US2835808A

US2835808A - Transfer-storage circuits

Info

Publication number: US2835808A
Application number: US541340A
Authority: US
Inventors: John R Bethke
Original assignee: Burroughs Corp
Current assignee: Unisys Corp
Priority date: 1955-10-19
Filing date: 1955-10-19
Publication date: 1958-05-20
Anticipated expiration: 1975-05-20

Description

I May 20, 1958 J. R. BETHKE 2,835,808

, TRANSFER-STORAGE CIRCUITS Filed Oct. 19, 1955 67K yvw-woov TRANSFEROR GATING COMMUTATING SWITCHING CIRCUIT 37 1 7 300v I TRANSFER 5 TRANSFER INPUT b 28 I I52 39 5 38 l INVENTOR s5 Ii 62 EVEN GR'DS JOHN R. BETHKE ONE *-vG(+3ov) 5/93 Y R 64GATE i 000 GRIDS 5 ATTORNEY United States Patent TRANSFER-STORAGE CIRCUITS John R. Bethke, Paoli, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application October 19, 1955, Serial No. 541,340

9 Claims. (Cl. 250-27) This invention relates generally to multi-pos-ition electron beam position tubes and more particularly to means for gating signals from any one of a plurality of positions of a multi-position electron beam tube circuit to a corresponding utilization device.

There is now available in the art a multi-position beam switching tube having a plurality of compartments each containing one of a plurality of target electrodes arranged concentrically around an elongated cathode. Each of the target electrodes is associated with a corresponding spade electrode used for locking the cathode ray beam in a stable position upon its target electrode in a selected compar'tment. A magnetic field is created substantially parallel to the elongated cathode throughout the tube so that an electron beam formed at the cathode of the tube will tend to follow a substantially equipotential path established by the potentials coupled to the various electrodes. By analogy the tubes are known as magnetron cam switching tubes. A potential source coupled to the spade electrodes creates an electrostatic field which is converted by lowering the potential of a single spade electrade to establish a substantially equipotential line from a particular target electrode to the cathode so that the electron beam will flow from the cathode to a single compartment defined by the said particular target. A small portion of the electron beam locks upon the associated spade electrode and reduces its potential by means of a load impedance to thereby hold the spade at reduced potential and direct the remainder of the electron beam upon the corresponding target electrode.

Because of the magnetic field, the electron beam has a tendency to continuously rotate in a tight spiral around the cathode in one direction and would re-enter the cathode if it were not locked upon a particular spade elec trode. When a substantially equipotential line is created between the cathode and the compartment adjacent to the compartment upon which the electron beam is impinging, the electron beam is caused to advance to the said adjacent compartment where it locks upon the spade electrode thereof. In some of the earlier tubes, this type of advancing may be accomplished by lowering the potential of either the spade electrode or the target electrode, as is described in the Backmark U. S. Patent 2,591,997. A more recent development has resulted in the provision of a switching or control grid electrode in each compartment for producing more reliable beam switching and locking. Such tubes are described in U. S. Patent No. 2,721,955 of Sin-pih Fan and Saul Kuc'hinsky, issued October 25, 1955. The switching electrode of one compartment, upon being reduced sufliciently in potential, performs the function of establishing an cquipotential path between the cathode and a spade electrode of an adjacent compartment to deflect the electron beam and cause it to become locked in upon the adjacent compartment. If the potentials of successive ones of :the switching electrodes are caused to assume a potential such as to establish an equipotential path between the associated compartment and the cathode, the electron beam will be caused to step consecutively from one compartment to the next. This has been accomplished in one manner by connecting one set of alternate switching electrodes (hereinafter referred to as even numbered electrodes) to one output terminal of a circuit such as a complemented flip-flop or binary counter circuit and connecting the other set of (odd numbered) alternate switching electrodes to the other output of the flip-flop or binary circuit. Successive input pulses to the flip-flop circuit would then cause the electron beam to advance progressively from one compartment to the next.

