US2540478A - Multivibrator - Google Patents

Description

Feb. 6 1511 G. R. FRQST 254,47

-MULTIVIBRATOR Filed June 4, 1945 "ME TIME VOLTA GE vog'jcs ZQLZAGE TIME TIME TIME F/ FIG /Z to F/G. A3 il@ ls u if; v' E U l l l TIME TIME T/ME FIG. /4 f F/G /5 fo F/G. i165 T//WE TIME g TIME' /AH/E/VTOR G. i?. FROST A T TOR/VEV Patented Feb. 6, 1951 UNITED STA-res PATENTQor-'Flc George R. Frost, Great Neck, N, Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application June 4, 1945, Serial No. 597,463 l r v- 11 Claims. (Cl. Z50-36) This invention relates to self-oscillating generators, and particularly to multivibrator type generators.

One of the objects of this invention is to provide a simplied form of'multivibrator type generator capable of generating voltage wave forms of various shapes, as square wave forms. sawtooth wave forms and many other types of wave forms including all of the conventional types ofwave forms found in various types of known multivibrators.

Another object of this invention is to provide a multivibrator type generator having a simple form of control for the frequency of vibration.

Another object of this invention is to provide a simple form of amplitude control for the output wave generated by a multivibrator type generator.

Another object of this invention is to provide switching means capable of delivering various forms of generated wave shapes to test equipment or to other associated circuits and apparatus.

For testing and other purposes, it is often desirable to have apparatus that is capable of generating various kinds of voltage wave forms among which may be certain wave forms difficult to produce. The multivibrator arrangement in accordance with the present invention is capable ofproducing many kinds of wave shapes and Ais of special interest because of the ease with which certain difficult wave forms may be directly generated. Thus, thebasic circuit of this' inventionvmay be used to produce directly square type wave forms free from horns, and triangle type waveforms, and also many other types of wave forms such as upwardlyv extending pips, downwardly extending pips, different pips comprising upwardly extending pips alternating with downwardly extending pips, saw-tooth wavev forms, half sine wave type wave forms and many others. It will be noted that a square wave may be -generated directly, and without reshaping a sine wave.

v*In a particular arrangement, the multivibrator system in accordance with this invention mayl source. A common cathode coupling resistor,

variable from zero to a considerable value of resistance, may be provided in the lead from the cathodes of both space discharge devices to the negativeterminal oi the power supply source. A resistance-capacitance (R.C.) network circuit may be provided either between the anodes of the two space discharge devices or between one of such anodes and the. positive terminal of the. power supply source, the network circuit referredV to comprising a central resistor which is isolated by means of one or more series connected capaci-` tors from each of the anodes, or from one of such anodes andthe positive power supply terminal, according to the particular connection used forfthe.v networkcircuit. Connections are provided from the grid electrode of each space discharge ydevice to different and opposite ends ofthe central or grid network resistor referred to, each connection being from theY grid to vthe far end of the central resistor.

J A suitable switchlmay be provided for connect-` justable yin resistance Value for control of the frequency of vibration of the generated voltage waves, and vthe ,common cathode resistor ymay be made adjustable in resistance value for control of the amplitude of the voltage waves generated.- -One of the network capacitors may have its.

capacitance made of considerabls7 greater or larger yvalue rthan that of the other, in order to provide a square wave form at the anode terminal associated with the larger capacitor referred to.A

Also, a grid vleak resistor may or may not be used vto connect the power supply positive ter-` minal with the actual or the effective mid-point of the central network resistor or with eitherV one of rtheindividual grids. The output voltages maybe of variouswave forms and maybe taken off atranyypoint whatever inthe circuit such as at the cathode, grid, orplate electrodes of either of-thexelectron tubes.

Fo'r a' clearer understanding of the nature of this invention :andthe additional advantages, features and kobjects thereof, reference is made toathe following description taken in connectionl Also awith the accompanying drawings, in which like reference characters represent like or similar parts and in which:

Fig. 1 is a circuit diagram illustrating a multivibrator system in accordance with this invention;

Figs. 2 to 16 are graphs illustrating examples of various forms of Voltage versus time wave shapes which may be generated by the multivibrator system illustrated in Fig. l, Fig. 8 for example illustrating a triangle wave shape form', and Figs. 12 and 13 illustrating square type wave shapes.

