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15, 1946. c. H. SMITH, JR., ETAL I 2,409,229 SELECTOR CIRCUIT Filed June 13, ‘1945 E 2 Sheets-She'et 1 5 IO 3mm CARL HARRISON SMITH JR. MILTON L. KUDER ‘Get. 15, 1946. c. H. SMITH, JR., ETAL 2,409,229 SELECTOR CIRCUIT Filed June 15, 1945 2 Sheets-Sheet 2 I LET-E _ (G) _W (b) _“KV—WVJW_ 1/ 7/ V ‘TE-45 . (qhWM (b)— V (c)_ CARL HARRISON SMITH JR. MILTON L; KUDER Patented Oct. 15, 1946 2,409,229 UNITED STATES PATENT OFFICE‘ 2,409,229 SELECTOR CIRCUIT Carl Harrison Smith, Jr., Arlington, Va., and Milton L. Kuder, Washington, D. 0. Application June 13, 1945, Serial No. 599,287 7 Claims. (01. 177-380) (Granted under the act of March 3, 1883, as 1 amended April 30, 1928; 370 0. G. 757) This invention relates in general to a pulse transmission system and in particular to a means According to the invention, a time base gener ator, which may comprise a delay line energized by a pulse generator or any'other suitable ar for producing a group of pulse signals wherein the number and the relative time occurrence of the pulse signals comprising the group are selec rangement as hereinafter described, is provided tively determined. In an application ?led May 11, 1945, Serial No. 593,174, by E. H. Krause et al., a pulse transmis ' I and arranged to cooperate with a series of pulse selector vacuum tubes. Associated with each of the tubes is a separate switching means which may be operated to effectively withdraw any one or number of tubes from the series. The vac sion system is disclosed in which a group of pulse signals is transmitted over a given time interval. 10 uum tubes and the time base generator are so The number and the relative time occurrence of interconnected that when the latter is set into the pulses comprising the group are made con operation it functions to successively render con'. trollable. In this system a time base made up ducting those tubes left in the series by the of a number of successive unit time intervals is switching apparatus. Connected to the tubes in generated at the transmitter and comprises a 15 the series, but, not shown for purposes of sim time pattern from which the group to be trans mitted is formed. In any given transmission a pulse signal is always transmitted coincident with the ?rst unit time interval in the time base and at such other unit time intervals as may be de sired. At the receiving system a second time base generating device and a series of amplifying channels are provided and arranged so that each pli?cation, is a pulse transmitter which is held under control of the pulse selector tubes and ar-' ranged to emit a pulse signal each time one of, the tubes in the series becomes conducting. With particular reference to Fig. l a detailed circuit diagram of the invention is shown. As indicated in the ?gure, the time base generator comprises a pulse generator l0, and a scale-of unit time interval generated by the time base de ?ve counter chain, including stages ll, vice renders a different one of the amplifying :3. Tubes l4 through l8 represent the pulse se channels operative. In operation the ?rst pulse lector tubes with which the time base generator received from the transmitter starts the time base is to operate, while tube 24 is representative of at the receiver then each pulse signal arriving a coincidence tube which is connected in com after the ?rst pulse signal is made to pass through a different amplifying channel according to its 30 mon to the pulse selector tubes by way of a‘bias ing tube 23. Also, a pulse transmitter, not shown, time relationship with respect to the ?rst pulse in is connected to the output terminal 55. As will the group. In this manner any given pulse sig hereinafter be described in detail, the pulse gen nal occupying a de?nite time position relative erator ll} may be a multivibrator or any other to the start of the interval of transmission can be made to pass through a particular amplifying 35 suitable pulse-generating device, such'as that channel and can therefore be used to perform a de?nite function at the receiving system.‘ shown in the aforementioned patent application, which may be started and stopped either auto matically or manually, such as by the off-on switch ‘H, for example. The primary function It is an object of this invention to provide a means for producing a group of pulse signals of this pulse generator is to provide a source for wherein the number and relative time occurrence 40 driving the counter chain, comprising stages H, of the pulse signals are selectively determined. 