US3071734A

US3071734A - Coaxial filament transformers for pulse circuits

Info

Publication number: US3071734A
Application number: US89326A
Authority: US
Inventors: Dean O Kippenhan
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-02-14
Filing date: 1961-02-14
Publication date: 1963-01-01
Anticipated expiration: 1980-01-01

Description

Jan. 1, 1963 3,071,734

COAXIAL FILAMENT TRANSFORMERS FOR PULSE CIRCUITS Filed Feb. 14, 1961 D. O. KIPPENHAN 2 Sheets-Sheet 1 INVENTOR DEAN O. KIPPENHAN ATTORNEY Jan. 1, 1963 D. o. KIPPENHAN 3,071,734

COAXIAL FILAMENT TRANSFORMERS FOR PULSE CIRCUITS Filed Feb. 14, 1961 2 Sheets-Sheet 2 1 N V ENTOR mOEDOw mmJDm ozEE DEAN O. KIPPENHAN ATTORNEY United States Patent ()filice ifillfllit i atentecl Jan. ll, 1963 3,071,734 COAXIAL FHLAMENT TRANSFORWER FOR PULSE ClRCUiTfi Dean 6). Kippenhan, Castro Valley, Califi, assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Feb. 14, 1961, Ser. No. 89,326 12 Claims. Cl. 328270) The present invention relates to filament power supplies for electron tubes in pulse circuits and more particularly to means for isolating a filament power supply from the high voltage, high speed pulses in such circuits whereby the shape of such pulses may be more accurately controlled and maintained.

In high voltage, high speed pulsing circuits it is highly desirable that means he provided to prevent unwanted interaction between the filament power supply and the pulse load portion of the circuit. Such means will aid in preserving the desired waveshape and also provide for keeping high voltage pulses out of the filament power supply. The severity of this problem varies directly with the pulse voltage, indirectly with the pulse duration and directly with the rise time of the pulse. The very high power pulse characteristics of recent developments, such as controlled thermonuclear reaction containment devices, have greatly increased the problem and have tended to result in undue complication of the circuitry.

To meet the problem discussed above, previously used high voltage, high speed pulsing circuits have depended largely on filtering circuits to maintain desired pulse shapes and keep pulses out of the filament power supply. With the use of high voltages and greater speeds this filtering has become both cumbersome, expensive and often inefiective. From these standpoints previously used methods of isolating the filament power supply equipment are not satisfactory and may not produce pulses of the desired form. Another method which has been used in the past has consisted of a switching arrangement which removes the filament power supply from the circuit prior to pulsing. This arrangement is also expensive and has not been very satisfactory in operation due to repetition rate limitations.

The present invention, by making use of coaxial cable and balanced coaxial load circuits, balances out the pulse eifects from the filament power supply and efiectively removes the filament power supply from influencing the pulse shape. In this manner the requirement for the unsatisfactory and expensive filter or switching circuits formerly used is eliminated and a circuit which will produce properly spaced pulses at high output power is achieved.

The invention provides for the foregoing result by means of a filament transformer having a coaxial cable as a secondary winding. The outer conductor of such cable is broken at the midpoint so that no transformer secondary current is carried in the outer conductor. Current to the filament of the associated tube is carried by the inner conductor which is continuous throughout the coaxial cable. As will hereinafter be described in detail the foregoing structure allows the coaxial cable to be used as a component of the tube pulse circuitry inasmuch as currents within the cable, other than the filament current, may be balanced.

Therefore it is an object of this invention to provide a means preventing unwanted interaction between the filament power supply and the pulse load circuit of a pulse generator.

it is an object of the present invention to provide. a circuit which will preserve desired output wave shapes in a high voltage high repetition rate pulsing circuit.

It is another object of this invention to provide a means for supplying a filament through balanced coaxial lines in an arrangement whereby pulse effects of associated circuitry are blocked from the filament supply.

A further object of the present invention is to provide a filament power supply with which a high power pulse generator may be made to produce pulses having very short rise times.

Another object of the invention is to eliminate the need for cumbersome and expensive filter equipment for the purpose of maintaining desired output pulse shapes in a high wattage high repetition rate pulsing circuit.

