US2306386A

US2306386A - Electronic apparatus

Info

Publication number: US2306386A
Application number: US391169A
Authority: US
Inventors: John M Hollywood
Original assignee: Columbia Broadcasting System Inc
Current assignee: CBS Broadcasting Inc
Priority date: 1941-04-30
Filing date: 1941-04-30
Publication date: 1942-12-29
Anticipated expiration: 1959-12-29

Description

1942- J. M. HOLLYWOOD 2,306,386

ELECTRONIC APPARATUS Filed April 30, 1941 2 Sheets-Sheet l y 1 Tube 6' INVENTOR ATTORNEYS 2 snts-sheet 2 INVENTOR J. M. HOLLYWOOD ELECTRONIC APPARATUS Filed A ril 30. 1941 h k \NN NW k E hm w jlAAl Dec 29, 1942.

%M ATTORNEYS MAM Patented Eco. 29, 1942 UNITED STATES PATENT OFFICE 2,306,386 nmc'momc manarus John M. Hollywood, Red Bank, N. 1., assignor to Columbia Broadcasting System, Inc., New York, N. Y., a corporation of New York 18 Claims.

This invention relates broadly to the field of electronic switching circuits. The invention particularly contemplates an electronic switching circuit of the so-called "ring type, but in certain respects the invention is of broader application. The invention is particularly important in the field of color television, being especially adapted for use in changing the balance between difierent color components of a color television signal. However, the invention may be applied to other fields of use.

The term electronic switching may be applied to the making of circuits operative or inoperative, or the changing from one condition of operation to another, by means of an electronic device. The switching may be efiected, for example, by a change in polarity or magnitude, or both, of a voltage or current.

There have heretofore been proposed a. number of electronic switching circuits, including those of the ring type, employing gas-filled triodes of the so-called 'I'hyratron" type. The switching is effected by impressing suitable control pulses on the circuit. In the case of a ring circuit, the control pulses cause the tubes to be fired successively around the ring. Such circuits, while satisfactory for many purposes, are subject to some eccentricities of operation due to the pres ence of the gas. and the abruptness of the switching is limited by the time of ionization and deionization of the gas in the tubes as well as by the circuit constants required.

A primary object of the present invention is to provide circuits employing vacuum tubes, rather than gas-filled tubes, which are therefore free from the eccentricities of gaseous discharge tubes andfaster in operation. Furthermore, the invention provides circuits in which the electronic switching can be readily controlled and involves a min mum of interaction on the control voltagesl In accordance with the invention, one or more pairs of electronic vacuum tubes are employed, each tube having a plurality of control electrodes. The anode circuit of each tube is interconnected with a control electrode of the other tube of the pair so that anode current exceeding a given value in one tube restricts anode current in the other tube below a lower limiting value. Preferably the anode current of the tubes is switched between substanially cut-oft and a relatively large value. Control voltages are impressed on the other control electrodes of the tubes of a pair in order to switch current flow from one tube to the other. The use of two control electrodes in each tube of a pair facilitates the ready and precise control of the switching and enables the switching to be performed'with a minimum of interaction on the control voltages.

For convenience of description hereinafter.

. when anode current is flowing in the second tube of a pair, that pair will be considered to be in an actuated state, whereas current is flowing in the first tube of a pair, that pair will be considered to be in an unactuated" state. These terms will be understood to be employed for convenience in description, only, since output voltages or currents may be derived from the circuits of either or both tubes of a pair, as the use dictates.

The ring switching circuit, in accordance with the invention, comprises three or more pairs of vacuum tubes interconnected so that current is switched in the pairs of tubes successively around the ring. Provision is made whereby switching of current in one pair of tubes to an actuated state automatically reswitches the current in the preceding pair to an unactuated state and resets the succeeding pair of tubes so that the next control pulse can switch current in that suceeding pair to an actuated state.

The specific ring circuit described hereinafter is particularly adapted for use in the color mixer described in the application of-Peter C. G'"1d mark, Ser. No. 357,082, filed September 1'7, 1940. In that application a color television signal is passed into three channels and blank ng waves are applied to the channels to blank out all but the red signal in one channel, all but the green signal in a second channel, and all but the blue signal in the third channel. In order to properly synchronize and phase the blanking waves with the color television signals, the control pulses for the ring circuit are derived from the television signal. For example, the field synchronizing pulses or the peaks of the vertical sawtooth waves may be employed.

The invention will be more fully understood by reference to the specific embodiments illustrated in the drawings and the following de scription thereof. In the drawings:

Fig. l is a circuit diagram of a pair of vacuum tubes interconnected in accordance with the invention;

Fig. 2 is a circuit diagram illustrating a ring connection of three pairs of tubes; and Fig; 3 is a diagram showing the manner in which a train of operating pulses causes current to change in the various tubes.

Referring to Fig. 1, a pair of vacuum tubes A and A are employed having cathodes K and course be understood that other .types, or tubes, may be employed i1 desired. The anode'will ordi-:

narily be the plate or the tube, and the control electrodes will be in the form of grids. Also, the cathodes will usually be thermionic and heated by a suitable current source (not'shown); :The

cathode K or tube A is grounded, and the,cathode K of tube A is-connected to ground'through if l2. Preferably l2 has a low resistance relative to that of R. The suppressor grids it andiil are connected to the respective cathodes, the.

usual manner.

