US1856116A - Thermionic amplifier - Google Patents

Description

y 3, 1932- M. s. SATEREN 1,856,116

THERMIONIC AMPLIFIER Filed June 16 1950 uuun 015?. i m a INVENTOR all Marf/n GJafer n ATTORN EY Patented May 3, 1932 UNITED STATES PATENT orncr.

mm G. SATEREN, OI EADDONFIELD, NEW JERSEY, ASSIGNOB TO WESTINGHOUSE ELECTRIC & IANUFAGTUBING COMPANY, A CORPORATION OF PENNSYLVANIA THERMIONIG AIIIIIIIEB Application filed June 18,

My invention relates to thermionic amplitiers and it has particular relation to volumecontrol devices therefor.

Substantially everyone who has operated aradio receiver has noted that the incoming signals often vary in amplitude above and below a mean value. The variation in signal-intensity, which is known, popularly, as fading, may be caused by changes in the sigio rial-conveying medium or ether, by changes in the operation of the transmitting station or by variations in the height of the so-called Heaviside layer. Irrespective of the actual cause of fading, however, it results in a very i3 annoying variation in the amplitude of the ultimate sound-output of a receiving set, at times causing the signal to decrease to almost below audition and, at other times, causing the loud-speaker to he over-loaded.

It is, accordingly, an object of my invention to provide, in an amplifying system of the type comprising a plurality of inter-coupled thermionic tubes, instrumentalitics and circuit connections whereby fluctuations in the amplitude of an incoming signal shall be an tomatically compensated.

Another object of my invention is to provide an automatic volume-control system having a minimum number of parts.

A still further, and more specific, object of my invention is to provide means whereby one of the thermionic tubes embodied in an amplifying system shall function also as a volnme-control device without interference with its normal function.

In general, I propose to utilize thermionic tubes of the screen-grid type as radio-fro quency amplifiers and a similar tube as a power detector. I further propose to rovide means whereby the space current owing in the power-detector shall provide biasing potentials for the screen-grids of the amplifying tubes, and I so organize my improved system that any change in the amplitude of an incoming signal shall be so com- 1930. Serll'l R0. 481,287.

pensated by the said biasing potentials that the effect of fading will be counteracted.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing.

The single figure of the drawing is a diagrammatic view of a complete amplifying system organized in accordance with my invention.

The amplifying system illustrated in the drawing comprises a plurality of radio-frequency am lifying tu es 1 and 3, a powerdetector tn e 5, and an audio-frequency amplifying tube 7. The radio-frequency amplifying tubes and the power-detector tube are each of the type having an equipotential cathode 9 provided with a heater 11, an anode 13, a control-grid and a screen-grid 17, while the audio-frequency amplifying tube may be of the usual threeelectrode type having a cathode 19, a grid 21 and an anode 23.

Heater and cathode potentials for the screen-grid tubes and the audio-frequency amplifying tube, respectively, are derived from the secondary winding of a power-transformor 25 the primary winding of which is energized from any convenient source 27 of alternating current at commercial frequency.

A common source of plate and biasing potentials is provided, the said source preferably taking the form of a rectifier and filter 29, energized from the alternating-current source 27 and having an output resistor 31.

The radio-frequency amplifying tubes and the detector tube are connected in cascade by suitable energy-transfer networks, exempli fied by the transformers 33 shown in the drawing, while the output circuit of the del.

tector tube is impedance-coupled to the input circuit of the audio-frequency amplifying tube over a filter-network 35, a coupling choke-coil 37 and a coupling condenser 39.

The coupling network also prevents the impression of radio-frequency potentials upon the audio-fre uency amplifier.

Each secon l pling-transformer is provided with a tuning condenser 43 and is conductively isolated from the cathode of the corresponding thermionic tube by a blocking condenser 45. The rotor plates of each tuning condenser are conductively connected together and to a grounded conductor 47 leading to the negative terminal of the rectifier output-resistor 31.

