US2447495A - Register switch utilizing a plurality of discharge tubes - Google Patents

Description

Aug. 24, @948. M DEN -roe. ETAL 2,447,495

REGISTER SWITCH UTILIZING A BLURALITY 0F DISCHARGE TUBES 2 Sheets-Sheet 1 Filed May 8, 1945 MOPOUJUQ du jowtrzou MMPEQMK v aim M; DEN HERTOG ETAL REGISTER SWITCH UTILIZING A PLURALITY Aug. 24, 1948.

OF DISCHARGE TUBES 2 Sheets-Sheet 2 Filed May 8, 1945 KOPQuJuw x .5353 wuzuzumum I INVENTORY M171? 77/W/J 0671 17158706 i of l the --tube.

Patented Aug. 24, 1948 REGISTER SWITCH UTILIZING A PLU- RALITYZOF DISCHARGE TUBES Martinus (den .Hertog and Lucien Alfred .B. v.Cabes, Antwerp, Belgium, assignors to International Standard*ElectricCorporation;NewYork,N.Y,,

a corporation or Delaware Application -May 8, 1943; Ser-ial No. '=486;27:5 In the Netherlands aluly -11, 1941 Section 1, Public Law 690, August-83194.6

Patent expires July 1 1, 1961 :12 Glaims.

-'-'.['his invention relates 'to new :and useful improvements in electricalswitching sdevices which rmay be used, e. g. in :telephonea systems or similar systems, and more particularly to special devices for the electrical control :of "moving 'apparatus, in which the switching-time must :bereiducedto aminimum.

The object /of the invention is lto-obtain the required accuracy-of .setting (of :apparatuswhich :is :operated :at "the :greatest possible speed. This is accomplished by ..using :electrical discharge tubes f to 'controlthe operations.

According to zone siof' the features-70f :the "inven- .tion 'two or more electrical dischargetubes are .used in 1 combination :f or the control 'of a -switching apparatus, oneof these tubescontrolling the moving. mechanism I 0115av switchingapparatus and being controlled :in $111311 by the othertube or tubes "in accordance .with rthewpositiontreached by theiapparatus.

According to another feature of-the-invention, the .power -magnet of switchingapparatus is energized in series with thedischarge space of a .vacuum tube and the switch is, put into vmotion and-the control of a;g1idrt0"WhlCh .througha condenser -a potentialisrapplied:to operate the tube.

According .to .-a further .feature. of the invention the operation. of the first. tubeis interruptedwhen the second tube .starts .upon .the desired setting of .the moving apparatus. The interruption-is caused by a briefdecrea-se of the..potentia1.-applied .to the discharge space a of .the .first tube by .the change of the charge of a condenser, which is connected between electrodes .of the first .and second tubes.

.The. invention will berdescribed with reference to the drawings .in. WhlQhrFig, ,1" diagrammatically i illustrates the circuit of. a :register..=controller-.for

cathode discharge tube is :used, together -'with :a'

relaywconnectediii-series with thedischarge space A contact of the :relayis connected in :series with :the circuit controllin'g the switch, and When the switch arrives in azpred'eltermined gposition :in "which the -ztube functions,-

more. .gagement of twoconsecutive contact sets .islDO -22 the relay in'sseries-xwith theidischarge space operates :and causes 'fthe-switch to step.

In :such aidevices tthe zxrelay serves therefore as a test; relaybecause it operates "when the switch finds a free :outlet .in a required-group and stops the switch. In such devices useamay -be-madeof free test potentials derived irom -a direct current course 'or an' alternating current source and both arrangements are. appliedto some of -the "embodiments described. tin FSflid 'zpatent rapp'lications. Y

The combination "ofzamol'd cathode tube -:with

. a 'relay rinsures aquicker'zoperation ithanwa :relay connected directly in xserics 'with the free 'test potential.

This issowbecause the tube operates practically *without anyzdelay (iniabout 10 '-sec;-) and :perzmits the connection -,of the -..test -.relay.--.in a circuitindependentlyof the test potential. Allar- :rangements made he made-fora quick operation 'iOf the relay, -.e. is. byiapplying 'ahigh potential,

by .connectinguin series :a resistance shunted .by

a 'condenser;etc.

