US2172746A - Thermionic valve circuits - Google Patents

Description

Sept. 12, 1939. A. J. YOUNG THERMIONIC VALVE CIRCUITS Filed March 29, 1935 INVENTOR ARTHUR YOU/VG Patented Sept. 12, 1939 UNITED STATES PATENT GFFICE THERMIONIC VALVE CIRCUITS of Delaware Application March 29, 1935, Serial No. 13,701 In Great Britain March 29, 1934 5 Claims.

This invention relates to thermionic valve circuit arrangements for use as electrical time period devices.

Electrical time period devices are required for 5 many purposes, notably in connection with cathode ray tube television and like systems vwherein a cathode ray is required to be moved within a tube to scan a picture area a predetermined number of times per second and with a predetermined l number of lines per picture, the scanning action being obtained by electric potentials or currents which are fed to electrostatic deflector plates or electro-magnetic deflecting coils provided in the tube structure. It is usual in such cathode ray l tube systems to employ electric time period devices for controlling the periodicities of these scanning potentials or currents and numerous forms of such devices have been proposed.

Known electric time period devices suitable for use for cathode ray tube television systems and vlike purposes consist for the most p-art of thyra- .tron valve circuits of the relaxation oscillation generator type or other circuit arrangements embodying gas lled electric discharge devices. Such arrangements have disadvantages which are `apparently inherent in gas iilled electricdischarge devices, the three principal disadvantages being (l) that the striking or igniting voltage for a gas iilled electric discharge device depends in part upon the vapour pressure within the envelope thereof and this is likely to change from time to time, e. g. as a result of varying temperature (2) ionisation of the gas iilling in a gas iilled electric discharge device requires a period of time which, though short, is appreciable and this limits the upper frequency which may be reached by known time period devices incorporating such gas filled devices, and (3) gas lled electric discharge devices will in practice, not be all exactly alike even though made apparently to the same design, the characteristics of a plurality of nominally identical gas iilled electric discharge devices generally varying from device to device.

It is known that these disadvantages can be avoided by employing instead of gas iilled or soft electric discharge devices, so-called hard electric discharge devices, i. e. thermionic valves having electrode systems enclosed in evacuated 50 envelopes. Known electric time period devices of the hard valve type are, however, somewhat complicated and involve the use of at least two valves. Furthermore, so far as the present applicant is aware the known hard valve type 55 time period devices have been of such a nature (Cl. Z-36) as to involve that the cathode of at least one valve is at relatively high potential-which is obviously undesirable-while the periodic impulselike action has not been so rapid and nearly instantaneous as is often required in practice in tel- 5 evision and like systems.

The object of the present invention is to provide an improved electric time period device of the hard valve type wherein only a single valve need be employed and wherein the above men- 10 tioned further disadvantages are avoided.

According to this invention an electrical time base circuit comprises a condenser, means for continuously charging said condenser at a predetermined rate; a thermionic valve having a 15 cathode, an anode and at least three control electrodes for periodically discharging said condenser; means for applying to the anode of said valve a potential depending upon the potential across said condenser; a connection for causing a pulse 20 to be applied to one control electrode of said valve when said anode reaches a potential at which anode current ows; and means interconnecting two other control electrodes of said valve for causing a pulse to be applied to that which is nearer the anode when a pulse occurs on the other of said two control electrodes as a result of the application of a pulse to said one control electrode, said two other control electrodes being between said anode and said one control elec- 30 trode; the whole arrangement being such that the pulse applied to that of the three control electrodes which is nearest the anode is in such direction as to increase the anode current whereby a cumulative action accelerating discharge of said condenser is obtained.

The invention is illustrated in the accompanying drawing which shows diagrammatically three embodiments thereof.

