US1947084A - Signal repeating system - Google Patents

Description

H. R. HAYDEN SIGNAL REPEATING- SYSTEM Feb. 13, 19.34.

med sept. so, 19:52

MMAAAAMMA J W n Mw mm INVENToR fara/d @Haya/ef? BY m ATTORNEY Patented Feb. 13, 1934 UNITED STATES PATENT oFFicE Application September 30, 1932 Serial No. 635,509

7 Claims.'

Thisinvention relates to vacuum tube signal repeating systems and more particularly to an.

improved amplifying system.

In the specific embodiment of my .invention herein disclosed, the system comprises successive radio frequency amplifying stages, a detector stage and audio frequency amplifying stages.

One of the audio frequency amplifying stages is a push pull stage and my invention consists in 10 part of an improved resistance or similar coupling between the push pull stage and the preceding stage. One characteristic of such a coupling is that the impulses transmitted to the push pull are dependent upon variations of potential of points l5 Tn the plate circuit of the preceding stage.

Among the objects of my invention is to provide -an improved receiving and reproducing system of this general character which is free from disturbing noises, such as may be caused by regeneration, feed back or hum derived from an alternating current source of supply-and further to provide a system which will accurately reproduce n incoming signals over a wide frequency range.

The drawing shows diagrammatically one embodiment of my invention.l

The system disclosed in the drawing comprises three stages of radio frequency amplification, a detector stage and two stages of audio frequency amplication, the second of which is a push pull stage which as shown is coupled to a dynamic loud speaker. Power for energizing the system is supplied from alternating current lighting means which are connected to a transformer AT and thence through a rectifier R to supply the field coil F of a loud speaker L. A second transformer T is provided with secondaries S and S1 for supplying alternating current for heating the tube cathodes, whilesecondaries S2 and S3 energize the plate and cathode heating circuits respectively of a rectifier tube R which supplies the plate circuits of the signal tubes through a filter F.

Reference character 10 represents an antenna for receiving signal waves and Sw .a double throw switch designed to connect the antenna to ground through a tuning condenser l1, primary 12 of a transformer 13 and a resistance R2 shunted by a fixed condenser C1 of small capacity. A

tuning condenser 15 connects a point in the antenna circuit between condenser 11 and coil 12,

with ground. The secondary 16 of the transformer 13 isconnected at one end to the grid of tube lRF and its oppositeend is connected to ground through condenser.C1 and resistance R2.

Grid of tube IRF is also connected to ground through a tuning condenser 1'? shunted by a trimming condenser 14.

When it is desired to receive incoming signals without using the antenna 10,- switch Sw is moved to a position to connect the upper terminal of coil 12ste ground through condenser 11 and a resistance R1.

In the embodiment of the invention disclosed tubes IRF, 2RF, SRF and the detector tube DET are screen grid tubes having indirectly heated cathodes as shown conventionally in the drawing. Tube 1AF and tubes 2AF and 2AF' are three electrode tubes, the cathodes of the latter being directly heated by current passing therethrough. The plate or anode of each of the radio frequency tubes and the detector tube is connected to the supply conductors 18 and 21 through the primary of the coupling transformer 19, 24 and 25 respectively for the radio frequency tubes and a resistance R11 for the detector tube.

The heater for the cathodes oi.' the radio frequency, detector and first audio frequency tubes are connected to the secondary S of the transformer T through a supply circuit 2D. A potentiometer P is connected across the supply circuit and an adjustable contact or slider 22 connects an intermediate point with the ground or negative side of the fllter.

The screen grids of tubes IRF, ZRF, and 3RF are connected to a Acommon conductor 28 and the screen grid of tube DET is connected to this conductor through a high resistance R10 shunted by acondenser C10. Conductor 28 is connected to ground through a condenser` C4 and is connected to a low voltage tap t of the filter F. Conductor 28 is also connected to ground through three resistances R5, R6 and R7 arranged in series. Resistance R6 is provided with a slider 30 which is connected to the cathodes of'tubes lRF and 2RF and the cathodes of these tubes are also connected to ground through a condenser C5.

Radio frequency transformer 24 has two secondaries 30' and 31 ipspectively. Secondary 30 is grounded at one end through an adjustable condenser 33 shunted by a trimming condenser 34 and at the other end grounded through a xed condenser C6- shunted by a resistance R2, this resistance and condenser also serving as aconnection to ground for one end of `coil 31. The other end of coil 31 is connected to the grid of tube 3RF and also connected to ground through a tuning condenser 35 shunted by a trimming condenser 36.

