479,113

PATENT SPECIFICATION

Application Date: April 29, 1936. No. 12118/36.

Complete Specification Left: April 17, 1937.

Complete Specification Accepted: Jan. 31, 1938.

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

PROVISIONAL SPECIFICATION

Improvements in or relating to Thermionic Valve Circuits particularly for Use in Television

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

This invention relates to thermionic valve circuits particularly for use in television. It is known in television apparatus to employ a thermionic valve to drive a current of substantially saw-tooth wave form through an inductive circuit comprising the scanning coils of a cathode ray tube and in which negative feed-back from the output circuit of the valve to the input circuit thereof is employed to improve the wave form of the saw-tooth current. this negative feed-back is derived from potentials set up across resistances in series with the scanning coils in the output circuit of the valve. This arrangement is to some extent disadvantageous in that, since it is desirable that the feed-back voltage shall be large, the introduction of the resistance in series with the scanning coils from which the feed-back voltage is derived necessitates an increased voltage output from the valve.

It is the chief object of the present invention to provide an improved thermionic valve circuit employing negative feed-back for the purpose of correcting wave form in which this disadvantage is reduced or avoided.

According to the present invention a thermionic valve circuit is provided comprising a source of saw-tooth potential adapted to feed the input circuit of an amplifying or driving valve, the output circuit of which is adapted to feed the current to a scanning device and a circuit in parallel with said scanning device arranged to feed-back in the negative sense to the input circuit of the amplifying or driving valve potentials derived from potentials developed across the output circuit. The scanning device may either comprise the coils of an electro-magnetic scanning arrangement or the plates of an electro-static scanning arrangement. Preferably, the saw-tooth wave form is generated by charging a condenser and at intervals discharging it, the charging or discharging being affected at one end of the condenser, the other end of the condenser being fed with potentials derived from potentials across the output circuit as aforesaid. When employed for magnetic scanning, the negative feed-back potential applied to the condenser is substantially proportional to the scanning current and in the case of electro-static scanning the negative feed-back potential is proportional to the potential across the electro-static scanning plates.

Preferably, in connection with electro-magnetic scanning, the output of the amplifying or driving valve is applied to the scanning coils through the medium of an output transformer. Distortion occurs in such cases at low frequencies owing to the inductance of the transformer not being sufficiently high, and this difficulty is avoided in the present invention by employing the negative feed-back to the input of the amplifying valve.

In one example of a circuit, in accordance with the invention, a condenser is arranged to be charged and discharged at intervals through a resistance in the anode lead of a discharge valve, which may be a valve arranged in a circuit to function as a blocking oscillator and serving to generate a saw-tooth potential. The anode of the discharger valve is coupled through a condenser and leak resistance to the control grid of an amplifying or output valve, having a resistance inn its anode circuit which is adapted to feed the primary winding of an output transformer though a condenser, the secondary winding of the transformer being connected to the scanning coils. The lower end of the primary winding of the transformer is connected to earth, whilst the upper end is connected to the condenser which, as aforesaid is charged and discharged at intervals by the blocking oscillator. As the condenser is charged positively through the resistance in the anode circuit of the discharger valve, the increase of valve current causes the upper end of the primary winding of the transformer, to which the condenser is connected, to assume a negative potential thus neutralising the greater part of the change of voltage across the condenser. So long as the upper end of the transformer primary winding rises uniformly in potential, a saw-tooth input will be applied to the control grid of the output valve. If, however, due to the inductance of the transformer the rise of potential at the upper end of the primary winding is less rapid than a true saw-tooth, a relative increase of potential occurs on the anode of the valve of the blocking oscillator, with a consequent increase of current from the output valve tending to neutralise this departure from true saw-tooth wave form. A similar effect will occur due to distortion in the output valve. Since the ambit of potential on the anode of the valve of the blocking oscillator is only the grid swing applied to the output valve, despite the large voltage accumulated on the condenser, the current flow through the resistance in the anode of the valve of the blocking oscillator is nearly uniform whereby substantially true saw-tooth output is obtained. It will be appreciated from the above description of a circuit in accordance with the invention that a potential derived form potentials developed across the output circuit is fed back in the negative sense to the input of the amplifying valve, such potential being derived from a circuit in parallel with the scanning coils.