A further object of this invention is the elimination of the need for using a switching arrangement to remove the filament supply from a pulsing circuit prior to and during pulsing. I

It is also an object of this invention to provide a filament circuit for a pulse generator, portions of which filament circuit may be used to transmit pulses without such pulses affecting the filament power supply.

Other objects and advantages of this invention will become obvious to those skilled in the art upon consideration of the following description and accompanying drawing, of which:

FIGURE 1 is a partially cut away, partially schematic view of the invention as applied to a pulsing circuit designed to deliver positive square wave pulses to a load.

FIGURE 2 is a cross sectional view of a modified form of a cross connector utilized in the invention, and

FIGURE 3 is a partially cutaway, partially schematic, view of the invention applied to a pulse circuit designed to deliver negative pulses to a load.

Considering now a first embodiment of the invention as illustrated in FIGURE 1, the pulse switching structure 11 is partially contained within a cylindrically shaped metallic tank 12 provided with flanges 13 and 14 at the ends. Circular metallic end plates 16 and 18 are secured against the ends of tank 11 by means of bolts 17'. Mounted coaxially within the tank 12 is an electron tube 21 which may be a type 5C22 thyratron, for instance, having anode 22, control grid 23, cathode 24 and heater element 26. The tube 21 is so mounted in the tank 12 that the base is nearer the end plate 16 and the anode terminal is nearer the end plate 18. One suitable physical arrangement for the coaxial mounting of the tube 21 within tank 12 is disclosed in US. Patent No. 2,776,368, issued January 1, 1957 to Harvey M. Owren, Vernon L. Smith and David R. Barnum and entitled Coaxial Tube Coupling. To more clearly illustrate the present invention, tube 21 and certain associated components are shown schematically in FIGURE 1, and reference should be made to the specified patent for suitable physical structure. Anode 22 is connected through a resistor 27 and coaxial cable 28 to a source of positive high voltage 29, the coaxial cable 28 being secured to the end plate 18 by means of a suitable cable connector 31. For high voltage usage, for instance at 16 kilovolts, the coaxial cable connector 31 comprises a metal tube 32 brazed or otherwise secured into an opening in end plate 18. The inner conductor insulation 33 of the coaxial cable passes through the tube 32 with a fairly snug fit and protrudes a short distance into the tank 12 with inner conductor 34 protruding from the end thereof. An exposed section of outer braid conductor 36 covers the outer end of tube 32 and is held thereon by a clamp 37. All of the cable connectors used in this invention are preferably of the described type for the high voltage usage herein considered, however it is evident that where lower voltages are used a standard type of cable connector may be employed.

The braid contact with tube 32 provides an electrical connection through end plate 18 to the tank 12 which tank is provided with an electrical ground 38 placing the entire enclosure at ground potential. For the purposes of pulse generation anode 22 is also connected to both ends of a length of coaxial cable 39- Which may be 60 feet in length, for instance, or if desired a pulse forming network of the proper constants may be used instead. This coaxial cable 3 is secured to the end plate 13 by means of coaxial cable connectors 41 and 42 which ground the outer conductor of the cable to the plate 18, the inner conductor remaining insulated therefrom. Coaxial cable 39, serving as a charging line, may be used in one piece as shown or may be cut at the exact midpoint forming two 30 foot lengths of cable each of which is unterminated at the end remote from the coaxial enclosure 11. The double ended connection for cable 39 is made for the purpose of matching the impedance of the anode circuit to the cathode circuit, which will be described later, and to obtain the desired pulse current.

Control grid 23 of the tube 21 is connected through a resistor 43 to the cathode 2 and through a second resistor 44- and a capacitor 46 to a coaxial cable 47. A first end of cable 57 is secured to the end plate 16 by means of coaxial connector 48 and the other end of coaxial cable 47 is connected to a firing pulse source 49. The outer conductor of the cable 47 is grounded to end plate 16 through connector 48. The cathode 24- is further connected to one side of the heater element 26 across which element a capacitor 51 is connected to bypass pulses from the heater element 26.

The side of the heater element 26 to which the cathode is connected is further connected to an end of the inner conductor of a coaxial cable 52. The outer conductor of the coaxial cable 52 is electrically and mechanically connected to the end plate 16 by means of a connector 53 which permits the inner conductor of the cable 52 to pass therethrough. Similarly the other side of heater element 26 is connected to the inner conductor of another coaxial cable 54, of exactly the same length as cable 52, the outer conductor of cable 54 being electrically and mechanically secured to end plate 16 by means of a coaxial connector 56. The ends of

coaxial cables

52 and 54 remote from end plate 16 are both terminated in a novel coaxial cross connector 57 which will hereinafter be described.