The very short \time in whichtheqtestvrelaywin these arrangements -.attracts its u armature, is of very greatimportanceif .the switches operate at .very highspeedewg. 100.contact sets per sec.:or

At such "speed the time-betweenttheren- .milli-seconds or less, -butthe time available for the .energizin of the test ,relay is --on1y asmall fraction of this because .a continuously moving switch-must be stopped between the firsten age- .mentby the .test .brush' of the-test .contacttand the "moment when the brush .is about half-way .over the-contact.- At -a-speed --.of 100 contacts this time interval will 'z'amountrto about 3.5- millseconds, duringavhich the relay-must attract'its -armature and stop :the :switch by dc-energizing the power magnet andxbraking I of the rotor.

Even an operating time of i1 mini-second for the test-relay *will =leavezlittle time available TfOI safely and. accurately stopping the switch.

The a invention makes possible the stopping of 'a hunting :switch without -:energizing a test .re-

.lay. A "gaseous discharge tube controlled by ;a

grid, a soacalled-thyratronftis used :inconjunction with a mold-cathode .tube in "such a Way :that the :latter lI'GSDOIld'SflFO the :signal received from the"switch, indicatingthat 'the': desired outlet'is reached; and the thyratron stops the r-switch by openingithe' circuitcontroliingfit.

Fig. 1 7 shows part of :a register controller and tarselector switch sas idescribedin :theabove-men- 55 f'tioned United fist-ates :xp tent app t 4: 8

' this resistance.

3 filed January 22, 1943. The principal difference between Fig. 1 and the embodiment shown in said application consists in that the tube Ty is added together with the condensers C1, C2, C3 and the resistances R1, R2, R3, R4. Further small differences, which are not of an essential importance for the invention, will become clear from the further description.

The tube Ty is a gaseous discharge tube with an indirectly heated cathode containing asfurther electrodes a grid and a plate or anode. The grid is connected to a potential which is negative with respect to the cathode and high enough to prevent the starting of the ionization of the discharge space. Once the discharge hasstarted, the continuance thereof is not influenced by the potential of the grid, but is dependent solely on the potential between cathode and anode. The extinguishing of the discharge takes place only when the cathode-anode circuit is interrupted, or when the potential between these electrodes is decreased below a critical discharge potential. With a, tube of this type, which may allow a rather high current to pass, it is possible to control a magnet of a selector switch in the manner described below.

. Starting the selection The starting of the movement of the selector switch is determined by the closure of ground at a register switch marked a, whereby relay Chr is energized in the circuit: ground via brush and terminal of bank a of switch OM, back contacts of Vrr, Str and Ftr, winding of Chr to battery.

The operation of relay Chr causes the anode and cathode circuits of the cold-cathode tube T2 to close, whereby this tube is prepared to respond to a signal received fromi a selector switch.

Moreover, relay Chr makes a connection to ground, by which condenser C1 is charged in series with resistance Rz. This condenser is normally kept in a discharged condition over the resistances R2 and R3 in series. The charging of Cr causes a short decrease of the negative potential on the grid resistance R1 of thyratron Ty. This decrease of potential is suihciently large to discharge the thyratron; After a very short time the condenser C1 attains its full charge and the potential on the grid resistance is restored to the original value. This potential has, however,

no further influence on the discharging of the tube. The time of lighting the thyratron takes practically no time (of the order of 10- sec.)

The condenser C1 may be chosen very small and the entire charging process thereof, and the change of potential on the grid via the grid resistance R1 may be completed in one milli-second or less. Thus almost immediately after the ionization of the thyratron it may be extinguished and the potential on the grid will not produce a new discharge, because the condition p sistance R4, power magnet P to ground.

The resistance R; is connected in parallel to a condenser G3, which is normally discharged by through the discharge space and the power magnet of the selector, first condenser C3 will be charged and, as 03 has a rather high capacity, the current-in P will rise to a relatively high value and will then decrease slowly to the poten- When current begins to flow 4 tial at the terminals of R4 until C3 is charged. The value of C3 is selectedso that the duration of the increased current is sufiiciently long fully Alternating current test of selector switch The controlling electrode of the cold-cathode tube T2 is normally connected over a high resistance and a second resistance of 15,000 ohms to a potentiometer, consisting of three resistances of 7500, 2500 and 7500 ohms. The potential connected to the controlling electrode by means of this potentiometer via the back contact of relay W1? is such, that ionization of the tube T2 will occur if this potential is not decreased by a rectified alternating current supplied by the rectifier bridge Re in series with a retardation coil RC to the resistance of 15,000 ohms. The direct current potential obtained from the rectifier Re is normally of opposite direction to that obtained from the potentiometer. In the known way, the alternating current connected to rectifier Re will decrease to zero only by the receipt of a signalling current in the transformer H01, which has the same characteristics as the reference current which is supplied to the transformer HCz, so that it cannot supply direct current to the resistance of 15,000 ohms. The potential of the controlling electrode is then increased to the potential supplied by the potentiometer, and the cold-cathode tube is ionized.

