacities may cause considerable attenuation of high frequencies with respect to low frequencies and may introduce other harmful effects.

This invention provides means by which the effects of certain stray capacities can be eliminated or substantially reduced.

According to this invention, in a resistance coupled circuit where devices are required to supply power or bias, or to dissipate power, in which these devices introduce undesired stray capacity, it is arranged that these devices are connected to the points at which they are required, through high impedances (at least at high frequencies) which effectively eliminate all or the greater part of the unwanted stray capacities to ground.

According to a further feature of this invention, in a coupling circuit, devices having unwanted capacity are connected to the points at which they are required through high impedances (at least at high frequencies) and the resultant coupling circuit is built out to appear as a substantially pure resistance throughout the required frequency range.

A further feature of the invention consists in connecting the devices having unwanted stray capacity to the point at which they operate through an inductance or inductances, which inductance or inductances are shunted by resistance, so that the resultant overall impedance introduced is substantially a pure resistance throughout the operating frequency range.

A further feature of the invention consists in the feeding in of power or a biasing potential from a source to a resistance coupling circuit serving to couple two elements such as thermionic valves together, through two tightly coupled chokes, the chokes being suitably damped and the resultant coupling being built out to appear as a substantially pure resistance throughout the operating range.

A further feature of the invention consists in the introduction of impedance elements between the two "live" ends of the tightly coupled chokes referred to in the preceding paragraph, these impedance elements serving to build out the effective impedance between these points to appear as a constant resistance over substantially the whole working frequency range.

The invention will now be described by way of example with reference to the accompanying diagrammatic drawings wherein

Fig. 1 shows a circuit for supplying potential to the anode which collects photo-electrons in a cathode ray television transmitting tube,

Fig. 2 shows a modification of a part of Fig. 1,

Fig. 3 shows a modification of a part of Fig. 2,

Fig. 4 shows a circuit of a direct coupled amplifier,

Fig. 5 shows a modification of Fig. 4.

Fig. 6 shows another arrangement of a direct coupled amplifier according to the invention,

Fig. 7 shows a circuit of a direct coupled modulator according to the invention,

Fig. 8 shows a circuit according to the invention for feeding heating current to the cathode of a vale of the cathode follower type and

Fig. 9 shows a modification of Fig. 8 in which provision is made for the supply of bias potential to the control electrode of a subsequent amplifying valve.

Referring to the drawings, Fig. 1 shows a circuit for maintaining the potential of a collecting electrode 1 positive with respect to the signal plate 2 of a double ended cathode ray transmitting tube 3. The signal plate 2 carries a large number of conducting particles insulated therefrom, and from one another, each particle having an exposed conducting surface on each side of the plate 2. The exposed surfaces of the particles on the left of the plate 2 are rendered photo-electrically active, an image of the object to be transmitted is cast upon the photo-electric mosaic surface thus formed and photo electrons are emitted by the mosaic surface and collected by the electrode 1 when this is maintained at a suitable positive potential with respect tot he signal plate 2. The surfaces of the particles on the right of the signal plate are scanned by an electron beam from an electron gun (not shown). The particles are thereby consecutively caused to return to a datum potential and currents representative of the light and shade of the picture are set up in a load resistance 4 which is connected between the signal plate 2 and earth. Potential differences are thus set up between the point 5 and earth and may be fed by means of lead 6 to the input of an amplifier. It is desired to apply a difference of potential between electrode 1 and the point 5. If battery 7 were directly connected between electrode 1 and point 5 its capacity to earth indicated by the dotted condenser 8 would appear as shunt capacity across load resistance 4. This shunt capacity would reduce the effective impedance of load 4 at high frequencies and would therefore attenuate the output of these frequencies which is obtained from lead 6.

The battery 7 is connected between electrode 1 and point 5 through two series resistances 9, 10 of high value, a by-pass condenser 11 of capacity large compared with the capacity 8 being connected between point 5 and electrode 1. The effective shunt impedance across load resistance 4 is then the resultant of capacity 8 in series with the two resistances 9, 10 is parallel. By making resistances 9, 10 of sufficiently high value, for example one or two megohms each, it is usually possible to arrange that this effective shunt impedance has a negligible effect on the frequency characteristic of the system over the range of frequencies which it is required to handle. In some cases the shunt impedance may cause a small amount of attenuation of the highest frequencies which may be corrected in a subsequent amplifier.

As an alternative to correcting the residual attenuation, the load resistance 4 the magnitude of which will be denoted by R may be so modified that the resultant load (including the shunt impedance mentioned above) behaves as a pure resistance equal to R. If each of the resistance 9, 10 has a magnitude 2r and if the capacity 8 has a value C, then the effective shunt impedance is the resultant of resistance r in series with a condenser C.

Now if an inductance shunted by a resistance is inserted in series with load resistance 4, it is possible to correct the effective impedance of the load for the effect of C. the shunt resistance r may be considered as made up of two parts, one equal to R, and the other equal to (r - R). The required inductance shunted by resistance R will the be the inverse of C and (r - R) about the resistance R. the resistance 4 is therefore replaced by a circuit comprising an inductance 12 of magnitude L shunted by a resistance 4 of magnitude R as shown in Fig. 2 where r1 is equal to EQUAT. HERE and L is equal to CR2. In this example, the impedance between the point 5 in Fig. 2 and earth is still not a pure resistance owing to the large shunt capacity of the signal plate 2 of Fig. 1, and the input capacity of an amplifier electrode connected to lead 6. However, the load portion of the circuit, (that is the elements forming the substitute for the simple resistance 4 and the battery feed) is resistive, thus enabling a simple correction to be made later for the shunt capacity of the signal plate. The load circuit 4, 12, 13 which is shown in Fig. 2 may be replaced by the equivalent circuit shown in Fig. 3 without departing from the spirit of the invention. This alternative arrangement can by suitable choice of components, be made an exact counterpart to that given in Fig. 2.

Figure 4 shows a circuit similar to that of Fig. 2 used for a direct coupling between two valves 14, 15 of a direct coupled amplifier. As in Fig. 1 the battery 7 (or other source of potential, such as a rectifier) which is necessary to maintain the potential of the grid 16 of valve 15 at a suitable value with respect to the anode 17 of valve 14 is built out by resistances 9, 10 to hold off its stray capacity, represented by condenser 8, to earth, and the main anode resistance 4 has in series with it an inductance 12 and resistance 13 in parallel to make the total effective resistances in the circuit a constant value. Alternatively, the arrangement of Fig. 5 may be employed wherein a resistance 13 and inductance 12 in series are connected in shunt with resistance 4 in order to correct the impedance change produced by the battery feed resistance and stray capacity of the battery.

