US1996507A - Amplifier - Google Patents

Description

April 2, 1935. w. w. EITEL AMPLIFIER Filed Dec. 9, 1932 2 Sheets-Sheet l I O O INVENTOR.

WILL/AM W. E/TEL.

ATTORNEY April 2, 1935.

w. w. EITEL 1,996,507

AMPLIFIER Filed Dec. 9, 1932 2 Sheets-Sheet 2 F z'g.5

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Wm hunk INVENTOR WILL/AM WI E/TEL.

ATTORNEY Patented Apr. 2, 1935 omrro STATES Application December '9, 1932, Serial No. 646,469

9 Claims.

My invention relates to .amplifiers, and particularly to amplifiers designed for operation at the higher radio frequencies.

Among the objects .of my invention are: To

c provide .an amplifier capable of providing large amounts of output power; to provide an amplifier having extremely low output impedance and relatively high input impedance; to provide an amplifier wherein the output circuit is substantially without effect upon the input circuit; to provide an amplifier which may .be used almost at the point of self-oscillation without afiecting materially the input constants of the amplifier; and to provide an amplifier wherein the type of vacuum tube characterized by a plate-like control electrode mounted in opposition to a similarly formed output electrode maybe utilized to provide large power outputs at relatively ,high efficiency.

Other objects of my invention will be apparent or will he specifically pointed out in the description forming a part of this specification, but I do not. limit myself to the embodiment of my invention herein described, as various forms may be adopted within the scope of the claims.

Referring to the drawings;

-Figure 1 is a view, partly in elevation and partly in section, of a tube adapted for usein the amplifier of this invention.

Fi u 2 is a transverse section of the tube shown in Figure 1, the plane oi projection being on the line '2.2 of the first figure.

Figure 3 is a fragmentary sectional view of the tube, taken on the line 3?3 of Figure 2, and showing the auxiliary accelerating electrode.

Figure 4 is .a circuit diagram of the amplifier.

Figure 5 is a similar diagram showing a modified form of the amplifier.

The invention involves the use of a vacuum" tube having the usual cathode, anode, and control electrode, and, in addition, an accelerating electrode whose function is to increase the mutual conductance or transductance of the tube by increasing the velocity of electrons leaving the fila-' 45 ment, and neutralizing or partially neutralizing the space charge thereof. Such an electrode, it will be seen, has a certain degree of control over the space current, and this control is in the same sense as that of the control electrode, i. e., a negative swing in potential of the control electrode decreases the space current, while apositive swing increases this current.

The input circuit of the amplifier is connected to the control electrode in the usual manner, while the anode connects to the outpu c rc case by a band or clamp l2 surrounding a 're- I entrant stem M at one-end of the tube.

The accelerating electrode is coupled to the anode in such a manner as to augment the effect of the control electrode on the space current; i. e., so that adecrease in space current impresses a less positive potential upon the accelerating eIectrode. In this manner theeffectiveItransductance of the tube is very greatly increased, as is the effective amplification constant,.butthere is no reaction upon the input circuit of the device as is the case where regeneration or feedback is used. It is therefore possible greatly to increase the amplification and power output of the tube without introducing the distortion present inregenerativ vamplifiers. Furthermore, since the accelerating electrode is operatedat d5 a'positive potential, the output impedance of the tube may be made. very low, and, large effective power output may be obtained even with'relatively low amplification factors. j.

In order to take fluIIestadvantage-oi the latter feature of the device, it is preferable that the tube used be .of the type wherein-a plate-like control electrode is positioned on oneside of .a

filamentary cathode, while the anode ,or. platelis' positioned on the other side and at .a greaterdistance therefrom.. A prefer-red form of such a tube is illustrated in Figures 1, 2 and 3, wherein an envelope I is provided with side stems 2 through which are sealed support rods 4 for holding the plate-like control electrode 5. 0n the opposite side of the envelopeia similar set of side stems 6 and support rods "I hold the anode 9. Between the control electrode andithe anode the filament i0 is positioned, the filament being much more. closely adjacent/the control electrodethan the anode.

The acceleratingelectrode, which is of reticulated or grid-like form is positioned between the anode and the filament, being supported-in this A tube of the character shown, but without the accelerating electrode, is capable of handling relatively large amounts of power, but is limited as to amplification. Thus acommerciallybuilt tube of this type will have an amplification constant of perhaps three or four, but its output impedance will be lowo-f the order of 500 or 600 ohms.

The addition of the accelerating electrode H, which should be operated at a potential positive with respect to the cathode, has two efiects. First, it greatly decreases the efiective capacity between thecontrol electrode and the anode,'thus reducing the reaction between the output and input circuits of the device, and second, it still further decreases the output impedance of the device.

The application of the tube to the amplifier of my invention is shown schematically in Figure 4. An input circuit comprising leads 2E] and 2| connects to the cathode l0 and control electrode 5. The anode or plate 9 is connected toan output circuit comprising an inductor 22 tuned by a condenser 24, a tap 25 on the inductor being connected to ground through a by-pass condenser 26. Anode current is supplied to the output circuit from a battery or other suitable source 21, the accelerating electrode H being connected to an intermediate point on this battery through a choke-coil 29. The electrode II is also connected to the terminal of the tuned output circuit opposite that to which the anode-9 is connected, through a blocking condenser 30.