The anode-cathode circuit'of each tube --in eludes an impedance, here shown as resistance R (8), connected between the-respective anode and the anode voltage (3+) supply. The anodecathode circuit is completed in the usual manner by connecting the negative side of the B+.-supply to ground. The anode voltage may bebbtained in any convenient manner, such as fromv bat-s teries or the more usual rectifier supply. Bee tween the anode-cathode circuit'oteach tube and a first control electrode oi'=:the other tube is an interconnection II- II). This interconnection is connected to the anode-cathode circult at a point of the anode impedance which is remote from the cathode so that the a voltage drop through at least a portion or the impedance is impressed on the control electrode ot'the other tube when anode current flows through theimpedance. As specifically illustratedyeach'interconnection is directly from; the anode '0! one tube to the control grid SG of the other tube,

and includes a source of biasing voltage D (D) for biasing each control electrode below the potential or the corresponding anode of the other tube. Y

Wih the interconnections asshown, it-willbe seen that when no anode current-is flowing in one tube, say, tube A, there will be no substantial voltage drop across resistance R and the algebraic sum of. the anode voltage source B and the additional biasing source D will be im pressed upon the 'grid -SG' 0! tube A. If the voltage of D is small compared with that of B, for example, 45 volts against 150 volts, the potential oi the grid SG' will be highly positive with respect to the cathode K and will exert little if any l m ting action on the flow or current in tube A. when current flows in tube A, howeveruthe an output impedance, here shown as a resistance above cut-oi! to allow the required amount of anode current to flow to produce the desired voltage drop in resistance R.

It will be understood that the particular tubes. voltages, values of resistanee, 'etc., given above are .1or,speciile,example only, and the invention is:,not limited thereto." The selection of tubes. voltages and circuit constants may vary widely depending on the use contemplated, and will be clear to thoseskilled in the art from the description; given herein BEO Q Y. eachglnterconnection is made to a Yn'oiatfo'r the'anodefcathode circuit of one tube "suchfthatwlncrease {in anode current decreases the 'potential'impre'ssed on the control electrode oi the ..othertube; :The voltage and polarity oi the additional bias source is then selected in view of 'the change in potential and other voltages between control electrode and cathode so that the change/in/potential due. to current in one tube operateswtheiother-tube between cut-ofland a relatively; large current.

. Consideringnowthe-switching of current from one tubeto -the other, assume that both grids G and- G: are.- biased considerably above cut-oi! and that tube "A is-passing anode 'current, thus impressing: a-potential on central grid 8G to prevent current flow in tube A. It, now, a negative pulse is applied to grid G of sufficient magnitude torsubstantially cut of! anode current intube A,.'the. vpltage'dropgin resistance R will become verywsmallzandthe potential of grid SG of tube A willbechanged trom=beyond cut-oi! to a relativelylarge positive value, since the 13+ voltage exceeds that of 1). Current will thereupon flow in tube A. It grid G is sumciently above cutofl, sufllcient' anode current will flow in tube A to cause the voltage drop in resistance R to bias the :control grid 8G of tube A beyond cut-on. That is, anode current: in tube A exceeding a limiting .valuewill .biasgrid SG of tube A beyond cut-om: (It will :be understood that the term biasing beyond cuteoff. includes "to". cut-oil, Ordinarily a negative potential somewhat greater than that Just suilicient to cut off anode current will 'be employed-to insure reliability of operation.) ThereafterQeven though the negative pulse beremoved from grid G and the grid returned toits initial values above cut-oil, tube A will be prevented from passing'current by the voltage on 8G. On the other hand, current will continue to flow in tube A until ca negative pulse is applied tovgrid'G of suflicient magnitude to subvoltage drop across resistance R reduces the potential on grid SG. By selecting a suitable value of R, in conjunction with the other circuit constants. the potential on SG will be altered to completely out of! current in tube A.

For specific example, with the battery voltages just given, 6C6 tubes, and anode resistances R,

.R' of. say, 100,000 ohms, theanode current in tube is such that the voltage drop across the tube i relatively low, say, 10 or 20 volts, andthe voltage drop across resistance R will be relatively large, say, 140 or 130 volts. Thus the bias on 8G will be made negative, say 35, or 25 volts negative to the cathode K. Under these conditions when anode current flows in one tube, it completely cuts of! current in the other, tube.

Toobtain this operation the potential of the second control electrode in the tube passing current, for example, G in tube A, must be sufficiently stantially cut oil current therein, whereupon the voltagedrop in R will become very small and the voltage on grid 8G or tube A will rise to a large positive value. It grid G is sufllciently above cutoil', the anodecurrent in tube A will produce a sufllcient' voltagedrop in R to bias grid 8G in tube Axbeyond cut-om'thus preventing current flow in Aeven though'the negative pulse on G is removed.