Cables

52 and 54 must be of sufiicient length that a number of turns of one of the cables, cable 54 in this instance, may be utilized as secondary turns on the core 58 of a heater supply transformer 59. The number of turns of cable 54 on the core 58 is selected to have the proper ratio with the turns of a primary winding 61 thereon to provide the proper heater voltage when the primary winding is connected to electrical power source 62.

Considering now the detailed structure of the cross connector 57, such connector is formed with four mutually perpendicular arms. An inner conductor 63 and outer conductor 64 of the first arm are connected to the inner and outer conductors respectively of coaxial cable 52. Inner conductor 66 and outer conductor 67 of a second adjacent arm of the cross connector are connected to load 70 with which the pulse current is used. Inner conductor 63 and outer conductor 6% of a third arm of the cross connector are connected to the inner and outer conductors respectively of coaxial cable 54. Inner conductor '71 and outer conductor 72 of the fourth arm of the cross connector are connected to a termination 75 equaling the pulse load in impedance, in order to balance the circuit. The inner conductors 63, 66, 63 and 71 of the cross connector 57 are all connected in a common junction 73. The outer conductors 64 and 67 of the first two arms are joined together electrically and mechanically and the outer conductors 6% and 72 of the third and fourth arms are joined together in a similar manner, the two sets of joined outer conductors being insulated from each other electrically by a gap In operation, since the inner conductors of the crossconnector 57 are joined at the junction 73,, the inner conductors of the

coaxial cables

52 and 54 form a closed loop with the heater 26 thus providing heater current to the tube filament 26. Such current arises through the voltage developed in the turns of cable 54 which form the secondary winding of transformer 59. The same voltage is developed in the outer conductor of cable 54, but the open circuit at gap 86 of coaxial cross connector 57 blocks the flow of current in this path and causes the heater current to flow only in the inner conductors of the cables.

A high positive voltage from source 29 is applied to the inner conductor of coaxial cable 28 which, through resistor 27, charges the coaxial cable 39 to the positive voltage applied. During this period tube 2.1 is in a nonconducting condition. After the coaxial cable 39 is fully charged, a positive voltage pulse is delivered to the grid 23 of tube 21 through coaxial cable 4-7 and through capacitor 4-6 and resistor 44. Such pulse causes the tube to become conductive and the charged coaxial cable 39 discharges through the tube. Such discharge is through the tube cathode, and approximately half of the discharge passes through coaxial cable 52, and inner conductors 66 and 71 of cross-connector 57 to the load and the load balancing impedance respectively. The other half of the discharge passes through capacitor 51, which capacitor eifectively short circuits heater 26 to high frequency cur rents, and thence through coaxial cable 54 to the inner conductors 66 and 71 and to the load 70 and the load matching impedance '75. Thus the two branches of the current reach junction 73 and conductors 66 and 71 simultaneously through the two described parallel paths and are transmitted to the load and the load balancing impedance. The pulse in passing through cable 54 is influenced only by the coaxial cable 54 and sees no inductance from the turns Wound on core 58. The portion of the current passing through the load takes a return path through the outer shells 67 and 64 and the outer conductor of the coaxial cable 52 and through coaxial connector 53 and end plate 16 to ground. The currents pass ing through the load matching impedance pass

outer shells

72 and 69, the outer conductor of coaxial cable 54, the shell of coaxial connector 56 and end plate 16 to ground.

Since the pulse currents in the inner and outer conductors of coaxial cable 54- are equal and opposite in direction the discharge pulse has no eifect on the core 58 and the heater supply is thus effectively isolated from the pulses generated in the circuit. The pulses delivered to the load in this instance are positive and pulses of high power short duration and having square waveshape may be successfully developed.

