US3395684A

US3395684A - Solid state ignition system

Info

Publication number: US3395684A
Application number: US539533A
Authority: US
Inventors: Floyd M Minks
Original assignee: Brunswick Corp
Current assignee: Brunswick Corp
Priority date: 1966-04-01
Filing date: 1966-04-01
Publication date: 1968-08-06
Anticipated expiration: 1985-08-06

Description

Aug. 6, 1968 F. M. MINKS SOLID STATE IG NITION SYSTEM 2 Sheets-Sheet 1 Filed April 1, 1966 INVENTOR F1070 Al film/Ks BY fiIu/rus /-$idrk lffdrlys .IIIIIIIIIZIIIZ IZZIZZJ 6, 1968 F. M. MINKS 3,395,684

SOLID STATE IGNITION SYSTEM Filed April 1, 1966 2 Sheets-Sheet 2 af 11 :5 55 4g) afqfvigr====== INVENTOR Fzova M AIM/K5 United States Patent 3,395,684 SOLID STATE IGNITION SYSTEM Floyd M. Minks, Campbellsport, Wis., assignor, by mesne assignments, to Brunswick Corporation, Chicago, 11]., a corporation of Delaware Filed Apr. 1, 1966, Ser. No. 539,533 22 Claims. (Cl. 123148) ABSTRACT OF THE DISCLOSURE The present disclosure relates to an ignition system mounted within a rectangular cast aluminum box having shallow ribbed side walls. The ignition system includes a blocking oscillator connected to the battery to charge a capacitor which is discharged to the spark plugs by firing of a controlled rectifier. The solid state components of the blocked oscillator and the controlled rectifier are securely attached in good heat exchange relationship in the interior bottom Wall of the box and potted with a combination of sand and a polyurethane potting material. A main power transistor of the blocking oscillator is bonded by an adhesive to a coined surface on the bottom wall with a thin plastic insulating sheet therebetween to provide maximum heat transfer characteristics without dam.- age to the insulating sheet. The ignition unit is located within the cowl and is mounted on an engine cowl assembly support which is resiliently mounted to the drive unit and substantially isolates the cowl assembly and ignition unit from the drive unit. The boxed unit is mounted in front of the carburetors such that air drawn into the several carburetors passes over the box. The potted construction and vibration isolation essentially prevents damage associated with the vibration characteristics of an outboard motor and permits application in the severe environmental conditions encountered in the outboard and the like.

This invention relates to a solid state ignition system for internal-combustion engines and particularly to the construction and mounting of the ignition system as a part of an outboard motor.

Ignition systems of a solid state variety have been suggested for internal-combustion engines in order to minimize some of the problems associated with conventional ignition systems, such as firing failures due to spark gap fouling. However, the use of solid state ignition presents problems of reliability and life. For example, solid state components are generally quite temperature sensitive and the components and the connections should preferably be protected from adverse environments and undue heating. Further, internal-combustion engines establish substantial vibrations which tend to disrupt or damage the circuit components and the connections.

The present invention is particularly directed to a solid state ignition system or unit and its mounting as a part of an internal-combustion engine and particularly an outboard motor unit which presents a severe vibrational environment. Generally, in accordance with the present invention, the ignition system is mounted within a metal box with the solid state components securely attached in good heat exchange relationship to the base of the box and potted or encapsulated in a suitable potting material. The ignition unit is mounted to an engine cowl assembly support which is resiliently mounted to the drive unit and substantially isolates the cowl assembly and ignition unit from the drive unit. This support is preferably a ribbed cast aluminum member having the box secured in heat exchange relation for maximum cooling of the unit. An important feature of the present invention is the location of the transistor unit particularly in a multicylinder as- 3,395,684 Patented Aug. 6, 1963 sembly adjacent the carburetion means such that air drawn into the several carburetors is generally passed over or adjacent -to the solid state ignition system. As a result, the solid state components which are temperature sensitive are provided with maximum cooling with a resulting increase in the reliability and life of the unit. The direct mounting of the ignition unit to the vibrationally isolated cowling support also provides an improved heat sink to maintain optimum cooling and thereby prolonging the operating life of the ignition system. The potted construction and vibration isolation essentially prevents damage associated with the vibration characteristics of an outboard motor and permits application in the severe environmental conditions encountered in outboard motors and the like.