Cathode of tube 3R11' is' connected to ground denser C7.

6' through resistance R2 shunted by a .xed condenser C8 and the other terminal is `connected to the grid of the detector tube and alsogto ground through a tuning condenser 37 shunted byfa trimming condenser 38.

The cathode of the detector tube is 'connected to ground through resistance R9 shunted by a iixed condenser C9. J

The detector tube is coupled to the rst audio frequency amplifying tube by a resistance coupling, comprising a resistance R11-in the plate circuit of the detector tube, a resistance R12 between the grid of the tube IAF and the ground, a coupling condenser C11 connected to this grid and to the plate of the detector tube through an i inductbnce I and condensers C12 and C13 connectedrespectively between opposite ends of the inductance and ground.

The second audio frequency stage which in the present form of my invention is the last stage, is al pushpull stage, comprising tubesv2AF and 2AF' connected to the preceding stage by a resistance coupling of special construction. While my improved coupling may be used in connection with systems other than the one comprising a radio frequency and detector stage -above described, the entire system disclosed. represents one complete and operative embodiment of my invention. l

The cathode of tube IAF is connected to ground through a resistance R20. The plate of tube x1AF is connected to conductor18 through a coupling resistance R13, the conductor 18 being^connected through conductor 21` to an intermediate voltage tap t of the lter F. Plate of tube 1AF is connected to the grid of tube 2AF by a coupling condenser C16. and the cathode of tube IAF is con' nected to the grid of tube 2AF' by a coupling condenser `C1'7. The grids of tube 2AF and 2AF are' connected to ground respectively through resistance R14 and R15 which in the present embodiment of my invention are of equal values.

The filaments of tubes 2AF and 2AF.' are supplied with heating current from the secondary S'f and across the supply circuit is connected a potentiometer P having a slider '39 which is,

connected to ground through a resistance' R18. The plates of tubes `2AF and 2AF are cori--v nected through an inductance I' an intermediate 'point of which is tapped and connected to the.

high voltage 'tap t" pf the filter. The output circuit to the coil 33 of the loud speaker includes a condenser C19 and this circuit is connected across the inductance I.

The filter comprises inductances I3 and I4 inl between a point condenser C24 and the resistance R20 and -the intermediate tap for the plate circuit of the radio frequency tubes, the detector tube andthe rst audio frequency tube is linwted through a resistance R8 shunted by a xed conto a point t between C23 and resistance R19, while the high voltage tap t" for the plates of the tubes 2AF and 2AF' is connected to a point between inductances I3 and I4.

In the operation of the resistance coupled push pull stage it will be noted that changes ofpotential of the grid of tube lAF produce opposite changes of potential of the plate and of the cathode of this tube. Thus an increase in potential of the grid lowers the internal impedance of the tube, lowers the potential of the plate of the tube with respect to ground at the same time, however, raising the potential of the cathode of tube lAF. Thev changes in potential of the plate and cathode are transmitted respectively to grids of tubes 2AF and 2AF through the respective condenser C16 and C17. y

'Ihe resistance ,R13 in the plate circuit of the tube 1AF is of the same value as the resistance R20 inthe cathode return circuit. Changes of impedance in the tube IAF due to changes of potential ci the grid of this tube will therefore effect equal and opposite changes of potential atl the points X and X', that is, the plate and cathode respectively of the tube 1AF. The changes in potential of the grids of the push pull tubes 2AF and 2AF' will therefore be equal and opposite and the tubes 2AF and 2AF' fwill each bear one half of the signal load.

One important feature of my invention is the construction of a push pull amplier of this character wherein variations of potential of the currents supplied to the tubes will not produce disturbing hum in the output circuit. Itawill, of course, be understood that the connections between tubes 2AF and 2AF' are such vthat disturb- 'ing variations due, 'for example, to variations of the potential of the source supplied to these particular tubes tends inherently to be eliminated. However, the portion of the system preceding this-stage may be affected by uctuations from the source of supply so as to feed into the push pull stages hum currents which would then be passed on to the loud speaker. It is one purpose of my invention to so construct the system. disclosed, that substantially no hum, arising in the stages preceding the push pull stage, is carried forward to the loud speaker.