Although the above operation is that preierred, particularly for :the application to color mixing :above referred to, wherein abrupt changes in currentpare desired, the circuit constants'may beselected toproduce a change between two diflerent current values. For example, instead orchanging the current in each tube between substantially cut-oil. and a relatively men value vsubstantially unaffected by control potentials on the two grids, the current in the tubes maybe changed between a lower value and an upper value. The desired lower value may be obtained by adjustingthe voltages of the B and D batteries and the value of the plate impedonce so that the potential on, say, SG when current is flowing in tube A does not completely cut oil current in tube A but limits it below a lower limiting value. The maximum current flowing may be limited by appropriately selecting the voltages and anode impedance or by applying suitable potentials to other control electrodes in the tubes. In the present specification and claims the term upper limiting value of the anode current in either tube means the value which will restrict anode current in the other tube at a given lower limiting value. Normally, current in excess of the upper limiting value in one tube will bias the control electrode of the other tube below the lower limiting value.

In the foregoing description of the operation, current is always flowing in one or the other of the tubes of the pair. This type of operation is advantageous, particularly in connection with the ring circuit hereinafter described. However, for other uses it may be desirable at intervals to cut oil or restrict current in both tubes simultaneously. This may be done by impressing suitable voltages simultaneously on both control grids G and G, or on other control electrodes provided in the tubes. Further uses and adaptations of the circuit of Fig. 1 will be apparent to those sk lled in the art in view of the foregoing description.

In Fig. 1 the anode-cathode circuit of tube A contains a load impedance l2 and an output circuit connection i3. From the foregoing explanation it will be understood that the current flowing in. resistance l2 -will change abruptly between cut off and a relatively high value, or between lower and upper limits, in accordance with the control pulses impressed-upon grids G and G through input circuit connections l4 and 15. Output connections may of course be take from any other desired portion of the circuit where the shape of the current or voltage wave is that desired.

It is considered advantageous to connect the cross-connections to the screen grids of the tubes and apply the external operating pulses to the control grids thereof. However, the grids may be reversed if desired. It will beunderstood that in the specification and claims the terms first and second control electrodes are used for purposes of differentiation only, and do not refer to the order in which the grids are spaced from the cathode.

Fig. 2 illustrates a ring connection of pairs of tubes particularly adapted to yield the waves shown in Fig. 3, when controlled by a train of uniformly spaced pulses. Fig. 2 employs three pairs of tubes AA', B-B', C-C'. The tubes of each pair are interconnected in the manner shown in Fig. 1. However, batteries D and D of Fig. l are replaced by respective combinations of a condenser 2|, 2| and a parallel resistor 22,

22'. The values of these resistors and condensers should be selected with respect to the screen grid current and the frequency of operation to provide a bias equivalent to batteries D, D, as will be understood by those in the art. Batteries may of course be employed, particularly with a train of control pulses of low frequency.

The train of operating pulses from the input 23 is applied simultaneously to the control grids G of one tube of each pair, called the first tube for convenience of description. As specifically illustrated, the pulses are applied to the grids G of tubes A, B and C through respective condensers 24 and resistances 25. For the specific operation here contemplated, it is desired that an output voltage be generated by only one pair of tubes at a time. (See Figs. 36, 3e and 39.) Therefore interconnections are provided so that only one pair of tubes is in condition for current to be switched from an unactuated to an actuated state by a control pulse at any given time, and the switching of current in this pair will cause the reswitch of current in the previous pair, thereby cutting off the output voltage generated by the previous pair.

To yield this operation resetting interconnections are provided from each pair of tubes to a control electrode of a tube of the following pair adapted to bias the control grid to an upper level above cutoff when the first pair is in an unactuated state, and to a lower level above cutoff when the first pair is in an actuated state. The levels are selected with respect to the operating pulses so that a pulse cannot cut ofi a tube at the upper level, hence preventing the switching of current in that pair, but can cut oil current in a tube at the lower level, hence allowing current to be switched in that pair.

As specifically illustrated, the resetting connections 26 include resistances 21 connected, respectively, between the anode circuits of the second tubes of the pairs A, B, C, and the grid resistances 25 of the first tubes of the following pairs B, C, A. (Following pairs are the next pairs around the ring from left to right, tube A being considered to follow tube 0'.)

The point at which the resetting interconnection is. connected to the anode circuit is selected so that when no current is flowing in the anode circuit of any one of tubes A, B, C, a suflicient positive bias above cutoff will be applied to the grid G of the following tube to over-balance a negative operating pulse from the input circuit 23 and thus prevent the following tube A, B or C, as the case may be, from being cut off by the operating pulse. This thereby prevents the corresponding paired tubes A, B or C from developing an output voltage. On the other hand, the point of connection to the anode circuit is such that when current is flowing in the anode circuit the bias above cutoff on the grid G of the following tube is reduced to a value such that a negative operating pulse can cut oil current in that tube. thereby switching current to the other paired tube and developing an output voltage.

In the specific embodiment of Fig. 2, the resetting interconnections 26 are connected directly to the anodes of tubes A, B, C, respectively. Thus when any of tubes A, B, C is not passing current, the high positive voltage of the B+ supply is impressed on the grid G of the following tube and is sufficient to far overbalance an operating pulse. On the other hand, when a second tube, say B, is passing current, the voltage drop in its corresponding anode resistance R will reduce th positive bias on the grid G of the following tube C to a lower value above cutoff thereby resetting tube C- and permitting the next starting pulse to cut oil current therein. The

next pulse will then cause current to flow in C to create an output potential at I30.