Referring to the drawing, Fig. 1 is a-circuit diagram illustrating a self-oscillating. multiv brator type generator in accordance with this in-v vention. As shown in Fig. 1, the multivibratory may comprise a pair of suitable vacuum or gaslled space discharge devices or multielement tubes I and I2, each having a cathode I4, a cathode heater I5, a grid electrode I6 and an anode or plate electrode I'I. While the electronic tubesI and I2 are illustrated in Fig.- 1 as having. a single grid electrode I6 and an indirectly heated cathode Ill, it will be understood that the tubes ID :and I2 may be provided in the form using directly or indirectly heated cathodes, one or. more grid elements, and separate envelopes or a single envelope, and that the space discharge tubes I0 and I2 'may be any suitable space discharge devices which can be alternately .driven tosaturation and cut off by the circuit voltages applied thereto.

Plate voltages for the space discharge devices III-and I2 may be supplied by a battery I8 or other vsuitable power supply source capable of maintaining the anodes II of the electronic devices IU and I2 at a suitable positive bias potential in relation to and with respect to the cathodes I4 of the space discharge tubes I0 and I2. Plate load resistors and 2| may be connected in one or in both of the connection leads from the `plate electrodes I'I of the electron tubes II) and I2 to the positive terminal B-I- of the plate supply source I8. The plate resistors 20 and 2| asl shown in Fig. 1 are connected between the anodes II or" the electron tubes I0 and I2 and may be made of selected resistance values for wave shaping of the output waves taken o` from either of the anode output load terminals 2 and 5.- Tlie insertion orvthe omission or the changing ofthe resistance Value of the resistors 20 and 2I are of any resistance in series with the power supplycircuit I8 interconnecting the anodes II with the cathodes I4 of the space discharge tubes IIl vand I2 has the eiect of changing the shape of the-output voltage wave. It will be notedthat the plate resistors 20 and 2| may provide aplate loading function as well as a wave shaping function, and are also part of the timing circuit which determines the frequency of vibration of the multivibrator system illustrated in Fig. 1.

The timing circuit as shown in Fig. 1 also includes a resistance and-capacitance or R.C. c ircuit comprising the elements 22, 23 and 24 which may be connected in series circuit relation'between the anodes II of the space discharge tubes I0 `and I2 as illustrated by the contact position 3I1of the switch 3U in Fig. 1, or betweenione of such anodes I'I and the positive terminal B-I- of the anode supply source I8 as illustrated Vby. the connection to the other contact position 32 of the-switch 3U in Fig. 1. With either` of these connections, as determined bythe contact position of the switch 30, the R.-C. circuit comprises a central grid resistor 23 which is isolated from each of the anodes I 'I, or from one of such anodes I 'I and the positive terminal B-I- of the plate supply source i8, by means of the capacitors 22 and 2 disposed at the opposite ends of the central resistor 23. The central resistor 23 may be conveniently utilized as a simple means for control over the frequency o vibrationxand for that purpose its resistance value may be varied over a wide range as from 0 to 100,000 ohms for eX- ample.

A grid leak resistor 23A may be connected between the positive power supply terminal B+ and the Yactual or eiective midpoint of the central network resistorv 23.- While the circuit illustrated in Fig. l is capable of vibrating with a stability equal to that of any resistance-capacitance type vibrator, to prevent possible external source interference blocking the free grids I6 of the space discharge devices I andI2, the grid leak resistor 23A'having a resistance of the order of 2 to 10 megaohms valueA may be connected from the mid-point or from either terminal of the lnetwork resistor 23 to either plate Il of the space discharge tubes I0 and I2 or to the power terminal'B-I-- The grid circuit'comprising the grids I6 and the resistor 23 isolated by the capacitors 22 and 2li must be well insulated from the B- supply circuit for oscillations to maintain, whether the resistor 23A is employed or not. The grid leak resistor 23A does not enter into either the frequency control or the lwave shaping control when used, but serves merely asa leak to prevent blocking of the grids I6 under conditions of potential shock from external influences.

The capacitors 22 and 24 may be made of equal capacitance values with respect to each other and may be made of adjustable capacitance values to relate one to the other, to provide for diierent frequencies of vibration of the multivibrator, and for other purposes. Where either or both of the capacitors 22 and 25 are to be made adjustable, the variable capacitance thereofv may be obtained either from one Yof a plurality of fixed condensers connected into the circuit separately by a suitable switch or from a single adjustable condenser unit in a known manner.