Figure 6 shows a D.C. coupling arranged between two valves 23, 24 of which valve 24 is to be operated into the region in which the grid 25 is positive with respect to the cathode 26, so that grid current will flow. It is no longer practicable to feed the necessary coupling potential through very high resistances on account of the low impedance feed required by a valve running into grid current if distortion is to be avoided. Potential from a battery 27 or other source is therefore fed throughout two chokes 28, 29 which are tightly coupled. These chokes are preferably wound side by side on the same core so as to constitute in effect one bifilar choke having a parallel aiding inductance equal to L. The chokes 28, 29 are shunted by a resistance 30 of magnitude R and the capacity dented by condenser 31 of value C of the battery to earth is shunted by a further resistance 32 also of magnitude R, which instead of being taken to earth, is taken to a higher potential such as that of the anode of valve 23, so s to avoid loss of H.T. current. The whole shunt effect of the battery feed as regards the anode load of the valve 23 is that of a pure resistance equal to R shunting its anode impedance denoted by resistance 33, and it can be arranged that such a resistance R constitutes the only anode resistance, the resistance 33 in the diagram being omitted.

In previous figures showing battery feeds (Figs. 1, 2, 4 and 5) the top two points of the battery feed impedances are shunted by a condenser 11. In the case of Fig. 6, however, such a condenser may resonate with the series opposing impedance of the two inductances. A further resistance 34 of magnitude r is shown in series with the battery 27 and represents the loop resistance of the inductances, the internal resistance of the battery and any added resistance. The top points of the two inductances 28, 29 are closed by a resistance 35, also of magnitude r in series with a condenser 36 of capacity c1. If the series opposing inductance of the two coils is equal to 1, then EQUAT. HERE is made equal to r2, so that as regards the grid feed to the next valve 24 a constant series impedance equal to r is obtained in the coupling at all frequencies. If the value of r is small, it may not be necessary to insert resistance 35 at the top point of the coil, provided that condenser 36 causes no violent resonance with the inductances, it will be seen that this diagram illustrated a method whereby the stray capacity C of the battery 27, which may represent quite a low impedance compared with R or with resistance 33 at the highest frequencies, is removed and replaced by the innocuous resistance R.

Figure 7 shows a circuit of the same general type as that shown in Figure 6, but applied to a direct coupled modulator suitable for a wide range of frequencies. In Figs. 6 and 7 the magnitude of components bearing like references are denoted by like symbols and the valve 23 passes modulation signals to the modulation resistance 33, through the anode battery or rectifier 27 which is floated and inserted between the anode 37 and modulation resistance 33. The top point of the modulation resistance 33 is passed out to the radio frequency modulation (not shown), for example, to the grid of a valve for grid modulation. The battery or H.T. rectifier or other source of anode potential 27, is connected into the line through two tightly coupled inductances 28, 29, which are non-inductive as far as possible for the passage of normal anode electron current which flows from the valve 23 through inductance 28, through the source 27, through inductance 29 and so to the modulation resistance 33. As before, a condenser 36, and small resistance 35 are used to build out the battery and leakage inductance of the chokes 28, 29 to a pure resistance equal to r. The choke 29 is shunted by a resistance 30, and similarly the self capacity and any building out capacity 31 is shunted by another resistance 32. The combined battery feed circuit then appears as a resistance of value R to earth, provided the inductance of the two coils in parallel equals CR2. If desired, the resistance 33 may be omitted, so that the composite resistance R constitutes the whole modulation resistance. If resistance 33 is included in the circuit, the effective modulation resistance is R and the resistance of 33 in parallel. If the battery 27 is replaced by a rectifier, this may conveniently be built out to a pure resistance equal to r (less any choke loop resistance0 and built out again as shown in the drawing, to correct for the leakage inductance of the tightly coupled chokes. Furthermore, resistance 30 may be divided into two parts, each equal to say 2R, one bridged across each choke 28, 29. Again, it will be noted that the steady D.C. dissipation occurs in resistance 32 (and of course in 33 as well, through the latter may conveniently be omitted) which resistance 32 can have self capacity which forms part of the condenser 31.

Figure 8 shows the same mechanism applied to feeding current to a vale 37 required to have a floating cathode, as for example, when the valve is employed with the load in the cathode circuit. Such a valve is known as a cathode follower since the potential of its cathode can be arranged substantially to follow that of its control grid. In this case the filament 38 is fed with alternating current from a transformer 39 which has capacity denoted by condenser 31 of value C between the live filament windings 40 and the earth primary or core, or both primary and core. This capacity is eliminated by feeding the filament 38 through tightly coupled chokes 28, 29. These chokes are shunted by a resistance 30 and a further resistance 32 shunts the stray capacity C. resistance 30 is bridged off from the centre tap 41 on a low resistance 42 across the filament 38, and the two halves of resistance 42 in parallel constitute in effect a portion of resistance 30. As the choke comprising inductances 28, 29 requires low self-capacity and has to carry heavy currents requiring thick wire, it is advantageous to wind this choke on a metal core resembling a transformer bore, but having a large gap (preferably in the middle of the coil) and formed of very thin laminations. As the filament current passes through the coils in series opposition, the core is not magnetised by the filament heating current, but is magnetised by the space current of the valve 37. The transformer capacity 31 also comprises the self-capacity of the resistance 32. The same circuit may be employed to allow for the capacity to earth of a battery, machine, or rectifier feeding the filament with direct current.