Condensers 24 associated with the resetting interconnections introduce a small time lag in resetting, if the input circuit 23 is of low impedance compared to resistor 21, so that a single operating pulse will not switch current in each pair of tubes in quick succession. If the input circuit is of high impedance, other suitablemeans for introt'akeiilace'bei'oreth name Inthlsmamiemnlyone o a isinconditiontobeactuated byastarting'pulse,

output voltage.

"Cut-oil interconnections are also provided between each pair of tubes and the preceding pair so that when one pair is "actuated" by an operatingpulse,currentintheprecedingpairwillbe switched to the unactuated state. To accom plish-this result, the cut-oil-interconnections may be connected between the anode circuit of the second tube of a pair and a second control electrode of the second tube 01' the preceding pair, designed so that current flow in one second tube cuts oil flow in the preceding second tube. In the speciflc embodiment of Fig. 2, the control grids G'oi' tubes A, B, C' are connected through resistances ii to the control grids 86 of the following tubes B, C, A, respectiveLv, the grids SG being in turn connected to the anode circuits oi the paired tubes B, C, A.

Thus, cut-oil interconnection B is connected to the anode circuit 01' tube B through the condenser-resistor biasing source II, 22, and to the grid G of tube A through resistance 3|. When no current is flowing in the anode circuit oi tube B the control electrode 8G of tube B will be at an elevated potential and this same potential will-be applied through resistance 3| to control electrode G of tube A. In this condition. tube A is allowed to pass current under the control oi its control electrode SG'. However, when anode current is flowing in tube B, the voltage drop in its plate impedance It not only impresses a negative potential on grid 80 of tube B but also impresses a negative potential on grid G oftube A. Thus, flow of current in tube B cuts oil cur-' rentintubeA,aswellasintubeB.

To summarize the operation of the speciflc circuit of Fig. 2, assume that the pair of tubes B, B is in the actuated state (B cut oil and B passing current) and that the other pairs are in the unactuated state. Grid 3G in tube B will be at cutofl', and so will grid G of tube A because of cutof! interconnection 293. Current in B will also have reset the succeeding pair of tubes C. C by reducing the potential on grid G oi tube C to its tionwillobtainimtilthenextmratingwlle comes along.

Thenextoperatingpuleewillswitchcurrent thepairoihibesLA'bycuttingoflcurrentin tubeAandtherebvallowingtullcurrenttoflow in A, thus placing tubes A, A in the actuated state. Theactuation o!-tub esA,A-willintun i reswitchtubesC,C'totheunactuatedstate,in the manner Just described for the preceding pulse,andwillreeetthspalroitubesB,B'so thatthenextpmsewillactuateEB."

As a result oi the operation just described, it

.starting pulsesot brie! duration recur at,say 120 1 corresponding currents of tubes A, B and C. It

will be noted that when current is flowing in one tube of a pair it is cut oil in the other paired tube. V

In the color television system for changing the relative magnitudes oi the different colors in a video signal, described hereinbefore, the output waves from terminals HA. "3', IIC may be connected to the three channels for blanking out all but the desired color in each channel. The precise control of the circuit of Fig. 2 by synchronising pulses correlated with the color video signal, and the sharpness oi the generated rectangular waves, results in very satisfactory blanking.

Any number of pairs of tubes, more than three,

may be employed in the ring connection of Fig. 2. Output voltages or currents may be taken from any convenient point where the shape of the wave is that desired. In particular, instead of taking an output voltage from output impedances HA, I23, "C, as shown, waves of s milar shape but opposite polarity, may be taken from lower level above'cutofl. An output voltage will appear at I33.

When the next operating pulse comes along it will cut ofl current in tube C by reducing the potential on its grid G from the lower level above cutoi! to a value beyond cutofl'. This will cause iull current to flow in tube C, thus creating an output voltage at 13C. At the same time, the flow of current in C will cut oil current in tube B through cutoi! interconnection 290, thus cutting ofl output voltage in "3. Current in C will also reduce the potential on grid 8G of tube C to beyond cutoii, thus preventing tube C from passing current after the operating pulse has passed. In addition, current in tube C will reset the pair of tubes A, A by reducing the bias on grid G of tube A from the upper to the lower value above cutoff. In the meantime, the cutting off of current in tube B will have changed the potential on grid G of the tube C to its upper value above cutofl' (through reset connection the grids 8G of tubes A, B and C. Blight inl-' perfections in the waves may dictate which should be employed.

It may be desired in a ring oi 11" pairs of tubes to modulate the operating pulses so that every 1: pulse is distinguished in some way from the others, and to have the output from a particular pair 01 tubes always follow one oi these distinctive pulses. This operation may be achieved by having a difl'erent resetting voltage applied to this particular pair of tubes, so that the resetting is insuiilcient for any other pulse to actuate this pair, but sufllcient for one of the distinctive pulses to actuate this pair,

As a specific example, it may be desired in the arrangement of Fig. 2 to have every third operat'ng pulse larger than the others, and to have the output IIA always follow the larger operating pulses. To yield'this operation, the resetting voltage applied through connection." to the associated pair of tubes A, A can be taken from an intermediate point of the resistance R which forms the anode resistance for tube C. If this point is properly chosen, when the pair of tubes C, C is actuated, the resetting voltage will be at such a level that only a distinctive pulse will bias the grid G of tube A beyond cut-oil. and

For some applications it may be desired to use a chain connection of pairs of tubes, instead of a ring connection. This may be effected by omitting the resetting and cut-ofl interconnection between the first and last pairs. Also. the cut-oil interconnections between pairs may be omitted if desired.