12, and i3, through a complete cycle of operation It is another object of this invention to pro and at the same time to provide transmitter key; ‘ vide a means for alternately producing two dis; ing pulses to the first control grid 35 of the coinci tinct groups of pulse signals wherein the dispo dence tube 24. By-intlerconnection of the control sition of the pulse signals in each group is selec 45 grid of each of the selector tubes l4 through I 8 tively determined. ' to predetermined points in the counter chainyas Other objects and features of the present in vention will become apparent upon a careful con_ sideration of the following detailed description hereinafter described in detail and in accordance with the principles taught in the patent appli when taken together with the accompanying 50 cation of E. H. Krause Serial No. 582,964, ?led March 15, 1945, the counter circuit is made to drawings. successively render each of the selector tubes Fig. l is a circuit diagram of one embodiment conducting, as far as their grids are concerned, of the invention, and Figs. 2 and 3 show a series during a cycle ‘of operation. When any of the se of wave forms illustrative of the operation of the lector tubes conducts, a voltage drop appears circuit shown in Fig. 1. » ' 55 across their common plate load resistance 29. 2,409,229 3 The presence or absence of this voltage drop re resistance of the second tube llb in the ?rst counter stage and is applied in parallel through sults respectively in either non-conduction or a second short-time-constant circuit similar to conduction of the biasing tube 23, which by way capacitance 60 and resistance SI to the second of its connection to the second control grid 34 of 5 control grids of tubes lie and I2!) of the second the coincidence tube 24, renders the latter either counter stage I2. Finally, the input to the last sensitive or insensitive, respectively, to positive counter stage I3 is taken from a tap on the plate voltage pulses applied to its ?rst control grid 35 load resistance of the second tube IZb in the sec by the pulse generator In. Any one of the selec ond counter stage and applied in parallel through tor tubes I4 through I3 can be prevented from go 10 another short-time-constant circuit similar to ca ing into conduction in response to the action of pacitance 6i) and resistance 51 to the second con the counter chain by opening the cathode circuit trol grids of tubes I3a and I31) of the ?nal counter of the respective selector tube. Therefore to se stage I3. As hereinafter described, the quiescent lectively suppress or produce output pulses at the or zero state for the counter chain exists when terminal 55 of the coincidence tube 24, a num 15 tubes I la, I2a, and H51) are conducting and tubes ber of multi-position switches numbered I9 Ilb, I21), and I3a, are non-conducting. In trac through 22 are inserted in the respective cathode ing a complete cycle of counter operation, the ?rst circuits of the selector tubes I-5 through I8. In input pulse applied to counter stage II renders the zero position of these switches the cathode tubes I'Ib, I21), and I311 conducting and tubes Ila, circuit is complete to ground and the selector 2O I2a, and l3b non-conducting‘ The second input tube is capable of conduction in response to the pulse renders tubes Ila, I21) and I3a conducting. action of the counter chain. In the No. 3 posi A third pulse from the pulse generator will render tion of the switches the cathode circuit is open tubes III), In and I3a conducting. The fourth and the corresponding selector tube will be in input pulse renders Ila, I2a and I3a conducting. capable of conduction regardless of its grid bias 25 The ?fth negative input pulse would normally voltage as provided by the counter circuit. Con render tubes I lb, I21) and I3?) conducting but due sequently, during any given cycle of counter op to a feedback pulse obtained from the plate of tube eration the appearance or absence of a trans ~ I31) and applied through capacitance 58 to the mitter keying signal at the output terminal 55 suppressor grids‘59 and 63 of tubes Ill) and I21) depends upon the setting of the cathode switches 30 respectively, the tubes Ila, I2a and I3b will be l9 through 22. conducting, and tubes IIb, I21) and I3a non-con In the typical counter chain shown here all of ducting. It will be noted that this state is identi the counter stages II, I2, and I3 are similar in structure, also the grid biasing resistances and cal to that which existed when the counter was in the zero or quiescent state. Thus the counter plate resistances employed at corresponding 35 chain is of a scale-of-?ve variety. points in each half of each counter stage are of In the selector circuit the control grid of each similar resistive value, resistances 43, 46 similar tube ‘I4 through I8 is connected to a separate to 4|, 45 and so on. Therefore for purposes of junction point I08, 260, 300, 400, and 500. Each simpli?cation, only the ?rst counter stage II will be described in detail. In this stage the