In the drawing Fig. 1 shows a schematic diagram of my invention;

Fig. 2 shows a modication of the embodiment shown in Fig. 1; and

Fig. 3 shows schematically a further modication of Fig. 1. 45

Referring to Figure 1 an electric time period device comprises a hard thermionic valve V shown as constituted by a pentode having three grids G1, G2, G3 arranged in succession between the cathode F and the anode A. A condenser K 50 of say 0.01 mid. capacity is connected effectively in shunt with the anode-cathode discharge path of the valve, the condenser K being in series with a resistance R1 (which may be adjustable and lfor example of about 5,000 ohms maximum value) circuit 40 between itself and the anode A. The condenser K which is the output condenser (the output terminals are marked O) is charged at a predetermined constant rate through any known form of constant current device at X and the potential of the grid G1 adjacent the cathode is caused to vary in dependence upon the potential across said condenser K said grid being connected to the junction point oi a condenser K1 of say .001 mid., with a resistance R2 of, for example 100,000 ohms which is in series with said condenser K1 between anode and cathode. The second grid G2 is connected to the positive terminal HT-iof the source of positive potential (not shown) through a resistance R3 which may be adjustable and have .a maximum value of about 100,000 ohms while the third grid G3 is connected through a condenser K2 of (say) .001 mfd. to the grid G2 so that said grid G3 receives voltage set up in the resistance R3, said grid G3 being connected to the cathode through a leak R4 of say 250,000 ohms in series l'with a grid bias source (not shown) whose terminals are marked GB- and GB-{. The Value of the source connected at HT+ and HT- will depend upon design details but 500 volts is quite a practical value. The whole arrangement is such that in the absence of potential across the condenser K the current to the anode of the valve from the cathode thereof is substantially zero, While, as the potential across said condenser rises, the relative potentials on the succession of grids between cathode and anode change until a point is reached when substantial anode current suddenly ows.

In the modification shown in Figure 2 the valve V is a so-called pentagrid having a cathode F, and anode A and ve grid electrodes G1 G2 G3 G4 and G5 arranged in succession in the electron stream therebetween. The rst grid G1 is connected to the cathode through a resistance R2 of about 100,000 ohms and is also connected to the anode through a condenser K1 of about 0.001 mfd. 'Ihe anode of the valve is connected through a preferably variable resistance R1 of about 5,000 ohms in series` with a constant current device X of any known form, to a source of anode potential (not shown) at I-IT-l and the junction point of X with R1 is connected to the cathode F through a condenser K of about 0.01 microfarad which (like the similar condenser K of Figure 1) acts as the output condenser and is gradually and rectilinearly charged through said constant current device X, the output terminals of the whole arrangement being constituted by the terminals of this condenser K. The grid G2 is connected through a resistance R3 (preferably adjustable) of about 100,000 ohms tothe source of anode potential (not shown) at HT-land is also connected through a condenser K2 of about 0.001 mfd. to the fourth grid G3 which is connected through a resistance R4 of about 250,000 ohms in series with a source of negative bias potential (not shown) to the cathode F. As so far described the arrangement is much the same as that of Figure 1 the principal diierence being the provision in the valve of two further grids constituted by screen grids G1 and G5. These screen grids which are the third and fifth grids, are connected together, for example within the valve envelope, and connected to the source of anode potential at HT-lthrough a resistance R5 of about 50,000 ohms and which may be adjustable. The resistance R1 is preferably made adjustable in order tol enable the best relaxation conditions for the whole arrangement to be obalvajrzlc tained. Synchronising pulses are applied at the terminals I and are applied to the third and fifth grids through condenser K3.

Assume the output condenser K to have zero charge. The grid G1 will then be at cathode potential. Current ilows. through X to charge condensers K and K1, but no current will flow through the anode because the grid G3 will be highly negative. Electron current ilow will occur to the grid G2 but none will flow in the anode circuit. As the condensers charge up the charge in condenser K1 will develop in the grid circuit of grid G2 a voltage which is fed to the grid G3 through the condenser K2 making the grid G3 still more negative. At the same time the anode voltage will rise steadily due to the accumulating charges on K and K1 until the anode takes current. When this happens a negative pulse will be fed through condenser K1 to grid G1 with the result that grid G3 alters potential in a positive direction. This causes increase in the anode current so that the action is cumulative and proceeds until K and K1 are discharged Whereupon the cycle recommences. Provided that the grid current of G1 is small condenser K can be omitted and the output taken from across K1. This Ywill be found considerably to increase the ratio of the time taken during the charging part of the cycle to that taken during the discharging part. If the charging current for K1 be small, the device X can be replaced by a very high resistance and the charging current derived from the I-I. T. supply for the cathode ray tube oscillograph (assuming the time base to be employed in co-operation with such a device). Of course the voltages for G4 and G5 would have to be obtained from another source but such a source will often be availablefor example in the case of a cathode ray tube type television radio receiver, the necessary voltage could be obtained from a suitable point in the radio receiver.