Figure 9 shows a direct coupling for a valve having its load placed between its cathode and earth, it being required not only to supply cathode current to the valve, but also to supply a bias potential for a subsequent valve, which may require instead of the positive potential of the cathode 38 of the valve 37, a negative potential. The valve 37 is working into a cathode load R and it is required to eliminate, as far as possible, the capacities to ground of the load resistance (required to dissipate the heat produced in the standing feed of the valve), the capacity to ground of the cathode rectifier, (and any associated transformer capacities) and finally the capacity to earth (and associated transformer capacities) of the rectifier supplying the bias potential. In Figure 9, 43 represents a low voltage heavy current rectifier providing the cathode current, 44 represent a comparatively high voltage rectifier supplying the bias to a subsequent valve, which it is assumed is liable to run into grid current on extreme amplitudes. The cathode load is formed by two resistances 30, 32 in series, of which resistance 32 is required to dissipate the heat produced by the steady and low frequency space current. Resistance 30 is only required to dissipate the heat produced by the high frequency alternating currents. The unwanted capacities are held off by means of a triply wound choke coil, the three windings 28, 29 and 45 being coupled as tightly as possible. The two windings 28, 29 correspond to windings 28, 29 of Fig. 9 and are of thick copper, so as to carry the cathode current, whereas the winding 45 is of thinner wire but well insulated from the other two windings on account of the higher voltage of rectifier 44. The insulation of the choke end to end, must stand the peak amplitude of the valve output. The cathode rectifier 43 and the cathode are shunted by resistances 46, 42 being of small value, do not materially affect the design, but can be allowed for if desired. The centre point 41 of the cathode and the upper end of the choke winding 45 are closed by a resistance 48 and condenser 49 in series, designed to build out to a pure resistance, the effective impedance of rectifier 44 as seen through the leakage inductance of the choke. Any choke capacity shunting this leakage inductance can be allowed for by a modification of the circuit building it out to a pure resistance. By this means the effective shunting capacity across the cathode due to the heat dissipating resistance 32 and the two rectifiers 43 and 44 is effectively removed and replaced by the self capacity of the choke coil. If this coil is well designed and if it can be given an iron core to reduce its size, it is in general possible to effect a reduction of stray capacity of as much as 10:1 for a frequency range extending from 0 to 2 megacycles per second.

Dated this 8th day of July, 1935.

REDDIE & GROSE,

Agents for the Applicant,

6, Breamís Buildings, London, E.C.4.

PROVISIONAL SPECIFICATION

No. 25070 A.D. 1935.

Improvements in or relating to Electric Circuits for Reducing the Effective Shunt Capacity introduced by Circuit Elements such as, for example, Electric Batteries

I, ALAN DOWER BLUMLEIN, of 32, Audley Road, Ealing, London, W.5, a British Subject, do hereby declare the nature of this invention to be as follows:-

The present invention relates to electric circuits for reducing the effective shunt capacity introduced by circuit elements such as, for example, electric batteries and relates more particularly but not exclusively to circuits which are required to handle signals covering a wide range of frequencies.

In many resistance coupled devices, especially amplifiers used in television, trouble is experienced owing to the stray capacity introduced by certain circuit elements. For example, if a D.C. coupling is required between two valves and it is effected by introducing a source of D.C. between the output of one valve and the input of the next, the stay capacity to ground of this source may be to great to allow the circuit to be operated in the normal manner. Similarly, the capacity of a cathode heating battery to ground may be excessive when the load is put in the cathode circuit of a valve. Finally, in valves where the coupling resistance is required to dissipate much energy, it may be found difficult to provide a resistance which will dissipate the power and at the same time have a reasonably low self capacity. These stray capacities may cause considerable attenuation of high frequencies with respect to low frequencies and may introduce other harmful effects.

This invention provides means by which the effects of certain stray capacities can be eliminated or substantially reduced.

In co-pending application No. 19480/35 there is described apparatus in which devices having unwanted capacity are connected to the points at which they are required through impedances having high values (at least at high frequencies) and the resultant coupling circuit is built out to appear as a substantially pure resistance throughout the operating frequency range.

According to the present invention a circuit component or circuit components which have unwanted stay capacities are connected to the circuit through inductances, so arranged as to remove or reduce the effects of these stray capacities at the upper end of the band of frequencies to be handled, and the arrangement is such that any resonance of the inductances with stray capacity is damped by associated resistance either with the inductances or the self-capacity of both; the resistance may comprise the natural resistance of the inductances, the construction of the inductances being such that their resistances have suitable values.

The present invention may be carried into effect in the manner described with reference to Figs. 6 to 9 of co-pending Application No. 19480/35 with the modification that, instead of building out the circuits so that they behave as substantially pure resistances, the resonance of the inductance and capacity is so damped by means of one or more resistances that, within the working range of frequency, the impedance of the circuit, including any loads such a s anode resistance or shunt capacity associated with the circuit, does not vary by more than about Ī20% due to the resonance of the inductance with the capacity associated therewith.

Dated this 9th day of September, 1935.

REDDIE & GROSE,

Agents for the Applicant,

6, Breamís Buildings, London, E.C.4.

PROVISIONAL SPECIFICATION

No. 33805 A.D. 1935.

Improvements in or relating to Electric Circuits for Reducing the Effective Shunt Capacity introduced by Circuit Elements such as, for example, Electric Batteries

I, ALAN DOWER BLUMLEIN, a British Subject, of 32, Audley Road, Ealing, London, W.5, do hereby declare the nature of this invention to be as follows:-

The present invention relates to electric circuits for reducing the effective shunt capacity introduced by circuit elements such as, for example electric batteries and relates more particularly but not exclusively to circuits which are required to handle signals such a television signals covering a wide range of frequencies.

In co-pending Application No. 19480/35 there are described arrangements in which the whole or the greater part of the effect of a stray shunt capacity is eliminated by building out the circuit so that it behaves more nearly as a pure resistance. The shunt capacity is preferably shunted by a resistance and is associated with an inductance also shunted by a resistance, the values of the components being such that the circuit behaves as a substantially pure resistance.

In some practical cases, difficulty is encountered in constructing components of suitable values. Thus it may be difficult or impossible to construct an inductance of sufficiently high value and which has no objectionable resonances within the band of frequencies to be handled by the circuit. Even if such an inductance can be constructed, it may be excessively bulky and expensive.

It is an object of the present invention to overcome, at least in part, the above difficulties.

According to the present invention there is provided an arrangement for reducing the effect of stray capacity in a circuit, the arrangement being such that a first stray capacity is shunted by two resistances in series with one another, one of said resistances being arranged in shunt with a second stray capacity.

According to a feature of the present invention, the effect of two stray capacities is eliminated or substantially reduced by shunting one stray capacity with a resistance, adding a similar resistance shunted by a choke so as to form with this stray capacity a substantially constant resistance network, shunting the second stray capacity with a resistance and connecting a choke in series therewith shunted by a further resistance, one of said two latter resistances being constituted by said constant resistance network.