Connectors 25 and 26 may be utilized to establish separate electrical connections from the grid electrode IB 'of each of the space discharge devices I and I2 to that end of the central resistor 23 which isadjacent the capacitor 22 or 24 associated with and connected to the anode II of the other of the space discharge devices I0 and I2. Thus, as shown in Fig. 1, the grid electrode I6 of the space discharge tube I0 may be connected by the connector 25 to the right-hand end of the grid resistor 23 at a point intermediate the central resistor 23 and the 'capacitor 2- that is connected with the anode Il of the other space discharge tube I2; and they grid electrode I6 of the space discharge tube I2 may be connected by the connector 26 to the left-hand end of the 'central resistor 23 at a -point intermediate the resistor 23 and the other capacitor 22 that is connected with the anode I'I 'of the other space discharge tube Ill. It will'be understood that the switch 30 may be associated with either of the capacitors 24 and 22A in cases where it is desired to provide an R.-C. circuit connection directly to the positive terminal B+ of the plate supply source I8, and to one of the anodes Il' of the electronic tubes I0 and I2, the switch 3U being utilized for connect- 7a ing vthe circuits 22, 23 and24 betweenY the two als-40,4%*

anodes I1 of the space discharge devices II) and I2, or between one of such anodes I1 and the positive lead B+ of the power supply source I8. A common cathode resistor 21 connected at one of its ends with the cathodes I4 of both of the space discharge tubes IIJV andl I2 and connected at its opposite end with the negative terminal B of the power supply source I8 provides a common cathode coupling resistance lof variable value in the negative voltage lead from the power supply source I8. The resistor 21 may be of variable resistance values from a zero value to a considerable resistance values such as for example to 25,000 ohms or more. The common coupling resistor 21 provides a simple control of the signal amplitude and may contribute a modiiied form of wave at the junction terminal 3 of the resistor 2'I with the common connection to the cathodes I4 of the space discharge tubes I0 and I2. A shunt capacitor 28 may be bridged across one of the plate load resistors 2| by means of ay switch 29 in order to provide control of the voltage wave shape produced at the adjacent out, put anode terminal 5. Also, it will be noted that the left and righthand plate load resistors 20 and.

2I may be made adjustable for wave shaping purposes, and the variable central resistor 23 used for control of the frequency of vibration. The cathode resistor 2'I may be made adjustable for control of the amplitude and for wave shaping of the cathode wave at the output terminal 3. T he condenser 28 may be made adjustable for` wave shaping purposes and may be shunted across either of the plate resistors 20 and 2 I. The output may be taken off from any of the output terminals I to 5, such as from the anode terminals 2 or 5, which may be coupled to a suitable amplifier by means of known capacitance and resistance coupling devices. v

As a specic illustrative example, the values of the component elements of a particular multi vibrator constructed in accordance with the circuit arrangement of Fig. 1 may be approximately as iollows:Y Resistor 20=10,000 ohms, resistor 2I=10,000 ohms, capacitor 22=.05 microfarad, resistor 23:0 Ato 100,000 ohms, capacitor 24:.05 microfarad, resistor 2I=0 to 25,000 ohms, capacitor 28:1.0 microfarad, power supply source I8=approximately 300 volts, tube I0 a conventional vacuum tube such as a 1/2 6SN7, a 1/2 6SL7, a 6J 5, a 6L6, or other suitable spacedischarge device, and tube I2 the same as tube I0. o Y