multi of these junction points is in turn connected 40 through three separate resistances to the ?rst grid' tubes Ila and Ill) represent the vacuum ccntrolgrid of one of the tubes in each of the tube components of a conventional scale-of-two counter circuits II, I2 and I3. This connection counter circuit. The ?rst control grid 38 of tube is typi?ed at the‘ ?rst junction point I00 by resist Ila is connected through the shunt combination ances 41, 48 and 49. In this relation it should be of resistance 43 and capacitance 44 to the plate 45 noted that all the resistances at each junction of tube Ilb and also, through the grid return point are equal in size and are current limiting resistance 46 to a source of C: potential. Like in function. At the ?rst junction point I00 cur wise, the ?rst control grid 39 of tube III) is con rent limiting resistance 41 is connected to the nected through the shunt combination of resist ?rst control grid of tube Ila and resistance 48 to ance'4l and capacitance 42 to the plate of tube 50 the ?rst control grid of tube I2a and the third I la and also, through the grid return resistance resistance 49 to the ?rst control grid of tube I3b. 45 to a source of 0: potential. The circuit is As abovementioned, the ?rst control grid of any thus made regenerative and only one of the tubes tube in the counter circuit varies from zero po will conduct at any instant. To change the con tential to a potential determined by voltage divi duction condition of either tube a negative signal sion across resistances 43, 46 as that tube passes is applied in parallel to the second control grids 55 from conduction to non-conduction. Thus, when 36 and 31 of both tubes. As the conduction state the counter is in the zero or quiescent state where of the circuit changes, the ?rst control grid of the in the tubes I la, IZa and I3!) are conducting, the tube passing from conduction to nonconduction potential at the junction point I00 will be zero will vary from about zero potential to a negative and theselector tube M will conduct since its divider action 6 potential determined by the voltage cathode is returned directly to ground. If each from the positive potential at the plate of III) to of the resistance connections of the remaining the negative supply potential across resistances junction points 200, 300, 400 and 500 are traced 43, 46. The input to the counter circuit as ob it will be found that in the zero state of the count tained from the pulse generator IE] is applied in 65 er, a minimum of at least one resistance at each parallel to the control grids 36 and 31 through of the other junction points is returned to a a coupling circuit comprising capacitance 6B and grid in the counter circuit which is at a nega resistance 6|. In one case this circuit may con ‘tive potential. v The minimum negative voltage stitute a short time-constant compared to the existing at any one of these junction points due time duration of the applied pulse and therefore 70 to the voltage divider action of the current limit functionto, produce an abrupt positive pulse in ing resistances is therefore at least 1/3 of the nega response to the positive-going edge of each of the tive voltage existing at the junction of resistances applied pulses and an abrupt negative pulse in re 43, 45 when tube llb is conducting. Thus, if sponse to the negative-going edge of each of the the negative potential is made large relative to applied pulses. The input to the second counter 75' the cut-off bias for the selector tubes the grids circuit I2 is taken-from a tap on the plate load 5 2,409,229 of the remaining tubes in the selector circuit will be biased below cut-off. Then as the counter cir cult is driven into its No. 1 state where tubes I lb, 6 comprising capacitance 69 and resistance 6| to the input of the counter circuit and also through the short time-constant circuit comprising ca !2b and 13a are conducting and tubes Ha, l2a pacitance 60 and resistance 62 to the ?rst control and I3?) are non-conducting, it will be observed that the voltage at the junction point 2 08 will now 5 grid 35 of the coincidence tube 24. Waveform b is the result of the action of the foregoing short be at zero while the voltage existing at the other time-constantcircuits and is representative of junction points I99, 300, 403 and 500 will be suffi the actual signal voltage applied to the input of ciently negative to hold the other selector tubes the counter circuit and to the ?rst control grid below cutoff. Tube l5 will now be able to conduct 10 35 of the coincidence tube 24. Since the counter circuit was initially assumed as being in the zero of the counter circuit tube I6 will be the only or quiescent state with the selector tube l4 con tube in the selector capable of conducting and so as far as its grid