The modification described in connection with Fig. 1 in which current in either tube changes between lower and upper limits, rather than between cut-ofl and a large value, may be employed in a ring circuit of the type shown in Fig. 2, if desired.

With respect to the specific embodiments described herein, it will be understood that the circuit elements included in the cross connections between the tubes of a pair, in the cut-off interconnections and in the resetting interconnections, and the points between which they are connected, may be changed in many respects by those skilled in the art within the spirit and scope of the invention.

In particular, in the specific embodiment described the resetting and cut-ofi interconnections are connected between the anode-cathode circuit of the second tubes of a pair and the proper control electrodes. However, the interconnections may be made to other suitable points in the connected pairs of tubes if desired. For example, a cathode resistor for the first tube and sensitive grid control for the second tube made he employed for cutoff, with more or less success. Moreover, although symmetrical interconnections in each pair of tubes and similarity between pairs of tubes are advantageous, unsymmetrical interconnections and dissimilar pairs may be employed if desired.

In other respects, also, it will be understood that the present invention is not limited to the mere details of design, construction and arrangement of the elements disclosed, since many modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

The invention may be employed with advantage for a number of purposes in addition to those mentioned hereinbefore. In particular, it is useful in connection with frequency division where the frequency of the output of one pair of tubes is a sub-multiple of the incoming operating pulses, and in pulse distributing circuits in general.

I claim:

1. In an electronic switching circuit, the combination which comprises a pair of electronic vacuum tubes each having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube, interconnections between the anode-cathode circuit of each tube and a first control electrode of the other. tube for restricting anode current in either tube below a lower limiting value when current in the other tube exceeds an upper limiting value, and circuit connections for each tube for receiving operating pulses and applying the pulses to a second control electrode of the respective tube to change the potential thereof between a potential suflicient to restrict anode current below said lower limiting value and a potential suiiicient to allow anode current exceeding said upper limiting value to flow.

2. In an electronic switching circuit, the combination which comprises a pair of electronic vacuum tubes each having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube including an impedance and a source of anode voltage, interconnections between a first control electrode of each tube and a point of the anode-cathode circuit or the other tube selected so that increase of anode current in either tube decreases the potential impressed on the first control electrode of the other tube, said interconnections and impedances being selected so that anode current in either tube exceeding an upper limiting value yields and maintains a potential for the first control electrode of the other tube sufilcient to restrict anode current therein belowa lower limiting value, the bias on the first control electrode of either tube when anode current in the other tube is below said lower limiting value being sufiiciently above cut-oi! to allow anode current exceeding said upper limiting value to flow, means for biasing a second control electrode of each tube to allow anode current exceeding said upper limiting value to flow therein, and circuit connections for. each tube for receiving operating pulses and applying the pulses to said second control electrode of the respective tube to restrict the anode circuit therein below said lower limiting value.

3. In an electronic switching circuit, the combination which comprises a pair of electronic vacuum tubes each having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube, interconnections between the anode-cathode circuit of each tube and a first control electrode of the other tube for substantially cutting ofi anode current in either tube when anode current in the other tube exceeds a limiting value, and circuit connections for each tube for receiving operating pulses and applying the pulses to a second control electrode of the respective tube to change the potential thereof between substantially cut-oil and a value suflicient to allow anode current exceeding said limiting value to flow.

4. In an electronic switching circuit, the combination which comprises a pair of electronic vacuum tubes each having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube, interconnections between the anode-cathode circuit of each tube and a first control electrode. of the other tube, designed so that anode current exceeding 9. limiting value in either tube yields and maintains a potential for the control electrode of the other tube sufiicient to substantially cut ofi anode current therein, means for biasing the first control electrode of each tube to allow anode current exceeding said limiting value to flow therein when anode current is substantially cut off in the other tube, and circuit connections for each tube for receiving operating pulses and utilizing said pulses to change the potential on a second control electrode in the respective tube between substantially cut-off and a value sufllcient to allow anode current exceeding said limiting value to fiow.

5. In an electronic switching circuit, the combination which comprises a pair of electronic vacuum tubes each having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube including an impedance and a source of anode voltage, interconnections between a first control electrode of each tube and a point of the anode-cathode circuit of the other tube selected so that increase of anode current in either tube decreases the potential :impressedion the first control electrode of the other tube,;said interconnections and impedances. being designed so that anode current-exceeding a limitingvalue in either tube yields and maintains a potential for the first control electrode ointhe othertubepsume cient to substantially 'cut .oilanode current therein, means for biasing: the first control electrode of each tube to allow anode current. exceeding said limiting value torfiow thereingwhen anode current is substantially cut oil in the other tube, means for biasing a second control electrode of each tube sufilciently' above cut-oi! to-allow"anode current exceeding 'saidlimiting value to now therein, and circuit connectionslior each: tube for receiving operating pulses and applying .the pulses to said second control electrode ofthe ,respective tube to substantially cutofi'anode current therein. I