The operation of the circuit is as follows: When an impulse applied to the input circuit swings the control electrode negative, the space current between cathode and anode is decreased, swinging the anode positive in accordance with the well known functioning of tubes of this type. The decrease in current through the inductor 22 induces a negative potential at the end of the coil opposite to the anode connection, and this potential is applied to the accelerating electrode ll, superposed upon the constant potential applied thereto by the battery 21 through the chokecoil 29. The decrease in positive potential applied to this electrode serves further to decrease the space current, thereby tending-to increase the positive potential on the anode and augment the effect produced thereon by the control electrode. A positive potential applied to the control electrode 5 has the opposite effect, swinging the anode negative and the accelerating electrode positive. 7

There is, however, no reaction produced on the input circuit by this action. Not only is the control electrode shielded from the plate by the accelerating electrode, but since the control electrode actuallyswings in the opposite sense to the swing in plate potential, this has a reverse effect to that of the plate, and completely cancelling out any tendency toward capacity feedback into the input circuit. ,7

The amount by which the auxiliary electrode augments the effect of'the control electrode may be controlled by varying the point at which the tap 25 connects to the inductance 22. It is possible under certain circumstances to increase this eifect until the circuit becomes self-oscillatory,

although this point is not reached as readily as it would be were the accelerating electrode operated at a mean negative potential with respect to the filament. At points below self-oscillation, however, there is very much less tendency to produce distortion through the effect of this augmentation than is the case where feedback or regeneration is used. It is to be noted that the entire circuit still remains primarily under the control of the control electrode 5, and that there is no feedback to this circuit. Accordingly there is no effective reduction of resistance in this circuit, and hence there is less tendency toward excessive amplification on a single frequency than in circuits in which feedbacks occur. The amplifier is therefore applicable to audio frequency circuits or other circuits where tuning is undesirable, the only difierence in such applications being that the tuning condenser 24 isomitted.

Power may be withdrawn from the output circuit either through the leads 3| and 32, or by making coil 22 the primary of a transformer.

A slight modification of the circuit is shown in Figure 5. In this instance the connections, although differently arranged in the diagram, are essentially the same as in Figure 4-, the diiference being that a neutralizing condenser 35 connects between the electrode H and the control electrode 5. This arrangement is applicable for use with tubes wherein the shielding effect and neutralizing effect of the accelerating electrode II are not sufiicient completely to counteract capacity coupling between the anode 9 and the con- 'trol electrode 5.

since this results in minimum impedance in' the 5 tubes. Where such tubes are used, however, the effective-impedance of the tube will be much greater than in the cases described above.

In practice I have found that the connection as shown will raise the effective amplification constant of a tube of this class approximately three-fold, and at the same time will reducethe elfective a-c. impedance of the tube approximately to one-half. It will therefore be apparent that the effectiveness of the amplifier, as measured by the watts output divided by the watts input, is greatly increased, as is the total'amount of power which the amplifier will deliver.

I claim:

1. The combination with a thermionic tube having a cathode, a plate electrode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating'electrode between said cathode and said anode, of means for applying impulses to said control electrode, and means for coupling said accelerating electrode to said plate electrode in such phase relationship that potential changes in said plate electrode initiated by said control electrode are augmented by said accelerating electrode.

2. The combination with a thermionic tube having a cathode, a plate electrode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating electrode between said cathode and said anode, of an input circuit connected to said control electrode, an output circuit connected to said plate electrode, and a connection coupling said accelerating electrode to said plate electrode to impress on said accelerating electrode a potential of opposite sign to that on said plate electrode.

3. The combination with a vacuum tube having a cathode, an anode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating electrode between said anode and cathode, of an input circuit connected to said control electrode, an output circuit connected to said anode, and coupling means connecting, said anode and said auxiliary electrode in such phase relation that voltages derived from said output circuit afiect said accelerating electrode to augment the efiect of said control electrode on the current flow.

4. The combination with a vacuum tube having a cathode, an anode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating electrode between said anode and cathode, of an input circuit connected to said control electrode, an output circuit connected to said anode, coupling means connecting said anode and. said auxiliary electrode in such phase relation that voltages derived from said output circuit affect said accelerating electrode to augment the effect of said control electrode on the current flow, and means for preventing reaction between said output circuit and said input circuit.

5. The combinaion with a vacuum tube having a cathode, an anode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating electrode between said anode and cathode, of an input circuit connected to said control electrode, an output circuit including an impedance element connected to said anode, and coupling means between said impedance element and said accelerating electrode for impressing thereon voltages of opposite phase from the voltage on said anode.

6. The combination with a vacuum tube having a cathode, an anode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating electrode between said cathode and said anode, of an input circuit connected to said control electrode, an output circuit connected to said anode, and means coupling said anodeland said accelerating electrode for transferring therebetween voltages reversed in phase relation.

'7. The combination with a vacuum tube having a cathode, an anode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating electrode between said anode and cathode, of an input circuit con-- nected to said controlelectrode, and a tuned output circuit, one end of said tuned circuitbeing connected to said anode and the other connected to said accelerating electrode, whereby the potentials of said anode and said auxiliary electrode are maintained in opposite phase relationship.

8. The combination with a vacuum tube having a cathode, an anode on one side of said cathode, a control electrode on the other side of said cathode, and an accelerating electrode between said anode and cathode, of an input circuit con-,1

nected to said control electrode,a tuned output circuit, one end of said. tuned circuit being connected to said anode and the other connected to said accelerating electrode, and means for maintaining the alternating current potential of said cathode intermediate that of said anode and accelerating electrode. 1'

9. The combination with a vacuum tube having,

accelerating electrode, and means for maintaining the mean potential of said cathode negative with respect to both said anode and said accelerating electrode.

WILLIAM W. EITEL.

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