is concerned. In the second state ducting and therefore with the bias removed from on down the circuit, each selector tube rendered capable of conducting in its proper order with 15 the second control grid 35 of the coincidence tube 2:’! and since the ?rst pulse in waveform b is pos each change in state of the counter circuit. itive and does not eifect a change in the counter The coincidence tube 24 is preferably of the pentagrid type having two control grids 34 and state, this pulse will appear at the output termi nal 55 as a negative pulse such as that shown in 35. The ?rst control grid 35 provides a means by which the pulse signals from the pulse gen 20 waveform c. The next pulse in waveform b is neg ative and will therefore be blocked from the out erator Ill may be applied to it, while the second put terminal 55 of the coincidence tube 24 by control grid 34 provides a means by which the the action of the cathode bias 5‘! but will, how coincidence tube may be blocked and unblocked, ever, produce the number one state in the counter so as to speak, by the joint action of the counter circuit and the selector circuit to thereby con 25 circuit wherein tubes lib, I21), and l3a are con ducting and tubes Ila, [2a and I32) are non-con trollably suppress or produce an output pulse at ducting. This action will render the selector tube the terminal 55. The ?rst control grid 35 is re I5, as far as its control grid is concerned, con turned through resistance 62 to the juncture point of the cathode resistances 32 and 33. As a result ducting but since its cathode switch I9 was as sumed adjusted to the No. 3 position its cathode 30 circuit will not be complete and therefore the sistances, and the cathode bias voltage 57, the tube will not conduct. In this case, the second coincidence tube is held unresponsive to negative control grid 34 of the coincidence tube 24 will be signals applied to this grid. The second control biased negative and therefore the second positive grid 34 is directly connected to the plate of the biasing ampli?er 23 which in turn is grid driven 35 pulse will not produce an output at the terminal The second negative pulse operates to produce from the common plate load resistance 29 of the the second state in the counter circuit with tube selector tubes. During the time when all of the i6 conducting as far as its grid is concerned and selector tubes are non-conducting, the grid of since this is one of the tubes whose cathode switch tube 23 will rise above cathode potential until lim iting by resistance 29 occurs. This results in 40 20 was set in the zero position, the tube will con duct and the bias will be removed from the sec heavy conduction by the biasing tube 23 produc ond control grid 34 of the coincidence tube with ing a large voltage drop across its plate load re the result that the third positive pulse causes sistance. The plate potential of tube 23 willthen conduction by tube 24 producing, with negligible become only slightly higher than the positive delay, a negative pulse at the output terminal 55. cathode potential 56. This latter potential is made some suitable value less than the cathode 45 Thus the combined actions of the counter circuit and the selector circuit operate to produce at the potential 5? on the coincidence tube so that in output terminal 55 a pulse group formation such this condition the bias on the second control grid of the voltage dividing action of these two re as that shown by waveform c. In this case the 34 is such as to hold the coincidence tube blocked ?rst, third and fourth pulses were produced at or non-conducting regardless of the signal ap the output terminal 55 while the second and ?fth plied to the ?rst control grid 35. When, how 50 were suppressed. ever, any one of the selector tubes becomes con ‘From the foregoing it was seen that whether ducting, a voltage drop appears across their com or not a pulse appears at the output terminal mon plate load resistance 29. This drop is suf? 55 and is therefore transmitted depends upon the cient to bias tube 23 beyond cut-off potential. The plate voltage of this tube then rises to its 55 setting of the cathode switch arrangement in the selector circuit. In some instances it may be de plate supply voltage 64. This supply voltage is sired to transmit for a given interval of time made equal to the cathode bias voltage 51 of one group of pulse signals and then to transmit the coincidence tube and the second control grid for another interval of time a second group of 36 of the latter is therefore possessed with zero bias and the coincidence tube is ready to respond 60 Pulse signals having a different formation. To accomplish the foregoing, a multivibrator com to any positive signal applied to its ?rst control prising tubes 25 and 26 and a pair of diodes 