6. In an electronic switchingtcircuit, the combination which comprises a pair-oi electronic vacuum tubes each having an anode, cathode and a plurality of control electrodes, an anodecathode circuit for each tube including an ima,sos, sss

bination which comprises a pair of electronic vacuum tubesleach having an anode, cathode and a3 pluralityoi control electrodes, an anode-cathodeclrcuitior eachtube including a source oi substantiallyconstant anode voltage and a resistance connectedinzcircuitbetween the corre flp ndingtnodeandsaid voltage source, interconnections between a: firstcontrol electrode of each tube land a point: ot the resistance of the othertube remote from the corresponding anode voltage source, a source 0!: biasing voltage in each pedance and a sourceiof; anode voltage, interconnections between a first control electrode voi. each tube and a pointot the impedancepot the other tube remote from the correspondingcathode, said interconnections and'impedances .being designed so that anode current exceeding a limiting value in either tube yields and maintains a potential for the first control electrode of the other tube suflicient to substantially cut oil anode current therein, means for biasing the first control electrode or each tube to allow anode current exceeding said limiting value to now therein when anode current is substantially cut off in the other tube, means for biasing a second control electrode of each tube suificiently above cut-oil to allow anode current exceeding said limiting value to fiowtherein, and circuit connections for each tube for receiving negative operating pulses and applying the pulses to said second control electrode or the respective tube to substantially cut oil anode current therein.

'1. In an electronicswitching circuit, the combination which comprises a pair of electronic vacuum tubes each having an anode, cathode and a plurality of control electrodes,an anode-cathode circuit for each tube including an impedance anda source or substantially constant anode voltage in series, interconnections between-a first control electrode of each tube and a point or the impedance of the other tube remote from the corresponding cathode, a' source of biasing voltage in each or said interconnections, said sources 01' voltage and impedances being designed so that anode current exceeding 'alimiting valuein either tube yields and maintains a potential tor the first control electrode 01' the othertube sufficient to substantially cut oil' anode current therein, the bias on the first control electrode of either tube being sufliciently above cut-on to allow anode current exceeding said'limiting of said interconnectionsior biasing each first control electrode below the potential 01' said remote cpoint of: the respective resistance, said sources orvoltage and resistances being selected sothat anode current exceeding a limiting value inieither tube yields: and maintains a potential iorthefirst'control electrode of the other tube sumcient to substantially cut oil anode current therein; thev bias onzthe first control electrode or either tube being-.suiilciently above cut-oil. to

allow anode current exceeding said limiting value tofiow therein when anode current is substantially cut oil. in the other tube, means for biasing a'second controlrelectrode' of each tube sufiiciently above cut-oi! to allow anode current exceeding said-limiting value to fiow therein, and circuit connections for each tube for receiving negative operating pulses and applying the pulses to said second control electrode of the respective tube to substantially cut oil anode current therein.

9,.An electronic switching circuit which comprises a plurality of pairs of electronic vacuum tubes, each 01' said tubes having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube, interconnections between the anode-cathode circuit of each paired'tube and a first control electrode of the other paired tube for restricting anode current in either tube below a lower limiting value when anode current in the other tube exceeds an upper limiting value, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to a secpotential level when anode current exceeding said upper limiting value fiows in the second tube value to fiow therein when anode current is substantially cut oil in the other tube, means for biasing a second control electrode of each tube sufilciently above cut-ofi to allow anode current exceeding said limiting value to flow therein, and circuit connections for'each tube for receiving operating pulses and applying the pulsesto said second control electrode of the respective tube to substantially cut of! anode current therein.

8. In an electronic switching circuit, the com of said other pair, said potential levels being correlated with said operating pulses so that a pulse restricts anode current below said lower limiting value in'a first tube biased to said lower potential level but not in a first tube biased to said upper potential level.

10. An electronic switching circuit which comprises three or more pairs of electronic vacuum tubes forming a ring, each or said tubes having an anode, cathode and a plurality oi control electrodes, an anode-cathode circuit for each tube, interconnections between the-anode-cathode circuittoi' each paired tube and a first control electrode oi the other paired tube for restricting anode current in either-tube below a lower limiting value when anode current in the other tube exceeds an upper limiting value, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to a second control electrode 01' a first tube of each pair, means for biasing the second control electrodes of said first tubes to an upper potential level, re-setting interconnections from each connected pair or tubes to the second control electrode of the first tube of the succeeding pair for changing the bias thereon to a lower potential level when anode current exceeding said upper limiting value flows in a second tube of a pair, said potential levels being correlated with said operating pulses so that a pulse restricts anode current below said lower limiting value in a first tube biased to said lower potential level but not in a first tube biased to said upper potential level, and interconnections from each connected pair of tubes to a second control electrode of the second tube of the preceding pair for restricting anode current therein below said lower limiting value when anode current exceeding said upper limiting value flows in a second tube of a pair.

