US2201345A - Thermionic valve repeating arrangement - Google Patents

Description

Patented May 21, 1940 UNITED STATES PATENT OFFICE THERMIONIC VALVE REPEATING ARRANGEMENT Application May 7, 1938, Serial No. 206,644 In Great Britain May 11, 1937 9 Claims.

The present invention relates to thermionic valve circuit arrangements for repeating signals from one line or circuit into another, and more especially to thermionic valve circuit arrangements which include valves each having a loading impedance inserted in its cathode circuit so that the potential of the cathode varies in correspondence with the potential of the grid. The potential variations of the cathode may be arranged to be in phase with the potential of the grid and to be comparable in magnitude with those of the grid. Examples of such circuits are described in British patent specification No. 448,421.

According to the invention a thermionic valve circuit for repeating signals from one line or circuit into another is provided comprising a pair of similar valves connected in push-pull relation and each having a control electrode to which input potentials are applied, the anode of each valve being connected to the cathode of the other valve at least in respect of currents of signal frequency, and the two signal frequency paths constituted by the inter-connection of the cathodes and anodes having associated with them a symmetrically disposed load or loads including at least one output circuit into which signals are to be repeated, said load being so arranged that the potential at a point of connection of each anode and the cathode of the other valve is caused to execute variations of potential in dependence on variations in the applied input potential or potentials.

In one preferred embodiment of the invention each valve has a loading impedance between its cathode and earth, there being an output circuit connected between the cathodes of the two valves or across one or each of the loading impedances. The loading impedances may be made large com- 40 pared with the reciprocal of the mutual conductance of a valve, in which case the output impedance of the arrangement with respect to an output line connected between the two cathodes will be of the order of said reciprocal, so that from abalanced or anunbalancedline the arrangement may be used for repeating from an unbalanced line into a balanced line. However, if required, a pair of unbalanced outputs may be obtained from the arrangement so that the invention may also be applied where signals are to be repeated from a balanced line into an unbalanced line, though in the case where only one output is utilised a dummy load must be provided on the other output. Conveniently, one of the pairs of 10 unbalanced outputs may be used to supply a monitor circuit.

Owing to the fact that even harmonic distortions do not appear or are negligible in an arrangement according to the invention, the power 1 output of the arrangement may be considerably higher in proportion with reference to known are rangements, than that indicated above before serious distortion appears in the output.

The nature of the invention and the method of carrying the invention into eifect will be clearly understood from the following description in detail reference being made to the accompanying drawing of which Figures 1, 2 and 4 are each a circuit diagram of a possible arrangement em bodying the invention, and Fig. 3 is the equiva lent circuit or" the repeater arrangement shown in Fig. 2.

Referring to Fig. l of the drawing, the arrangement thereon shown is seen to comprise two similar triode valves l and 2, the control grids of which are connected one to each side of a balanced input line indicated by 3. The gridcathode circuit of each valve may be completed in any suitable way, for example, through a leak resistance I2 or l3 as the case may be and bias battery M or l5, as shown in the drawing. The anode of each valve is connected to the cathode of the other through high tension batteries 4 and 5 respectively, and between the cathode of each valve and the earth lead 6 is connected a resistance 1 or 8 over which the D. C. path for the anode currents of the valves is completed, both resistances being of the same value. The valves are thus of the cathode follower type.

The cathode sides of the resistances 1 and 8 have connected to them the two sides of an output line 9 as shown, which is shown as being carried through a shielded cable It), the shield being'earthed over leads II and 6. Lines 3 and 9 are both balanced.

The method of operation of the arrangement is as follows: v

The anode current of valve I flows from bat tery 4 to the anode of valve I, from. anode to cathode of valve I, through resistance I, over lead 6, through resistance 8 and back to battery 4, or from battery 4 to the anode of valve I, from anode to cathode of valve i, from the cathode of valve I over, cable l and the load connected thereto, and then back to battery 4. g

Similarly the anode current of valve 2 flows from battery 5 to the anode of valve 2, from anode to cathode of valve 2, over resistance 3, over lead 6, through resistance 1 and back to battery 5, or from battery 5 to the anode of valve 2, from anode to cathode of valve 2, from the cathode of valve 2, over cable it! and the load connected thereto, and then back to battery 5. It will be seen that the steady currents of both valves l and 2 flow through each resistance 7 and 8, and the output load in parallel, the direction of flow of each current being in opposite directions. As the circuit is syrmnetrical, if equal signals or D. C. potentials are applied to the two control grids simultaneously, the resulting anode currents will be equal. As these anode currents flow in opposite directions in each resistance, the net potential developed in each impedance, due to the flow of anode current, will be nil, and no effeet will be produced in line 9. Thus effects due to varying D. C. bias on the two control grids, or push-push effects, do not appear in the output line 9. On the other hand, if positive and negative signals respectivel are applied simultaneously to the control grids of valves 5 and 2, the changes in potential due to the variation of each anode current flow in resistances I and 8 together, and as the net potential changes on each impedance are opposite in sense, the signal arriving over line 3 will be repeated into line 9, and second harmonic components due to curvature of the valve characteristic are balanced out.