The invention will now be described as applied to the circuit of Fig. 9 of co-pending Application No. 19480/35 to which reference will be made. Reference will also be made to the accompanying drawing, designated Fig. 10, which shows one way in which Fig. 9 may be modified in order to embody the present invention. Like parts in the two Figures bear the same references.

In Fig. 9 the cathode heating current for valve 37 flows through the winding 28, 29 of a triply-wound choke coil. In the case of a large valve, this current may be of considerable magnitude and it may be difficult or impossible to construct a choke which will carry this current, have a sufficiently high inductance, and yet neither have any undesirable resonances within the working range of frequencies nor be inconveniently bulky.

In Fig. 10, a doubly wound choke comprising coils 50, 51 is connected in the leads to rectifier 44, coil 50 being connected in series with coil 45 and coil 51 being connected between the rectifier and point 47. Resistance 32 is, as in Fig. 9, connected between the left hand terminal of rectifier 44 and earth. A resistance 52 is shunted across coil 51.

It will be seen that coils 50, 51 do not have to carry the heating current for valve 37. Coil 51 carries only the anode current of valve 37 an coil 50 carries only the grid current of the extent stage (not shown). It is therefore readily possible to make the inductance of the double wound choke 50, 51 substantially greater than that of the triply wound choke 28, 29, 45. If C2 is the capacity, to earth, of rectifier 44, L2 the magnitude of the inductance 51 and R1 the magnitude of resistance 32 and also of resistance 52, then this part of the circuit behaves as a pure resistance if L2 = R12C2.

If C1 is the capacity, to earth, of rectifier 43, if L1 is the inductance of the triply wound choke, and if resistance 30 have a value R1, then the whole system behaves as a pure resistance if L1 = R12C1 and if L2 had the value given above.

In the circuit of Fig. 9 the necessary inductance L1 of the triply wound choke is given by L1 = R12(C1 + C2). In many cases C1 is much less than C2 and therefore the magnitude of the inductance of the triply wound choke can be very much reduced by employing the circuit of Fig. 10 instead of that of Fig. 9.

It will thus be seen that the stray shunt capacity C1 of rectifier 43 is shunted by resistances 52 and 32 in series with one another, resistance 32 being in shunt with the stray capacity C2 of rectifier 44.

In practice it may be preferably to provide heating current for the cathode by means of a direct current generator. If this method is employed, the generator is connected in place of rectifier 43 and, by well spacing and insulating the generator from earth, it is possible to keep C1 small compared with the capacity C2 of the floating rectifier 44.

It is to be noted that, provided they are small, the self capacities of coil 51 and resistance 32 may be included in the effective value of C2.

The source 43 of cathode heating current may be so shielded that it has capacity to rectifier 44 only. In this case the upper end of coil 51 is connected to point 41 instead of to point 47 and the upper end of coil 50 is connected directly to the right hand terminal of condenser 49, coil 45 being emitted. It will then be seen that the stray capacity of source 43 is shunted by resistance 52 and these are in series with the inductance 28, 29 shunted by resistance 30. This part of the circuit is arranged to form a substantially constant resistance network. The stay capacity of rectifier 44 is shunted by resistance 32 and is built out by inductance 51 shunted by the resistance network to form a further substantially constant resistance network.

The above description is given by way of example only and many modifications thereof will be apparent to those versed in the art.

Dated this 5th day of December, 1935.

REDDIE & GROSE,

Agents for the Applicant

6, Breamís Buildings, London, E.C.4

COMPLETE SPECIFICATION

Improvements in or relating to Electric Circuits for Reducing the Effective Shunt Capacity introduced by Circuit Elements such as, for example, Electric Batteries

I, ALAN DOWER BLUMLEIN, a British Subject, of 32, Audley Road, Ealing, London, W.5, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

The present invention relates to electric circuit arrangements, and is particularly concerned with the provision of means for reducing the effects of unwanted capacity introduced by circuit elements such, for example, as electric batteries; the invention relates more particularly, but not exclusively, to circuit arrangements which are required to handle electric signals covering a wide range of frequency.

The effects of stray capacity are observed, for example, in many resistance-coupled circuits, such as amplifiers for handling televisions and like signals; thus if a D.C. coupling is effected between two valves by connecting a battery between the anode of one valve and the control grid of the other, the stray capacity of the battery to the cases of the amplifier may result in a relative attenuation of the higher frequencies of the signals to be amplified; similarly, when a thermionic valve has a load impedance arranged in its cathode circuit, the stray capacity of the cathode-heating battery, or other source, to the chassis may introduce a similar relative attenuation of the higher frequencies. Furthermore, the stray capacities may produce other harmful effects, such as undesired phase shifts.

It is the object of the present invention to provide novel or improved means for reducing the effects of unwanted capacity introduced in electric circuit arrangements by certain circuit elements.

It has already been proposed, in order to avoid the effects of the capacity to earth of a coupling battery, to connect the poles of the battery to the two points to be coupled, respectively, through resistance, the ends of these resistances remote from the battery being connected together through a condenser. Such an arrangement is, however, of limited application; since the resistances are often required to be of high value and to pass substantial current; there is then a large dissipation of power and loss of potential in the resistances; for many purposes, therefore, the known arrangement referred to is impracticable.

A further object of the invention is, therefore, to provide means for reducing the effects of unwanted capacity introduced in electric circuit arrangements by circuit elements such as electric batteries and the like which, in practice, are required to deliver power.

In United States Patent Specification No. 1,894,322, it has been proposed, for the purpose of neutralising the effects of the capacities to earth of valves, coupling elements and interstage wiring in thermionic amplifiers, to provide in shunt with these capacities to earth a circuit comprising an inductance and a resistance in series. This known arrangement has the disadvantage that, as is explained in the specification, it is capable of providing only partial neutralisation of the effects of stray capacity.

The means provided by the present invention for compensating for the effects of stay capacity differ in important respects form those described in the United States specification above referred to and are applicable only to certain of the stray capacities which are present in electric circuit arrangements; where, however, the present invention is applicable, it can be arranged that the effects of stray capacity are reduced to any desired extent. The nature of the stray capacities to which the present invention is applicable will be clear from the following description, but it may be pointed out here that the invention may be utilised to reduce the effects of the stray capacity due to circuit elements which have two terminals and are therefore suitable for connection in series in the circuit. Among such circuit elements may be mentioned, by way of example, sources of potential difference serving as coupling means in thermionic valve amplifiers, or as sources of filament heating current in certain forms of D.C. coupled amplifier.