The cathodes of the radio-frequency amplifying tubes are connected, by a conductor 49,

to a point 51 upon the output resistor 31 which go is slight] positive with respect to the ounded end t iereof to thereby maintain t e control-grids of the said tubes at a negative potential. The control-grid of the detector tube is normally maintained at zero otential, with respect to the cathode thereof, y a gridleak 53 extending between thesaid electrodes.

Negative grid-bias potential for the grid of the audio-frequency amplifier tube is derived from a resistor 55 which carries'the space-current flowing in the said tube when it is in operation. v

A volume-control resistor, 57, having a magnitude of approximately 50,000 ohms, is interposed between the cathode of the detec- 88 tor tube and the negative terminal of the rectifier-output resistor. The screen-grids .17 of the radio-frequency amplifying tubes 1 and 3 are, respectively, connected to movable contact-devices 5,9 and 61 associated with the volume-control resistor. As an alternative, the two contact devices may be dispensed with, and both screen-grids may be connected, in parallel, to a single contact device associated with the volume-control resistor.

In the operation of my improved amplifying system, the maximum space-current flow in the detector tube occurs when no signal is being received. The magnitude of the said space current and, consequently, the drop in 50 potential across the volume-control resistor 57 in the no-signal conditions, is controllable b proper adustment of the screen-grid and 8 ate potentials applied to the detector tube y a connection 63 leading from the rectifier 5| output-resistor 31. When a screen-grid thermionic tube of the type lmown commercially as UY224 has been used as a detector, screengrid and plate potentials of 180 volts and 260 volts, respectively, have given satisfactory operation.

S nce the power-dectector is provided with a grid-condenser 65, in addition'to the gridleak 53, as soon as an incoming signal is .tuned in the space current flowing therein decreases, resulting m a lessened drop in potential across the volume-control resistor 57 to which are connected the screen-grids of the radio-frequency amplifying tubes. The sensitivity of the system depends upon the screen-grid potential of the radio-frequency amplifying tubes; it decreases as the screengrids become more he ative than the normal ary winding 41 of each cou-' potential determined y the no-si a1 condition and increases if the screen-'grlds acquire a more positive potential than normal.

Any tendency, therefore, for a signal stronger than normal to overload the system is met and counteracted by the decrease in the positive potential applied to the said screen-grids from the volume-control resistor and, conversely, a decrease in the amplitude of the incoming signal is compensated by an increase in the positive potential applied to the screen-grids.

In order that the system shall not so respond as to prevent momentary changes in signal amplitude, such as a fortissimo passage in a musical program, a pistol shot, or the like, from being properly reproduced by the loud-speaker, I have found 1t expedient though not essential, to connect one or more condensers 67 in shunt relation to the volume-control resistor. Thefcondensers also function to prevent inter-coupling between the several amplifying stages by reason of their common connection to the volume-com fore, is not to be restricted except insofar as is necessitated by the prior art and by .the spirit of the appended claims.

I claim as my invention:

1. In an amplifying system, a power detector of the grid-rectification type, a plurality of thermionic amplifiers of the screengrid type, acommon source of plate potential for said detector and said amplifiers, a connection including a resistor between the cathode of said detector and the negative terminal of said common source, and a con-V nection from the screen-grid of one of said amplifiers to an intermediate point on said resistor, whereby an increase or'a decrease in the amplitude of a signal applied to said system gives rise to a decrease or an increase,

respectively in the sensitivity of said ampli- 2. In an amplifying system, a power detector of the grid-rectification type, a plurality of thermionic amplifiers of the screennot iid type, a common source of plate potential or said detectei' and said amplifiers, a c0nhectien including a resistor between the cathode of said detector and the negative ti terminal oi" said common source and a con inectien from the screen grids at said ampii tiers to intermediate points on said TQSiStOIt'. whereby an increase or a decrease in the amplitude ot" a signal applied to said system Wt gives rise to a decrease or an increase, respectit ei y' iii the sensitivity of said amplifiers.

In testimony whereof, I have hereunto satisciihed my name this twenty-eighth day out Itt/tagy 1930. MAPLHN G. SATERIEN.

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