2‘! grid 35. and 28 are disposed within the cathode circuits For purposes of illustration assume that the of the selector tubes and are arranged so as to cathode switches 26 and 21 in the selector tubes 53 and i 3‘ are set in the zero position while 65 produce cathode switching in a predetermined manner. The multivibrator is preferably a sym switches 59 and 22 in the selector tubes 15 and metrical free-running type having a period much #8 are set in the No. 3 position. With this as longer than the time required to make several sumption and the further assumption that the successive transmissions during the conduction counter circuit is initially in its zero or quiescent 70 period by either of the tubes. When tube 25 is state, the circuit will now be described with refer conducting, tube 26 will be non-conducting. Dur ence to the wave forms shown in Fig. 2. Wave ing this time the voltage at the plate of tube form a is representative of the output signal from 25 will be near that of its cathode which is biased the pulse generator Hi. This output wave is ap negative as indicated at 18, while the plate of plied in parallel to the short time-constant circuit 75 the non-conducting tube will be substantially 3+. 2,409,229 As arranged, the cathodes of the associated di odes 2‘! and 28 are connected through the re spective current limiting resistances 30 and 3! to the plates of tubes 28 and‘ 25. Thus when tube 26 is conducting its plate potentia1 is nearly that of source 10 which is su?iciently negative to permit conduction by the associated diode 21. At the same instant tube 25 is non-conducting so that its plate potential will be at B+ with the result that the associated diode 28 is also held non-conducting. The diode that conducts ap pears essentially as a short circuit to ground while the non-conducting diode appears as an open 8 tain amount of time delay is inherent in the operation of the selector tubes. This delay is primarily due to the large resistances employed at 41, 48 and. 49 and other similar positions which impose a ?nite time delay when charging or dis charging the stray capacitances associated with these points. In addition this delay may be ac centuated by actually inserting physical capaci tances at these points. Therefore this invention is not to be limited to the embodiment shown ex cept insofar as is necessitated by the spirit of the prior art and the scope of the appended claims. The invention described herein may be manu circuit. Thus by Connecting the cathode, for factured and used by or for the Government of 15 example, of diode 2"! to all the Number 1 posi the United States of America for governmental tions in parallel of the switches 5% through 22, purposes without the payment of any royalties and the cathode of diode 23 in parallel to all thereon or therefor. the No. 2 positions in the switches, the multi What is claimed is: vibrator action can make the No. 1 and 2 po sitions of the switches appear alternately as open and closed circuits respectively. 1. A means for producing a group of pulses wherein the number and relative time occurrence of the pulse signals in said group are selectively determined, comprising a means generating a time base which is comprised of a ?nite number With reference to the waveforms shown in Fig. 3 the operation of the circuit including the action of the multivibrator and the associated of voltage pulses, each of which is predeterminate diodes 21' and 28 will now be described. In Fig. 3, 25 ly spaced in time, a plurality of vacuum tubes, waveform a is representative of the alternating means associating each of said tubes with said positive and negative voltage pulses obtained from the pulse generator ill and applied in parallel to both the counter circuit and the coincidence tube 24. For purposes of illustration let it be assumed that the cathode switch 22 is set in the #2 po sition and the remaining cathode switches i9, 25 and 2i are set in the #1 position and that tube 25 in the multivibrator circuit is conducting. During this condition diode ‘28 appears as a short circuit and all the #2 positions in the switches l9 through 22 appear at ground while diode 2'1 and consequently all the Number 1 positions in the switch appear as an open circuit. In this ?rst named means in such a manner as to be successively rendered conducting thereby, sep arate means associated with each of said tubes and arranged to render any one or number of said tubes unresponsive to the action of said ?rst named means, a coincidence tube, means con necting the output from said ?rst named means to said coincidence tube, and means connecting said coincidence tube in common with said plu rality of tubes in such a manner that the pulse output from said ?rst named means will appear at the output of said coincidence tube only dur ing the time when one of said plurality of tubes is conducting. case only the ?rst pulse and the ?ith pulse will be transmitted as represented by waveform I). 