The present invention accordingly provides a circuit arrangement comprising a circuit element which is associated in series with a first conductor and has stray capacity to a second conductor, wherein an inductance coil is provided between each of the terminals of said circuit element and the points of connection of said element to said first conductor, the two coils being coupled to one another by mutual inductance and the arrangement being such that the effects of said stray capacity are reduced or eliminated, and wherein there are provided damping means for substantially reducing or eliminating the effects of resonance within a predetermined working range due to said coils and the stray capacity of said circuit element to said second conductor.

The first conductor referred to in the preceding paragraph may, for example, be the lead between the anode of a thermionic valve and the control grid of a further valve, or it may be the filament of a valve. The second conductor may, for example, be the chassis of an amplifier, or any other part of the circuit arrangement the potential of which does not vary substantially in operation; the second conductor may be connected to earth.

The circuit element may be one which is required, in operation, to delivery power; in this case, the arrangement according to the invention provides the advantage that the inductance coils which are employed to "hold off" the stray capacity of the circuit element may be arranged to cause only a relatively small drop of potential.

The damping means may comprise a resistance arranged effectively in shunt with the coils or with the stray capacity, or two resistances arranged effectively in shunt with the coils and with the stray capacity respectively; where to resistances are employed, the arrangement may be made such that these resistances form with the coils and the stray capacity a composite circuit which simulates substantially a pure resistance. This composite circuit may form the whole or a part of the load impedance of a thermionic valve.

It will be noted that circuit arrangements according to the present invention differ from those disclosed in United States Patent Specification No. 1,894,322 above referred to in that in arrangements according to the present invention, the circuit element to which the undesired stray capacity is due is arranged in series with two inductance coils which are coupled together by mutual inductance whereas in the United States specification in question, the inductance coils provided are connected effectively in shunt with the stray capacities to be neutralised and are not inductively coupled to one another.

A coupling condenser may be connected between the ends of the coils remote form the circuit element, the coupling condenser tending to by-pass the coils and the circuit element for currents at frequencies in the upper part of the working range. Means may be provided for reducing or eliminating the effects of resonances between the coils and the coupling condenser.

Other features of the invention will appear from the following description and appended claims.

The invention will be described by way of example with reference to the accompanying drawing, in which

Fig. 1 shows a part of a D.C. coupled amplifier according to the invention,

Fig. 2 illustrates the application of the invention to a modulator which is required to work over a wide range of frequency down to zero frequency,

Fig. 3 shows a circuit arrangement according to the invention in which *** are provided for reducing the *** of stray capacity due to a source cathode heating current,

Fig. 4 shows a modification of the arrangement of Fig. 3 in which provision is made for the supply of bias potential *** the control electrode of a subsequent ***, and Fig. 5 shows a modification of the arrangement of Fig. 4.

Like parts in the several Figures have been give the same references.

Referring now to Fig. 1, the arrangement shown illustrates a D.C. coupling circuit according to the invention arranged between two amplifying valves *** and 24, the cathodes of which are at *** potential. The two valves are coupled by a floating battery 27, or other suitable source of potential, the battery *** having a capacity to earth which is shown in dotted lines at 31. According to the invention, in order to reduce the effects of the capacity 31, the poles of the battery 27 are connected into the lead *** the anode of valve 23 and the control grid of valve 24 (this lead constituting the first conductor referred to above) through chokes 28 and 29 which are coupled to one another by mutual inductance; the resistance 34 represents the resistance of battery 27 and the inherent resistances of chokes 28 and 29, together with any resistance which may be added in order, as explained more fully below, to give resistance 24 a convenient value. The ends of chokes 28 and 29 remote from battery 27 are connected together through a coupling condenser 36; for the moment, it will be assumed that resistance 35 is omitted. The junction of battery 27 and choke 28 is connected through a resistance 32 to the positive terminal of a source B of anode current, the negative terminal of which is earthed.

The chokes 28, 29 are preferably wound *** by side on the same former so as to constituted, in effect, one bifilar choke, and *** that there is a tight coupling between them; a tight coupling may also be achieved in other ways, for example by winding the two chokes on a common core of magnetic material. The chokes 28, 29 serve effectively to isolate the battery 27 from the remainder of the circuit at the higher frequencies to be handled, so that attenuation of the higher frequencies due to the stray capacity 31 is reduced. It will be noted that, in operation, there is a difference of potential between the ends of chokes 28, 29 remote from the battery at all frequencies within the range to be amplified, and if grid current follows in valve 24, power is supplied by the battery 27.

The arrangement as so far described has the advantage that, if the circuit is required to handle very high frequencies, it may be found that resonances between the chokes and the stray capacities of the circuit may occur within the working a frequency range, and the amplifier will then not have a recliner characteristic. According to the present invention, therefore, damping means are associated with the chokes, or with the stray capacities or with both in order to damp out such resonances. In Fig. 1, resistance 32 serves effectively as a damping resistance across capacity 31, and the resistance 30 arranged ins shunt with choke 28 may also serve a damping function. By a suitable choice of the values of the damping resistances, it can be arranged that the impedance of the coupling circuit as a whole with a desired working range of frequency, does not vary by more than above Ī20% due to resonances between the chokes and the stray circuit capacities.

In a preferred arrangement, however, the coupling circuit is made to simulate a pure resistance, or a purely resistive network: thus, if the capacity 31 is equal to C, and resistances 30 and 32 are both of the same magnitude R, then the parallel aiding inductance L of chokes 28, 29 is made such that the relationship

EQUAT. HERE

 

is substantially satisfied; in these circumstances, assuming the two chokes to be coupled as tightly as possible, so that the series impedance introduced thereby is negligible, the whole coupling circuit simulates a pure resistance of magnitude R, this pure resistance constituting the anode load of valve 23. If desired, this valve may have a separate load resistance 33, shown dotted, and resistance 32 may then if desired by taken to earth instead of to the positive terminal of the anode current source. By taking resistance 32 to the positive terminal of the source, however, loss of current is avoided.

