US2550029A - Electron discharge valve amplifier - Google Patents

Description

April 24, 1951 v E. L. c. WHITE 2;550,029

ELECTRON DISCHARGE VALVE AMPLIFIER Filed Aug. 8, 1947 e/273r' ERIC LAWRENCE CA SLING WHITE 66712571;

Patented Apr. 24, 1951 ELECTRON DISCHARGE VALVE AMPLIFIER Eric Lawrence Casling White, Iver, England, as-

signor to Electric & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application August 8, 1947, Serial No. 767,412 In Great Britain July 10, 1939 Section 1, Public Law 690, August 8, 1946 Patent expires July 10, 1959 6 Claims.

The present invention relates to electron discharge valve amplifiers.

The object of the present invention is to provide an electron discharge valve amplifier arrangement in which the gain of the arrangement is stabilised for small fluctuating potentials by means which is only operative in respect of fluctuations of very low frequency outside the range of frequencies which it is desired to amplify. In the preferred embodiment of the invention an electron discharge valve is employed which operates with electron multiplication.

Due to space charge limitation, the mutual conductance of a thermionic valve, such as a trlode or pentode as ordinarily operated, should theoretically var approximately proportionately to the cube root of the anode current, though it is found in practice that the mutual conductance varies more nearly as the square root of the anode current. However, in the case of a valve having several stages of electron multiplication, the primary cathode emission may be so small as not to be limited by space charge and it is then found that due to the thermal distribution of velocities of the electrons emitted from the cathode, the primary current varies exponentially with control grid voltage. Thus, for example, in the case of a multiplier valve having a screening grid between the control grid and the first multiplier electrode, if i1; is the current flowing towards the screen of the valve and Vg the potential applied to the control grid, then 'Zk Ae Q where A and B are constants. Difi'erentiating with respect to V we have dik BV --A.Be 9

Furthermore, let m be the fraction of the current in passing through the screen to the first multiplier electrode, m, the number of multiplier electrodes, is the multiplying factor of each multiplier electrode and z the final anode current.

Thus from Equation 1 above,

And from Equation 2 above, we have That is to say, the mutual conductance of the valve is proportional to the anode current and will be constant if z is constant.

It will be seen from Equation 1 that the direct proportionality between mutual conductance and anode current also holds in the case of a valve operating without multiplication provided that the emission from the cathode is exponentially related to grid voltage.

According to the present invention an electron discharge valve amplifier arrangement for small fluctuations is provided comprising an electron discharge valve having a cathode, an anode and a control electrode arranged to be operated in such manner that the emission from said cathode to said anode is substantially related exponentially to the voltage between said control electrode and said cathode, a resistive impedance connected between said anode and a source of positive potential, and a negative feedback circuit between said anode and said control electrode, said feedback circuit being arranged to be substantially inoperative at the frequencies of the signals which it is desired to amplify, but to be operative at frequencies below said signal frequencies in such manner that in operation the mean anode current of the valve is maintained substantially constant in respect of slow fluctuations whereby the amplification of said signals is stabilised.

In order that the said invention may be clearly understood and readil carried into effect, the same will now be more. fully described with reference by way of example to the single figure of the accompanying drawing, which is a circuit diagram of a thermionic valve amplifier embodying the invention and including several stages of secondary'emission multiplication.

Referring to Figure 1, I is a thermionic valve for operation with electron multiplication having a cathode 2, control or input grid 3, screen grid 4, secondary emitting electrodes 5, 6, I and 8, at which multiplication is effected, and anode I I. Each secondary emitting electrode is connected to a point of successively higher potential on the potentiometer 9 which is connected across the high tension supply source It, the various divisions of the potentiometer 9 having decoupling condensers 9a arranged in parallel. The poten- '.tial for the screen grid '4 is derived from the lowest tapping on the potentiometer 9. The

anode of the valve is indicated at I l and is shown as connected to the positive pole of source l through load resistance I2 and decoupling resistance [3, a decoupling condenser l4 being con nected to resistances I2 and I3 and also to earth in well known manner. connected between the anode ll of the valve I and the negative pole of a source of potential l6 of which the positive pole is connected to earth and to the negative pole of source |0,and the grid 3 is connected to a tapping on this potentiometer. The bias potentials should be chosen so that the emission from the cathode of the valve is so small as to be substantially xpo-: nentially related to the voltage between the grid and cathode. Signals to be amplified may be applied to the grid 3 through the condenser, 1| 1,.

A potentiometer i is I at the signal frequencies which it is desired to amplify and to be operative at frequencies below said signal frequencies, thereby causing the mean anode current of said valve to be maintained sub- ""-stantially constant in respect of slow fluctuations of said anode current, whereby the amplification of said signals is stabilized.