In accordance with the teaching of this invention, as applied to a highly practical construction particularly for outboard motors, the ignition unit includes a metallic open-ended mounted box or housing having a plurality of locating recesses in the base for the several components. The outer edge or edges of the housing are notched and terminal units are press-fitted or otherwise secured within the appropriate notch. The solid state components connected to ground are secured with the appro priate recesses and the non-grounded components are mounted on suitable insulating members, with the components secured in 'place with a suitable ad hesive. A main power transistor, Where employed is specially mounted on a coined or similarly finished surface with a thin plastic insulating sheet therebetween to provide maximum heat transfer characteristics without damage to the insulating sheet. Transformers, capacitors and the like may also be disposed within appropriate recesses and secured in place by a suitable plastic adhesive or the like. After the several components are properly located and connected in the circuit, the housing is substantially filled with coarse sand or the like and then filled with a suitable potting compound to completely enclose the components in a manner which makes the unit highly suitable for outboard motors.

The drawings furnished herewith illustrate a preferred construction of the present invention in which the above advantages and features are clearly disclosed as well as others which will be clear from the following description.

In the drawings:

FIG. 1 is a partial side elevational view of the upper end of an outboard motor with parts broken away and sectioned and with the engine proper shown in phantom to more clearly illustrate the novel mounting of the ignition system;

FIG. 2 is an elevational view of a potted ignition unit taken generally on line 2-2 of FIG. 1 with the potting and adhesive removed to show details of construction;

FIG. 3 is a reduced view of the ignition unit housing showing the base construction;

FIG. 4 is a cross-sectional view taken generally on broken line 4-4 of FIG. 2 with portions broken away to show inner details of construction;

FIG. 5 is a simplified schematic circuit diagram of a solid state ignition system shown in FIGS. 1-3;

FIG. 6 is an enlarged fragmentary view taken on line 66 of FIG. 2;

FIG. 7 is a further enlarged fragmentary view taken on line 7-7 of FIG. 6 and more clearly showing a resistor connection of FIG. 6;

FIG. 8 is another view of the connection shown in FIG. 7; and

FIG. 9 is a side elevational view of the transformer unit taken generally on line 9-9 of FIG. 1.

Referring to the drawings and particularly to FIG. 1, a partial view of an outboard motor for driving a watercraft is shown generally corresponding to that shown in the copending application of L. P. Post et al. entitled Outboard Motor Cowl Mounting which was filed on Aug. 3, 1965, with Ser. No. 476,817 and which is assigned to the same assignee as the present application. Generally, the motor includes an internal-combustion engine 1 sup ported upon a drive shaft housing 2, of which only the upper portion is shown, and coupled through a suitable drive mechanism to a rotatable propeller unit, not shown, carried by the lower end of the housing. The engine 1 is of any suitable construction and is shown as an in-line four-cylinder engine having spark plugs 3, one for each cylinder to the rear of the engine and a pair of vertically arranged and spaced carburetors 4 to the front of the engine. The engine 1 is enclosed within a decorative cowl assembly 5 supported on a frame assembly 6 which is attached to and vibrationally isolated from the engine 1 and the drive shaft housing 2, as more fully disclosed in the above-identified Post et al. application. In accordance with the present invention, a solid state ignition unit 7, such as schematically shown in FIG. 5, is mounted directly to and in good heat exchange relation with a front frame member 8 of assembly 6 which is located immediately adjacent the portion of the engine 1 including the carburetors 4, as more fully discussed hereinafter. Member 8 is formed of a suitable metal havinggood heat dissipating characteristics such as cast aluminum.

The input circuit of the ignition unit 7 is connected to a battery, not shown, through a suitable releasable coupling unit 9. For purposes of simplicity and clarity'of illustration, the physical arrangement of the wiring of unit 7 is not shown in FIG. 1. Such wiring will be obvious to those skilled in the art particularly in view of the schematic FIG. 5. The output of the ignition unit 7 is connected to the spark plugs 3 through a spark transformer unit 10 for firing of the spark plugs and operation of the engine.