An arrangement much like that of Figure 2 except that the condenser K is omitted is shown in Figure 3. In this figure the positive and negative terminals of the high voltage supply (e. g. 2,000 volts) are marked HT1-land BT1- respectively and the positive and negative terminals of the screen grid voltage supply (e. g. 500 volts) are marked HT2-{ and HT2- respectively. R is a high resistance. Where an arrangement as shown in Figure 3 is used in conjunction with a cathode ray tube the cathode ray may (if desired) be suppressed during the discharge periods by applying a pulse from` the anode circuit of the valve shown in Figure 3 which pulse may be obtained from across the resistance Re to the control grid of the cathode ray tube. It will be appreciated that during the charging interval of the condenser K1, anode current does not flow as pointed out above in connection with Fig. 2, with the result that there is no potential drop across the resistance Re. When, however, the potential of the condenser K1 is such as to enable anode current to flow through the tube, the anode current owing through the resistance Rs produces a potential drop equal to the magnitude of the anode current multiplied by the resistance of the resistor Re. By using the connection shown in Fig. 3, it will be readily appreciated that the terminal marked HT1- will be negative with respect to the other side of the resistor Re connected to the cathode of the tube, so that during the time when anode current ows, a connection from the terminal HT1 to the control electrode of a cathode ray tube and a connection from the terminal H'Iz-Y to the cathode of a cathode ray tube, will impress a negative voltage on the grid to cut off the beam. It will be appreciated that it is necessary to supply two separate sources of potential I-lTz and I-IT1 in View of the fact that there must be complete independence between the input terminals I at which the synchronizing pulses are inserted and the output terminals O. Further, in order that the voltage developed across the resistor R6 shall be eective to produce suppression at the control grid of the cathode ray tube, the voltage supply I-IT1 is not grounded, but is connected to the resistor Re to ground or cathode potential. Under these conditions, the flow of anode current through R6 produces a negative potential which may be utilized as described above to supply such negative potential to the control grid of the cathode ray tube to suppress the beam during the synchronizing interval. Since the negative terminal of the supply HT1 must be above cathode potential, while the negative terminal of the voltage supply HTz must be at cathode potential, it is clear that separate power supplies arenecessary.

It will be noted that in the electrical time base circuits above described and illustrated a saw tooth like wave form which is highly suitable for deection control in a cathode ray tube oscillograph is obtained by charging a condenser con.- tinuously as in the well known manner and discharging the condenser periodically by a valve having at least three control grids the arrangement being such that, as the condenser charges the anode potential rises till the said anode starts to take current, whereupon a pulse is fed from the anode to one of the valve grids. This pulse exerts a control action upon the electron stream in the valve and produces a pulse upon a second grid which is nearer the anode than said one grid, the pulse upon said second grid being transferred to a third grid which is still nearer the anode. The result of this transfer of the pulse through the electron stream of the valve is to bring about a phase reversal such that the pulse upon the third grid is in such direction as to increase the anode current. In this way a cumulative accelerating action upon the rate of discharge of the condenser is obtained and the discharge proceeds until the anode potential again falls to a cut-off value. In the arrangements of Figures 2 and 3 synchronising action is obtained without any need for additional valves, and, since the synchronising pulses are fedv to the screen grids (the grids G4 and G5) there is substantially zero feed back of relaxation oscillations to the synchronising circuit (connected at terminals I). The arrangements of Figures 2 and 3 co-uld be modied by employing an octode (i. e. a. valve with six grids) and using the sixth grid for the synchronizing pulses.

