US1795172A - Amplifying system - Google Patents

Description

' March 3, 1931. T. H. KINMAN. 1,795,172

AMPLIFYING SYSTEM Filed Sept. 21, 1928 Inventor Thomas.H-Kinma.n, u WYM Hts Attorney- Patented Mar. 3, 1931 (UNITED STATES PA EI FFCE THOMAsH. KINMAN, or BILTON, RUGBY, ENGLAND, ASSIGNOR 'ro GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK- V 'AMPLIFYING SYSTEM,

Application filed September 21, 1928, Serial No The present invention relates to amplifying systems which include electric discharge devices and are particularly intended for the amplification of high frequency electric oscillations.

The Object ofthe invention is to simplify.

the operations necessary for the adjustment of a high frequency amplifier so that it may be especially suitable for incorporation in a 10 radio receiving system adapted to receive alternatively on a number of specified wave lengths or frequency channels.

In accordance with the invention, an amplifying system of the above-named type for 16 high frequency oscillations is rendered simultaneously selective to oscillations of two or more predetermined frequencies. In order to obtain this result, the anode circuit of one or more of the electric discharge de- 20 vices employed,- which may be ordinary receiving vacuum tubes, for example, is 'ren dered selective to the predetermined frequencies'by including therein a plurality of circuits tuned to the various frequencies it is desiredto select, the constants and arrange ment of each tuned circuit being such that it affords a negligible impedance to oscillations of the frequencies to which the other circuits are tuned.

In 7 carrying the invention into effect, I preferably employtubes Of the type now commonly/ known as screen-grid tubes, that is to say. tubes having the usual cathode, anode andcontrol grid and'provided, in addition, with a screen grid located between the control grid and the anode, the purpose of which is to eliminate the inter-electrode capacity which would otherwise exist between the control grid and the anode. Two or more inductances connected in series or in parallel in the anode circuit of the tube are tuned to the frequencies itisi particularly desired to amplify, The tuned circuits are so designed that whichever one of the tuned circuits offers a high impedance to that frequency, :while the remaining tuned circuits offer littleor no impedance to that frequency. Thatis to say, the remaining tuned circuits freely pass oscillations of a frequency other than that to which they are with, an antenna or like receiving device for frequency is being amplified,

. 307,474, and'in Great Britain October 10, i927.

specifically tuned. By a suitable coupling device, the voltage pulsations set up across the circuit tuned to the frequency being amplified is transferred to-the grid of the next tube in the system, which may be another amplifying tube, or means arranged to 'de- I tect thehigh frequency oscillations. I v

. The input circuit of the first tube of the system is preferably coupled to, or associated the high frequency oscillations, the antenna orinput circuit being tuned to the frequency it-is desired to receive and to amplify selectively. V p p p The arrangement in accordance with the present invention although not limited there'- to, is particularly adapted for use with an antenna, Or'like receiving device, arranged to receiveon alternative wave lengths in the manner described in my copending application, Serial NO.219,088, filed September 12, 1927. The tuned circuits situated in the anode circuits of the tubes are then tuned to the same-frequencies as those to which the antenna or input circuit-is tuned,and when oscillations of either of the selected frequencies'are received, they are selectively amplified in the systeml Any adjustment is unnecessary other than those adjustments made when the circuit arrangement is first assembled. V

My invention will be better understood vfrom the following description when confication stages arranged in accordance with the invention and utilizing electric discharge devices of the screened grid vacuum tube type. a

Referring to the drawing, a signal receiv-. ing device 5, provided in the present example with an inductance 6 coupled with an antenna 7 by a coil 8, is connected to thefilament and control grid of the first tube 9, and