Generally, in operation, power is supplied through the ignition unit 7 and the associated components such as the battery, shown in FIG. 5 and transformer 10 to sequentially fire the spark plugs 3 in proper order to thereby operate the engine. The operation of the engine 1 draws air in through the carburetors 4 in accordance with known functioning. In the present invention, such air passes over the adjacent cowl mounting frame member 8 and the attached solid state ignition unit 7 to provide optimum cooling thereof.

More particularly, in the illustrated embodiment of the invention, the cowl support frame assembly 6 corresponds to that shown in the above identified Post et al. application and generally includes the forward or front frame member 8, an intermediate or top frame member 11 and a rear frame member 12 interconnected to form a generally unitary inverted U-shaped unit. The frame assembly 6 fits over the engine 1 and is secured by a plurality of resilient mounts 13 to the upper end of the engine. Each of the mounts 13 includes a cylindrical block 14 of relatively soft rubber or the like interposed between attachment bolts 15 and 16 which are fixed or bonded thereto and project axially therefrom in opposite directions. The opposed bolts 15 and 16 are respectively bolted to the intermediate frame member 11 and suitable projections 17 on the engine 1 to provide a resilient support for the fra me assembly 6.

The cowl assembly 5 generally includes an upper inverted cup-shaped cowl member 18, a lower cup-shaped cowl member 19, and an intermediate wrap-around cowl member 20 mounted as disclosed in the previously identified application of Post et al. Briefly the upper cowl member 18 is supported on the frame assembly 6 by a plurality of spaced rubber mounts 21 secured to the frame assembly 6 with two of the mounts attached to the rear frame member 12 and one attached to the front member 8. The cowl member 18 includes supporting columns 22 resting on the respective mounts and secured in place by a suitable clamp means 23 extending forwardly from the rear frame mmeber 12 on opposite sides of the engine 1. The lower cowl member 19 is bolted or otherwise secured to the cowl support frame assembly 6 as by attachment bolts 24 which pass through suitable embossments on the lower end of the forward cowl support frame member 8 and thread into suitable openings provided in the upper end portion of the lower cowl member 19. The cup-shaped member 19 is also attached to the upper end of the drive shaft housing 6 with suitable resilient sealing strips 25 interposed between the cowl structure and the drive shaft housing 2.

The intermediate cowl member 20 wraps around the engine between the upper and lower cowl members and is secured in place by suitable toggle clamps 26 or the like.

Generally, the engine 1 is centrally located within the mounting frame assembly 6 with the spark plugs 3 located in alignment with the rear cowl mounting frame member. The carburetors 4 are located to the front portion of the engine 1 and generally in inwardly spaced .alignment from the front frame member 8.

In accordance with the illustrated embodiment of the invention as most clearly shown in FIGS. 24, the solid state ignition unit 7 includes an open front rectangular box or housing formed of a metal having good heat transfer characteristics such as cast aluminum or the like. The housing is formed with base 27 from which relatively shallow side walls 28 integrally project. Mounting flanges 29 extend outwardly from opposite sides of the housing integrally with the base 27 and have suitable mounting openings through which mounting bolts 30 pass and thread into appropriately tapped openings in aligned portions of the forward cowl support frame member 8.

Referring particularly to FIG. 2, the cowl frame member 8 is generally a ribbed structure having a number of coplanar fiat surfaces 31 to which the housing is secured with the exterior face of base 27 in firm contact with the fiat surfaces to maintain good thermal conductivity between the base of the housing and the adjacent frame.

The ignition housing thus opens inwardly toward the engine 1 and has the ignition unit components other than the spark transformer 10 potted therein.

Although the ignition system as such may take any desired form, a simplified schematic circuit diagram of a highly satisfactory capacitor discharge ignition system corresponding to that of applicants copending application en titled Triggered Ignition System, filed on October 4, 1965, with Serial No. 492,571, and assigned to the same assignee as this application, is shown in FIG. 5 for purposes of illustration and clearly describing the manner of mounting the temperature sensitive solid state components and the other related components within the housing within the present invention. Reference may be made to this application for a more detailed description of the circuit.