For many different output circuit applications of these multi-position tubes, it has been desirable to effect selective gating of the beam arriving at a particular target electrode to a load circuit. For example, in multiplexing operations, it is usual to gate in at a number of different circuits modulated signals at corresponding successive time intervals. In this manner, the beam tubes hereinbefore described are well adapted to switch a plurality of dilferent modulated signals at high speeds. However, when such devices are used to produce high speed commutating of a plurality of channels and it is desirable to gate the channels selectively only at specified intervals, in the past it has been necessary to provide a separate gating circuit in each of the multiple channels. Whenever a gating circuit is necessary for each of the target electrodes of a beam switching tube, in all except extremely high speed operations, circuit economy has been marginal in use of the beam tubes in view of alternative circuits such as conventional cascade flip-flop distributors.

Thus, in the copending application for Multi-Position Electronic Gating Circuits, filed September 14, 1955, Serial No. 534,232, a circuit is disclosed for selectively gating a signal at any one of several individual load circuits respectively coupled to any one of the multiple target positions in response to gating pulses at a single electronic gating circuit. This gating circuit may comprise a normally cutoff triode amplifier tube which is commonly coupled to one terminal of each of a plurality of load devices which have their other terminal connected respectively to each of the beam tube targets for receiving beam current as the beam dwells upon the corresponding targets during switching from one target position to the other. To effect the gating operation an auxiliary beam current path is provided for each target so that the beam current is not passed through the corresponding loads unless the gating tube is made conductive by a corresponding gating input signal pulse. In the simplest configuration the auxiliary path may comprise a crystal diode coupled to a supply voltage somewhat less positive with respect to the beam tube cathode than a further potential coupled to the gating tube anode. Thus, the preferred beam current path is through the gating tube when it is put into a conductive condition by a corresponding gating pulse. In this manner, coincidence of the beam switching tube current upon a target, and a gating signal at the single gating tube is required to operate any one of the multiple loads directly from beam current of the switching tube.

One specific embodiment of this gating circuit comprises a transfer circuit for switching information from one magnetron type electron beam switching tube to another by means of the single gating tube. In this instance resistive load circuits are coupled to the target positions of the transferor tube. In using such resistive load ciremits Father than inductive load circuits such as magnetic cores or relays, the gating operation is subjected to critical component values.

Accordingly a first object of the present invention is to provide improved gating circuits for transferring information from one beam switching tube to another.

A general object of the invention is to provide improved multi-position electronic gating circuits for beam switching tubes of the type described hereinbefore.

In connection with the transfer of information from one switching tube to another 'with the circuits described in the co-pending application, a critical width transfer pulse is necessary under some conditions. This occurs when continuous beam switching from target to target is in progress in the transferor tube at the time of the transfer. Thus, if the transfer pulse persists longer than one switching interval the transfer pulse maybe passed on to a different position in the transferee tube.

Accordingly another object of the invention is to provide improved transfer circuits assuming that the 'beam is passed from one position of a transferor tube to the same position in the transferee tube under various circuit operating conditions.

Therefore, in accordance with the invention, a circuit is provided for coupling one magnetrom beam switching tube to another for transfer of information from any targetposition by means of a single gating circuit. Means operable simultaneously with the gating circuit is provided for clearing the transferee tube of prior held information. in order to produce reliable gating With resistive load cir cuits, the gating tube is coupled to reduce the potential afforded in a preferred bypass circuit for all the targets of the transferor tube at a selected time to thereby cause the beam to pass alternatively through the load resistance and thereby set the transferee tube to a corresponding position. To keep the transferee tube from displaying wrong information in response to a transfer pulse obtained during continuous stepping of the transferor tube at the transfer time, the coupling is made in different order from transferor tube targets to transferee tube input electrodes. Thus, counting is obtained in the transferee tube in an opposite to normal direction so that by'the influence of the magnetic field, the first input electrode excited will register the transfer, and even if the transfer pulse persists for several switching steps, the transferee tube will be unaffected.