It will be noted that the basic circuit illustrated, in Fig. 1 comprises two space discharge tubes I0 and I2 having a common cathode connection connected with the negative power supply lead B-, one or more plate load resistors 20 and 2I connected with the positive power supply lead B+, and 'R.C. network circuit comprising capacitors 22 and 24 disposed at each of the opposite ends of a central or grid resistor 23 and connectedk across both plate resistors 20 and 2'I, and a connection from the grid of each tube I and I2 to the far or remote end of the network central refl sistor 23. An examination of this circuit will disclose that a. drop in potential takes place alternately at the plate terminals 2 and 5 of the platel resistors 20 and 2I, the period being controlled primarily by the total values of the resistance and capacitance in the grid circuit network.` The I2 which alternately charges the condensers 2ij and 24 to one polarity and then to the Opposite polarity. During the alternate charging periods a potential difference will exist across the network Aresistor 23 because of the electron movement through the resistor 23 in the act of-charg-l ing the capacitors 22 and 24. The potential difference is at a maximum value at the beginning of each charging period and decreases as the charging period progresses. The time constant of this network therefore controls the period of alternation of this vibrator. With the grid electrodes I6 cross-connected with the resistor 23 as shown in Fig. 1, the space discharge tubes III and I2 are alternately driven toward saturation and cut off by the positive and negative potentials at the opposite ends of the network resistor 23. As the condensers 22 and 24 progress in charge, the voltage drop across the network resistor 23 decreases exponentially and the gridv electrodes I6 of the space discharge tubes I0 and I2 return toward zero voltage. This changing voltage on the grid electrodes I6 results in an opposite change of potential on the respective plate electrodes I'I which decreases the potential difference between the plate terminals 2 and 5 thereby diminishing the charging voltage on the condensers 22 and 24. Eventually a cross-A over point is reached when the voltage on the condensers 22 and 24 equals the potential difference between the plate terminals 2 and 5, and when such cross-over point is` passed, the condensers 22 and 24 will attempt to discharge. The process is repeated, with the opposite space discharge tubes I0 and I2 alternatively reaching saturation and cut oi. The circuit thus vibrates at a frequency determined by the resistance and capacitance values making up the timing network 20 to 24, and the cut-01T value of the particular tubes I0 and I2 that are used. The frequency of vibration is easily adjusted over a wide range by varying the value of the grid timing resistor 23.

More particularly, the operation of the circuit illustrated in Fig. 1 may be described as follows.v It is assumed that the switch 30 is disposed ony the contact position 3I thereby connecting the or 20 or 2I, will change with a resulting change This' in the potential ofthe plate or anode Il'. change in plate potential will be applied to the circuit comprising the elements 22, 23 and 24 andv cause a current flow through the resistor 23,v

when and as the capacitors 22 and 2d change their values of charge. The effect is such that should the current iiow through the space discharge device I0 be increased, the potential at its plate or anode I1 will decrease, thereby caus- Y ing electron flow through the resistor 23 from the capacitor 22 towards the capacitor 12dfand driving the grid electrode I6 of the space discharge tube I0 in a positive direction.` At the same time, the grid electrode I5 of the other space discharge device I2-will be driven in a neg-Yv ative direction by the same electron ilow. Through the grid action mentioned, the plate current in the space discharge device i0 will increase while the plate current in the space discharge device I2 will decrease, thus vincreasingthepotential difference across the circuit comprising rthe capacitors 22 and 2d and the resistor 23. Accordingly, the electron ow through the resistor 23 is increased and the eiect, being cumulative, is to rapidly drive the space discharge tube I0 to saturation and the other space discharge tube-I2 to cut off. When and as the capacitor 22 and the resistor 23 cease to change their charge due to the impressed potential diierence across the network 22, 23 and 2d reaching a steady state value, the electron flow through the resistor 23 diminishes and the grid electrode I5 oi the space discharge tube i0 now moves in a negative direction While the grid electrode I5 of the space discharge tube I2 moves in a positive direction. Reversed action is thus instituted, and again the effect is cumulative, now driving the tube I0 toward cut off and the other tube I2 toward-saturation. Thereafter, the potentials on the grid electrodes I6 of the space discharge devices I and I2 will be moved oppositely and the action outlined above will be repeated over and over again, the multivibrator thus becoming free running. Control over the frequency may be obtained `by adjustment of the resistance value of the resistor 23, and control over the amplitude of the generated signal voltage may be obtained by adjustment-oic the resistance value of the common coupling resistor 2'I.

The operation of the circuit diiiers somewhat from the above description when the switch 30 is placed on the contact position 32, thus connecting the network 22, 23 and 2li between the positive power supply lead B+ and the anode Il of one of the space discharge tubes which, as particularly illustrated in Fig. 1, is the plate electrode I'I of the space discharge tube lil. En this arrangement, the circuit action diiers in that changes in the potential across the R.C. network 22, 23 and 24 are now impressed by one -i plate load resistor 20, and the coupling between the space discharge devices E@ and I2 is afforded in one direction through the common coupling resistor 21. Typical values for the component elements of this circuit connection are the same as given hereinbefore. It will "e understood that the invention is not restricted to any particular values as given in the illustrative example, or to the particular switching arrangement illustrated, or to the particular embodiment illustrated. It will be noted that the electron tubes i9 and I2 utilized may be of any suitable type, may be heated directly or indirectly, and may be of the single or multigrid type, and that outputs may be taken from any point in the circuit-according te the wave form desired.