The coupling between chokes 28 and 29 need not be so tight as that effected by winding the chokes in a bifilar manner, or on a common magnetic core; in the case in which the coupling is looser than this, it is preferably arranged that the mutual inductance between the chokes 28, 29 is substantially equal to the inductance of coil 28, that is, the coil which is shunted by a damping resistance.

If the chokes 28, 29 are air-cooled and are required to be or large inductance, the length of wire in each choke 28, 29 may be such that at some frequency within the working range, a resonance occurs between the coil and its distributed self-capacity, the resonance usually occurring at a frequency at which the length of wire in the coil is substantially half a wavelength. The effect of this resonance is that, at the resonant frequency, the impedance of the chokes becomes very low; the effect can be avoided by making either or both the coils 28, 29 in a plurality of separate sections, each section having in shunt with it a separate damping resistance: thus each coil may be wound in two halves, each half being damped by a resistance equal to EQUAT. HERE .

Now it may be found that the series opposing inductance of the chokes 28, 29 resonates within the operating frequency range with condenser 36, and this residual reactance may be damped by means of series resistance 36; preferably, however, resistance 35 is given the same value, say r, as resistance 34 (which, as has been exampled, may be made up to a suitable value) and it is arranged that

EQUAT. HERE

 

Where l is the series opposing inductance of chokes 28, 29 and c is the capacity of condenser 36; the series impedance between the anode of valve 23 and the grid 25 of valve 24 is then a pure resistance equal to r.

It will be noted that, in the amplifier described, the grid 25 of valve 24 may be allowed to become positive relative to the cathode thereof - in other words, grid current may flow, without the introduction of substantial wave form distortion, since the grid circuit of valve 24 is one of relatively low resistance; it will of course be observed that when grid current flows, battery 27 serves not only as a source of bias, but also to supply power.

Fig. 2 shows a circuit of the same general character as that shown in Fig. 1, and illustrates the application of the invention to a direct coupled modulator suitable for a wide range of frequencies. In Figs. 1 and 2, the magnitudes of components bearing like references are denoted by like symbols; referring to Fig. 2, the valve 23 is arranged to establish modulation signals across the modulation resistance 33, the floating anode battery high-tension rectifier or other D.C. source 27 being inserted between the anode 37 of valve 23 and modulation resistance 33 and serving as a D.C. coupling. The end of the modulation resistance 33 remote from earth is connected to the input of a radio frequency modulator (not shown). The source 27 of anode potential is connected into the circuit through two mutually coupled inductances 28, 29, which are arranged to present as small an impedance as possible for the passage of normal anode electron current, which flows from the valve 23 through inductance *** through the source 27, through inductance 29 and so to the modulation resistance 33.

The two inductances are preferably tightly coupled, for example, by being wound on a common magnetic core. If the coupling is less tight than this, it is preferably arranged that the mutual inductance is substantially equal to the inductance of coil 29. As before, a condenser 36 and a resistance 35 are used to build out the battery resistance 34 and the series-opposing inductance of the chokes 28, 29 to simulate a pure resistance equal to r. The choke 29 is shunted by a resistance 30, and similarly the capacity 31, which represents the capacity of source 27 to earth together with any capacity which it may be convenient to add thereto, is shunted by a resistance ***, resistances 30, 32 having, as before, the same magnitude R. The combined battery feed and coupling circuit thus appears as a resistance of value R between the anode of valve 23 and earth, provided the parallel-aiding inductance of the two chokes equals CR2.

If desired, the resistance 33 may be omitted, the composite resistance R then constituting the whole modulation resistance. If resistance 33 is included in the circuit, the effective modulation resistance is R in parallel with the resistance 33. If the source 27 is a rectifier, the latter may conveniently be built out to simulate a pure resistance equal to r less the series resistance of the two chokes and built out again as described with reference to the drawing, to correct for the leakage inductance of the tightly coupled chokes. Furthermore, resistance 30 may be divided into two parts, each equal say to 2R, one shunted across each of chokes 28, 29. Again, it will be noted that the D.C. component of the anode current of the valve 23 is dissipated to resistance 32, and this resistance can have substantial self capacity, since such self capacity forms part of the capacity 31.

Fig. 3 illustrates the application of the invention to circuits for feeding current to the cathode of a valve which is operated, for example, with its load in the cathode circuit. Such a valve may be one known as a cathode follower, the potential of the cathode of which can be arranged substantially to follow that of the control grid thereof. Referring to Fig. 3, the filament 38 of valve 37 is fed with alternating current from a transformer 39, the secondary 40 of which has capacity to the earthy core 39, or to both the primary winding and the core. In this case, filament 38 constitutes the first conductor. The effects of the stray capacity, which is indicated in dotted lines by condenser 31, of a capacity which will be referred to as C, is eliminated by feeding the filament 38 through two tightly-coupled chokes 28, 29. These chokes are shunted by a resistance 30 and a further resistance 32 shunts the stray capacity 31. The end of resistance 30 remote from earth is taken to the centre tap 41 on a slow resistance 42 across the filament 38, and the two halves of resistance 42 in parallel constitute in effect a portion of resistance 30.

As the choke effectively constituted by inductances 28, 29 requires to have a low self-capacity and has to carry heavy currents, so that thick wire is necessary it is advantageous to wind the inductances 28, 29 on a magnetic core resembling a transformer core, but having a large gap (preferably in the middle of the coil) and formed of very thin laminations. As the filament current passes through the coils in series opposition, the core is not magnetised by the filament heating current, but is magnetised by these space current of the valve 37. The transformer capacity 31 also comprises the self-capacity of the resistance 32.

As in the previous arrangements, it is arranged that L, the parallel-aiding inductance of chokes 28, 29, is equal to CR2, R being the magnitude of resistances 30 and 32. The capacity to earth of a battery, machine, or rectifier feeding the filament with direct current may be effectively eliminated in a similar manner.

Fig. 4 shows a modification of the arrangement of Fig. 3 in which a D.C. coupling is provided between valve 37 and a second valve 50; in this case it is required not only to supply cathode heating current to the valve 37, but also to supply a grid bias potential for the subsequent valve 50, the grid of which requires, instead of the positive potential of the cathode 38 of the valve 37, a negative potential relative to earth. The valve 37 works into a load resistance arranged in its cathode circuit, and it is required to eliminate, as far as possible, the effects of capacities to earth of the load resistance (which, since it is required to dissipate the heat produced by the steady component of the anode current of the valve, has a substantial self capacity), the total capacity to earth of the source of cathode-heating current, and finally the effective total capacity to earth of the rectifier or other source supplying the bias potential for valve 50.