2. A means for producing a group of pulses Then, after a given number of such transmissions wherein the number and relative time occurrence the multivibrator changes states wherein tube 25 of the pulse signals in said group are selectively is conducting and tube 25 is non-conducting. determined, comprising a means generating a During this time diode 21 will conduct and the 45 time base which is comprised of a ?nite number of voltage pulses each of which is predetermin #1 terminals in the cathode switches will be sub stantially at ground potential while all the Num ately spaced in time, a plurality of vacuum tubes, ber 2 positions appear as open circuits. The means associating each of said tubes with said resulting transmission is that shown by Wave ?rst named means in such a manner as to be form 0. In this case the ?rst, second, third and 50 successively rendered conducting thereby, sepa fourth pulses produce transmission, the ?fth pulse rate switching means associated with each of is suppressed. Although we have shown and described the use of a scalc-of-?ve circuit as a time base genera tor it must be understood that if a counter cir cult is to be used, one of a larger scale and a selector circuit having a correspondingly larger number of tubes may be employed without de~ parting from the spirit of the invention. It is also to be understood that selection switches may be inserted in all of the selector tubes rather said tubes and arranged to render any one or number of said tubes unresponsive to the action of said ?rst named means, a coincidence tube, means feeding the output from said ?rst named means to said coincidence tube, and means con necting said coincidence tube in common with said plurality of tubes in such a manner that the pulse output from said ?rst named means will appear at the output of said coincidence tube only during the time when one of said plurality of than all except the ?rst tube as shown in the tubes is conducting. 3. A means for producing a group of pulses speci?c embodiment. Furthermore, it is not nec essary to restrict the operation to a pulse gen wherein the number and the relative time occur erator providing alternate peaked positive and 65 rence of the pulse signals in the group are selec negative pulses to the counter circuit and the co tively determined, comprising a plurality of the incidence tube 24. For example, a series of pulses scale-of-two type of counter stages connected in of negative polarity may be used to trip the cascade so as to form a scale-of-N counter cir counter circuit while an inverter tube can sup cuit, a plurality of vacuum tubes each of which ply positive pulses to the second control grid 3%‘: 70 is connected to said counter circuit in such a of the coincidence tube 24 or the negative pulses manner as to be successively rendered conducting may be applied directly to the cathode of tube thereby as said counter circuit passes through a 2d. Despite the fact that the counter pulses and cycle of operation, separate switching means con the transmitter keying pulses occur simultane~ nected to each of said tubes for rendering any cusly the system is still operative because a cer 75 9 2,409,229 one or number of said tubes unresponsive to the 10 generator to said coincidence tube, and means connecting said coincidence tube in common with action of said counter circuit, a pulse generator arranged to produce a series of voltage pulses, said plurality of tubes in such a manner that the means applying the output of said pulse gener pulse output from said pulse generator will appear ator to said counter circuit, a coincidence tube, 01 at the output of said coincidence tube only during means also applying the output from said pulse the time when one of said plurality of tubes is generator to said coincidence tube, and means conducting. connecting said coincidence tube in common with said plurality of tubes in such a. manner that the 6. A means for alternately producing two dis tinct groups of pulses wherein the number and pulse output from said pulse generator will 10 the relative time occurrence of the pulse signals appear at the output of said coincidence tube only in each group are selectively determined, com during the time when one of said plurality of prising a plurality of the scale-of-two type of tubes is conducting. counter stages connected in cascade so as to form 4. A means for producing a group of pulses wherein the number and the relative time occur rence of the pulse signals in the group are selec tively determined, comprising a plurality of the scale-of-two type of counter stages connected in cascade so as to form a