At the moment theselector switch reaches an outlet in the desired group, an alternating current with a certain phase difference is applied via the d brush of the selector switch and by the primary winding of transformer HCI. In the above-indicated way the tube T2 is then ionized, whereupon current flows from -130 volts viaf front contact of Chr, cathode, discharge space and anode of T2, front contact of 0hr, winding of Vtr to ground.

As a result of the closure of this circuit, the potential on the anode of T2, which till this moment was equal to the ground potential, is increased to a value which is equal to 130 volts, less the potential of the tube T2, which amounts to about "75 volts. This increase of about 55 volts of the potential of the anode of T2 causes a charge displacement of the condenser C2. Since the anode gets a, negative charge, an impulse of negative direction is applied to the plate of the thyratron Ty for a short time. The potential of this plate with respect to the'potential of the cathode of the thyratron is decreased to such an extent'that the discharge of the thyratron is V suddenly interrupted, because the potential falls below the critical point at which discharge is still possible. As the grid of the thyratron is constantly negative with respect to the cathode, the discharge cannot start again when the negative pulse" to the plate is at an end. The current through the power magnet P, is, therefore, very quickly interrupted, i. e. at the speed of the deionizatlon time of the thyratron, which amounts to approximately 10-* per second. In this way ashamed the-rotor or brush carriage of the selector-switch stops on theset of conta'cts-belongingto an=outlet in the desired group.

Repetition. of the aliermiting current. test order todeterminewhether the rotor has, stopped on' these terminals, the alternating' currenttest isrepeat'ed after the rotor-has stopped;1-and if 'it appears that noalternating current potential is present on the d terminal, then the hunting movement starts again. This takes place as follows:

The response of tube Tz-causes also theenergizing' of relay Vtr in series with the discharge space; Relay Vt? closes-'thefollowin'g circuit for the-energizing of relay-Fir: ground; front-cont-actof 'Vtr, back cont'actsof-Gbrand Fhr; wind"- ing of-Ft'r, to battery.

Relay Fir prepares atemporarylocking circuit for itself, in series with the winding of-relay Fhr; but as long asrelay Vtr is energizedg Fhr cannot operate. Relay Ftr opens also the circuit for relay Chr, which'is thenreleased and: opens the cathcdeand' anode circuits of'tube T2. The' tube T2 is'thus extinguished and relay Vtr' released.

Upon the release of relay Chr the condenser Ci,-which was kept chargedvia a front contact of relay Chr; may now dischargevia the res-istancesR'z and R3.

Uponthe release of" relay Vtr relay Fhr energizesand'this relay' again closes the circuit for relay Chr. This relay now again closes the'cathode-anode circuits oftube T-and'also the-following-circuit for relay-Kir: ground to'bacli contact of Vtr, front contacts of Chr and Ftr, windings oi Kir, battery.

As soon asthe brushes of the selector switch are on the set of contacts of the desired outlet, tube 'I'zwill immediately respond again'andrelay Vtrwill'be energized: This relaythen-opens over its backcontact the operating circuit-of""relay Kir. If; however; tube T2 'does not respond; relay Kir'energi'zes and closes an operating circuit for relay Vrr, which releases thetworelays Ftr'an'd Fhr-by' interrupting the lockingground: Relay Vrr also releases relay C717, by'which' the circuit for relay Kir is opened. Relay Kir releases": and also Vrr; which new again closes the circuitfor relay Chr. Since relay Chr is operated the hunting action can again start" by the charge" of condenser C1.