The output of the multivibrator system illustrated in Fig. 1 may be taken from various points of the circuit, such as for example from any of the output terminals I to 5 which are separately connected with the two plate electrodes il, the two grid electrodes I3 and the common cathodes I4 of the two space discharge devices i3 and I2. The output terminals may be any of the terminals I to 5, the other connection that cooperates with the terminals I to 5 being the ground connection, as illustrated in Fig. 1.

Figs. 2 to 16 are graphs illustrating some of the various forms of voltage versus time wave shapes which may be generated by the multivibrator circuit shown in Fig. l, depending upon the output terminals I to 5 selected, and depending upon the position of the switches 29 and 30. The ordinates of the curves in Figs. 2 to 16 represent voltage values, and the abscissae represent' time values.

Figs. 2 to 6 are a group of graphs illustrating.

ve various rforms of voltage wave shapes which may be generated by the multivibrator shown in Fig. 1, when the switch 30 is on the contact position 3I connecting the R.C. circuit 22, 23 and 24 between the plate electrodes I'l of the electron tubes IG and I2, and when the switch 2@ is ini open circuit position so that the capacitor 28 is taken off from the ground connection and thev anode terminal 5 which is connected with the plate electrode I'I of the other space discharge The curve illustrated in Fig. i repretube I2. sents the form of voltage wave taken off from the ground connection and the grid terminal I' which is connected with the grid electrode i6 of the tube I0, and the curve illustrated in Fig. 5 represents the form of voltage wave taken off from the ground connection and the grid terminal 4 connected with the grid electrode I6 of the other space discharge tube I2. The curve illustrated in Fig. 6 represents the form of voltage wave taken on' from the ground connection and'` 'the common cathode terminal 3 connected with the common cathodes I4 of both of the space discharge tubes` I0 and I2.

Figs. 7 to 11 are a group of five graphs showingthe modifications in the generated voltage wave forms which occur when the shunt capacitor 28 is placed across the plate load resistor 2I by the switch 29` in its closed position, the switchl 30. being, as before, on its contact position 3| which' connects the R.C. circuit 22, 23 and 24 between the plate-electrodes I7 of both of the space dis- Figs. 7 to 11 illustrate the -various types of voltage wave forms taken charge tubes l0 and I2.

in Fig. 8, an equilateral triangle type voltagel wave form-instead of the form illustrated in` Fig. 3--isV generated at the plate terminal 5 connected with theV resistor 2I and the plate electrode Il of the tube I2 when a shunt capacitor 28 of suitable value is bridged across the plate load resistor 2I; andas illustrated in Fig. 9, a capacitative triangle form of wave is obtained from the grid terminall I, instead of the wave form shown in Fig, 4.

It will be noted that a useful Wave in the form This wave of a triangle is illustrated in Fig. 8. may be generated at the anode terminal 5 in cooperation with the ground connection by the circuit of Fig. l when the switch 30 is on the c ontact position 3I, when the condenser 28 of about "f 1 microfaradcapacitance value is bridged across the resistor 2I by closure of the switch 29, and

when the common cathode resistor of aboutv 15,000 ohms resistance value is in series circuit 'v relation betweenV the cathodesld of the tubes I'0' f 9 and l2 and the negative power supply terminal of the source yI B. The frequency of vibration of the triangle form of wave referred to is determined by the resistance values of the resistors 20, 2l and 23 and the capacitance values 'oi' the condensers 22 and 24 and its amplitude may be controlled by the value of the cathode resistor 21. The triangular shape of the wave is determined by the bridging condenser 28. circuit which produces the triangle form of wave at the plate terminal 5 of the tube I2, a square pulse ,of the form Villustrated in Figs. 12 and 13 may be simultaneously taken 01T from the ground connection and the plate terminal 2 of the tube I0 by merely making the condenser 22 of greater capacitance value than thatv of the condenser 24, the relative values of capacitance being roughly o f the order of 10. to 1.