Other objects and features of the invention will be more fully understood from the following detailed description thereof when read in conjunction with the drawing, in which:

Fig. 1 is a perspective assembly view of a multi-position magnetron beam switching tube utilized with the invention;

Fig. 2 is a schematic circuit diagram of a multi-position electronic gating circuit employed in the invention;

Fig. 3 is a schematic circuit diagram of a magnetron beam tube information transfer circuit embodying the in vention; and

Fig. 4 is a simplified block diagram of a transfer circuit incorporating the invention.

Referring now to Fig. 1, there is shown a perspective view of a magnetron beam switching tube which is used in accordance with this invention.

This type tube is well known in the art, and is supplied by Haydn Brothers of New Jersey now the Electronic Tube Division of Burroughs Corp. under the type number 6700 (MO-). Consequently, only enough description will be given herein of the structure and theory of operation of the tube 9 of Fig. 1 to enable an understanding of the present invention. The cathode 41 is positioned within the hermetically sealed envelope 10. A plurality of elongated spade electrodes 31 through 40, having a U- shaped cross section, are positioned concentrically about the cathode 41. In the structure shown in Fig. 1, there are ten such spade electrodes.

Similarly, there are ten elongated target electrodes 11 through 20, having an L-shaped cross section, likewise positioned concentrically around the cathode 41, and each having the extension of the L positioned within the trough of one of the ten spade electrodes, and having the base of the L spanning the space between two adjacent spades.

ill)

4 1 Each target with its two adjacent spades defines a compartment for receiving the beam in one of its ten stable locked in positions. Ten switching electrodes 21 through 30 are also positioned concentrically around the cathode 41 and are each individually positioned in one of the compartments between the open base end of a target electrode and one extending leg of a spade electrode. For example, switching electrode 21 is positioned between the extending leg of spade electrode 40 and the open base end of target electrode 11. The concentric magnet 42 placed about the envelope produces a magnetic field in the tube that is substantially parallel to the elongated cathode 41. This magnetic field is of a polarity which will cause an electron beam extending outwardly from the cathode 41 to sweep around the tube in a clockwise direction (viewed from the top of the tube) in accordance with well known principles. Each of the spade electrodes is adapted to lock the electron beam in a particular compartment by a lowering of its potential. The beam remains locked in by means of the electron beam flowing through a spade impedance connected to the particular spade electrode upon which the electron beam is impinging thereby causing enough potential drop across said impedance to establish a substantially equipotential path somewhere between the two adjacent spade electrodes and the cathode to cause the beam to impinge upon the intervening base of the associated target electrode. The switching electrodes perform the function of deflecting the electron beam to impinge upon the next consecutive spade electrode by distorting the electric field within a particular compartment to cause the electron beam to advance to that clockwise spade electrode which will hold the beam in the compartment adjacent the one upon which it impinges in the absence of a switching potential.

With reference to the embodiment of Fig. 2, the vari ous elements of the tube of Fig. 2 are schematically drawn in order to make the schematic presentation of the drawing more easily understood. This type of presentation, which is related to the tube of Fig. 1 by utilization of similar reference characters, is used throughout the following specification and drawings. Thus, the three groups of tube electrodes comprising the

targets

20, 19, etc., the

spades

40, 39, etc., and the switching

electrodes

30, 29, etc., are arranged in a straight line so that the respective groups of electrodes for the tube positions 0, 1, etc., are adjacent to each other. In Fig. 2 only the first five tube compartments are illustrated, and similar construction is employed for further tube elements such as found in a ten position tube of the type described in connection with Fig. 1. Each of the spade resistors 60, 59, etc. is chosen to have a value such as 100,000 ohms for locking the beam in at a particular target position by flow of beam current to the

corresponding spade electrodes

40, 39, etc. The beam is switched from position to position by the switching circuit 61 which couples a normally positive grid potential V of about 30 volts at terminal 62 to all the