Generally, the illustrated circuit is a capacitor discharge system having a capacitor 32 connected through a triggered blocking oscillator 33 to be charged from the battery 34. The oscillator 33 includes a charging transistor 35 connected in a charging circuit with a transformer 36 and a control transistor 37 in the base circuit of the transistor 35. A current control resistor 38 and a discharge control pulse transformer 39 are also connected in the base circuit of transistor 35. A silicon controlled rectifier 40 is connected in the base circuit of transistor 37 to periodically trigger the blocking oscillator into conduction and a magnetic unit 41 is connected to terminate a cycle of the blocking oscillator.

A triggering circuit 42 for rectifier 40 includes the contacts or points 43 connected to the battery 34 through a pulse transformer 44, the output of which is connected to the gate circuit of rectifier 40. The oscillator 33 and trigger circuit 42 includes appropriate bias and protective resistors and the like which are not of particular significance to an understanding of this invention and are not therefore further described.

The capacitor 32 is provided with a predetermined charge during each cycle of the blocking oscillator 33 through appropriate steering diodes 45 and a stabister or double diode unit 46.

The capacitor 32 is connected in a discharge circuit with the transformer unit by a high powered silicon controlled rectifier 47 for discharging of the energy to the spark plugs 3 through a suitable distributor 48. The controlled rectifier 47 is triggered from the pulse transformer 39 during the initiation of a blocking oscillator cycle. A protective Zener diode 49 is connected across the rectifier 47.

The several components shown and briefly described in FIG. 5 are similarly identified in FIGS. 2-4 and 68 to clearly illustrate a physical construction providing a highly practical unit for outboard motors and the like.

The charging transistor 35 which should be provided with maximum cooling is specially mounted, as most clearly shown in FIG. 6, in the lower right corner of the ignition housing.

The illustrated transistor 35 is a germanium type and includes the usual enclosure with an enlarged mounting member and cooling base 51 which is secured to the housing base 27 by a suitable adhesive 52 with a wafer 53 of insulating material disposed therebetween. The transistor 35 is mounted over a slot 54 in the base. The slot 54 is lined with a suitable insulator 55 with the transistor leads 56 projecting into the slot and connected to an appropriate resistor 57 within the slot. As shown in FIGS. 68, the resistor leads 58 project from opposite ends of the resistor 57 and are wrapped about the transistor leads 56, soldered thereto and then brought out through the slot to the opposite sides of the transistor.

In order to produce excellent heat transfer characteristics and prevent possible damage to the insulating material, the surface 59 on which transistor 35 is mounted is provided with a smooth surface, in accordance with this invention. A highly satisfactory method of manufacture and assembly includes coining of the interior mounting surface as by pressing a tool onto the surface 59 under high pressure. The surface is covered with the adhesive 52 and transistor 35 and wafer 53 in the form of a thin film-like insulating sheet which may be of the order of .001 inch thick are mounted on the coined surface 59 and clamped thereon with an epoxy to both sides of the insulating sheet and then heated to securely bond the transistor in place. A highly satisfactory material is a polyimide material sold by E. I. du Pont de Nemours and Company under the trademark Kapton. This material bonds well to an epoxy adhesive and is a good insulator even at high temperatures.

As most clearly shown in FIG. 3, the base 27 of the housing is provided with a plurality of recesses for receiving several of the components, as follows.

The stabister 46 is a small cylindrical member disposed in a recess 60 in base 27 along the right side wall 28 of the housing, as viewed in FIGS. 2-4. The silicon controlled rectifier 47 and the Zener diode 49 are similarly secured within suitable cylindrical recesses in the upper left corner as viewed in FIG. 2 adjacent the main capacitor 45. In assembly, the recesses or components are covered with an epoxy resin which serves as a lubricant to assist in assembly. Although the adhesive is not a good thermal conductor, it is a very thin film which has been found to operate in a highly satisfactory manner.

The capacitor 32, the thermally enclosed resistor 38, the transformer 36 and magnetic unit 41 are similarly secured within partial recesses 62-65, respectively, to properly locate the elements which are held securely by a suitable adhesive 66 such as a thin film of epoxy resin. In assembly, the adthesive 66 is placed in the recesses and the components inserted therein. Further, resistors 67 are secured by a similar epoxy or the like to the top of the transformer 36. The resistor 38 is constructed as a thermally insulated unit having an outer shell 68 with a mass of thermal insulation 69 within which a resistance element 65 is embedded, preferably in accordance with the teaching of applieants copending application entitled Resistor Unit filed on the same data as this application.