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 saw-tooth oscillator comprising a condenser, means for continuously charging the condenser at substantially a constant rate to a predetermined value of potential, a thermionic tube having a cathode, an anode and a plurality of grids exceeding two in register between said anode and cathode, means to control the potential of the grid nearest the cathode in accordance with the potential of the condenser, a connection from the charging means to the anode to control the anode potential in accordance with the potential of the condenser, biasing meansto prevent anode current from flowing until the anode potential reachesl said predetermined value of potential, a condenser connected between the grid adjacent to the grid nearest the cathode and one of the other grids, a circuit connected between the grid adjacent the grid nearest the cathode and the cathode, and terminal means to derive output energy from the condenser.

2. A saw-tooth oscillator comprising a ccndenser, means for continuously charging the condenser at substantially a constant rate to a predetermined Value of potential, a thermionic tube having a cathode, an anode and a plurality of grids exceeding two in register between said anode and cathode, a second condenser connected in series with a resistance between the anode and the cathode, a connection between the junction point of the resistance and second condenser to the grid nearest the cathode, a circuit between the anode and the charging means, a condenser connected between the grid adjacent to the grid nearest the cathode and one of the other grids, biasing means connected between the cathode and the third named grid, a circuit connected between the grid adjacent the grid nearest the cathode and the cathode, and terminal means to derive output energy from the rst named condenser.

3. A saw-tooth oscillator comprising a condenser, means for continuously charging the condenser at substantially a constant rate to a predetermined value of potential, a thermionic tube having a cathode, an anode and a plurality of grids exceeding two in register between said anode and cathode, a second condenser connected in series with a resistance between the anode and the cathode, a connection between the junction point of the resistance and second condenser to the grid nearest the cathode, a circuit between the anode and the charging means, a

condenser connected between the grid adjacent;

to the grid nearest the cathode and one of the other grids, biasing means connected between the cathode and the third named grid, a circuit connected between the grid adjacent the grid nearest the cathode and the cathode, a fourth grid intermediate the second and third named grids, a fth grid intermediate the anode and the .third named grid, means to supply synchronizing impulses to the fourth and fth grids, and terminal means to derive output energy from the rst named condenser.

4. A saw-tooth oscillator comprising a condenser, means for continuously charging the condenser at substantially a constant rate to a predetermined value of potential, a thermionic tube having a cathode, an anode and a plurality of grids exceeding two in register between said anode and cathode, means to control the potential of the grid nearest the cathode in accordance with the potential of the condenser, a connection from the charging means to the anode to control the anode potential in accordance with the potential of the condenser, biasing means to prevent anode current from owing until the anode potential reaches said predetermined value of potential, a condenser connected between the grid adjacent to the grid nearest the cathode and one of the other grids, a circuit connected between the grid adjacent the grid nearest the cathode and the cathode, a fourth grid intermediate the second and third named, grids, a fth grid intermediate the anode and the third named grid, means to supply synchronizing impulses to the fourth and fifth grids, and terminal means to derive output energy from the condenser.

5. A saw-tooth oscillator comprising a condenser, means for continuously charging the condenser at substantially a constant rate to a predetermined value of potential, a thermionic tube having a cathode, an anode and a plurality of grids exceeding two in register between said anode and cathode, means to control the potential of the grid nearest the cathode in accordance with the potential of the condenser, a connection from the charging means to the anode to control the anode potential in accordance with the potential of the condenser, biasing means to prevent anode current from owing until the anode potential reaches said predetermined value of potential, a condenser connected between the grid adjacent to the grid nearest the cathode and one of the other grids, a circuit connected between the grid adjacent the grid nearest the cathode and the cathode, a fourth grid intermediate the second and third named grids, a fifth grid intermediate the anode and the third named grid, means to supply synchronizing impulses to the fourth and fth grids, terminal means to derive output energy from the condenser, and means to derive a voltage pulse in accordance with iiow of anode current.

ARTHUR JAMES YOUNG.

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