Direct current testlifter the termination of the alternating cur rent test, the registertests'whether afroedirect current potential is present on the terminal on which the selector switch stopped; Iftliisis the case, the outlet is definitely seized and the'hunting selector switch is connected throughby op; erating its relay Br. In the absenceof direct current potential on the selected terminal, the selector switch must continue hunting". This must take place also in-case alternating current potential ispresent on the dterminal,-andit must be possible forthe selector switch to stop on the next terminal to which" this potential applied; This happens as follows:

In the second alternating current. test; relay Vtr operates for the secondtim'e'aml energizes feritseif under-"thecontrol of'a back contact-of relay* WZ r 'to-aback" contact of relay- Vrr. It opens ground" for-relay-C'hr, whereuponthis relay releases: and tube' T2" extinguishes. Furthermore; it OOBIIGCtS-fthEWihdiHgS of the test relay Tr to the--c brush of the-switch viaaa backcontact and winding of--relay Br; The direct currentpotentia'l; if presentat the outlet, is connectedt'o the -c 'cont'a'ct and relay T1" operates in the know-n way in series :with relay 1B1. By operating relay a circuit of low resistance is closed ove'r windings of "Dtr and Tr, by which thefree test' potential to -the "c brush is decreased to -avalue at which" other test relays cannot operate: The operating o'f Dir is; therefore, the signal that the free outlet is definitelyseized and this causes-the operatingofrelay Sm, which now connects the register to the position in which the next selectibncan-be performed by the stepping-movement ofthe-wipersof switch OM. Relay'Vrr iso'perated by'rel'ay' Saw; whereupon the" relays Fir" and Flu release: Relay s'tr is-kept operated by relay Sar, until the magnet of switch OM is fully en'ergi'ze'd' a-nd'theswitch opens its interrupter contact, "and? until relay Dtr" is released; Thistakes place when the circuit'for the free test potential is op'ened at the seizedoutlet.

If; however, for somereason no freetest poten tial is-presentat the outlet, e. g; because the fuse blew, relays Tr and Dtr do not operate and the following-circuit is closed for-the slow=operating relay-G57: ground'tofrontcontact of Stu-back" contactof-Tr; winding'of' Gbr, battery.

Relay GUT closes a temporary'locking circuit for'its'elfto groundover the-back contact of relay V'Tr'anct in turn operates relay Wlr. This relay op'ensuna'back contact theenergizing circuitof relays Ftr, Fhr and Str. Uponthe release-of relay-Str'acircuit-is again closed forrelay'Chr, whichconnects again the'anode andhathode-cib' cuit's of tube Th; Theconditions under which tube Ti t-operates are now; however, changed" by relay-Wit as'comparedtotho-se that existed when rel'ayChr wasnot energized. In the first place, thecontrolling electrode of T2 is now connected to another" point of the potentiometer, the potentia l atwhich is such that it alone cannot produce the ionization of tubeTz'. .In the'second place, relay'Wlr'has-now interchanged, via two changeovercontacts; the connections of the rectifier bridge to'the l5,000"o'hm resistance. If now'alternating current is received by the rectifier bridge; the direct current delivered thereby will he of-the same direction as the direct" current derived" from the potentiometer; At: that nice m'ent.two casesmay'occur: V L I,

(m Atthe seized outlet the alternating current may still be present, notwithstanding the fact that" no directcurrent was found.

In this case the. alternating. current obtained fromtheoutlet is equal to the reference. potential whereby no alternating current wil1 be delivered tbfiih'e rectifier. 'I'ube'Tz' can,.therefore, not resporr'd. When relay Chr is now energized, con-.- denser C1 is again charged via the front contact of 'relay.Ghrandtube Ty. is again ioniz d; Whereupon th'epower magnet' is operated andtlie selector switch leaves the selected outlet. Atthe moment the df' brushcf the selector switch opens itscontactythe alternating current potenttiarisinterrupted, an alternating current po- I which operates.

7 tential will again be delivered to the rectifier. The direct current delivered by the rectifier, added to the potential from the potentiometer, is sufficient to ionize tube T2. The tube operates, the thyratron is again deionized and the selector switch stops. Relay Vtr now responds for the third time and energizes, this time viathe alternate contact of relay Gbr the relay Vrr, which is locked via ground to front contact of relay Vtr.

The energizing of relay Vrr causes the release of relay 0711' and tube T2 extinguishes. After that, relays Gbr and Wlr will also release. The latter will restore tube T2 to normal condition.

Upon the extinguishing of tube T2 the relay Vtr releases, which in turn releases relay Vrr. This relay again applies ground to relay Chr,

All other relays are de-enersized, and the circuit is in the same condition as at the start of the hunting movement. By the charging of condenser 01 relay Chr provides for the ionization of the thyratron and. the control operation starts anew.

(17) Durin direct current testing, the alternating current potential disappears. This may be the case if two selectorstest the same outlet simultaneously and the other selector seizes the outlet.