grids

30, 29, etc. The switching grids are connected in two alternating groups designated schematically by the open and filled circular notation, which may be designated respectively as the even and odd grid groups. As hereinbefore described, application of a negative switching signal of about 50 volts to one of the respective groups will cause the tube to switch the beam a single position regardless of the duration of the switching signal above a minimum amplitude and time (in the order of 0.2 microsecond). The next switching signal to effect switching must therefore be applied to the alternate group of grids. Thus, negative switching signals may be applied at the zero and one

gate terminals

63 and 64 from a suitable circuit such as a conventional bistable flip-flop counter which is actuated by successive switching pulses at an input complementing terminal. This type of binary counter circuit is indicated in block diagram form 65 in Fig. 3. a 1

Each

target electrode

20, 19, etc. is coupled to the spade voltage supply at terminal 66 by one of the respective assasos U diodes 8t 79, etc. which provides a low impedance uniateral conductive path for the beam current arriving at any one of the corresponding target electrodes. A load circuit illustrated by the

inductances

90, 8% etc. is coupled to the

corresponding target electrodes

20, 19, etc. to alternatively receive beam current whenever the beam impinges upon a corresponding target electrode. These coils may be, for example, relay coils which are operated to select digits of a teletype code in the manner described in the U. S. Patent 2,099,065 to W. H. T. Holden, issued November 16, 1937. Likewise, the

inductances

90, 89, etc. may comprise bistable state magnetic storage devices. in general the magnetron beam switching tubes hereinbefore described provide suflicient beam current to operate either relay coils of the type applicable to the hereinbefore described circuit, or conventional bistable state magnetic storage devices of the type well known in the art. In either instance, it is desirable to selectively actuate one or more of the

inductances

90, 89, etc. individually in response to input signal intelligence. For this reason, the gating circuit 67 is provided for connection between the common bus 63 coupled to one end of each of the load :iductances 3?, etc. and a supply potential more positive the spade potential available at terminal 66. in particular, for operation with a gating triode tube 91 which may comprise one-half of a 5687 type duo-triode tube, the voltage provided at terminal 69 may be 200 volts, whereas the spade potential at terminal 66 is 100 volts. The triode 91 is normally maintained at cutoff potential by means of the -C supply potential and the proper setting of the potentiometer 92. Accordingly, a suitable positive gating pulse for overcoming cut-off and causing tube 91 to tend to fully conduct is applied at the gate input terminal 93 through condenser 94. The gating potential is developed across the grid resistor 95 to turn on the normally cutoff triode tube 91 and thereby estab lish a preferred beam current path through any one of the

respective load inductances

90, 89, etc. as the beam strikes the corresponding target. Because of the unidirectional properties of the diodes 8t 79, etc. no current will pass to the spade potential terminal 66 from the target supply terminal 69. However, when the beam impinges upon a particular target such as 20, because of the higher potential at terminal as, current will flow to the load inductor 9d for the duration of the period that the beam is striking the target 2ft or the duration of the gating pulse, whichever is the shorter. This action causes the diode to be completely cutoff by sending the cathode more positive than the anode potential at the spade supply level of terminal Accordingly, upon coincidence of a gating input signal at terminal ,3 and presence of the beam upon one of the targets 2t 19, etc., a particular one of the inductance load circuits 9 3, 89, etc. will be chosen. This circuit is described and claimed in the above mentioned copending application Serial No. 534,232.