Whilst the circuit described above operates satisfactorily provided the leaking inductance of the transformer and the inductance of the scanning coils is negligible compared with the resistance of the coils and transformer windings, distortion of wave form may occur particularly during the return stroke of the saw-tooth which, being rapid, causes the inductance of the windings to be effective. In order to overcome this difficulty, according to one construction the primary winding of the transformer is shunted by an inductance and resistance in series, the condenser which is charged and discharged at intervals being connected to the junction between the shunt resistance and inductance. By adjusting the ratio of the shunt inductance and resistance to the same order as the ratio of the inductance and resistance of the scanning coils, including any leakage inductance and resistance of the transformer windings, the voltage developed across the shunt resistance is strictly proportional to the current in the scanning coils. Under these conditions, the negative feed-back serves to produce a more true presentation of the saw-tooth wave form in the scanning coils, providing the output valve is capable of delivering the necessary current. By making the capacity of the charging and discharging condenser very small, it is possible to obtain the necessary discharging current of this condenser through the shunt resistance without the shunt resistance and inductance constituting a serious shunt across the transformer primary winding.

If desired, instead of employing a shunt inductance, the inductance may be replaced by a resistance and the resistance by a condenser and time constant of the resistance and condenser being made of the same order as the time constant of the inductance and resistance of the scanning coils, including leakage inductance and resistance of the transformer.

If the resistance of the transformer primary winding is relatively high, a further correction for wave form distortion, which may occur particularly at the frame scanning frequency may be effected with the last-mentioned circuit by inserting a shunt resistance across the resistance and condenser in series and by inserting a further series condenser between the upper end of the primary winding of the transformer and the series resistance and condenser and the shunt resistance. The shunt resistance represents the shunt inductance of the transformer and the additionally inserted condenser the resistance of the primary winding of the transformer.

In this circuit, the resistances represent inductances in the scanning circuit and the condensers represent resistance. The impedances of the scanning circuit are multiplied by a factor EQUAT. HERE, where k is a numeric giving suitable values to the shunt circuit. Instead of the extra condenser and resistance described above, the feed-back may be obtained from a third winding on the transformer.

Where electro-static scanning is employed, the transformer may be omitted together with the capacity in the anode circuit of the amplifying valve, and the anode of the amplifying valve may, in such cases, be coupled through a condenser to the electro-static scanning plate, the lower end of the charging and discharging condenser being connected to the anode of the amplifying valve, the charging and discharging condenser in this circuit having a small capacity of the order of 20 µµF for line frequency and 1000 µµF for frame frequency.

The amplitude of the saw-tooth oscillation may be adjusted by altering the value of the anode resistance of the valve of the blocking oscillator, or the value of the charging and discharging condenser, or by varying the potential applied through the anode resistance to the anode of the valve of the blocking oscillator.

The circuits described are equally applicable for line scanning as well as for frame scanning.

Dated this 28th day of April, 1936.

F. W. CACKETT,

Chartered Patent Agent.

COMPLETE SPECIFICATION

Improvements in or relating to Thermionic Valve Circuits particularly for Use in Television

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:-

This invention relates to thermionic valve circuits particularly for use in television. In British Patent Specification No. 401,990 a television apparatus is described and claimed in which a thermionic valve is employed to drive a current of substantially saw-tooth wave form through an inductive circuit comprising the scanning coils of a cathode ray tube and in which negative feed-back from the output circuit of the valve to the input circuit thereof is employed to improve the wave form of the saw-tooth current. in the arrangements described in the prior specification, the negative feed-back is derived from potentials set up across resistances in series with the scanning coils in the output circuit of the valve. This arrangement is to some extent disadvantageous in that, since it is desirable that the feed-back voltage is derived necessitates an increased voltage output from the valve.

Furthermore such feed-back is effective in increasing the apparent impedance from which the circuit is fed, which has the effect if an output transformer is employed to feed the scanning coils, of increasing distortion due to the leakage inductance of the transformer, this is, the valve tends to supply a perfect saw-tooth current to the transformer primary of which some is lost in magnetising current for the transformer, so that the resultant output current to he scanning coils is not a good saw-tooth.