In Fig. 4, 43 represents a low voltage heavy current rectifier providing the cathode-heating current for valve 37, and 44 represents a comparatively high voltage rectifier supplying the bias to the valve 50, which it is assume is liable to run into grid current on extreme amplitudes. The cathode-circuit load of valve 37 is formed by two resistances 30, 32 in series, of which resistance 32 is required to dissipate the heat produced by the steady and low frequency space current. Resistance 30 is only required to dissipate he heat produced by the high frequency alternating currents. The unwanted capacities are held off by means of a triply-wound choke coil, the three windings 28, 29 and 45 of which are coupled together as tightly as possible. The two windings 28, 29 correspond to windings 28, 29 of Fig. 3 and re of thick copper wire, so as to carry the cathode current without overheating, whereas the winding 45 is of thinner wire but is well insulated from the other two windings on account of the higher voltage of rectifier 44. The insulation of the composite choke, from end to end, must be such as to be capable of withstanding the peak amplitude of the output of valve 37. The inductances of coils 28, 29 are preferably made substantially equal, and the average mutual inductance between the coil 45 and the coils 28, 29 is preferably made substantially equal to the average inductance of coils 28, 29.

The cathode rectifier 43 and the cathode are shunted by resistance 46, 42 respectively, the centre points 47, 41 of which are connected through resistance 30. The resistances 46, 42 are of small value, and if desired, they can be regarded for purposes of design as forming part of resistance 30. The stray capacity 31 of rectifier 43 and the stray capacity 311 of rectifier 44 are eliminated in the manner discussed with reference to Fig. 3.

The centre point 41 of the resistance 42 and the upper end of the choke winding 45 are connected by a resistance 48 and a condenser 49 in series; the magnitudes of components 48 and 49 are so chose that the impedance of rectifier 44 as seen through the leakage inductance of the composite choke, is effectively a pure resistance. Any capacity due to the windings of the choke which effectively shunts the leakage inductance can be allowed for to a large extent by a modification of the circuit employed to build out the rectifier impedance to a pure resistance by application of the principles already discussed which govern such building out. In this way, the effective stray capacity across the cathode load due to the heat-dissipating resistance 32 and to the two rectifiers 43 and 44 is effectively removed any residual self-capacity being relatively small and due solely to the choke coils. If the choke is suitably designed and particularly if it is given an iron core to reduce its size, it is, in general, possible to effect a reduction of effective stray capacity of as much as 10:1 for a frequency range extending from 0 to 2 megacycles per second.

Difficulties may be encountered in certain practical cases in carrying the invention into effect in the ways so far described, since it may be found that it is difficult or impossible to construct or utilise components of the desired values; thus it may be found that choke coils of the desired inductance have objectionable resonances with the band of frequency to be handled, or are excessively bulky or expensive.

A further arrangement according to the invention y the use of which the difficulties referred to may be eliminated or much reduced, will now be described with reference to Fig. 5, which illustrates a modification o the arrangement of Fig. 4. Like pats in Figs. 4 and 5 bear the same references.

Referring to Fig. 5, a doubly-wound choke comprising coils 51, 51 is connected in the leas to the grid bias rectifier 44, coil 52 being connected in series with coil 45 and coil 51 being connected between he rectifier 44 and tapping point 47 on resistance 46. Resistances 32 is, as in Fig. 4, connected between the left hand terminal of rectifier 44 and earth. A resistance 52 is shunted across coil 51.

It will be seen that coils 51, 52 do hat have to carry the heating current for valve 37. Coil 51 carries only the anode current of valve 37 and coil 52 caries only the grid current of the vale 50. It is therefore readily possible to make the inductance of the doubly-wound choke 51, 52 substantially greater than that of the triply-wound choke 28, 29, 45. If C2 is the value of the capacity 311 to earth of rectifier 44, L2 the magnitude of the inductance 51 and R1 the magnitude of resistance 32 and also of resistance 53, then this part of the circuit behaves as a pure resistance if L2 = R12C2. The capacity C2 may be regarded as comprising in addition to capacity 311, the shunt stray capacity of resistance 32.

If C1 is the magnitude of the capacity 31, to earth, of rectifier 43, if L1 is the effective inductance of the triply-wound choke as seen from the cathode 38, then the whole system behaves as a pure resistance if L1 = R12C1, and if L2 has the value given above.

In the circuit of Fig. 4 the necessary inductance L1 of the triply-wound choke 28, 29, 45 is given by L1 = R12(C1 + C2), C1 and C2 having the values given above. In many cases C1 is much less than C2 and therefore, by employing the circuit of Fig. 5 instead of that of Fig. 4 the magnitude of the inductance of the triply-wound choke can be very much reduced.

It will be seen that in the arrangement of Fig. 5, the stray shunt capacity 31 of rectifier 43 is shunted by resistances 53 and 32 in series with one another, resistance 32 being also in shunt with the stay capacity 311 of rectifier 44.

In practice, it may be preferably to provide heating current for the cathode by means of a direct current generator instead of from a rectifier. If this method is employed, the generator is connected in place of rectifier 43 and, by well spacing and insulating the generator from earth, it is possible to keep capacity 31 small compared with the capacity 311 of the floating rectifier 44.

It is to be noted that, provided it is relatively small, the self capacity of coil 51 may be included in the effective value C2 of capacity 311.

The source 43 of cathode heating current may be so shielded that it has capacity to rectifier 44 only. In this case the upper end of coil 51 is connected to tapping point 41 instead of to tapping point 47, and the upper end of coil 52 is connected directly to the right hand terminal of condenser 49, coil 45 being omitted. It will then be seen that the stray capacity of source 43 is shunted by resistance 52, and the circuit so constituted is in series with the effective inductance of coils 28, 29 shunted by resistance 30. This part of the circuit is arranged to form a substantially constant resistance network by application of the principles already stated. The stay capacity of rectifier 44 is shunted by resistance 32 and is built out by inductance 51 shunted by the resistance network also referred to, to forma further substantially constant resistance network.