In general, the operation of a system in the manner described in connection with Fig. 2 may be desired in connection with resistive load circuits as illustrated in Fig. 3, wherein similar elements to those hereinbefore described are identified by similar reference characters. For example, this occurs when it is desirable to use the switching tubes themselves as storage devices for decimal numbers, and in this case it is sometimes necessary to transfer the stored information comprising the beam position from one beam switching tube to another. The inn proved gating and transfer circuit of the present invention is employed in performing this transfer function as shown schematically in Fig. 3. The gating operation of the left hand tube section is similar to that hereinbefore described, with the exception that the load circuits are replaced with 150K ohm resistors )b", %9, etc. in this embodiment and the preferred high potential path established by the gating tube is provided through the auxiliary target paths of diodes St), 79, etc. It is desirable to transfer the indication from the transfcror tube 9 to the transferee tube 9. To assure that the transfer is properly made, it is necessary to clear or blank the beam in the transferee tube 9'. For this purpose the clearing circuit is provided, which comprises the normally cutoff amplifier tube 121, which may be similar to tube 91 in the gating circuit 67. This tube is maintained at cutofi by proper adjustment of the -C bias voltage at the potentiometer 122 so that an input signal arriving by way of capacitor 123 and developed at the grid input resistor 124 may cause the tube to conduct through its load resistor 125. This conduction when resistor 125 has a value of about 10.0 ohms is effective to reduce the potential at the bus 126 about 70.0 volts, which thereby reduces the potential of all the

spade electrodes

31, 32, etc. enough to cause the beam in the tube 9 to extinguish. When the beam is extinguished, all of the spade electrodes are returned to the same potential and one spade electrode must be reduced in potential in order to re-establish the beam at a particular tube position. Thus, a transfer of the beam position of transferor tube 9 is made from one of the transfer leads 190, 189, etc. by means of a decrease of spade potential developed across the corresponding 500K ohm resistors 130, 129, etc. When the transferee tube 9' is cleared, therefore, it is evident that the transfer is effected by an input signal at the terminal 93 of the gating circuit 67, which causes a decrease in potential at the auxiliary target load resistor of enough magnitude to assure that the diodes 8t}, 79, etc. are cut off and thereby target current flows through resistors 90", 8%, etc. to thereby select the position of the beam the transferee tube 9'. By supplying 25 mllliamperes through an 8000 ohm resistor, the potential at the anodes of

diodes

80, 79, etc. is reduced to about 100 volts, assuring cutoff because of the higher potential cathodes. Thus the target current reduces the potential at one of the load resistors 90", 89", etc. This reduced potential is coupled to the corresponding spade electrodes 40', 39, etc. of the transferee tube 9' along one of the corresponding transfer leads 190, 189, etc. by means of the intervening capacitors 140. The diodes 141 in the absence of the gating operation normally serve to uncouple the spade circuits of the transferee tube 9' from the target circuits of the transferor tube 9 because of their unilaterally conductive characteristics.

As signified by the reverse, or

complementary numbering

9, 8, etc. of the target positions of the transferee tube, which indicates relative positions as compared with the transferor tube, the magnetic field H is reversed to cause the tube to attempt to switch in a direction opposite to that of the transferor tube.- This is significant in the transfer operation because it permits transfer of identical information even though switching pulses are applied to the transferor tube during the transfer interval and while the transfer pulse may exist longer than one switching interval. Thus, a much less critical circuit is afforded by this expedient. Note that the information at target 9 is really representative of a 0 signal transfer and that the terminology is used only to point out the significance of this feature contributed by the present invention. The mechanism which prevents the switching of the tube after transfer even though two or three switching pulses occur, is that the beam inherently prefers not to step backwards against the influence of the magnetic field, and will only step ahead several positions.

In order to effect automatic clearing and. transfer, synchronous operation of the clearing and gating tubes is accomplished by means of the

waveforms

150, 151 and 152 applied at the corresponding terminals, A, B, C and D. in this respect the input waveform 15b is applied to input terminals A and C of the respective gating circuit 67 and transfer circuit 120. However, the RC coupling circuit 94, 95 of the gating circuit is designed to couple the input waveform in undistorted form to the grid circuit B of the gating tube 91 as shown by the waveform 151, whereas the RC coupling circuit 123, 124 of the clearing tube 121 serves to differentiate the input waveform 15.0

to provide a Waveform of the type 152 at the grid terminal D of the clearing tube 121. Thus, the positive leading edge of the waveform causes the clearing tube to conduct and thereby clear the transferee tube 9 to a properly receptive condition for receiving the transfer of information from the transferor tube 9 in response to operation of the gating circuit 67. Since the clearing tube 121 is normally cutoff, the negative spike of the waveform 152 has no effect upon circuit operation.