Now to a certain extent, the disadvantage of the arrangement described in the aforesaid British Patent Specification can be avoided by arranging the feed-back circuit in parallel with the output circuit.

However, if the voltage feed-back is proportional to the voltage across the out-put satisfactory operation can only be obtained of the load presented to the valve by the scanning coils is a substantially pure resistance. That is to say, the inductance of such coils must be negligible compared with their resistance. Similarly, if the coils are transformer-coupled to the valve, then the leakage inductance of the transformer must also be negligible. If this is not the case, distortion of the wave form occurs, particularly during the return stroke of the saw-tooth, which, being rapid, causes the inductance of the windings to be effective so that the current variations in the secondary winding of the output transformer will not have wave form similar to that of the wave form of the potential applied across the primary winding of the transformer.

It is the chief object of the present invention to provide an improved thermionic valve circuit employing negative feed-back for the purpose of correcting wave form in which the effect of the above disadvantage is reduced or avoided.

According to the present invention a thermionic valve arrangement is provided comprising a source adapted to produce potential variations of saw-tooth wave form in the input circuit of an amplifying or driving valve the output circuit of which feeds current to a coil for producing an electro-magnetic field of saw-tooth form, and a circuit in parallel with an inductive impedance in said output circuit, arranged to modify the input potential to the said amplifying or driving the output circuit of which feeds current to a coil for producing an electro-magnetic field of saw-tooth form, and a circuit in parallel with an inductive impedance in said output circuit, arranged to modify the input potential to the said amplifying or driving valve by feeding back in the negative sense to the input circuit potentials derived from the potentials developed across the inductive impedance in said output circuit, and sufficiently nearly proportional to the current flowing in the coil for the electro-magnetic field to be more closely proportional to the voltage of the source than it would be in the absence of the negative feed-back.

Alternatively, an arrangement according to the invention may comprise a source adapted to produce potential variations of saw-tooth wave form in the input circuit of an amplifying or driving valve the output circuit of which includes a transformer over which current is fed to a coil for producing an electro-magnetic field of saw-tooth form, and in which said transformer includes a tertiary winding across which is bridged at a circuit from which substantially saw-tooth potentials are fed back in the negative sense to the input circuit, such potentials being sufficiently nearly proportional to the current flowing in the coil for the electro-magnetic field to be more closely proportional to the voltage of the source than it would be in the absence of the negative feed-back.

Preferably, said source adapted to produce potential variations of saw-tooth form in the input circuit of the amplifier or driving valve includes a condenser or condenser adapted to be charged and discharged at intervals, the charging or discharging of the condensers being effected at one side thereof, and the negative feed-back potentials being fed to the other side of said condenser or some or all of the condensers. Preferably also said condenser or condensers are adapted to be charged through a charging impedance, discharging means adapted intermittently to discharge said condenser or condensers being connected at the junction of said condenser or condensers and said charging impedance, and negative feed-back potentials being applied to the side of said condenser or condensers remote from said charging impedance.

The method of carrying the invention into practice will be readily understood from the accompanying drawings in which:-

Fig. 1 is a circuit diagram of an arrangement according to the invention,

Figs. 2 and 3 show modifications which may be effected in the circuit arrangement of Fig. 1, and

Fig. 4 is a circuit diagram corresponding to Fig. 1, in which a different type of connection is used for deriving the feed-back potential according to the invention.

