US2670409A - Thermionic amplifier - Google Patents

Description

Feb. 23, 1954 V. J. COOPER THERMIONIC AMPLIFIER Filed Jan. 29, 1951 Alia Patented Feb. 23, 1954 UNITED STATES @ATEN T OFFICE THERMIONIC AMPLIFIER Victor James (looser, Writtle, England, .assi'gnor to Maintain Wireless Telegraph CcinpanyLi'm ited,.1zondon,- England, a com any hf "Great Britain Application January 29, 1951, Serial No. 208,377

Claims priority, applicationfireatxBritain February 24, 1950 This invention relates to thermionic valvecircuit arrangements and has for its object to provide improved and simple amplifiers and repeaters which may be, if desired, designed to exhibit zero or approximately zero output impedance, very high input impedance (infinite or approaching infinity), low distortion and other advantages which will be particular-ized later herein.

According to this invention an amplifier or repeater comprises a first valve with a load impedance in its cathode circuit, a circuit branch including a second valve, said circuit branch being in series with the first valve and in para1- lel with said load impedance, means cross-coupling the anode circuit of each valve with a control grid circuit of the other, and means for applying input signals to ag'rid of said second valve.

A referred embodiment comprises a first impedance, a first valve, a second impedance and a second valve all in series in the order stated between the positive and negative terminals of a common high potential source, terminals for the connection of a load impedance connected to the cathodes of the two valves, one to each, terminals for the application of input signals, connected one to a control grid of the second valve and the other to the cathode thereof and cross connections between the anode of each valve and the control grid of the other through suitable impedances.

In this specification it is to be understood that any single valve may be replaced by a bank of valves in parallel and the term valve is used in a wide sense to include banks of valves.

The invention is illustrated in the accompanying drawing which shows diagrammatically a preferred embodiment. In the description of the illustrated embodiment, for the sake of clarity identifying references used to identify the various impedances, are used also to define their values. Further, in the illustrated circuit triode valves are shown and described but this is done merely for the sake of simplicity, and other suitable forms of valve with more than one grid may be used. Also for the sake of simplicity only those parts of the circuit necessary to an understanding of the invention are desired, bias circuits and the like details being omitted.

Referring to the drawing two triodes VI, V2 are employed of which the valve VI has its anode Al connected to HT+ through an impedance ZI and the second valve V2 has its cathode C2 connected to HT- and earth. The cathode Cl 2 of the first valve is "connected to the anode in of the second through an impedance '22. The anode A2 is also connected to the grid GI of the first valve either directly-as shown (this will be assumed in the following mathematical statements) or through a desired suitable'networl'c. The anode A1 is connected to the gridGZ of the second valve through an impedance Z3. A load, represented by an impedance Z1. is connected at the output terminals Out between the cathode Cl and HT-. Input from a source, which is conventionally represented as a generator G "in series with its own internal impedance Zt is applied at the input terminals In between the control grid G2 and HT-.

With this arrangement the "load is shared between the 'two valves in a push-pull manner and sharing can be adjusted by adjusting Z! and Z2 in, relation to one another. It maybeeither equal or either valve-may be-caused to take'the major share as may be desired.

It may be shown that the output impedance may be broughtto zero by satisfying the equation:

(Rea-H22) (Rail-+21) (Zed-Z4) (Rea-f-Zz) Ra1Z1=,u1,w2Z1Z2Z4 where n and ,u.2 are the amplification factors of the valves VI and V2 respectively and R31 and Rita are the respective impedances of these valves.

It may also be shown that the input impedance is dependent on Z1. and can be made infinite by satisfying the equation:

In the condition where output impedance is zero and input impedance infinity a gain of the order of ,u/Z is attainable, it being assumed, for the purpose of this statement, that each of the two valves has the same amplification factor i.

By suitably biasing the valves (bias circuits have not been described or shown since they may be as well known per se) it is possible to increase the mean current through the valves to a high value without materially affecting the impedances operating in the circuit and the valves thus operated well away from low current regions where the characteristics become nonlinear. This expedient not only greatly reduces distortion but enables greater reactive currents to be handled without risk of cut-off and without need to reduce the load impedance as has to be done in the case of conventional class A amplifiers.

The two valves deliver current to the load in push-pull and. share the same mean current. Accordingly the high tension supply requirements are approximately halved as compared to a conventional amplifier, approximately doubling the conversion efliciency for a given output in terms of volt-amperes.

It will be observed that supply fluctuations will appear at the output terminals substantially.

in phase opposition to the fluctuations at the supply terminals. If, therefore, an amplifier in accordance with this invention and a driving amplifier therefor, are both supplied from the same D. C. source, supply fluctuations produce opposite effects in the amplifier described and in the driving amplifier and, by suitable design, it is possible to secure virtually complete cancellation overall of the effects of supply fluctuations.

I claim:

1. A thermionic valve amplifier or repeater comprising a first valve including at least a cathode, a control grid and an anode with a load impedance (ZL) in its cathode circuit, a circuit branch including a second valve, having at least a cathode, a control grid and an anode, said circuit branch being in series with the first valve and in parallel with said load impedance, said load impedance being connected between the cathodes of the two valves, and the cathode of said first valve being connected to the anode of said second valve through an impedance (Z2) forming part of said circuit branch, an impedance (Z3) connected between the anode of the first valve and the control grid of the second valve, a connection between the anode of the second valve and the control grid of said first valve, an input circuit connected to apply input signals between the control grid of said second valve and the cathode thereof, output terminals connected to the ends of said load impedance, a common high potential source having its positive terminal connected to the anode of said first valve through an impedance (Z1) and its negative terminal connected to the cathode ofsaid second valve and means for holding the 4 cathode of said second valve at anchored potential.

2. An amplifier or repeater as set forth in claim 1 and having its circuit elements dimensioned substantially to satisfy the equation:

V zzamplification factor of the second valve V 3. An amplifier or repeater as set forth in claim 1 and having its circuit elements dimensioned substantially to satisfy the equation:

in which ZL=load impedance Ra1=impedance oi the first valve Z1=impedance Ra2=impedance of the second valve Z2=impedance =amplification factor of valve V z=amplification factor of valve V VICTOR JAMES COOPER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,438,960 Blitz Apr. 6, 1948 2,631,197 Vilkomerson et a1. Mar. 10, 1953 FOREIGN PATENTS Number Country Date 412,182 Great Britain June 19, 1934.- 565,870 Great Britain Mar. 31, 1944

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