A general block diagram of the transfer circuit is shown in Fig. 4 to indicate the general nature of the circuit of Fig. 3. It is noted, in general, that the beam may be switched from position to position in the transferor and transferee commutating devices in synchronism in order to effect a one for one transfer of the indication from one device to the other by means of the and circuit 1&1 and the single switching circuit 65. Separate switching circuits for

commutators

9 and 9 may be employed whenever separate switching signals are required. Likewise the gating and clearing circuits are synchronized by and circuit 100. It is within the concept of the present invention to employ gating circuits other than specifically described and to clear the transferee tube in some other manner, if desired. It is clear, however, from the foregoing description of the invention, its operation and mode of construction that an improved and useful gating device is provided for direct high speed operation of relay and storage circuits in an efficient and economical manner. Therefore, the appended claims are directed to features of novelty believed descriptive of the nature and scope of the invention.

What is claimed is:

1. A multi-position gating circuit comprising in combination, a commutating device having a plurality of output positions, means for stepping the device from position to position to provide current pulses at sequential positions, a first potential terminal, a diode coupling each said output position to conduct current normally from said pulses with each diode connected to said first potential terminal, a load circuit coupled to each output position, a second potential terminal for providing apotential lower than the first terminal, a unilateral device coupling each of the said load circuits commonly to said second terminal, a single gating discharge device coupled to lower the potential at said first terminal below that of the second terminal thereby blocking the diode coupling devices to permit current flow between the output positions and the load circuits, and means for selectively operating said discharge device at discrete periods in synchronism with the means for stepping the commutating device.

2. A multi-position gating circuit comprising in combination, a commutating device having a plurality of output positions, means for stepping the device from position to position, a first potential terminal, a diode coupling each said output position to said first potential terminal, a load circuit coupled to each output position, a second potential terminal for providing a potential lower than the first terminal, a unilateral device coupling all the said load circuits commonly to said second terminal, a gating discharge device coupled to lower the potential at said first terminal below that of the second terminal, and means for selectively operating said discharge device at discrete periods in synchronism with the means for stepping the commutating device, wherein said commutating device is a multi-position transfcror magnetron beam switching tube, a further multi-position transferee magnetron beam switching tube is provided with input circuits coupled in complementary relationship with the load circuits of said transferor tube for selectively receiving the contents of the transferor tube in response to operation of said gating discharge device, means for switching both tubes from position to position, and means is provided responsive in synchronism with the operation of the gating discharge device for clearing the transferee tube before transfer.

3. A multi-position gating circuit comprising in combination, a magnetron beam switching tube having a plurality of target electrodes defining output positions for receiving beam current, means for switching the beam from position to position, separate resistive load circuits coupled to different target electrodes, a preferred low impedance unilateral beam current path coupled to each of said different target electrodes exclusive of said lead circuits to conduct beam current at the respective target electrodes, a further beam current path coupled to each target electrode and including said load circuits, a single normally non-operative gating circuit commonly coupled to impede beam current in said preferred current paths for defining in its operative condition a single beam current path from the corresponding target electrodes through the respective one of the further beam current paths, and means for selectively operating the gating circuit to permit beam current to energize the load circuits when the beam impinges upon corresponding target electrodes.

4. A circuit for transferring position indications from one tube to another, including two multi-position magnetron beam switching tubes, each having a plurality of target electrodes for receiving the beam to define the respective positions and each having a corresponding number of beam forming input electrodes comprising in combination, separate load impedance elements coupled to each target electrode of the first tube, a circuit individually coupling each of the elements to a complementary input electrode of the second tube to thereby cause the beam to be formed at the corresponding position in the second tube in response to beam current flow through the respective impedance element of the first tube, means for stepping the beams in the two tubes from position to position, a first alternative beam current path from each target electrode of the first tube, a second alternative beam current path from each load impedance element, selectively actuable gating means for selecting the second path, beam blanking means for said second tube, and means for synchronously operating the beam blanking means and actuating said gating means to thereby clear the second tube before transfer of the position indicated in the first tube to the second tube.