Referring to Fig. 1, it will be seen that the arrangement therein shown comprises a condenser 1 arranged to be charged over a resistance 2 from a source of positive potential connected to the resistance as indicated by the + sign above it. Connected to one end of the resistance 2 in parallel with condenser 1, is the anode of a discharger valve 3 of which the anode cathode path is made periodically conduction, for example, under the influence of control pulses applied to the control grid. The valve 3 may be arranged in a circuit to function as a blocking oscillator. The anode of the valve 3 is coupled through a condenser 5, and leak resistance 6, to the control grid of the amplifying or output valve 7, shown as a screen grid pentode. The anode circuit of valve 7 include resistance 8 which is connected at one end to the positive terminal of a high tension source, and at its other end to condenser 9. Condenser 9, together with condenser 1, is connected to the primary winding of output transformer 10, of which the secondary winding is connected to the scanning coils indicated generally by the inductance 11 of a cathode ray tube television receiver. The lower end of the primary winding of transformer 10 is connected to earth. A suitable biasing resistance 18 with bypass condenser 19 may be provided in the cathode lead of the valve 7 as shown.

With the arrangement as so far described, it will be seen that as the condenser 1 is charged and discharged due to the operation of the discharger valve 3, the condenser being charged positively, the increase of current in valve 7 causes the upper end of the primary winding of the transformer, to which the condenser 1 is connected, to assume a negative potential. So long as the upper end of the transformer primary winding rises uniformly in potential, a saw-tooth input will be applied to the control grid of the output valve 7. If, however, due to the inductance of the transformer 10 the rise of potential at the upper end of the primary winding is more rapid than a true saw-tooth, a relative increase of potential occurs on the anode of the valve 3, with a consequent increase of current from the valve 7 tending to neutralise this departure from a true saw-tooth wave form. A similar effect will occur due to distortion in the valve 7. Since the ambit of potential on the anode of the valve 3 is only the grid swing applied to the valve 7, despite the large voltage accumulated on the condenser 1, the current flow through the resistance in the anode circuit of the valve 3, if the secondary circuit of the transformer is substantially resistive, is nearly uniform, and the arrangement shown tends to maintain a saw-tooth potential across the primary of transformer 10. If this primary has low resistance, the magnetising current will not materially affect the saw-tooth output and the maintenance of a saw-tooth potential across the primary will produce a saw-tooth current in the resistive secondary.

However, the circuit as so far described above only operates satisfactorily provided the leakage inductance of the transformer 10 and the inductance 11 of the scanning coils is negligible compared with the resistance of the coils and transformer windings, distortion of wave form may occur particularly during the return stroke of the saw-tooth, which, being rapid, causes the inductance of the windings to be effective. Thus, in order to overcome this difficulty, in accordance with the present invention the primary winding of transformer 10 is shunted by an inductance 12 and resistance 13 in series, the condenser 1 being connected to the junction between the inductance 12 and resistance 13. By adjusting the ratio of the inductance 12 and resistance 13 to the same order as the ratio of the inductance and resistance of the scanning coils, including any leakage inductance and resistance of the windings of transformer 10, the voltage developed across the resistance 13 is strictly proportional to the current in the scanning coils 11. Under these conditions, the negative feed-back serves to produce a more true representation of the saw-tooth wave form in the scanning coils, providing the output valve 7 is capable of delivering the necessary current. By making the capacity of the condenser 1 very small, it is possible to draw the necessary discharging current of this condenser through the shunt resistance 13 without the shunt resistance and inductance constituting a serious current shunt across the transformer primary winding.

If desired, instead of employing a shunt inductance and resistance as shown in Fig. 1, the inductance 12 may be replaced by a resistance 14 and the resistance 13 by a condenser 15, as shown in Fig. 2. In this arrangement the time constant of the resistance 14 and condenser 15 is made of the same order as the time constant of the inductance and resistance of the scanning coils 11, including leakage inductance and resistance of the transformer 10.

If the resistance of the primary winding of transformer 10 is relatively high, a further correction for wave form distortion, which may occur particularly at the frame scanning frequency, may be effected with the last-mentioned circuit by inserting as shown in Fig. 3, a shunt resistance 16 across the resistance 14 and condenser 15 in series and by inserting a further series condenser 17 between the upper end of the primary winding of the transformer 10 and the series resistance 14 and condenser 15 and the shunt resistance 16. The shunt resistance 16 represent the shut inductance of the transformer 10 and the additionally inserted condenser the resistance of the primary winding of the transformer 10.