11. An electronic switching circuit which comprises three or more pairs of electronic vacuum tubes forming a ring, each of said tubes having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube including an impedance and a source of anode voltage, interconnections between a first control electrode of each paired tube and a point of the anode-cathode circuit of the other paired tube selected so that increase of anode current in either tube decreases the potential impressed on the first control electrode of the other tube, said interconnections and impedances being selected so that anode current in either paired tube exceeding an upper limiting value yields and maintains a potential. for the first control electrode of the other paired tube sumcient to restrict anode current therein below a lower limiting value, the bias on the first control electrode of either paired tube when anode current in the other paired tube is below said lower limiting value being sufiiciently above cut-oil to allow anode current exceeding said upper limiting value to flow, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to a second control electrode of a first tube of each pair, means for biasing the second control electrodes of said first tubes to an upper potential level, re-setting interconnections from the anode circuit of the second tube of each pair to the second control electrode or the first tube of the succeeding pair for changing the bias thereon to a lower potential level when anode current exceeding said upper limiting value flows in a second tube of a pair, said potential levels being correlated with said operating pulses so that a pulse restricts anode current below said lower limiting value in a first tube biased to said lower potential level but not in a first tube biased to said upper potential level, and interconnections from the anode circuit of the second tube of each pair to a second control electrode of the second tube of the preceding pair for restricting anode current therein below said lower limiting value when anode current exceeding said upper limiting value flows in a second tube of a pair.

12. An electronic switching circuit which comrises a plurality of pairs of electronic vacuum tubes, each of said tubes having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube including an impedance and a source of anode voltage, interconnections between a first control electrode of each paired tube and a point of the anode-cathode circuit of the other paired tube selected so that increase of anode current in either tube decreases the potential impressed on the first control electrode or the other tube, said interconnections and impedances being designed so that anode current exceeding a limiting value in either paired tube yields and maintainsa potential for the first control electrode or the other paired tube suflicient to substantially cut off anode current therein, means for biasing the first control electrode of each paired tube to allow anode current exceeding said limiting value to flow therein when anode current is substantially cut ofi in the other paired tube, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to-a second control electrode of a first tube of each pair, means for biasing the second control electrode of a first tube 0! at least one pair to an upper potential level, and a re-setting interconnection from the anode circuit of the second tube of another pair to the second control electrode of the first tube of said one pair for changing the bias thereon to a lowerpotential level when anode current exceeding said limiting value flows in the second tube of said other pair, said potential levels being correlated with said operating pulses so that a pulse substantially cuts off current in a first tube biased to said lower potential level but not in a first tube biased to said upper potential level.

13. An electronic switching circuit which comprises three or more pairs of electronic vacuum tubes forming a ring, each of said tubes having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube, interconnections between the anode-cathode circuit of each paired tube and a first control electrode of the other paired tube for substantially cutting ofi anode current in either tube when anode current in the other tube exceeds a limiting value, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to a second control electrode of a first tube of each pair, means for biasing the second control electrodes of said first tubes to an upper level above cut-01f, resetting interconnections from each connected pair of tubes to the second control electrode of the first tube of the succeeding pair to bias the electrode to a lower level above cut-ofi when anode current fiows in a second tube of a pair, said levels being correlated with said operating pulses so that a pulse substantially cuts off current in a first tube biased to said lower level but not in a first tube biased to said upper level, and cut-oil interconnections from each connected pair of tubes to a second control electrode of the second tube or the preceding pair to substantially cut off anode current therein when anode current flows in a second tube of a pair.

14. An electronic switching circuit which comprisesthree or more pairs of electronic vacuum tubes forming a ring, each of said tubes having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube, interconnections between the anode-cathode circuit of each paired tube and a first control electrode of the other paired tube designed so that anode current exceeding a limiting value in either tube yields and maintains a potential for the control electrode of the other tube suificient to substantially cut off anode current therein, the first control electrode of each tube being biased to allow anode current exceeding said limiting value to flow therein when anode current is substantially cut ofl in the other paired tube, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to a second control electrode 01' a first tube of each pair, means for biasing the second control electrodes of said first tubes to an upper potential level above cut-oil, re-setting interconnections from each connected pair 01' tubes to the second control electrode oi. the first tube oi the succeeding pair to bias the electrode to a lower potential level above. cut-oil. when anode current exceeding said limiting value flows in a second tube of a pair, said potential levels being correlated with said operating pulses so that a pulse substantially cuts oil. current in a first tube biased to said lower level but not in a first tube biased to saidupperlevel, time delay means associated with said re-setting interconnections for delaying a change from upper to lower potential levels, and cut-off interconnections from each connected pair of tubes toga second control electrode of the second tube oi the preceding pair to substantially cut oil! anode current therein when anode current exceeding said limiting value fiows in a second tube 01. a pair.

15. An electronic switching circuit which comprises three or more pairs of electronic vacuum tubes forming a ring, each or said tubes having an anode, cathode and a'plurality of control electrodes, an anode-cathode circuit for each tube including an impedance and a source of anode voltage, interconnections between a first control electrode oi each paired tube and a point of the anode-cathode circuit or the other paired tubes selected so that increase of anode current in either tube decreases the potential impressed on the first control electrode oi the'other tube, said interconnections and impedances being designed so that anode current exceeding a limiting value in either paired tube yields and maintains a potential for the first control electrode or the other paired tube suificient, to substantially cut oil anode current therein, the first control electrode 01 each tube being biased to allow anode current exceeding said limiting value to flow therein when anode current is substantially cut oil in the other paired tube, circuit connections for receiving a train 01' operating pulses and applying the pulses simultaneously to a second control electrode oi a first tube of each pair, means for biasing the second control electrodes of said first tubes to an'upper potential level above cut-ofi,

re-setting interconnections between .the anode circuit of the second tube 01' each pair and the second control electrode of the first tube of the succeeding pair to bias the electrode to a lower potential level above cut-oil. when anode current exceeding said limiting value flows in a second tube oi a pair, said potential levels being correlated with said operating pulses so that a pulse substantially cuts off current in a first tube biased to said lower level but not in a first tube biased to said upper level, and cut-oil interconnections between the anode circuit of the second tube of each pair and a second control electrode oi the second tube of the preceding pair for cutting oil anode current therein when anode current exceeding said limiting value fiows in a second tube of a pair.