Figs. 12 to 16 are a group of graphs showing further modications in the generated voltage wave forms which'occur when the bridging capacitor 28 is removed and the switch 30 is now placed in its contact position 32 which connects the R.C. circuit 22, 23 and 24 between the plate electrode I1 of the space dischargetube I0 and the f 3|. Thus, as illustrated in Figs. 12 and 13, a

useful square type wave form is obtained from either of the plate terminals 2 or 5 lcooperating with' the groundconnection, when the R.C. cirlcuit 22, 23 and 24 is connected between one of the plate electrodes I1 and the B+ terminal of the power supply source` `I8, as illustrated iny Fig. 1 bythe switch 3|] at the contact position 32.

, Whileparticular forms of voltage wave shapes are illustrated in Figs. 2 to 16, it will' be understood thatY many other forms of voltage wave shapes may beV generated by the multivibrator system of Fig. 1, and although thisinvention has been described and illustrated in relation to specic arrangements, it is to be understood that it is capableof application in other organizations and is therefore not tobe limited to the particular embodiments disclosed.

What is claimed is:

1. A multivibrator for generating a voltage wavek comprising' two space discharge devices each having a cathode, an anode and a grid elec-v trode, means including a'power supply source having positive and negative terminals for maintaining said anodes of said devices at a positive potential with respect to said cathodes, a resistor disposed in at least one of the leads from said anodes to said positive terminal, a common cathode resistor disposed in the lead from said cathodes to said negative terminal, a network connecting said anode of one of said devices with said anode of the other of said devices, said net- Work comprising a central resistor and'capacitors connected in series circuit relation with said central resistor and disposed at each oi` the opposite ends of said central resistor, said central resistor being isolated from each of said anodes of said devices by said capacitors, and connectors separately connecting said grid electrode of each of said devices to* the end of said central resistor Using the same.

ladjacent said capacitor that is connected to said anode of the other of said devices, said central resistor being adjusted to a resistance value co1'- responding to the value of the desired frequency of vibration for said generated voltage wave, and said common cathode resistor being adjusted to a resistance value corresponding to the value of the desired amplitude for said generated voltage wave.

2. A multivibrator for generating a voltage wave comprising two space discharge devices each having a cathode, an anode and a grid electrode, means including a power supply source having positive and negative terminals for maintaining said anodes of said devices at a positive potential With respect to said cathodes, a resistor disposed in each of the leads from said anodes to said positive terminal, a common cathode resistor disposed in the lead from said cathodes to said negative terminal, a network connecting said anode of one of said devices with said anode of the other of said devices, said network comprising a central resistor and capacitors connected inseries circuit relation with said central resistor and disposed at each of the opposite ends of said central resistor, said central resistor being isolated from each of said anodes of said devices by said capacitors, and connectors separately connecting said grid electrode of each of said devices to the end of said central resistor adjacent said capacitor that is connected to said anode of the other of said devices, said central resistor being adjusted to a resistance value corresponding to the value of the desired frequency of vibration for said generated voltage wave, and said common cathode resistor being adjusted to a resistance value corresponding to the value of the desired amplitude for said generated voltage wave.

3. A multivibrator for generating a voltage Wave comprising two space discharge devices each having a cathode, an anode and a grid electrode, means including a power supply source having positive and negative terminals for maintaining Vsaidanodes of said devices at a positive potential with respect to said cathodes, aresistor disposed in each of the leads from said anodes to said positive terminal, a common cathode connection disposed in the lead from said cathodes to said negative terminal, a network connecting said anode of one of said devices with said anode of the other of said devices, said network comprising a central resistor and capacitors connected in series circuit relation with said central resistor and disposed at each of the opposite ends of said central resistor, said central resistor being isolated from each of said anodes of said devices by said capacitors,` and connectors separately connecting saidgrid electrode of each of said devices to the Aend of said central resistor adja cent said capacitor that is connected to said anode of the other of said devices, and means for bridging a capacitor across one of said anode lead resistors.