In Fig. 3 the condenser 17 corresponds to the primary resistance of transformer 10, the resistance 16 corresponds to the primary inductance of transformer 10, the resistance 14 corresponds to the leakage inductance of transformer 10 plus the inductance of the scanning coils and the condenser 15 corresponds to the secondary resistance of transformer 10 plus the resistance of the scanning coils. In order to fix these values, the resistances and leakage inductance of the secondary and the resistance and inductance of the scanning coils must be transferred to the primary in well known manner. The impedances representing various transformer and coil impedances described above, are then multiplied by a factor EQUAT. HERE to determine the approximate values of 14, 15, 16 and 17. It will be realised that multiplication by this factor converts inductances into resistances and resistances into condensers. The factor k is a numeric factor to give convenient values to the components and the factor may be determined by fixing condenser 15. It should be noted in this respect and condenser 1 is in effect almost in parallel with condenser 15, because the end of condenser 1 remote from 15 executes a comparatively small potential variation as compared with the end of condenser 1 connected to condenser 15. In making a rough design of the circuit, condenser 1 may therefore be considered as being part of condenser 15 and the nominal value of condenser 15 and the nominal value of condenser 15 is rated as the sum of these two condensers in parallel. In practice it has been found convenient to make condenser 1 of the same order as condenser 15, but wide variations may be made from this ratio and the circuit has been found to operate quite satisfactorily in the absence of condenser 15, condenser 1 then performing the function condenser 15. The size of condenser 1 is usually fixed at a convenient value to be discharged by the discharging valve such as 3 in Fig. 1. Once k has been determined the other component values may be fixed approximately and may later be adjusted to give a good performance. In practice it has been found that adjustment of resistance 14 produces a good "return stroke" or "fly back" and adjustment of resistance 16 allows the forward wave form to be adjusted to give a good saw-tooth. The resistance 16 and condenser 17 to correct for the primary inductance and resistance of transformer 10 are necessary only for slow scanning circuits such as frame frequency scanning circuits used for television.

Instead of using the arrangement s described above, the feed-back according to the invention may be obtained form a third winding on the transformer 10, for example as shown at 20 in Fig. 4. The arrangement of Fig. 4 comprises a discharger valve 3 arranged similar to the corresponding element of Fig. 1, and also a blocking condenser 5 and coupling resistance 6 in the control grid circuit of valve 7 in the output circuit of which a transformer is arranged. In this figure, however, the condenser 1 of Fig. 1 the charging and discharging of which generates the saw-tooth wave form, is connected on the output side of condenser 5 in place of the input side as in Fig. 1. Since condenser 5 is merely a blocking condenser of a value large enough not to materially affect the operation of the circuit, the choice of this connection is of no importance. Condenser 5, however, can in the arrangement of Fig. 4 be made small enough to give a certain degree of potentiometer effect between the anode of valve 3 and the grid of valve 7. Basically this circuit consists of a connection between the end of condenser 1 remote from the grid of 7 and the end of the additional winding 20 in like manner to the connection to the end of the primary shown in Fig. 1. Such a direct connection would produce a feed-back with would tend to produce a saw-tooth E.M.F. in the secondary wining of transformer 10. For use at high scanning frequencies, however, or in order to obtain a good "return" or "fly back" time, it is necessary to take into account the leakage inductance of the secondary winding and the inductance of the scanning coils 11. Resistance 23 which corresponds to these inductances and condenser 21 which is effectively in parallel with condenser 1 and corresponds to the resistance of the secondary circuit have been inserted in like manner to those in the modification shown in Fig. 2. In practice resistance 23 is adjusted to give a good "return" or "fly back". If the inductance of transformer 10 is high, the feed-back effect should be sufficient to produce a good forward stroke. If, however, a very good wave form is required or the inductance of the transformer 10 for reasons of economy and due to the effect of the anode current of the valve passing through it, is not sufficiently high to enable the feed-back to correct the effects produced by it, a resistance 24 and condenser 22 may be inserted, whose function is to reduce the feed-back for the very low frequencies. This has the effect of increased the effect of low frequencies at the grid of valve 7, so correcting any remaining errors of wave form due to the finite inductance of transformer 10. It has been found with this circuit that if the condenser 19 which decouples the biasing resistance 18 in the cathode, is not made sufficiently large, a very low frequency oscillation is likely to take place, especially in the absence of any controlling signals on the grid of tube 3. It has been found that returning the earthy end of the tertiary winding 20 direct to the cathode instead of to earth, reduces this unwanted effect. Furthermore, it has been found in practice that during the return stroke the capacity between the primary and tertiary winding, together with their leakage inductance has produced an oscillation. This has been prevented by the introduction of condenser 25 and resistance 26. The values of these components are not critical and satisfactory values are given by making the resistance 26 approximately equal to the sum of the resistances of the primary plus the tertiary winding of the transformer an making the reactance of the condenser equal to the leakage inductance in the primary and tertiary windings, divided by the square of the value given above for resistance 26. In applying the invention to the arrangement of Fig. 4, the feed-back voltage is usually considerably greater than the voltage applied to the grid of the tube 7, so that the saw-tooth voltage developed across condenser 1 is quite large compared to the input to the valve. Resistance 2 must therefore be proportioned to provide the necessary current to charge the condense 1 during a cycle. This, however, does not tend to produce marked exponential charging of condenser 1, due to the fact that the end of condenser 1 towards resistance 2 is not subjected to a large voltage variation, so that there is substantially a fixed potential across resistance 2 during the charging of condenser 1, so that the current through resistance 2 is substantially constant. The value of resistance 2 can be found by trial and error so as to give the required output. A practical circuit for scanning at 50 cycles was found to have the following values:-