By a modification of the circuit the load matching impedance may be eliminated and the entire pulse output taken through the load. As shown in FIGURE 2, this may be accomplished by removing the fourth arm of cross-connector 57, which consists of the inner conductor 71 and outer conductor 72, which leads to the load balancing impedance. A small capacitor 74 may then be connected from the outer shell '64- of the first arm of cross-connector 57 to the outer shell 69 of the third arm. This capacitor may be so selected that the resistance to the low frequency heater current may be quite high for instance 2,000 to 3,000 ohms, and the voltage developed across the capacitor is very low as compared to output pulse voltage. This connection maintains circuit balance so that the pulse currents flowing in the inner and outer conductors of coaxial cable 54 are equal and opposite in direction thereby protecting transformer 59 from the effects of high voltage pulses.

For the switching of negative pulses only minor changes in the circuit are necessary. A second embodiment of the invention, for producing negative pulses, is shown in FIG- URE 3 the design thereof being similar to the embodiment of FIGURE 1 except as will now be described. In this embodiment the high voltage lead 28, instead of providing a high positive voltage through resistor 27 to the anode 22, provides a voltage from a negative high voltage source 76 to the cathode 24 through a resistor 27. The anode 22 of tube 21 is connected through a coaxial cable 77 to a pulse load 78 through a Coaxial cable connector 79. Similarly the anode 22 is connected to a load balancing impedance 83 through a second coaxial cable 81 and connector 82. In this embodiment the coaxial crossconnector 57 of FIGURE 1 is omitted from the circuit and the two filament supply

coaxial cables

52 and 54 together form the charging line, as well as the secondary winding of transformer 59. In this circuit as in the positive pulse switching circuit the two

coaxial cables

52 and 54 are made identical in length, for instance 30 feet each, and the inner conductors of these two cables are connected together at the ends remote from the

coaxial con nectors

53 and 56. The outer conductors are left unconnected or open at the ends remote from the

coaxial connectors

53 and 56 providing a break 84- in the outer conductor of the charging line at its midpoint. A suflicient number of turns of either coaxial cable 52 or coaxial cable 54- or a combination of the two is wound on the core 58 of transformer 59 to provide the required voltage to heater element 26 as described for the first embodiment. All other elements of the circuit are substantially the same as for the previously described positive pulse generating circuit.

In operation the negative pulse generating circuit is turned on by connecting a source of electrical power 62, for instance 115 volts, 60 cycles, to the primary coil 61 of transformer 59. This generates voltage in the inner conductors of

cables

52 and 54 to provide the current necessary for the heater 26 as heretofore described. 'As discussed, the same heater voltage is developed in the outer conductors of

cables

52 and 54 but since the outer conductors are not connected together the heater voltage appears across the break 84 in the outer conductor circuit but no current flows in this circuit as a result of this voltage. A high negative voltage is applied through resistor 27 to cathode 24 and to the

coaxial cables

52 and 54 thus charging this line negatively. During this period the tube 21 is in a non-conducting condition.

After the cathode is. heated and the charging line completely charged a firing signal, for instance a positive voltage pulse, may be introduced to the control grid 23 of tube 21 through capacitor 46 and resistor 44 causing the tube to become conductive and discharging the charging line circuit through the tube, and thence through the coaxial cable 77 and the load 78 and through the parallel circuit formed by coaxial cable 81 and load balancing impedance 83. Since the charging line and cathode 24 are at a high negative voltage and the anode 22 is at ground potential during cut off of tube 21, the firing of the tube sharply reduces the internal resistance thus suddenly lowering the voltage of the anode 22 and producing the negative pulse in the load circuit and in the parallel load matching circuit. The pulse of current discharging the

coaxial cables

52 and 54 is capacitative in nature between inner and outer conductors and therefore the pulse current in the inner conductor of each of these cables will be equal to and opposite in direction to the pulse current in the outer conductor. The voltage wave of the discharge pulse travels along the two

cables

52 and 54 and reaches the common point of juncture simultaneously thus balancing out and causing no current to flow around the loop. Therefore currents will balance in both directions whereby pulse shapes will be preserved and pulse currents will be kept out of the power supply unit.

In the negative pulse switching circuit as in the first embodiment of the invention it is possible to eliminate the load matching impedance by a proper balance of impedances. In such an arrangement the impedance of a single coaxial cable terminated in a load may be designed to equal the impedance of the parallel combination consisting of coaxial cables 77 and 81 connected to the load 78 and load balancing impedance 83 respectively. The

5 single cable with load may then be substituted for the parallel combination.

