US1853106A - Amplifying system - Google Patents

Description

April 12,1932. 5, w-

AMPLIFYING SYSTEM Filed Jan. 17, 1928 ATTORNEY Patented Apr. '12, 1932v P stares resales earner caries I SIDNEY ,Y. wnrrn, or New YORK, 1a. Y1, nssrenon, BY MESNE nssreu'nnnrs, To RADIO 7 ,coarozanrron or nivinnrcmon NEwYonK, N; Y., A conronnrron OF DELAWARE AMPLIFYING SYSTEM Application filed January 17, 1928. Seria1 No. 247,296.

-This invention relates to amplifiers and.

more particularlythose'in which space discharge devices are used to increase" the relative potential variations or current flow from the input to the output sides in which connected.

A particular object of thecinvention is the Control of feed-back or regenerative action through the interelectr'odal capacity of a three electrode vacuum tube "amplifying system, andmore, particularly a system of'the tuned radio frequency'type.

Arrangements for controlling the. regenerative action through the interelectrodal capacity of three electrode vacuum tubes in amplifying "systems have been heretofore proposed involving neutralizing the feed back efiects by certain connections between the output and input circuits ofthe stages of amplification, which form of connection is avoided ina system employing the features of my invention.

Further and more definite objectswill appear from the following specification, claims of the system and drawing, in which the single figure represents a system embodying features for accomplishing the results above set forth. Referring now more particularly to the drawinggthe.vacuumtube amplifier "1 is arranged with an input. circuit 2 having tuning element 3 and an output circuit 4 including the inductance 5 coupled to; a succeeding stage of amplification through a tunable circuit 18, 21. Energy is introchiced into the input circuit from the "antenna system 7 having a'coupling coil 8. Thiscoil 8 is coupled to the input coil 9. which has its terminals attachedto the grid 10 and the "filament ll of the tube 1. w

Q In *the ordinary three-element vacuum tube, or in tubes having more than three elements, there isa certain capacitive relation be tween the control electrode 10 and the plate or output element- 12, indicated by the condenser '0 shown in. dotted lines. This con denser is so located in the system as to permit the oscillating energy to be fed through it, and when in the right direction and time relation with that present in the coil 9 increases the natural amplification of the circuit, causing diificulty from excess amplifi cation and even oscillation. This is due to the reaction'of tunable circuit .18, 21 back are created in said output circuit, an effect well known in connection with operation.

In order to overcome this difficulty, thecircuit 14 is connected in parallel with the input electrodes of the vacuum tube and including therein the couplingarrangement 15. This may be in the form of an inductance coil or other equivalent coupling arrangement and it is desirable to s0=-l0cate the coils ,9 and 15 that reverse effects will be produced, the incoming energy, of course, being received through the coil 8. The coils 9 andl5 may be closely coupled or otherwise as desired, although a more nearly constant control of regeneration throughout a given range of frequencies issecured with a tight coupling.

It is thus seen that the amplified energy fed back from the output circuit through internal capacity C, upon arriving inthe input circuit, has two paths into which todivide its current flow. One-path is through Cir-- cuit 14; and the amount of regenerative cur: rent flow in this path is governed by the value of resistance 17. The other path, is through tunable circuit 9, 3. With the polarity of coil 15 with respect to coil 9 reversed so that the vacuum tube regenerative current flow in coil 15 induces a potential in coil 9 opposed to that set up by the regenerative current flow therein, it. is

obvious that the regenerative effect on the inthese coils inasmuch asthey are reversely associated- In this situation it would be impossible tointroduce signals into the input; electrodes of the-vacuum tube, but .in order to overcome" and adjust the circuits in a manner which will permit these signal currents to flow, a variable resistance or impedance 17 may be used. This impedance may be greater when tight coupling exists between coils 9 and 15 and smaller when less coupling is present. Its purpose is to permit reducing the coupling between the coils, thereby permitting a greater effective input signal application to the input electrodes of the tube. Reducing the resistance allows more feed back current energy to flow in circuit 14, thereby making a looser coupling between coils 15 and 9 effective for the desired reduction of regenerative eflect. The tighter the coupling the more uniform is the regenerative control throughout awide range of frequencies.

In the ordinary broadcast receiver circuit, which is used for radio frequencies only, the coil 9 having from to 100 turns depending upon the diameter of the coil, may be coupled to a coil 15 of like number of turns or impedance, and in such case the resistance or impedance 17 may be advantageously chosen having an impedance of the order of thousands of ohms. This arrangement has proven suitable to amplify electrical oscillations of frequencies from 200 to 600 meters wavelength substantially uniformly throughout the range. No attempt will be made to explain the exact reason for this, although it might be stated that it may be partially due to any energy absorption effect, which takes place within theresistance 17 superimposed upon the counter feed-back effect produced by the coil 15, these effects varying and counterbalancing each other throughout the wavelength range.

The output ofthis amplifying system may be taken off from the output circuit by means of another coupling coil 18 connected to vacuum tube 20 having a tuning elementv 21 in the input circuit. The output circuit 22 of this vacuum tube is connected to the common B battery lead 23, and both vacuum tubes may be energized from the same sources of energy indicated at 24.

The system shown connected to the tube 20 is of the customary amplifying type in which inherent capacitive feed-back of the vacuum tube is not neutralized by any special means. It therefore may be subject to self-oscillation or tendency to oscillate, which oscillations might affect the operation of the tube 1. However with the reverse feed-back circuit 14, the effect of this onthe tube 1 is considerably reduced as well as any high frequency currents which might be fed back into the antenna system 7. The system of tube 20 may also be arranged similar to that of tube 1 with a circuit similar to 14. This would cause further reduction of feed-back currents.

Any desired number of radio frequency amplifying stages with tubes therein might well be coupled together to produce an amplifier with high over-all efliciency. Also the present system might well be used with detectors or even audio-frequenc amplifiers to eliminate or exaggerate the e ects desired. It is apparent that the input circuit 2 of the vacuum tube is, in effect, split,.having two paths both coupled together. Energy is received by differing the impedance of these paths, or the coupling between them.

It is not intendedto be limited to the exact methods'and arrangements shown but deviations andmodifications might well be made therein within the scope of the appended claims.

I claim:

1. In an amplifying" system, thecombination of a vacuum tube having a tunable input circuit and an output circuit, said tube, input and output circuits having such constants that said system tends to produce sustained oscillations, a second circuit containing an inductance of substantially like impedance as that of the inductance in said tunable input circuit connected in parallel with said input circuit and reversely coupled to said input circuit, and means within said second circuit for apportioning between said input circuit and said second circuit the feed-back energy flowing through said tube whereby'the tendency of said system to produce sustained oscillations is substantially reduced.

2. In an amplifying system, the combination of a vacuum tube having a tunable input circuit and an output circuit; said tube, input and output circuits having such constants that said system tends to produce sustained oscillations a second circuit, containing an inductance of substantially like impedance to that of the inductance in said tunable circuit and a variable resistance series connected in parallel to said input circuit and reversely coupled thereto, whereby the feed-back energy within said input circuit is controlled and the tendency of said system to produce sustained oscillations is substantially reduced.

3. The method of controlling regeneration between the input and output circuits of a. space discharge device resulting from interelectrode capacity which comprises dividing the energy transferred by virtue of said interelectrode capacity into two parts changing the phaseof one of said parts with respect to the other so as to make it opposite to the'phase of said other part, reacting the two parts with one another and regulating the relative amplitudes thereof so as to produce the desiredconditions.

In testimony whereof I aflix my signature.

SIDNEY Y. WHITE.

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