Primary inductance of transformer 10

Ratio primary to tertiary (winding 20)

of transformer 10 - -

Resistance of primary winding of

transformer 10 - -

Resistance of tertiary winding of

transformer 10 - -

Combined resistance of secondary and

scanning coils transferred to

primary winding of transformer 10

Combined secondary leakage inductance

and coil inductance transferred to

primary winding of transformer 10

Condenser 1 - - - -

Condenser 21 - - - -

Resistance 23 - - - -

Resistance 24 - - - -

Condenser 22 - - - -

Condenser 25 - - - -

Resistance 26 - - - -

Resistance 2 - - - -

Resistance 18 - - - -

Condenser 19 - - - -

 

90 henries Hys.

1:1

4000 ohms.

7000 ohms.

 

5000 ohms.

 

7 henries.

.005 micro-farad

.02 micro-farad

100,000 ohms maximum (adjustable)

1 megohm maximum (adjustable)

.2 micro-farad

.02 micro-farad

20000 ohms.

2 megohms.

250 ohms.

250 micro-farads.

(N.B. In designing the circuit, the resistance of the tertiary winding 20 should be included with that of resistance 23.)

The screen was decoupled from the cathode by a condenser of 8 micro-farads capacity.

The output was controlled by varying the voltage applied to the upper end of resistance 2. In practice it has been found that the valve 3 can be a tetrode, the screen and grid being coupled together through transformer coils, which together with a condenser and leak in the grid circuit, makes the valve 3 perform blocking or relaxation oscillations, so that it is intermittently conducting, thus performing on its anode the necessary charging and discharging of condenser 1. For very rapid scanning circuits, the transformer inductance may be considerably reduced and condenser 22 and resistance 24 omitted. Similarly, smaller values for condenser 1 may be employed. If desired, condenser 1 may be considerably increased and condenser 21 omitted, as explained above in connection with Fig. 3. The value of the components may in practice be found either by calculation or by trial and error.

If desired, the condenser 1 may be supplemented by another condenser such as 11 shown dotted in Fig. 1, connected between the grid of the amplifying valve 7 and earth. This forms, in effect, an additional capacity from saw-tooth potential is derived, but which does not have the feed-back voltage applied to it. The arrangement comprising condenser 1 and 11 then forms a potentiometer in respect of the feed-back voltage. The condenser 1 might also be replaced by a capacity made up by a number of condensers arranged in any convenient way.