Again referring to the arrangement of Figure 1, assume that an input voltage of one volt balanced with respect to earth, be applied between the two cathodes of the valves i and 2, both grids being earthed. This is equivalent to applying volt and volt to the cathodes of valves l and 2 respectively. Now volt on the cathode of valve i would cause a change in anode current of 9/2 where g is the mutual conductance of the valve and the application of a potential of volt to the cathodes of valve 2 will cause a change in anode current of g/2. Hence the total potential of one volt distributed equally between the cathodes of the valves will cause a total change of current from cathode to cathode of g, so that the output impedance of the arrangement will be 1/9. Thus, with valves having the value of g of 2 milliamps per volt, which is quite a usual value, the output impedance will be 500 ohms, in parallel with ER, where R is the value of resistance l or 8, which is assumed tobe sumciently large to be neglected. Thus if the input impedance of the line 9 is substantially equal to 500 ohms, with the valves referred to, in an arrangement according to the invention, there is no need to provide an output transformer for matching the repeater to the output line.

In applying the invention in some cases, the requirements in respect to the transmission of low frequency signals may not be very rigorous. In such a case the circuit shown in Figure 1 may be replaced by a circuit such as shown in Figure 2 in which both valves l and 2 are supplied from a single high tension source over the lead 20, which is connected to the. anodes of valves 1 and 2 respectively, over equal impedances shown as resistances 2i and 22.

In this case the anode of valve l is connected to the cathode of valve 2 through condenser 23 and the anode of valve 3 is connected to the cathode of valve I through condenser 2Q, condensers 23 and 24 being equal. In this case, if the impedances 21 and 22 each have a value Z and the condenser 23 and 2d a capacity of c then, for a signal of pulsatance w applied over the input line 3, the current flowing from the anode of one valve to the cathode of the other will only be the fraction of the total anode current of each valve.

Now if a hypothetical potential of 1 volt is applied across the cathode of valves l and 2, as was done in the case of the arrangement of Fig. 1, it will be seen that the current flowing from the source will be:

g jwCz l+jwzc neglecting l/g compared with e.

The output impedance is therefore and the equivalent circuit of the output impedance is shown symmetrically in Fig. 3, one half of the impedance comprising a resistance of value l/g in series with a condenser of value yea and resistance of value l/g in series.

The output impedance of the arrangement of Fig. 2 reduces to substantially l/g for high frequencies as in the case of Fig. l, but for low frequencies the impedance increases to the value 2/g.

Thus with the arrangement of Fig. 2, when repeating low frequency signals, it may be necessary to use an equalizer.

If desired, instead of or as wall as the connecting output line 9 between the impedances and 8, on the cathode sides of the valves 1 and 2, an output line or circuit might be connected between the impedances 2| and 22 on the anode sides of the valves.

If desired, where the output load affords a suitable D. C. path for the anode currents of the valves I and 2, the resistances T and 8 may be omitted, the anode circuits of both valves being completed over the load into which the repeater works.

In the circuit shown in Figure i an arrangement according to the invention is shown which does not work into a push-pull output circuit but in which output lines may be connected across the resistances land 8 as indicated at 30 and 3!. The output loads in this case are of course unbalanced. In this case, the output impedance at either output is determined by the impedance other than the loading impedance included in or associated with the output in the anode circuit of the valve in the cathode lead of which the output is connected, and may be shown to be where Z represents the value of the loading impedance of the other valve of the pair. As both loading impedances have equal values, the output impedance of outputs taken from the cathode leads of either valve will be the same. The arrangement of Fig. 4 will be seen to be not en tirely suitable for supplying a load which requires to be fed from its own impedance unless Z is much greater than 1/9. The undistorted output power in each cathode load is twice that of a single cathode follower valve having characteristics similar to those of valves l and 2. Thus this arrangement gives as much power on one side only, as would be given by an arrangement of two valves in parallel worked off an unbalanced circuit. The arrangement of Figure 4 is advantageous Where a monitoring circuit is required to be connected in the arrangement as this circuit may furnish one of the loads, while the main transmission channel may constitute the other load.