4. A multivibrator for generating a voltage wave comprising two space discharge devices each having a cathode, an anode and a grid electrode, means including a power supply source having positive and negative terminals for maintaining said anodes of said devices at a positive poten- :anode of one ofsaid devices with said anode of the other of said devices, said network comprising a central resistor and capacitors connected in series circuit relation with said central resis- -tor and disposed at each of the opposite ends of said central resistor, said central resistor being isolated from each of said anodes of said `devices by said capacitors, and connectors separately connecting said grid electrode of each of said devices to the end of said central resistor adjacent said capacitor that is connected to said anode of the other of said devices, said central resistor being adjusted to a resistance value corresponding to the, value of the desired `frequency. of Vibration for said generated voltage wave, said common ca thode resistor being adjusted to a resistance value corresponding` to the value of the desired amplitude for said generated voltage wave, and means for bridging a capacitor across one of said anode lead resistors.

5. A multivibrator for generating a voltage wave comprising two space discharge devices each having a cathode, an anode and a grid electrode, means including a power supply source having positive and, negative terminals connected with leads for maintaining said anodes of said devices at a positive potential with respect to said cathodes, a resistor disposed in each of the leads from said anodes to said positive terminal, a common cathode resistor disposed in the lead from said cathodes. to said negative terminal, a network connected across at least onev of said ,resistors disposed in said leads from said anodes to said positive terminal, said network comprising a central resistor and capacitors connected .in series circuit relation with said central resistor and disposed at eachY of the. Opposite ends of said central resistor, said central resistor being isolated from said anodes and from said positive terminal by said capacitorsr a connector connecting said grid electrode of one of said devices to the, end of said central resistor adjacent said capacitor that is connectedY to said anode of the other of said space discharge devices, a connector connecting said gridY electrode of said lastmentioned space discharge deviceto the` opposite end of said central resistor, and means for bridging a capacitor across. one of said anode lead resistors.

6. A multivibrator comprising two space discharge devices each having a cathode, an anode and al grid electrode, means including a power supply source having positive and, negative terminals connected with leads for maintaining said anodes of said devices at a positive potential with respect to said cathodes, a resistor disposed in at least one of the circuit leadsl from said anodes to said positive terminal, a common cathode coupling resistor of selected resistance value, disposed in the circuit` leadl -from said cathodes to said negative terminal, a network comprising a central resistor and. a capacitor connected in series circuit relation with each of the opposite ends of saidcentral resistor, one of said network capacitors. at one end of said central resistor having a capacitance` value substantially greater than the capacitance value of the other of said network capacitors at the opposite end of said central resistor, means for connecting said network from said anode of one of said devices to said anode of the other of said devices, connectors independently connecting said grid electrode of each of said devices to different and opposite endsof-- said central resistor.

terminal of said source with substantially the eiective mid-point. of said network central resistor. 7. A multivibrator comprising two space discharge devices each having a cathode, an anode and a grid electrode, means including a power supply source having positive andr negative terminals connected withleads for maintaining said anodes of said devices ata positive potential with respect to said cathodes, a resistor disposed in at least one of the circuitleads fromY said anodes to said positiveiterminal, a common` cathode coupling resistor of selected resistance value disposed in the circuit lead from said cathodes to. said negative terminal, a network comprising a central resistor and a capacitor connected inv series circuit relation with each of the opposite, ends of said central resistor, one of said network capacitors at one end of said central resistor having a capacitance value substantially greater than the capacitance value of the other of said network capacitors at the. opposite. end of said central resistor, means for connecting. said network from said anode of one of said devices to said anode of the other of said devices, connectors independently connecting said grid electrode of each oi said devices to different, and opposite. ends of said central resistor, a. gridl leak resistor connect,-

ing said positive terminal of said source with substantially the eiective; mid-point ci said network central resistor, and a circuit including a capacitor bridging said anode lead resistor.

8.l A multivibrator for generating a triangle form of voltage wave comprising two electronic devices. each having a. cathode, an anode and a grid electrode, a power supply source having a positive terminal connected throughV resistors to said`V anodes of said devices and having a negative terminal connected through a, common resistor tosaid cathodes, a network comprising a central resistor `and a capacitor connected inseries. circuit relation, with each 0i the opposite. ends of said central resistor, means. connecting said network between saidV anodes of said devices,A and connectors separately connecting the grid electrode of each of said devices. to diierent ends of said central resistor, and a capacitor bridging one, of said anode resistors.