The small pulse transformer 39 is also secured to the base 27 by a suitable adhesive 70, such as an epoxy. The transistor 37 and control rectifier 40 are similarly secured by an epoxy or the like to the base with a ceramic wafer 71 similarly secured therebetween.

The one side of wall 28 of the housing is provided with four edge notches or slots 72 and the opposite wall is provided with a similar notch within which similar connecting terminal units 73 are mounted. Each of the terminal units 73 generally includes a small plastic insert 74 having opposed edge slots which mate with the edges of slots 72. A terminal pin 75 projects through the insert and is threaded on the exterior end for making external circuit connections. A terminal tab 76 is secured to the inner end of each pin 75 for making the internal connections to the potted components. Tap 76 projects from a body 77 clamped to insert 74 by the head 78 of pin 75 and includes a locating lip 79 projecting upwardly over a recessed wall of the insert.

The insert 74 with the terminal pin and tab secured thereto is press fitted into the appropriate edge slot 72 with the upper edge fiush or just beneath the outermost edge of the side walls. The edges of the slots 72 may be lubricated with an epoxy resin before insertion for ease of assembly.

After all of the components are assembled within the housing and the connections to the tabs 76 completed, the housing is essentially filled with coarse sand 80 and then filled with a suitable potting compound 81 such as an uncured polyurethane to completely encapsulate the components and to support the components and the internal connections and wiring within the housing, as most clearly shown in FIG. 4. The coarse sand 80 or other suitable filler reduces the thermal expansion as well as the cost and also improves the heat transfer characteristics.

This construction has been found to provide a particularly rugged and reliable unit for use with outboard motors.

Although any suitable transformer unit 10 can be employed, that illustrated is preferably constructed with a doughnut-shaped plastic body 82 within which the primary and secondary windings are embedded, preferably in accordance with the teachings of applicants copending application entitled Transformer Structure and Method of Making the Same filed on March 11, 1966 with Serial No. 533,542 and assigned to the same assignee as this application. Primary leads 83 connect unit 10 to the ignition unit 7 and a secondary lead 84 connects unit 10 to the distributor. The body 82 is preformed and a pair of E- shaped cores 85 are assembled with the central legs passing through the coil opening. The assemble-d body 82 and cores 85 are clamped together and mounted upon the lower cowl member 19 by a bracket unit, as follows.

The bracket unit includes an L-shaped member 86 which is bolted to the lower cowl member 19 and defines a horizontal mounting ledge. A clamp plate 87 is secured to the horizontal ledge and projects upwardly therefrom with a centrally struck-out U-shaped portion 88. A second clamp plate 89 is secured to the side wall of the leg portion of the member 86 and projects upwardly therefrom and includes a corresponding U-shaped struckout portion 90 aligned with portion 88. The

clamp plates

87 and 89 are generally spaced in accordance with the thickness of the transformer body with the struck-out portion defining a spaced enclosure of a somewhat greater length than the width of the assembled E-shaped cores 85.

A plurality of bolts 91 pass through aligned openings in the

clamp plates

87 and 89 and suitable corner recesses 92 formed in the potted exterior portion of the body to firmly support the unit 10 on the lower cowl assembly. Rubber pads 93 are inserted between the cores 85 and the central struck-out portions to securely and firmly mount the induction coil assembly within the clamp plates.

The ignition system construction and mounting of the present invention provides a highly satisfactory and practical mounting for a solid state ignition system providing a high degree of cooling for the ignition unit and isolation of the unit from the vibration of the engine proper.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. An ignition unit for an internal combustion engine, wherein the ignition circuit includes a solid state amplifying means having an input means for connection to a power supply and an output means connected to engine firing means by a solid state switching means, the improvement comprising,

a plurality of temperature sensitive solid state components forming a part of said amplifying means and switching means of the ignition circuit,

a metallic mounting member,

attachment means securing said solid state components to the mounting member and in good heat exchange relationship therewith,

connection means connecting the components in the ignition circuit, and

a potting material enclosing said components and connection means of the ignition circuit to seal the components and connection means and to physically support the connection means.