isshunted by two condenserslO and 11 in parallel, thelcondenser llhaving a switch 12 arranged to connect and disconnect it. When the aforesaid condenser 11 is disconnected, the remaining condenser 10 tunes inductance 6 to one of the frequencies it is desired to receive whereby the signal receiving device is responsive to that frequency or signals of that frequency. On connecting in the condenser 11 the increased capacity obtained is of such value as to tune inductance 6 toth-eother frequency it is desired to two tuned circuits 18-14 and- 1516 in series, each consisting of an inductance and capacity in parallel, 13 and 15 being the inductances and 14 and 16 their respective tuning; capacities. The resonant frequencies of these two tunedcircuits correspond respectively with the frequencies to which the signal receiving device is capable of being tuned. These frequencies should preferably be separated. by a fairly wide margin, whereby a response to a band of frequencies isprevented, and when employed for the reception of broadcasting, may correspond with the frequencies of a main station and another high power, long wave station, for example. The constants of the tuned circuits-in: the anodecircuit are so: arranged that at the frequency to which one of them is tuned, the condenser of the remaining tuned circuit constitutes a low impedance for that frequency, and vice versa. The potential variations set up at the terminals of the tuned circuits are transferred from the high potential end of the anode circuit tothegricl of the next tube 17, which may be a detector or another amplifier, but which in the arrangement shown is: a second amplifier, through the usual single coupling capacity 18,. and a resistor 19' is provided for applying ab-ias ing potential to the grid of tube l'Z. The connectionfrom the end of the tun-ed circuits 15-16, remote from the anode, to the anode through a second coupling condenser 26, and a grid biasing or load resistor 27 is connected across the output circuit which is indicated at 28.

The coupling between each of the tuned anode circuits and the succeeding tube or device may be: obtained in other ways, for example, through tuned circuits similarly as sociated in the grid circuit of the following tube, which are coupled respectively to the tuned circuits situated in the anode circuit of the preceding valve.

Likewise one skilled in the art will readily appreciatethatthe tuned anode circuits may similarly be arranged in parallel, instead of in series as described, one tuning condenser only being employed to tune the two inductances. Similarly, in the series: arrangement described, the tuning condenser for the shorter wave may be eliminated with. proper design of. the inductance- Thus ind uctances 13- and 22 may be wound: in the form of aperiodic radio-frequency chokes, so that they will respond to a definite or. predetermined wave band, such asthebroadcastband from 260- to 500- meters, while 15 24 may be tuned by fixed or variable condensers I6- and 2:5; to any longer wavelength, as previously described. I

It has been: found that the use of screengri-d tubes assists in the application and successful operation: of the amplifier, although it is desiredto: point out that the benefits of the invention can be obtained with other suitable tubes such: asthe more usual. three-elect trocle-type..

It is desirablethateach stage of high frequency amplification, with its; associated circuits, should be effectively screened-i from its neighbor all external influences.- This may be done by suitable metal enclosuresv or shields. now commonly known and used.

A: receiver or amplifier arranged in accordance with the invention is advantageous inas much as reception and amplification is possible on a plurality of alternative wave lengths without any adjustment other than theoperation of a simple switching device, which is" incorporated in the input or other tuned receiving circuit, as-herei-nbefore referred to. No adjustmen'tof the amplifier itself is necessary.

It will also be evident that, although the provision of two tuned circuits in each anode circuit of the tube has been specifically referred to in the present example, more than two tuned circuits: may be employed if desired, thereby rendering the arrangement selective to more than two predetermined frequencies;

hat I claim as new and desire tosecure by Letters Patent of the United States, is-:

1. Ina high frequency signal amplifying system employing a plurality of electric dis charge devices, a plurality of circuits tuned to different predetermined frequencies and included in a single anode circuit of one of said devices, said frequencies being separated to prevent band pass tuning in said circuit, the constants of each tuned circuit being such that it produces a negligible impedance drop when subjected to oscillations of frequencies to which the other circuits are tuned and produces a high impedance drop when subjected to the frequency to which it is tuned, a single coupling means connected with the high potential end of the anode circuit and with the control electrode of a second electric dis-- charge device, and selector means for selectively introducing into said system a signal of any one of said predetermined frequencies.

2. In a radio frequency amplifier including two electric discharge devices, the combination of a signal receiving device, means for selectively tuning said receiving device separately to each of a plurality of relatively widely separated predetermined frequencies, and a single tuned circuit introduced between said electric discharge devices and connected with the anode of the one and the grid of.

the other, said circuit being arranged to respond to any quencies and including a series of tuned inductance units each tuned to a different one of said predetermined frequencies.

In witness whereof, I have hereunto set my hand this fourth day of September, 1928.

THOMAS H. ICINMAN.

of said predetermined fre-'

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