3. An electron discharge valve amplifier arrangement comprising an electron discharge valve having a cathode, an anode and a control elec- It will be seen that in the arrangement de-' scribed above, if the grid 3 becomes more positive"ii with respect to the cathode 2, the anode current will increase and the potential of the anode M will become more negativeand will tend to cause the grid 3 to become more negative thereby tending to oppose the rise of potential on grid 3 by which the increasing anode current has been produced so that the anode current tends to remain constant. In order to prevent the feedback arrangement from being effective at the frequencies it isdesired to amplify, and thereby reducing the amplification at such frequencies, the coupling condenser i1 is chosen so that, together with the impedance of the source of signals, it provides a low impedance in shunt with the input resistance between the grid 3 and the cathode 2 down to the lowest signal frequencies. It will be appreciated that the input resistance between the grid 3 and the cathode 2 comprises the resistance of the lower branch of the potentiometer [5 in parallel with the resistance of the upper branch thereof divided by l +G, where G is the voltage gain from grid to anode of the valve I.

What I claim is:

1. An electron discharge valve amplifier arrangement comprising an electron discharge 'valve having a cathode, an anode and a control electrode, a source of bias voltage for said valve proportioned to cause the emission from said cathode to said anode to be substantially exponentially related to the voltage between said control electrode and said cathode, means for applying signal to be amplified to said valve, a resistive impedance connected between said anode and a source of positive potential, and a negative feedback circuit between said anode and said control electrode, said feedback circuit having an associated frequency selective impedance proportioned to cause said feedback circuit to be substantially inoperative at the signal frequencies whichit is desired to amplify and to be operative at frequencies below said signal frequencies, thereby causing. themean anode current of said valve to be maintained substantially constant in respect of slow fluctuations of said anode current, wherevby the amplification of said signals is stabilized.

" 2. An electron discharge valve. amplifier arrangement comprising an electron. discharge valve 7 having acathode, an anode, a control electrode and at least one. stage of electron multiplication between said control electrode and anode,-a source of bias voltage for said valve proportioned to. cause the emission from said cathode to said anode to be substantially exponentially related to the voltage between said control electrode and said cathode, means for applying signals to be. amplified ;to said valve, a resistive impedance connected trode, a source of bias voltage for said valve proportioned to cause the emission from said cathode torsaid' anode to be substantially exponentially related to the voltage between said control electrode and said. cathode, a source of signals to be amplified, means for applying said signals to said valve, aresistive impedance, connected between said anode and a source of positive potential, and a negative feedback circuit between said anode and said control electrode, said feedbackcirc'uit having an associated frequency selective impedance proportioned tocause said feedback circuit to be substantiallyinoperative at the signal frequencies which it is desired to amplify and to be operative at frequencies below said signal frequencies, thereby causing the mean anode current of said valve to be maintained substantially con- ,stant in respect of fiowfiuctuations of said anode i current, whereby the amplification of said signals is stabilized.

4. An. electron discharge valve amplifier arrangement comprising an electron discharge valve havingla cathode, an, anode and a control electrode, asource of bias voltage for said valve proportioned to causetheemission from said cathode to said anode to be substantially exponentially related to thevoltaige between said control electrode and said cathode, a source of signals to be amplified, a condenser coupling said source of signals to said control electrode, a resistive impedance connected between said anode .and a source of positive potential, and a negative feedback circuit between saidanode and said control electrode, said feedback circuit including a resistive impedance and said coupling condenser and being proportioned to the impedance of said source of signalsfto provide a low impedance in shunt with the input resistance between said control electrode and cathode for causing said feedback circuit to, be substantially inoperative at the signal frequencies which it is desired to amplify and to be operative at frequencies below said signal frequencies, thereby causing the mean anodecurrent of saidvalve -to-be maintainedsub- .stantially. constant in respect of slowfluctuations of said anodehcurrent, whereby the amplification of said signals is stabilized. I

5,. An electron discharge valve amplifier arrangement comprising an electron discharge valve having a cathode, an anode and a control electrode and at least one'stageof electron multiplication between said control electrode and anode, a sourcebfbias voltage for said "valve proportioned to cause thegemissionfrom said cathode to said anode to be substan'ti'ally exponentially related to the voltage between said control electrode and said cathode, a source of signals to'be amplified, means for applying said-signals to said valve, a resistive impedance connectedbetween said anode and a source of positive potential, and a negative feedback circuit between said anode and said control electrode, said feedback circuit having an associated frequency selective impedance proportioned to cause said feedback circuit'to be substantially inoperative at the signal frequencies which it is desired to amplify and to be operative at frequencies below said signal frequencies, thereby causing the mean anode current of said valve to be maintained substantially constant in respect of slow fluctuations of said anode current, whereby the amplification of said signals is stabilized.

6. An electron discharge valve amplifier arrangement comprising an electron discharge valve having a cathode, an anode and a control electrode and at least one stage of electron multiplication between said control electrode and anode, a source of bias voltage for said valve proportioned to cause the emission from said cathode to said anode to be substantially exponentially related to the voltage between said control electrode and said cathode, a source of signals to be amplified, a condenser coupling said source of signals to said control electrode, a resistive impedance connected between said anode and a source of positive potential, and a negative feedand to be operative at frequencies below said signal frequencies, thereby causing the mean anode current of said valve to be maintained substantially constant in respect of slow fluctuations of said anode current, whereby the amplification of said signals is stabilized.

ERIC LAWRENCE CASLING WHITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,621 Kapteyn Dec. 28, 1937 2,190,069 Hollmann Feb. 13, 1940 2,190,743 Vance Feb. 20, 1940 2,202,522 Gloess May 28, 1940

Images