In this case tube T2 will respond when rela Chr is energized and relay Str tie-energized, because the absence of signaling current. creates the required condition therefore in the energized condition of relay Wlr. The responding of tube T: will then have the same result as in the case described sub 11. 1

Figure 2 shows parts of a register controller and a selector switch, as described in the United States patent application Ser. No. 473,883. Here also the difference consists in that tube Ty, the condensers C1, C21, C22, C3 and the resistances R1, R2, R3 and R4 are added, apart from some further small differences, which are mainly the same as in Figure 1.

The last mentioned application describes an arrangement whereby a selector switch is controlled by two signal receivers in the register controller, in such a way that if one of them responds, then the selector switch is caused to stop. Depending on the seized outlet and on the signal receiver, the register determines what the reaction should be to the seizure of this outlet.

In case the movements of the selector switch must be controlled by means of a thyratron, the problem arises how two or even more signal recelvers may control these movements by means of thyratrons. It is not possible to give each signal receiver its own thyratron as in the case shown in Figure .1, because each thyratron must independently control the movements of a selector. It is very dificult to control the magnetof a selector switch by several thyratrons at the same time, because either the discharge spaces Of the thyratrons would have to be connected in series, in which case difiiculties would occur upon the lightin of the tubes and very high battery potentials would be required, or the discharge spaces would have to be connected in parallel, which would simplify the lighting, but make impossible to deenergize the switch magnet upon the extinguish ing of a single thyratron.

I Figure 2 provides a solution by using a single thyratron, which is common to more than one signal receiver. As in the United States patent to Den Hertog No. 2,431,313, dated November 25, 1947, relay Chr has front contacts connected to the anode and cathode circuits of the two coldcathode tubes B1 and B2 and as in Figure 1 this is the same relay which charges via a front contact the condenser C1 thereby producing in the thyratron the discharge condition when the wipers of the selector switch must be started to move.

The plate of the thyratron is now connected via two condensers C21 and C22 to the anode circuits of the two tubes B1 and B2. As soon as one of these tubes is ionized as a result of finding by the selector switch of a free outlet in accordance with the reference current connected to one of the two signal receivers, the thyratron will be extinguished, either by a charge displacement of condenser C21 when tube B1 responds, or by the charge displacement of condenser C22 when tube B2 responds. The operation will now be briefly explained.

Let us assume that the reference current X connected to transformer T1 of the upper signal receiver of Figure 2 is chosen in accordance with the called number digit designating the group of outlets to be selected, and the reference current Y is chosen in accordance with the designation of an alternative group. As soon as the selector is ready to start, a ground is connected via the brush a of switch OM. Relay Chr is operated, connects the tubes B1 and B2 and ionizes the thyratron by charging condenser C1. The switch power magnet P is energized in series with the thyratron. In case a desired outlet is found, the upper signal receiver responds and tube B1 is ionized. Condenser C21 applies a negative charge to the plate of the thyratron, which is extinguished and stops the selector. Relay Vtr is operated in series with tube B1 and this operates relay Ftr. Relay F'tr opens the circuit for relay Chr, which extinguishes tube B1 and discharges condenser 01. Relay Vtr releases and operates relay Fhr, which now again operates relay Chr and causes a second alternating current test to take place. In case this test is successful, relay Vtr operates again and in turn operates relay Sir, which now initiates the direct current test. In case the second alternating current test is not successful, relay Kir is operated via the back contact of relay Vtr and front contact of relay Chr, so that relay Vrr operates, which releases all operated relays and, after also relay Kir is released, will itself release and cause the hunting movement to start anew.

In case the direct current test is successful the relays Tr and Dtr operate, whereupon relay Sar is operated and the register is advanced to the position in which the setting for the next selection takes place.

If the direct current test is not successful, relay Gbr will operate via a front contact of relay Str and a back contact of relay Tr, as will also relay W111 via a front contact of relay Gbr and a back contact of relay Vtzr. Relay Sir opens the circuit of relay Chr, so that tube B1 is extinguished. Relay Wlr releases relays Ftr, PM and Sir, whereupon the circuit of relay Chr is again closed.

Relay W111 has in the meantime so changed the circuits of tube B1 that it will respond only in the absence of signaling current. By the operation of relay Chr the thyratron is again ionized and the selector switch hunts until its brush (1 open the contact. Tube B1 responds, extinguishes the thyratron and operates relay Vtr. This relay in turn operates relay Vrr, which releases all other relays, including Gbr and W111 and finally releases itself and causes the selecting movement to start anew.