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 thermionic valve arrangement comprising a source adapted to produce potential variations of saw-tooth wave form in the input circuit of any amplifying or driving valve the output circuit of which feeds current to a coil for producing an electro-magnetic field of saw-tooth form, and a circuit in parallel with an inductive impedance in said output circuit, arranged to modify the input potential to the said amplifying or driving valve by feeding back in the negative sense to the input circuit potentials derived from the potentials developed across the inductive impedance in said output circuit, and sufficiently nearly proportional to the current flowing in the coil for the electro-magnetic field to be more closely proportional to the voltage of the source than it would be in the absence of the negative feed-back.
  2. An arrangement according to claim 1 wherein the output of the amplifying or driving valve is applied to the said coil through the medium of an output transformer in which the primary winding of the transformer is shunted by an inductance and a resistance in series, and source adapted to produce potential variations of saw-tooth form in the input circuit of said valve being connected to the junction between the inductance and the resistance so that the voltage developed across the resistance is fed back into the input circuit, the ratio of the inductance and resistance being adjusted to ensure that the voltage developed across the resistance is substantially proportional to the current in the scanning coils.
  3. An arrangement according to claim 1 wherein the output of the amplifying or driving valve is applied to the said coil through the medium of an output transformer, in which the primary winding of the transformer is shunted by a resistance and a capacitance in series, said source adapted to produce potential variations of saw-tooth form in the input circuit of said valve being connected to the junction between the resistance and the capacitance so that the voltage developed across the capacitance is fed back into the input circuit, the time constant of the resistance and capacitance being made of the order as that of the inductance and resistance of the scanning coils, including any leakage inductance and resistance of the transformer, whereby the voltage developed across the capacitance is substantially proportional to the current flowing in the scanning coils.
  4. An arrangement according to claim 3 in which the said resistance and capacitance in series are shunted by a resistance, there being a further capacitance inserted in series between the one of the primary winding of the output transformer and the junction of the two said resistance, the shunt resistance and the additionally inserted capacitance being adapted to correct for the inductance and resistance of the primary winding of the transformer.
  5. A thermionic valve arranged comprising a source adapted to produce potential variations of saw-tooth waveform in the input circuit of an amplifying or driving valve the output circuit of which includes a transformer over which current is fed to a coil for producing an electro-magnetic field of saw-tooth form, and in which said transformer includes a tertiary winding across which is bridged a circuit from which substantially saw-tooth potentials are fed back in the negative sense to the input circuit, such potentials being sufficiently nearly proportional to the current flowing in the coil for the electro-magnetic field to be more closely proportional to the voltage of the source than it would be in the absence of the negative feed-back.
  6. A thermionic valve arrangement according to claim 5 wherein the tertiary winding of the transformer is connected to the circuit of the primary winding through a capacitance and resistance adapted to damp oscillations occurring due to the leakage inductance between primary and tertiary windings and stray capacities in the circuit.
  7. A thermionic valve arrangement according to claim 5 or claim 6 wherein a connection from the source adapted to produce potential variations of saw-tooth form in the input circuit of said valve is made to the circuit of the tertiary winding of the said output transformer, between a resistance and a capacitance so proportioned as to give a feed-back potential across the capacitance which is proportional to the current flowing in the scanning coils.
  8. A thermionic valve arrangement according to any of the preceding claims, in which said source adapted to produce potential variations of saw-tooth form in the input circuit of said valve includes a condenser or condensers adapted to be charged and discharged at intervals, the charging or discharging of the condensers being effected at one side thereof, and the negative feed-back potentials being fed to the other side of said condenser or some or all of the condensers.
  9. A thermionic valve arrangement according to claim 8 in which said condenser or condensers are adapted to be charged through a charging impedance, discharging means adapted intermittently to discharge said condenser or condensers being connected at the junction of said condenser or condensers and said charging impedance, and negative feed-back potentials being applied to the side of said condenser or condensers remote from said charging impedance.
  10. A thermionic valve arrangement substantially as herein described with reference to and as shown or illustrated in any of Figures 1, 2, 3 or 4 of the accompanying drawings.

Dated this 16th day of April, 1937.

F. W. CACKETT,

Chartered Patent Agent.

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

Leamington Spa: Printed for His Majesty’s Stationery Office, by the Courier Press. – 1938.