In cases where only one load is required to be supplied, however, a dummy load must be employed in connection with the other cathode.

If desired, an output or outputs from the arrangement of Fig. 4 might be obtained by providing loading impedances connected to the anode of each valve rather than to the cathode.

I claim:

1. A thermionic valve circuit arrangement for transmitting signals, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode to which input potentials may be applied, an anode and a cathode, a separate resistor connected between each cathode and ground, a source of potential connected to each anode, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, said paths having associated with them the cathode resistors which constitute a symmetrically disposed load so arranged that potential variations are set up at points in said paths in dependence on the applied input potentials and including at least one output line or circuit in which said potential variations are utilised.

2. A thermionic valve circuit arrangement for transmitting signals, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode to which input potentials may be applied, an anode and a cathode, a source of potential connected to each anode, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, said paths having associated with them a symmetrically disposed load including a loading impedance connected between each cathode and a point of fixed or reference potential, with respect to which said input potentials are applied, each path being connected to one of said impedances at the end nearest the cathode and an output line or circuit having at least one side connected to one cathode.

3. A thermionic valve circuit arrangement for transmitting signals, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode to which input potentials may be applied, an anode and a cathode, a separate resistor connected between each cathode and ground, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, each path including a source of high potential, said paths having associated with them the cathode resistors which constitute a symmetrically disposed load so arranged that potential variations are set up at points in said paths in dependence on the applied input potential and including at least one output line or circuit in which said potential variations are utilised.

4. A thermionic valve circuit arrangement for transmitting signals, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode to which input potentials may be applied, an anode and a cathode, a separate resistor connected betweeneach cathode and ground, a source of potential connected to each anode, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, said paths having associated with them the cathode resistors which constitute a symmetrically disposed load so arranged that potential variations are set up at points in said paths in dependence on the applied input potential and including a symmetrically disposed output line or circuitconnected one side to each of said paths and in which said potential variations are utilised.

5. A thermionic valve circuit arrangement for transmitting signals, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode to which input potentials may be applied, an anode and a cathode,

a source of potential connected to each anode, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, said paths having associated with them a symmetrically disposed load including a loading impedance connected between each cathode and a point of fixed or reference potential, with respect to which said input potentials are applied, each path being connected to one of said impedances at the end nearest the cathode, and there being at least one output line or 'circuit as symmetrically connected in saidload and connected across one of the said impedances to utilise'the potential variations produced thereover.

6. A thermionic valve circuit arrangement for transmitting signals, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode to which input potentials may be applied, an anode and a cathode, a source of potential connected to each anode, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, said paths having associated with them a symmetrically disposed load including a loading impedance connected between each cathode and a point of fixed or reference potential with respect of which said input potentials are applied, each path being connected to one of said impedances at the end nearest the cathode, and there being a pair of output lines or circuits symmetrically connected in said load, one line or circuit being connected across one said impedance and the other line or circuit being connected across the other said impedance.

7. In a signal transmission system, a thermionic valve circuit arrangement for repeating signals from an input line or circuit into at least one output circuit, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode to which one side of said input line or circuit is connected, a separate source of potential connected to each anode, a separate resistor connected to each cathode, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, said paths having associated with them the cathode resistors which constitute a symmetrically disposed load so arranged that potential variations are set up at points in said paths in dependence on potentials developed in said input line, said output circuit being arranged in said load in such manner as to utilise said potential variations.

8. In a signal transmission system, a thermionic valve circuit arrangement for repeating signals from an input line or circuit into a line or circuit which is balanced with respect to a point of fixed or reference potential, the arrangement comprising in combination a pair of similar thermionic valves connected in push-pull relation, each valve having a control electrode effectively connected to one side of said input line or circuit, an anode, and a cathode, a source of potential connected to each anode, paths connecting the anode of each valve to the cathode of the other at least in respect of currents of signal frequency, said paths having associated with them a symmetrically disposed load including a loading impedance connected between each cathode and said point of fixed or reference poten:

tial, each path being connected to one of said impedances at the end nearest the cathode, and

said balanced output line or circuit being connected one side to each cathode.

9. In a signal transmission system, a thermionic valve circuit arrangement for repeating signals from an input line or circuit into an output line or circuit unbalanced with respect to a point of fixed or reference potential, the arrangement comprising in combinationa pair of similar sociated with them a symmetrically disposed load including a loading impedance connected between each cathode and said point of fixed or reference potentialywith respect to Which said input potentials are applied, said output line or circuit being connected across one of the said impedances to utilize the potential variations produced thereover.

WILLIAM SPENCER PERCIVAL.

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