9.v A multivibrator for generating a. square type voltage Wave form at, one anode and a triangle type voltage wave form at, the other anode` comprising a pair of electronic devices. each having a cathode, `an, anode andv a grid electrode, a frequency timing and wave shaping circuit comprising parallel paths interconnecting said anodes of said devices, one of said parallel paths compris` ing series-connected plate load resistors and a condenser connected in shunt with one ofV said resistors, another of said parallel paths comprising series-connected capacitors and a central resistor disposed between said capacitors, one of said capacitors having substantially greater capacitance than the other, yand a connector connecting said grid of each 0f said electronic devices with the end of said centralv resistor that is adjacent said capacitor connected to the anode ci the other oi said electronic. devices.

10. A multivibrator for generating a voltage wave comprising a pair of electronicl devices each having a cathode, an anode and a grid electrode, means including a pair of series-connected anode resistors interconnecting said anode electrodes of said pair of electronic devices,l means including@ power supply source connected in series circuit relation with an adjustable common cathode resistor disposed in said series circuit leading from said cathode electrodes to the negative terminal of said source and connecting said cathode electrodes of said pair of electronic devi-ces with said anode electrodes thereof through a connection point intermediate said series-connected anode resistors, said power supply source constituting means for maintaining said anode electrodes of said pair of electronic devices at a positive potential with respect to said cathode electrodes thereof, means comprising a network connected in shunt circuit relation with at least one of said series-connected anode resistors, said network comprising a central resistor and a capacitor connected in series circuit relation with each of the opposite ends of said central resistor, means comprising a grid-leak resistor connecting substantially the effective mid-point of said central resistor of said network with said connection point intermediate said series-connected anode resistors, means connecting the grid electrode of one of said pair of electronic devices with one end of said central resistor that is connected with the anode electrode of the other of said pair of lelectronic devices, means connecting the grid electrode of the other of said pair of electronic devices with the other end of said central resistor that is opposite to said one end thereof, and means comprising a condenser connected in shunt circuit relation with one of said pair of anode resistors, said central resistor constituting means for controlling the frequency of said wave generated by said multivibrator and said common cathode resistor constituting means for controlling the amplitude of said wave, and means for taking off said wave in different shapes from separate output terminals connected with said cathode, grid and anode electrodes of said pair of electronic devices.

11. A multivibrator for generating a voltage wave comprising a pair of electronic devices each having a cathode, an anode and a grid electrode, means including a pair of series-connected anode resistors interconnecting said anode electrodes of said pair of electronic devices, means including a power supply source connected in series circuit relation with an adjustable common cathode resistor disposed in said series circuit leading from said cathode electrodes to the negative terminal of said source and connecting said cathode electrodes of said pair of electronic devices with said anode electrodes thereof through a connection point-intermediate said series-connected anode resistors, said power supply` source constituting means for maintaining said anode electrodes of said pair of electronic devices at a positive potential with respect to said cathode electrodes thereof, means comprising a network connected in shunt circuit relation with at least one of said series-connected anode resistors, said network comprising a central resistor and a capacitor connected in series circuit relation with each of the opposite ends of said central resistor, means comprising a grid-leak resistor connecting substantially the effective mid-point of said central resistol` of said network with said connection point intermediate said series-connected anode resistors, means connecting the grid electrode of one of said pair of electronic devices with one end of said central resistor that is connected with the anode electrode of the other of said pair of electronic devices, means connecting the grid electrode of the other of said pair of electronic devices with the other end of said central resistor that is opposite to said one end thereof, said central resistor constituting means for controlling the frequency of said wave generated by said multivibrator and said common cathode resistor constituting means for controlling the amplitude of said wave, and means for taking off said wave in diierent shapes from separate output terminals connected with said cathode, grid and anode electrodes of said pair of electronic devices.

GEORGE R. FROST.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,587,520 Hartley June 8, 1926 1,813,469 Taylor July 7, 1931 2,154,492 Clough Apr. 18, 1939 2,157,434 Potter May 9, 1939 2,211,750 Humby Aug. 20, 1940 2,213,820 Maxson Sept. 3, 1940 2,356,071 Macdonald Aug. 15, 1944 2,365,512 Bartelink Dec. 19, 1944 OTHER REFERENCES Phil. Mag. and Journal of Science, vol. 35, No. 250, Nov. 1944, pages 716 and 717.

Journal of Scientific Instruments, vol. 16, 1939, pages 285-290.

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