5. In combination, a first multi-position transferor commutating device, a second multi-position transferee commutating device, a switching circuit for causing each device to synchronously step from one position to another, output elements connected with the transferor device providing an electrical signal denoting a selected position, input elements connected in different order with positions of the transferee device for establishing a separate electrical condition in response to said electrical signals at any one of said output elements, a separate signal developing impedance device coupled to each said output element, a first low impedance path coupled to each impedance device to normally shunt the signal thereat, a single gating circuit common to all of said impedance devices coupled to disable said impedance paths and thereby provide a signal at the one impedance device denoting the position of the transferor commutating device, and means operable in synchronism with said gating circuit to clear the position of the transferee commutating device.

6. In combination, a first multi-position magnetron beam switching tube transferor device, a second multiposition magnetron beam switching tube transferee device, a switching circuit for causing the beam in at least one device to step from position to position, output elements connected with the transferor device providing an electrical signal denoting a selected position, input elements connected in different order with positions of the transferee device connected for establishing a separate electrical. condition in response to said electrical signals at any one of said output elements, a separate signal developing impedance device coupled to each said output element, a first low impedance path coupled to each said impedance device to normally shunt the signal thereat and provide a beam current path exclusive of the input elements, and a single gating circuit common to all of said impedance devices coupled to disable said low impedance paths and thereby provide a signal at the one input element coupled with the position of the transferee device upon which the beam impinges.

7. A multi-position gating circuit comprising in combination, a commutating device having a plurality of output positions, means for stepping the device from position to position to provide current pulses at sequential positions, a first potential terminal, a first diode coupling each of said output positions to said first potential terminal to conduct current normally thereto with each first diode having its cathode coupled to the output position and its anode coupled to said first potential terminal, a load circuit coupled to each output position, a second potential terminal for providing a potential lower than the first terminal, a second diode coupling each of said output positions through said load circuits to said second terminal, each second diode having its cathode coupled to the output position and its anode coupled to the second terminal, a single gating discharge device coupled to lower the potential at said first terminal below that of the second terminal thereby blocking the first diodes to permit current flow between the output positions and the load circuits, and means for selectively operating said discharge device at discrete periods in synchronism with the means for stepping the commutating device.

8. A multi-position gating circuit comprising in comhination, a commutating device having a plurality of output positions; each of said positions including a target output electrode, a spade electrode for forming and hold- 10 ing an electron beam on a corresponding target electrode and means for stepping an electron beam in the device from position to position to provide current pulses at sequential positions; a first potential terminal; a first diode coupling each of said output electrodes to said first potential terminal to conduct current normally thereto with each first diode having its cathode coupled to the output electrode and its anode coupled to said first potential terminal; a load circuit coupled to each output electrode; a second potential terminal for providing a potential lower than the first terminal; a second diode coupling each of said output electrodes through said load circuits to said second terminal; each second diode having its cathode coupled to the output electrode and its anode coupled to the second terminal; a single gating discharge device coupled to lower the potential at said first terminal below that of the second terminal thereby blocking the first diodes to permit current flow between the output electrodes and the load circuits; and means for selectively operating said discharge device at discrete periods in synchronism with the means for stepping the commutating device.

9. The circuit defined in claim 8 and including a second commutatingldevice similar to the first-mentioned commutating device and having a plurality of output positions, each position including a target output electrode and a spade electrode, each target electrode of the firstrnentioned commutating device being coupled to a spade electrode of the second commutating device.

2,591,997 Backmark Apr. 8, 1952 Harris Mar. 30, 1954