US1524580A - Amplifying system - Google Patents

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1,524,580 .1. scoT-TAGGART AMPLIFYING SYSTEM Filed Sept. 29 1924 Patented Jan. 27, 1925.

UNITED STATES 1,524,580 PATENT oFFlcE.

JOHN SCOTT-TAGGART, OF III'FORID,y NGLAND, .ASSIGNOR T0 ALFRED EB'NESJ..` WHITE,

OF LGNDON, ENGLAND.

AMPLIFYING SYSTEM.

Application led September 29, 1924. Serial N'o. 740,496.

To alt whom t may concern:

Be it known that I, JOHN Scorr-TAGGART, a subject of the King of Great Britain, residing at Ilford, in the county of Essex, England, have invented new and useful Improvements in and Relating to Amplifymg Systems (for which I have filed an application in Great Britain, No. 217,971, dated January 2, 1923), of which the following 1s a specification. I

This invention relates to ampllfying systems, particularly for use in wireless telegraphy and telephony.

It is of general' knowledge that whenv there are employed two or more stages of high-frequency amplification mvolvlng the use of two or more circuits tuned to the 1ncoming frequency, and arranged so that each of two anode circuits has a tuned circuit associated with it either by coupling or direct-connection, undesirable reactions or self-oscillations will very likely occur. This tendency toward undesirable reactions is due largely to capacity coupllng -in the valves themselves.

i It has been proposed to counteract the tendency to self-oscillation of asingle valve ampliiier due to inherent' capaclty coupling between the electrodes of the valves by the use of a condenser connected so as to pro- -duce a reverse reaction effect, but when a v' plurality of stages of high-frequency amplication is involved, it has not hitherto been contemplated, so far as I am aware,

that similar means could be successfully applied to said systems, owing to the relatively greater difliculties involved with each successive stage of amplification. I'v

have found that by the suitable use of condensers connected to pro r terminals of associated inductance coils 1n various stages,

it is possible to neutralize this natural reaction e'ect and thereby insure the stability of the amplifier.

Accordingly, the invention in part consists of a high-frequency amplifier in which the currents are amplified by a plurality of stages of amplification involving a plurality of circuits, one or more condensers being connected so as to produce a reverse reaction eifect to neutralize the tendency of the amplifier to generate oscillations.

.A further feature of the invent-ion consists in a wireless receiver in which the incoming high-frequency currents are ampli- `lied by a plurality of valves in cascade denser, `another and distinct condenser being employed to balance out the reaction effects. Y

, Other features of the invention and the methods for carrying the same into effect Vwill be seen from a consideration of the preferred embodiment of the same as disclosed in the accompanying drawing, and appended claims.

The diagram shows one circuit arrangement for carrying the invention into eilect.

This arrangement as illustrated utilizesv thermionic valves designated by reference characters' V1 and V2 which serve as hi h frequency amplifiers, and a third valve which acts as a detector or rectifying valve. lach of these valves, as is well known, is provided with a filament, a grid electrode and an anode.l

A source of incoming signals may be a tuned antenna of the 'well known construction. A tuned input circuit coupled to the antenna is connected to the .grid and to the filament of the valve V1, while the output circuit of this valve extends from its anode through the primary inductance L3, the high tension battery, and thence to the filament. As is well known, there exists an inherent capacity between the various elements of each valve, notablyv the grid electrode and anode, which in the case of the valve V1, is supplemented by the variable condenser C2. The output circuit of the valve V1 is inductively coupledto the input circuit connected to the grid of the lValve V2 and to the filament of this valve, and includes an inductance L4 shunted by a variable tuning condenser.

Variable condenser C1 is connected from the grid of the valve V1 to one terminal of the inductance L, in the input circuit. The

capacity of condenser C1 -is selected with respect to the value of the inherent capacity of the valve V1 and supplemental capacity C2, and is connected to the terminal of the inductance L, having such a polarity that the current ilowing through C1 'is equal and opposite in` hase to the currents owing through the lnherent capacity of the valve V1 and its supplemental capacity C2.

The output clrcuit of the valve V2 is connected from' its anode through the inductance L5 and the high tension battery to the ilament of this valve, and the variable condenser C4 is connected between the grid and anode of the valve V2 to supplement its inherent capacity. The inductance L in the circuit of the valve V2 is inductively coupled through the inductance Le to the input circuit of the detector valve V3. In this instance, also, the neutralizing condenser C3, which is similar to C1, is connected from the grid of the valve V2 which it serves to neutralize, to one terminal ofthe inductanceL.

The input circuit of the detector valve V2 is provided with a well-known grid condenser and grid leak which need not be described, while .the output circuit of the detector valve V3 includes the telephone receivers T or other indicating device 1n series with the high tension battery. A low tension battery supplies heating current to the filaments of ,thev respective valves through well known controlling rheostats.

.The natural interelectrode capacity in thermionic valves, such as that previously referred to as existing between the id electrode and the anode,` is usually o an extremely small magnitude, and consequently the balancing condenser, as for example, C1 or C3, must be correspondingly small. A practical ditiiculty is thus introduced both in the mechanical design of such a con denser and in its subsequent adjustment. For these and other reasons supplemental condensers C2 and C4 have been introduced to increase the natural inter-electrode capacities of these valves to a magnitude which eliminates the aforesaid diiculties. There is frequently an appreciable variation in the` inter-electrode' capacities of prevailing commercial types of thermionic valves and it has been found that the association of a supplemental capacity with the inter-elec? frode capacity of the valve may be used to compensate for such variation and provides a convenient means lfor effecting a more practicable and more readily neutralized inter-,electrode capacity.

Maso

extending between said anode and said lfilament, a transformer havin a primary winding and a secondary win ing, said primary winding being included in said output circuit, a rectifying device associated with said secondary winding, a condenser connecting one end of said secondary winding of said transformer to said tuned circuit, and a condenser connected `between said tuned circuit and said anode augment'- ing said inherent capacity between the grid electric and anode, and said first-named condenser neutralizing the combined capacity of said inherent capacity plus the augmenting capacity.

'2. An amplifying system embodying a plurality of thermionic valves, each of said thermionic valves havin a grid electrode and an anode between whlch inherent ca ac-l ity exists, an input circuit connecte to the grid electrode, and an output circuit connected to the anode of each thermionic valve, a condenser supplementing said inherent capacity connected in parallel there to, and a second condenser, one termin`l of which is connected to the grid electrode of one of said thermionic valves, the other terminal of said second condenser being connected to the input ycircuit of another 1 of said thermionic Valves. y Y

An amplifying system embodying a Aplurality "of thermionic valves'y coupled vin cascade, each thermionic valve being provided with a grid electrode yand an anode, an arrangement for neutralizing the inherent capacity existing between the grid elecrtrode and the anode of each thermionic valve comprising a condenser connected between the grid electrode and the anode of the thermionic valve in each stage, and a second condenser connected between the grid electrodes-of the thermionic valves of successive sta es. I

4. An amp ifying system embodying a plurality of thermionic valves, each of said thermionic valves being provided with electrodes including a grid and an anode coupled by an inherentv electrostatic capacity, an input circuit connected to each grid, an outut circuit connected to each anode, one input circuit being electrically linked to an output circuit, a condenser connected between the grid and the anode of one of said thermionic valves, a second condenser connected to the grid electrode of said last mentioned valve and to the input circuit of another of said thermionic valves, and means for adjusting said second condenser so that the current flowing therethrough will be equal to and opposite in phase to the currents owing through the electrostatic capacity and through vsaid irst' mentioned condenser.

JOHN SCOTT-TAGGART.

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