The above description is given by way of example only and many modifications of the invention, within the scope of the amended claims, will be apparent to those versed in the art.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

  1. A circuit arrangement comprising a circuit element which is associated in series with a first conductor and has stray capacity to a second conductor, wherein an inductance coil is provided between such of the terminals of said circuit element and the points of connection of said element to said firs conductor, the two coils being coupled to one another by mutual inductance and the arrangement being such that the effects of said stray capacity are reduced or eliminated, and wherein there are provided damping means for substantially reducing or eliminating the effects of resonance within a predetermined working range due to said coils and the stray capacity of said circuit element to said second conductor.
  2. A circuit arrangement according to claim 1, wherein said circuit element and said inductance coils are arranged in series in the lead between the anode of a first thermionic valve and the control grid of a second thermionic valve, said lead constituting said first conductor, and wherein the cathodes of said valves are connected to one another by means of said second conductor.
  3. A circuit arrangement according to claim 1, wherein said circuit element is a battery, a transformer winding or the like connected in series with the filament of a thermionic valve and is adapted to supply heating current thereto, said filament constituting said first conductor.
  4. A circuit arrangement according to claim 1 or 2, wherein said circuit element serves, in operation, a s a source of potential difference.
  5. A circuit arrangement according to any of the preceding claims, wherein said damping means comprise a resistance arranged effectively in shunt with said coils or with the stray capacity of said circuit element to said second conductor.
  6. A circuit arrangement according to any of the preceding claims, wherein said damping means comprise a first resistance arranged effectively in shunt with said coils.
  7. A circuit arrangement according to claim 6, wherein said first and second resistances are equal in magnitude, and wherein the magnitude of the inductance effectively shunting said second resistance is made such in relation to the magnitude of said stray capacity and the magnitude of said resistances that said resistances and said coils form with said stray capacity a circuit which simulates substantially a pure and constant resistance, and is effectively in shunt between said first and second conductors.
  8. A circuit arrangement according to any of the preceding claims, wherein said coils are tightly coupled to one another, the coils being wound, for example, as a bifilar solenoid, or on a common magnetic core.
  9. A circuit arrangement according to any of the preceding claims in which said damping means comprise a damping resistance arranged effectively in shunt with one of said coils, wherein the inductance of this coil is arranged to be substantially equal to the mutual inductance between said coils.
  10. A circuit arrangement according to any of the preceding claims in which said damping means comprise a damping resistance connected in shunt with one of said coils, wherein this coil is constituted by a plurality of separate coils connected in series, said damping resistance comprising a plurality of resistances each connected in shunt with one of said separate coils.
  11. A circuit arrangement according to claim 3, in which said damping means comprise a damping resistance arranged effectively in shunt with said coils, wherein a tapped resistance is connected between the ends of said coils remote from said circuit element, and wherein the end of said damping resistance remote from said circuit element is connected to a tapping pint in said tapped resistance, the magnitude of said tapped resistance being small compared to the magnitude of said damping resistance.
  12. A circuit arrangement according to claim 11, wherein a further tapped resistance of a magnitude small compared with that of said damping resistance is connected between the ends of said coils adjacent said circuit element, the end of said damping resistance adjacent said circuit element being connected to a tapping point in said tapped resistance.
  13. A circuit arrangement according to claim 1 or 2, wherein a coupling condenser is connected between the ends of said coils remote from said circuit element, said coupling condenser tending to by-pass said coils and said circuit element for currents at frequencies in the upper part of said working range.
  14. A circuit arrangement according to claim 13, wherein there are provided auxiliary damping means for reducing or eliminating the effects of resonances between said coils and said coupling condenser.
  15. A circuit arrangement according to claim 14, wherein the magnitudes of said auxiliary damping means and said coupling condenser are made such in relation to the impedance seen from the ends of said coils remote from said circuit element looking towards said circuit element that the total effective impedance between the ends of said coils remote from said circuit element is substantially a constant pure resistance.
  16. A circuit arrangement according to any of the preceding claims, wherein the composite circuit constituted by the stray capacity of said circuit element to said second conductor, said coils and said damping means constitutes the whole or a part of the load impedance of a thermionic valve.
  17. A circuit arrangement according to claim 16, wherein said composite circuit forms at least a part of a load impedance arranged between the cathode of a thermionic valve and the negative terminal of a source of anode current associated therewith.
  18. A circuit arrangement according to claim 15, wherein the total effective impedance between the ends of said coils remote from said circuit element constitutes effectively a resistance arranged in series between the node of one thermionic valve and the control grid of another.
  19. A circuit arrangement according to any of the preceding claims, and comprising a further circuit element connected effectively to said fist conductor and having stray capacity to said second conductor, wherein there is provide a third inductance coil which is coupled by mutual inductance to the coils associated with said first-mentioned circuit element, the three coils being so arranged that the effects of both said stray capacities in by-passing to different extents oscillations at different frequencies set up between said conductor are substantially reduced or eliminated.
  20. A circuit arrangement according to claim 1, in which said camping means comprise a damping impedance arranged effectively in shunt with said coils and in which there is associated with said form conductor a further circuit element having stray capacity to said second conductor, wherein further inductance coils coupled together by mutual inductance are provided in a circuit between said further circuit element and said first conductor, wherein damping elements are arranged effectively in shunt with the stray capacity of said further circuit element and with said further inductance coils, and wherein the composite circuit constituted by the stray capacity of said further circuit element, said further inductance coils and said damping elements is arranged to be effectively in shunt with the stray capacity of said first circuit element and to act as damping means therefore.
  21. A circuit arrangement according to claim 1, in which said damping means comprise a damping impedance arranged effectively in shunt with the stray capacity of said circuit element to said second conductor, and in which there is associated with said first conductor a further circuit element having stray capacity to said first-mentioned circuit element, wherein further inductance coils coupled together by mutual inductance are provided in a circuit between said further circuit element and said first conductor, wherein damping elements are arranged effectively in shunt with the stray capacity of said further circuit element and with said further inductance coils, and wherein the composite circuit constituted by the stray capacity of said further circuit element to said first circuit element, said further inductance coils and said damping elements is arranged to be effectively in shunt with the coils associated with said first circuit element and to act as damping means therefore.
  22. A circuit arrangement substantially as herein described with reference to any of the Figures of the accompanying drawings.

Dated this 6th day of July, 1936.

REDDIE & GROSE,

Agents for the Applicant,

6, Breamís Buildings, London, E.C.4

-----------------------

Leamington Spa: Printed for His Majestyís Stationery Office, by the Courier Press. - 1937.