scale-of-N counter cir cuit, a plurality of vacuum tubes each of which is connected to said counter circuit in such a manner as to be successively rendered conducting thereby as said counter circuit passes through a a scale-of-N counter circuit, a plurality of vac uum tubes each of which is connected to said counter circuit in such a manner as to be suc cessively rendered conducting thereby as said counter circuit passes through a cycle of opera tion, an electronic switching means, said switch ing means alternating back and forth between two electrical states, separate manual switching means connected to each of said selector tubes and to said electronic switching means, said man cycle of operation, separate switching means con ual switching means being arranged so that a nected to each of said tubes for rendering any ?rst group of said tubes becomes unresponsive to one or number of said tubes unresponsive to the the action of said counter circuit during one elec action of said counter circuit, a pulse generator trical state of said electronic switch and a second arranged to produce a series of voltage pulses, group of said tubes becomes unresponsive to said means applying the output of said pulse gener counter circuit during the second electrical state ator to said counter circuit, a Coincidence tube 30 of said electronic switch, a pulse generator having at least two control electrodes, means ap arranged to produce a series of voltage pulses, plying the output from said pulse generator to means applying the output of said pulse gener one of said control electrodes in said coincidence ator to said counter circuit, a coincidence tube tube, and means connecting the other control having at least two control electrodes, means electrode of said coincidence tube in common to applying the output from said pulse generator to said plurality of tubes in such a manner that the one of said control electrodes in said coincidence pulse output from said pulse generator will appear tube, and means connecting the other control at the out-put of said coincidence tube only dur electrode in common to said plurality of tubes in ing the time when one of said plurality of tubes such a manner that the pulse output from said is conducting. 40 pulse generator will only appear at the output of 5. A means for alternately producing two dis said coincidence tube during the time when one tinct groups of pulses wherein the number and of said plurality of tubes is conducting. ’ the relative time occurrence of the pulse signals '7. A means for producing a group of pulses in each group are selectively determined, com wherein the number and relative time occurrence prising a plurality of the scale-of-two type of of the pulse signals in said group are selectively counter stages connected in cascade so as to form determined, comprising a means generating a a scale-of-N counter circuit, a plurality of vac time base which is comprised of a ?nite number uum tubes each of which is connected to said of voltage pulses each of which is predetermin counter circuit in such a manner as to be suc~ ately spaced in time, a plurality of vacuum tubes, cessively rendered conducting thereby as said counter means interconnecting each of said tubes counter circuit passes through a cycle of opera to said ?rst named means whereby each of said tion, an electronic switching means, said switch tubes is caused to be successively rendered con ing means alternating back and forth between ducting as said counter means is driven through two electrical states, separate manual switching a cycle of operation, separate switching means means connected to each of said tubes and to said 1' associated with each of said tubes and arranged electronic switching means, said manual switch to render any one or number of said tubes unre ing means being arranged so that a ?rst group of sponsive to the action of said ?rst named means, said tubes becomes unresponsive to the action of a coincidence tube, means feeding the output said counter circuit during one electrical state of from said ?rst named means to said coincidence said electronic switch and a second group of said 60 tube, and means connecting said coincidence tube tubes becomes unresponsive to the action of said in common with said plurality of tubes in such a counter circuit‘ during the second electrical state manner that the pulse output from said ?rst of said electronic switch, a pulse generator named means will appear at the output of said arranged to produce a series of voltage pulses, coincidence tube only during the time when one means applying the output from said pulse gen of said plurality of tubes is conducting. erator to said counter circuit, a coincidence tube, means also applying the output from said pulse 65 CARL HARRISON SMITH, JR. MILTON L. KUDER.