Although the present invention has been disclosed with respect to a limited number of exemplary embodiments, it will be evident to those skilled in the art that many variations are possible within the spirit and scope of the invention. Therefore it is not intended to limit the invention except as defined by the following claims.

What is claimed is:

1. In a pulse circuit of the class utilizing an electron tube with a filament therein, a filament heater circuit for said tube comprising, in combination, a transformer having a core with a primary winding thereon, means for connecting said primary winding to a source of electric power; and a coaxial cable having an inner and an outer conductor, a portion of said cable being turned around said core of said transformer to form a secondary winding thereon, said outer conductor of said cable being discontinuous at a central portion thereof and said inner connector of said cable being continuous and. being connected to said filament to supply heater current thereto.

2. In a pulse circuit of the class employing an electron tube having a filament therein, a filament heater circuit for said tube comprising, in combination, a transformer having a core with a primary winding thereon, means for connecting said primary winding to a source of electric power, and a coaxial cable having an inner and an outer conductor, a portion of said cable being wound on said core to form a secondary winding thereon, said cable having a break in the outer conductor at the midpoint of the length thereof, the inner conductor of said cable being continuous and connected at the ends thereof to said filament, to supply heater current thereto.

3. In a pulse circuit of the class employing an electron tube provided with a filament, a filament heater circuit for said tube comprising, in combination, a transformer having a core and a primary winding thereon, means for energizing said primary winding, a coaxial cable having an inner and an outer conductor, a portion of said cable being turned around said core of said transformer to form a secondary winding thereon, said outer conductor of said cable being electrically discontinuous at an intermediate point thereof and said inner conductor of said cable being continuous throughout and having ends connected to said filament to supply heater current thereto, and a capacitor connected across said ends of said inner conductor.

4. In a pulse circuit of the class having an electron tube with a cathode and cathode heater therein, a cathode heater circuit for said tube comprising, in combination, a transformer having a core with a primary winding thereon, means for connecting said primary winding to a source of alternating current, and a coaxial cable having an inner and an outer conductor, a portion of said cable being wound around said core of said transformer to form a secondary winding thereon, said outer conductor of said cable having a gap at the midpoint thereof and said inner conductor of said cable being continuous and being connected to said cathode and connected in series with said cathode heater to supply heater current thereto.

5. In a pulse circuit of the class having an electron tube with a filament therein, a filament heater circuit for said tube comprising, in combination, a transformer having a core with a primary winding thereon, means for connecting said primary winding to a source of electric power, a coaxial cable having an inner and an outer condoctor, a portion of said cable being wound around said core of said transformer to form a secondary winding thereon, said outer conductor of said cable being electrically discontinuous at a central point thereof to separate said outer conductor into a first and second component of substantially equal lengths and said inner conductor of said cable being electrically continuous and being connected to said filament to supply heater current thereto, and means for connecting a load across said inner conductor of said cable and said first component of said outer conductor thereof, saidconnection being made at said central point of said cable.

6. A pulse circuit as described in claim 5 and comprising the further combination of impedance matching means connected between said inner conductor of said cable and said second component of said outer conductor of said cable, said connection to said impedance matching means being at said central point of said cable.

7. An electronic pulse circuit comprising, in combination, an electron tube with anode, control grid and filament therein, a charging line connected to said anode, means for providing firing signals to said control grid, a transformer having a core and having a primary winding thereon, means for connecting said primary winding to a source of electric power, a coaxial cable having a plurality of turns on said core to form a secondary thereon, the outer conductor of said cable being open at the midpoint of said cable and the inner conductor being continuous and connected at both ends to said filament to furnish heating current thereto, means for connecting a load between said outer and inner conductors of said cable at said midpoint thereof, and means for connecting a load balancing impedance between said outer and inner conductors.

8. An electronic pulse circuit comprising, in combination, an electron tube with control grid, anode and fila ment therein, said control grid being connected to a source of trigger pulses, a charging line connected to said anode, a transformer having a core with a primary winding thereon, means for connecting said primary winding to a source of electrical power, a coaxial cable having inner and outer conductors, said outer conductor having a break at the midpoint and said inner conductor being continuous and being connected at both ends to said filament, said cable having a plurality of turns wound on said core as a secondary winding thereon whereby heater current is provided for said filament, means for connecting a load to said cable at said break in said outer conductor said load being connectable from the inner conductor to the outer conductor of said cable at a first side of said break and means for connecting a load matching impedance between said inner conductor and said outer conductor of said cable at the second side of said break therein.