In case an alternative outlet is reached by the selector switch, tube B2 belonging to the second signal receiver responds. This causes the thyratron to extinguish by applying a negative charge to condenser C22. At the same time relay Vtrr is operated, which successively operates the relays Vt21 and Ftr. Relay Vt'21 locks itself to ground under the control of relay Vrr and establishes the circuits for the second signal receiver. The register must respond accordingly, e. g. by efiecting of an additional selector setting. This starts only if a second alternating current test and the direct current test are successful. These operations take place in the same way as described above. After the operation of relay Dir, not relay Sar, but relay Vtsr operates and locks itself independently of Vtzr via the front contact of relay Dtr and energizes relay Vrr. The latter releases all other relays, except relay Str, which remains operated via a front contact of relay Vtzr, so that the relays T1 and Dtr may release only if the free test potential on the seized outlet is opened. Then these relays will release, as will also Vtar, Vrr and Sir and a next selector setting may start. As relay Or was energized via a front contact of relay Vtar, the conditions for this selector setting under the control of relay Or are changed. The seized bypass selector may choose an outlet which leads to the desired group.

If the second alternating current test does not result in the seizing of the alternative outlet, then relay Kz'r responds in the known way, and by means of relay Vrr causes the hunting movement to start anew. Relay Vtzr is then also de-energized by relay Vrr.

If after the seizing of the alternative outlet the direct current test is not successful, relay Gbr, and under the control of a front contact of relay Vtzr, relay W121 will also respond. Relay W121 switches the elements of the second signal receiver in such a way that tube B2 may now only respond in the absence of signaling current, i. e. as soon as the selector switch has left the contact of the seized alternative outlet. The balance of the operations take place in the same way as des crlbed above.

What is claimed is:

1. In an electrical control system, a variably operable register switch, a plurality of selector switches variabl operable in accordance with the operation of said register, each selector having an operating magnet, a control circuit therefor, a plurality of multi-electrode discharge tubes in the register, a first one of said tubes having electrodes in said control circuit, a circuit for controlling a second one of said tubes controlled by the selector, and a control circuit for the first tube controlled by the second tube.

2. The system according to claim 1, and in which the control circuit of the magnet includes in series the discharge space of the first tube, the operation of a selector being started by the ionization of the discharge space, a grid in the first tube controlling th discharge space, and a condenser connected to said grid.

3. In an electrical control system, a variably operable register switch, a plurality of selector switches variably operable in accordance with the operation of said register, each selector having an operating magnet, a control circuit therefor, a plurality of discharge tubes in the register, each tube having a cathode and an anode electrode and a grid controlling the discharge path between said electrodes, a first one of said tubes controlling said control circuit in which the discharge path is included in series, a condenser connected with the grid of the first tube, a circuit for controlling the grid of a second one of said tubes controlled by the selector, and a circuit controlling the charging of said condenser controlled by the second tube.

4. The system according to claim 1, and means in the control circuits of the magnet and of the first tube for causing the successive energization and de-energization of the magnet.

5. The system according to claim 1, and in which the control circuit of the magnet includes a resistance, and a condenser in parallel with said resistance.

6. The system according to claim 3, and in which the control circuit of the magnet includes the magnet winding, and in series therewith a resistance and the anode and cathode of the first tube, and a condenser in parallel with said resistance.

7. The system according to claim 1, a condenser connected with one of said electrodes in the control circuit of the magnet, and means controlled by the second tube for charging said condenser,

8. The system according to claim 3, and a resistance shunt around said condenser.

9. The system according to claim 3, a condenser connected with the anode of the first tube, and means controlled by the second tube for charging the last-mentioned condenser,

10. The system according to claim 1, and a gas valve between the first and second tubes for relaying the operation of the latter.

11. The system according to claim 1, a plurality of second tubes, each arranged to be controlled by the selector, and means for connecting the control circuit of the first tube with the second tube operated by the selector.

12. The system according to claim 3, a plurality of second tubes, each arranged to be controlled by the selector, a gas valve associated with each second tube and operable under its control, and a connection including a condenser between the anode of the first tube and the anode of each gas valve.

MARTINUS DEN HER'I'OG. LUCIEN ALFRED B. CABES.

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

UNITED STATES PATENTS Number Name Date 2,285,815 Halden June 9, 1942 FOREIGN PATENTS Number Country Date 56,430 Netherlands May 16, 1944

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