US1642526A - Means for supplying power to thermionic valves - Google Patents

Description

, Sept. 13,1927.

I 1,642,526 a. M. WRIGHT MEANS FOR SUPPLYING POWER TO THERIIONIG VALVES Filed Aug. 17. 1926 nmmmmm INVEN TOR.

A TTORNEY.

Patented .-Sept. 13, 1927.

UNITED STATES}- P ENT i OFFICE.

PORATION OI- AHEBICA, A CORPORATION 01 DELAWARE.

mums iron surrLYnvG rowan 'ro rr'mimromc 'vanvns.

Application filed August 17, 1929, Serial No. 129,897, and in Great Britain August 15, 1995.

This invention relates to improved means for sup lying the high tension power for a thermionic valve from an ordinary power supply circuit or the like. 5 In many cases it is desirable for practlcal reasons to supply power from direct current generators or public supply mains, as, for example, to valves in central telegraph ofiices or to the valves of broadcast receivers.

When, however, power is supplied 'to the anode circuits of thermionic valves from ordinary power supply circuits, difiiculties arise from two main causes I (1') The fairly large semi-permanent :5 changes in the-supply voltage w ich occur fromtime to time owing to variations 1n the load on the feeders. These changes tend to affect the anode supply to the .valves and may put the direct current bridges ina telegraph oflice out of adjustment.

(23 The ripples superimposed on the stea y direct current voltage, which ripples are caused by commutation and .by the armature teeth in the generators supplying the ."5 circuit. Such ripples give rise to a hum in the filament, where R is the series resistance audio circuits or in broadcast receivers.

According to the present invention potential is so applied from a power circuit or the like to the anode and .to the grid of a thermionic valve, that when a change in the electromotive' force applied to the anode occurs, there will be a change of opposite effect in the electromotive force applied'to the grid,

the proportions between the electromotive forces applied being such that the effective output of the valve remains substantially constant.

In'one form of construction, suitable for use in a transformer coupled amplifier, the

40 terminals of the power supply are shunted by a resistance, and the positive terminal is connected through the primary of the intervalve transformer to the anode of the valve.

At a point along the resistance, a connection is taken to the filament of the valve and the grid circuit connection-is made to the negative terminal of the power supply. The

usual biasing battery may be included in series with the input terminal. The tapping .Q point for the filament connection is such that it divides the resistance into two parts, so

that the required compensating voltage is applied to the grid. I have found that this compensation is'obtained whenthepart of the resistance adjacent the anode is approximately 111, times that adjacent the id, where m is the magnification factor 0 With this arrangement so long as the valve the valve.

is working on the substantially straight partof its characteristic curve may change in the voltage applied to the am) will be compensated or by -a change of opposite effect in the voltageapplied to the grid, so that the effective output of the valve, which in this case isthe anode current, remains substantially constant.

In a modification, suitable for use in a re-' sistance coupled amplifier, the grid circuit connection'is made to the tapping point upon the reslstance, and the filament and anode circuit connections are made each to one end of the said resistance and to the-negative and positive terminals of the power supply respectively. With this arrangement I have found the required compensation to be obtalned and the effective output of the valve (in this case the anode voltage) to remain substantiall unafiected byvariations in the power supp y when the part of the resistance adjacent the anode is Ra times that adjacent Any potential dividing arrangement maybe used in place of the resistance hereinbefore referred to. A convenient method, in

.the case where the supply is from a local motor generator or the like, is to provide an extra brush resting on the commutator thereof, which brush serves as the filament tapping point. This arrangement avoids the losses which occur when resistances are used. It may be desirable to provide condensers in shunt across the tapping points of the resistances or the like. When such condensers are used, their impedances should be in the before-mentioned ratio.

The arrangements hereinbefore described are suitable for use with direct current'supply from an ordinary power circuit. If alternating current power supply only is available, such arrangements may conveniently be employed in con'unction with rectifiers. "The invention is i ustrated in the accomanying drawing, in which Figure l is a diagram of a transformer coupled amplifier, according to the invention; Figure 2 is 0. diaram of a resistance capacity coupled 'amplifier and Figure 3 is a diagram of a resistiaince battery coupled direct current ampli- Referrin to Figure 1, V is a thermionic valve and the input terminals, whercbythe impulses to be amplified are applied between the grid and filament of the said valve. T is an. output transformer, whose secondary v is connected to output terminals 0. M+

rent characteristic 0 and M- are the positive and negative terminals of the power supply, which is connected across the ends of a resistance NFP, the part PF of which is included in the anode circuit of the valve, the part NF being included in the grid circuit thereof. B is a rid bias battery. I have found that satisactory com ensation is obtained when the parts F, F of the resistance are so proportioned that p are where m is the magnification constant of the valve.

It will be seen that when fluctuation, say, an increase of anode potential, occurs, a compensating fall of grid voltageis occasioned, so that the anode current remains substantially constant.

In Figure 2, those parts corresponding to parts shown in Figure 1 are indicated by like reference letters. G is a coupling condenser.

The arrangement shown diagrammatically in Figure 3 is suitable for use as a direct current amplifier, and is generally similar to that shown in Figure 2, except that the caacitv G (of the said Figure 2) is replaced y a batte D, whereby the grid of the succeeding va ve (not shown) can be adjusted to the correct potential.

I have found that in this case satisfactory compensation results are obtained when stir FP Ra.

when R is the anode series resistance and a is the slope of the rid voltage-anode ourthe valve.

It will be seen, in this case, that if an increase in anode otential occurs, a compensating rise of grid voltage is occasioned, so that the anode potential to negative end of filament remains substantially constant.

The invention is also applicable to amplitiers of the so-called choke coupled or inductive resistance coupled type.

Having described my invention, what I claim is:

1. Means for supplying current from a power circuit to a resistance coupled thermionic tube having cathode, anode and grid electrodes, including a resistance shunting the terminals of the power supply, and a connection from said resistance to the grid of the tube, said connection dividing the resistance in such a manner that one art is included in the anode circuitof said tu e and the other part included in the grid circuit, the ratio of the resistance of the grid circuit to that in the anode circuit being equal to the reciprocal of the anode series resistance multiplied by the slope of the grid voltageanode current characteristic of the tube.

2. The method of maintaining the anode potential of a resistance coupled thermionic valve substantially constant when the valve is receiving its power from direct current generators subject to fluctuations. consisting in inserting resistances in the anode and grid circuits of the valve, the ratio between said resistances being equal in value to the anode series resistance multiplied by the slope of the grid voltage-anode current characteristic of the valve by any change occurring in the electromotive force applied to the anode will produce a corresponding change in the electromotive force applied to the grid.

3. In an amplifier arrangement having an output circuit, a series resistance in the output circuit, means for supplying current from a power circuit to'said amplifier arrangement, a resistance shunting said power supply, the cathode of the amplifier and the output circuit being connected to the terminals of the shunt resistance,.and the grid of said amplifier being tapped off from said shunt resistance at a point intermediate of its terminals, said resistance being divided in such manner that the ratio of the portions included in the input and output cireuitsis equal to the reciprocal of the anode series resistance multiplled by the slope of the grid voltage-anode current characteristic of the amplifier.

4. The method of maintaining the potential difl'erence between the anode and filament of an impedance coupled thermionic valve substantially constant when the valve is supplied with a resistance shunted fluctuating source of direct current which consists in including portions of the resistance in the input and output circuits of the valve in such a manner that the ratio of the portions included in the inputand output circuits is equal to the reciprocal of the anode series resistance multiplied by the slope of the grid voltage-anode current characteristic of the thermionic valve.

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