Considering for themoment, the effect of variations of the potential of the output of the filter F on the plate circuit of tube 1AF, these effects comprise the direct effect caused by the supply of varying current from the tap t through resistance R13 to the plate of the tube 1AF and the indirect eil'ect caused by the variations supplied to the plate circuit of the preceding tube o r tubes. Considering first the direct effect; a momentary rise in potential ofthe source has the direct effect of raising the potential at the point X with respect to ground and thisl same rise has theeffect of raising the potential at point X' with respect to ground, but the magnitude ofthe rise of potential atthe point X is much less than -the magnitude of rise at the point X. Considering the indirect eiects, a momentary rise of potential of the source causes a rise in potential of the plate ofthe detector tube, which rise, transmitted through the condenser C11, raises the potential of the grid o f tube IAF and this results in a lowering of the internal impedance of the tube. This tends to decrease the potential at the point X with'respect vto ground and to increase the potential at the effects at the point X are opposed to one another; whereas the direct and indirect effects at the point X assist one another. In view, however, of the fact that the direct effect at the point X is much greater than the direct effect at the point X', it is possible by taking away from the direct effect at the point x and adding 1:6 theo direct effect at the point X' to make the combined directl and indirecteffects at the point X equal to the combined direct and indirect effect at the point X. With this condition obtaining, the variations of potential of the grids of tube 2AF and 2AF' caused by these disturbing voltage variations will be equal and in phase with one another with the result that they will cancel one another in the push pull output circuit and no variations from this source will appear in'the loud speaker circuit. If desired, the system ymay be so constructed as to feed variations of the desired magnitude and phase to the coil 3 3 of the loud speaker so as to buck out disturbing variations in the -loud speaker field coil F. The direct and indirect effect at points X and X' may be` The indirect effect at the point X is:

stantially the same frequency and phase; a momentary lessening of the impedance of the tube IAF will have th effect of lowering the potential at the point X and raising the potential at the point X'. However, the simultaneous decrease in the impedance of the detector tube lowers the potential of the detector tubefplate and consequently lowers the potential of the grid of the tube IAF, thus tending to increase th internal impedance of the tube lAF which results in a tendency to raise thel potential at the point X` and lower the potential at the point X with respect to ground. It will thus be seen that the direct andfindirect effects of the variations in the tube impedance due to variations in the cathode heating current are opposed .to one another at the-point X and also at the point X'. It is thus possible substantially to eliminate hum variations at both of these points with the result that no hum variations a-re transmitted to the grids of the push pull or to transmit to the grids of the -push pull variations of either one` of two oppo- 'site phases and to any desired magnitude.

If DV: represents the change in potential at the left hand side of condenser C11 the change in voltage at the point X due to DV: will be where a is the amplifying factor of the tube lAF,

and -DVzp respectively at the points X and X', of the alternating current for heating the cathode pFDVf R of the tube lAF.

R DV DV 3 l la Il' u I?x7 2 R where DV.; are variations of potential of the grid of tube lAF. The indirect effectsat the point X' are the negative of expression 3 or passed onto the grid of tube IAE should'not vary greatly from It can readily be seen that by varying the terms of the Equations 1 to 5 this equality may be obtained in a varietyof ways.

The term DV; is dependent upon the magnitude of thel variations supplied'by thev lter to the detector tube plate circuit and to some extent upon the character of and the current supplied to that I"part of the system preceding the detector stage.

In practice, I find when using a 327 tube as the tube -lAF that resistances R12 and R13 may advantageously be made each of 10,000 ohms; where tube 2AF and 2AF' are each 345, I preferably make the resistances each 250,000 ohms with a tube 324 as the detector tube, R2 may be 1,000 ohms, R9 20,000 ohms, C9 l mfd., R10 100,000 ohms, C10 .5 mfd., and R11 250,000 ohms.