16. An electronic switching circuit which comprises three or more pairs of electronic vacuum tubes forming a ring, each of said tubes having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube inc uding a resistance and a source 01' substantially constant anode voltage in series, interconing cathode, a source of biasing voltage ineach of said interconnections, said sources or voltage and resistances being selected so that anode current exceeding a limiting value in either paired tube yields and maintain; a potential for the first control electrode or the other paired tube sufiicient to substantially cut oil anode current therein, the bias on the first control electrode or either paired'tube being sufiiciently above cutofi! to allow anode current exceeding said limiting value to flow-therein when anode current is substantially cut oi! in the other paired tube, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to a second control electrode oi a first tube of each pair, re-setting interconnections from a point oi the resistance oi 'the second tube or each pair remote from thecathode thereof to the second control electrode oi the first tube or the succeeding pair for biasing said electrode to an upper potential level above cut-oi! when anode current is not fiowing in said second tube and to a lower potential level above cut-oil when anode current is fiowing therein, said potential levels being correlated with said operating pulses so that 'a pulse cuts oil currentin 'a firsttube biased to said lower level but not in a first tube biased to said upper level, time delay means associated with the re-setting interconnections for delaying a change from upper to lower levels, and cut-oi! interconnections from a point or the resistance or the second tube of each pair remote from the cathode thereof to a second control electrode of the second tube of the preceding pair for biasing said electrode above cut-oi! when anode current is not flowing in said resistance and beyond cutoil when anode current is flowing therein.

v 17, An electronic switching circuit which comprises three or more pairs of electronic vacuum tubes forming a ring, each or said tubes having an anode, cathode and a plurality oi control electrodes, an anode-cathode circuit for each tube,-

interconnections between the anode-cathode circuit oi each paired tube and a first control electrode of the other paired tube for restricting anode current in either tube below a lower limiting value when anode current in the other tube exceeds an upper limiting value, circuit connections for receiving a train of operating .pulses and applying the pulses simultaneously to a second control electrode of a first tube of each pair, selected operating pulses difi'ering from the remainder, means for biasing the second control electrodes of said first tubes to an upper potential level, re-setting interconnections from each connected pair oi tubes to the second control electrode oi the first tube of the succeeding pair for changing the bias thereon to a lower potential level when anode current exceeding said upper limiting value fiows in a second tube of a pair, said potential levels being correlated with said operating pulses so that a pulse restricts anode current below said lower limiting value in a first tube biased to said lower potential level but not in a first tube biased to said upper potential level, the re-setting interconnection to the first tube oi one pair difiering from the re-setting interconnection to other first tubes' so that only said selected difierent operating pulses restrict anode current below said lower limiting 4 value in the first tube or said one pair, and internections between a first control electrode of each connections from each connected pair of tubes to a second control electrode of the second tube or the preceding pair for restricting anode current therein below said lower limiting value when anode current exceeding said upper limiting value flows in a second tube of a pair.

18. An electronic switching circuit which comprises three or more pairs of electronic vacuum tubes forming a ring, each of said tubes having an anode, cathode and a plurality of control electrodes, an anode-cathode circuit for each tube, interconnections between the anode-cathode circuit of each paired tube and a first control electrode of the other paired tube designed so that anode current exceeding a limiting value in either tube yields and maintains a potential for the control electrode of the other tube sufiicient to substantially cut oil anode current therein, the first control electrode of each tube being biased to allow anode current exceeding said limiting value to flow therein when anode current is substantially cut oil in the other paired tube, circuit connections for receiving a train of operating pulses and applying the pulses simultaneously to a second control electrode of a first tube of each pair, selected operating pulses having a magnitude greater than the remainder, means for biasing the second control electrodes of said first tubes to an upper potential level above cut-off, re-setting interconnections between the anode circuit of the second tube of each pair and the second control electrode of the first tube of the succeeding pair to bias the electrode to a lower potential level above cut-oil when anode current exceeding said limiting value flows in a second tube of a pair, said potential levels being correlated with said operating pulses so that a pulse substantially cuts of! current in a first tube biased to said lower level but not in a first tube biased to said upper level, the lower potential level yielded by the re-setting interconnection to the first tube of one pair exceeding the lower level of other first tubes so that only an operating pulse of said greater magnitude substantially cuts ofi current in the first tube of said one pair, time delay means associated with said re-setting interconnections for delaying a change from upper to lower potential levels, and cut-ofl" interconnections from each connected pair of tubes to a second control electrode of the second tube of the preceding pair to substantially cut ofi anode current therein,when anode current exceeding said limiting value flows in a second tube of a pair.

JOHN M. HOLLYWOOD.