9. An electronic pulse switching circuit comprising, in combination, an electron tube with control grid, anode, cathode and heater therein, means for transmitting trig- ;ger pulses to said control grid, a first coaxial cable connected to said anode and constituting a charging line therefor, a high voltage source connected to said first coaxial cable and said anode, a capacitor connected across said heater, a transformer having a core with a primary winding thereon, a second coaxial cable having inner and outer conductors, said outer conductor having a gap at the midpoint dividing said outer conductor into electrically separate first and second segments and said inner conductor being continuous and series connected to said heater, a plurality of turns of said cable being wound on said core as a secondary winding whereby current is provided for said heater, a third coaxial cable connected with said second cable at said gap therein for coupling a load to said circuit, said third cable having an outer conductor connected with said first segment of said outer conductor of said second cable and having an inner conductor connected to said inner conductor of said second cable, and a fourth coaxial cable connected with said second cable at said gap therein for coupling a load balancing impedance to said circuit, said fourth cable having an outer conductor connected with said second segment of said outer conductor of said second cable and having an inner conductor connected to said inner conductor of said second cable.

10. An electronic pulse circuit comprising, in combination, an electron tube with control grid, anode and filament therein, means for connecting said control grid to a source of firing pulses, a charging line connected to said anode, a high voltage supply connected to said charging line and said anode, a transformer having a core and having a primary winding thereon, a coaxial cable having inner and outer conductors with said outer conductor having a gap at the midpoint to form first and second electrically separate segments of said outer conductor, said inner conductor being continuous through said gap and connected at both ends to said filament, a plurality of turns of said cable being wound on said core as a secondary winding thereon whereby heater current is provided for said filament, means for connecting a load to said coaxial cable at said gap in said outer conductor said connection being from said inner conductor to the first segment of said outer conductor and a capacitor connected across said gap in said outer conductor.

11. An electronic pulse circuit comprising, in combination, an electron tube with control grid, anode and filament therein, said control grid having means for connection to a source of trigger pulses, means for connecting a load to said anode, a high voltage source coupled to said cathode, a transformer having a core with a primary Winding thereon and a coaxial cable having inner and outer conductors, said inner conductor being continuous and having the two ends thereof connected to said filament and said outer conductor having a break at the midpoint and being grounded at both ends whereby each half of said coaxial cable acts as a charging line, a plurality of turns of said coaxial cable being wound on said core providing a secondary winding to supply heater current to said filament.

12. An electronic pulse switching circuit comprising, in combination, an electron tube with a control grid and an anode and a connected cathode and heater therein and having means for connecting said control grid to a source of trigger pulses, a voltage supply connected to said cathode, a load connected to said anode, a capacitor connected across said heater, a transformer having a core with a primary winding thereon and having means for connecting said winding to a source of alternating current, and a coaxial cable having inner and outer conductors, said outer conductor having a discontinuity at the midpoint whereby each half of said coaxial cable acts as a charging line, said inner conductor of said cable being continuous through said midpoint and being connected at both ends to said heater, a plurality of turns of 7 said coaxial cable being wound on said core as a secondary winding thereon whereby current is provided for said heater.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. IN A PULSE CIRCUIT OF THE CLASS UTILIZING AN ELECTRON TUBE WITH A FILAMENT THEREIN, A FILAMENT HEATER CIRCUIT FOR SAID TUBE COMPRISING, IN COMBINATION, A TRANSFORMER HAVING A CORE WITH A PRIMARY WINDING THEREON, MEANS FOR CONNECTING SAID PRIMARY WINDING TO A SOURCE OF ELECTRIC POWER; AND A COAXIAL CABLE HAVING AN INNER AND AN OUTER CONDUCTOR, A PORTION OF SAID CABLE BEING TURNED AROUND SAID CORE OF SAID TRANSFORMER TO FORM A SECONDARY WINDING THEREON, SAID OUTER CONDUCTOR OF SAID CABLE BEING DISCONTINUOUS AT A CENTRAL PORTION THEREOF AND SAID INNER CONNECTOR OF SAID CABLE BEING CONTINUOUS AND BEING CONNECTED TO SAID FILAMENT TO SUPPLY HEATER CURRENT THERETO.