Having now described my invention what I desire to secure by Letters Patent is:

l. In a signal repeatingsystem, a .push pull stage comprising two vacuum tubes, a stage preceding said push pull stage comprising a vacuum tube having impedances in its plate supply and plate return circuits, a yconnection between a point of relatively negative potential of the former of said impedances and the grid of one of said push pull tubes,^a connection between a point of relatively positive potential of the later of said Aimpezlancesand the grid of the other of said push pull tubes, means for supplying a plate circuit electrode of said preceding tube with current sub-` ject to variations, and means for supplying the grid of said preceding. tube with variations of substantially the same frequency and bearing a predetermined relation in phase and magnitude to said first named variations so as substantially to reduce disturbing variations in the output of the system.-

2'.'In a signal repeating system, a push pull stagejcomprising a vacuum tubehaving equal resistances respectivelydn its plate supply and plate return circuits,'a connection between the nega-tive side off the former of said resistances andthe grid of onev o`f said push pull tubes and a connection between the positive side of the latterof `said impedancesand the grid of the other of said push pull tubes, means for supplying the tube. circuits with current subject to variations which tends to produce disturbing variations in the output circuit, and means for proportioning the variations supplied to dierent tube circuits so that variations carried forward t'o the grids of the push pull tubes are substantially nulliedin the output of the system.

3. In a signal repeating system a push pull stage comprising two vacuum tubes, a stage preceding said push pull stage comprising a vacuum tube having impedances in its plate supply and plate return circuits, a connection between a point of relatively negative potential of the former of said impedances and the grid of one of said push pull tubes and a connection between a point of relatively positive potential of the latter of said impedances and the grid of the other of said push pull tubes, means for supplying the plate circuit of said preceding tubewith current subject to variations, and means for supplying the grid of said preceding tube with variations of substantially the same frequency and bearing a predetermined relation in phase and magnitude to said rst named variations so as to cause variations of substantially the same frequency, phase and magnitude to be supplied to each of the grids of the push pull tubes.

4. In a signal repeating system, a push pull stage comprising two vacuum tubes, a stage preceding said push pull stage comprising a vacuum tube having impedances in its plate supply and plate return circuits, a connection between a point of relatively negative potential of the former of said impedances and the grid of one of said push pull tubes, a connection between a point of relatively positive potential of the latter of said impedances and the grid of the other of said push pull tubes, means for heating the cathode of said preceding tube with current subject to variations which tends to produce disturbing variations in the plate circuit, and means for supplying the grid of said preceding tube with variations of substantially the same frequency and bearing such a relation in phase and magnitude to said rst named variations as to cause substantially no variations to be transmitted to the grids of the push pull tubes.

5. In a signalrepeating system, a push pull stage comprising two vacuum tubes, a stage preceding said push pull stage comprising a vacuum tube having impedances in its plate supply and plate return circuits, a connection between a point of relatively negative potential of the former of said impedances ,and the grid of one of said push pull tubes, a connection between a point of relatively positive potential of the latter of said impedances and the grid of the other of said push pull tubes, means for heating the cathode of said preceding tube with current subject to variations which tends to produce disturbing variations in the plate circuit, and means for supplying the grid of said preceding tube with variations of substantially the same frequency and bearing such a relation in phase and magnitude to said rst named variations as to cause variation of any desired magnitude and either of two opposite phases to be transmitted to the grids of said push pull tubes.

6.l In a signal repeating system, a push pull stage comprising two vacuum tubes, two stages in tandem preceding said push pull stages and each comprising a vacuum tube, the later of said last named tubes having equal impedances respectively inits plate supply and plate return circuits, a connection between the negative side of said former impedance and the grid ofvone of said push pull tubes, a connection between the positive side of the latter impedance and the grid of the other of said push pull tubes, and means for supplying the plate circuits of said preceding tubes with current subject to fluctuations which tend to cause disturbing variations in the plate circuits, the parts being so proportioned and arranged that the combined effect of current supplied to the earlier of said tandem tubes and that supplied directly to the plate circuit ofthe later of said tandem tubes is to cause variations of the same frequency, phase and magnitude to be impressed on the grids of the push pull tubes.

7. In a signalvrepeating system, a push pull stage comprising two vacuum tubes, a stage preceding said push pull stage comprising a vacuum tube having equal impedances respectively in its plate supply and plate return circuits, a connection between the negative side of the former of said impedances and the grid of one of said push pull tubes and a connection between the positive side of the latter of said impedances and the grid of the other and said push pull tubes, means for supplying the plate circuit electrodes of said preceding tube with current subject to variations, and means for supplying the grid of said preceding tube with variations of substantially the same frequency and bearing a predetermined relation in phase and magnitude to said rst named vari; ations so as 'substantially to reduce disturbing variations in the output of the system.

HAROLD R, HAYDEN.

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