2. The ignition unit of claim 1 wherein said mounting member is a box-like member having a bottom wall and an open top, said attachment means is an adhesive securing said solid state components to the bottom wall of the box-like member, and the potting material fills the boxlike member to cover said components and connection means of the circuit.

3. The ignition unit of claim 2 wherein the potting material is a polyurethane.

4. The ignition unit of claim 2 wherein said box-like member is formed of an aluminum and includes a relatively heavy bottom wall, said bottom wall being provided With a plurality of depressions for receiving selected components of the ignition circuit and adhesive means bonding said components within said recesses.

5. T he ignition unit of claim 1 wherein the ignition circuit includes a power transistor having a planar mounting member, said bottom wall is provided with a finished flat surface, an insulating member overlying said flat surface, and adhesive means to secure the insulating member to the fiat surface and the mounting member in firm engagement with the insulating member.

6. The ignition unit of claim 5 wherein the transistor includes leads projecting from the mounting member and the bottom wall is provided with a recess to receive said leads and having connecting leads projecting through the recesses and outwardly of the recess past the transistor.

7. The ignition unit of claim 6 wherein said ignition system includes components connected to said leads and disposed within said recess.

8. The ignition unit of claim 5 wherein the surface is coined.

9. The ignition unit of claim 5 wherein the insulating member is a film-like sheet of a high temperature polyimide.

10. The ignition unit of claim 1 wherein said potting material is a mixture of a plastic resin and a coarse sand.

11. The ignition system of claim 1 wherein the ignition unit includes a resistor unit including a resistor embedded within a thermal mass, and an adhesive secured the resistor unit to the bottom wall.

12. The ignition unit of claim 2 wherein said box-like member includes a side wall having a plurality of edge notches, and including a plurality of terminal units one for each notch, each terminal unit including a plastic body having a terminal member projecting therethrough, said body being press fitted within a notch and having said potting material bonded thereto to securely lock the terminal unit in the notch.

13. In a marine motor for propelling a watercraft and having an internal combustion engine with carburetors and having an outer protective housing, the improvement comprising a solid state ignition unit including a solid state amplifying means having an input means for connection to a power supply and an output means connected to engine firing means by a solid state switching means, and

means to secure the ignition unit within said housing immediately adjacent the carburetors and in the path of the air passing into the carburetor.

14. The marine motor unit of claim 13 wherein the ignition unit includes a metallic mounting means with temperature sensitive components secured in heat exchange relation thereto.

15. In an outboard motor having an engine mounted on a lower support unit and mounted within an outer protective housing,

a cowl frame mounted in vibration isolation to the engine, said engine having a carburetor means adjacent the cowl frame, and

a solid state ignition unit having a solid state amplifying means having an input means for connection to a power supply and an output means connected to engine firing means by a solid state switching means and mounted to the cowl adjacent the carburetor means.

16. In the outboard motor of claim 15 wherein said ignition unit includes a generally shallow rectangular box open at one end with the components of the ignition unit disposed within the box and the temperature sensitive components secured to the base of the box and a potting material filling said box to encapsulate the ignition circuit.

17. The outboard motor of claim 16 wherein the frame member is a vertical member having a plurality of ribs with flattened surfaces to define a mounting surface for the mounting member, and means to secure the mounting member in firm contact with the flattened surfaces.

1 8. The outboard motor of claim 16 wherein a plurality of carburetors are mounted in spaced aligned relationship, said frame member is disposed in spaced alignment with the carburetor inlets and said ignition unit is secured to the inner surface of the frame member generally centrally between the carburetors.

19. The ignition unit of claim 9 having pulse transformer including a winding unit mounted on a core, said core projecting laterally of the winding and a pair of mounting plate members including offset portions accommodating the projecting portions of the core, resilient members disposed between the core and the offset portions, means interconnecting the plate members together to clamp the transformer therebetween, and means on at least one of the plate members for mounting.

20. The method of forming a semiconductor ignition system, having a solid state amplifying means having an input means for connection to a power supply and an output means connected to engine firing means by a solid state switching means, and including a box-like housing open at the top and having the components and internal connections Within the housing comprising the steps of securing selected components to the bottom of the housing by covering at least portions of the housing bottom with a liquid adhesive, inserting all of said selected components into the adhesive to secure the components to the bottom of the housing, connecting the components to complete a circuit, filling the housing with a filler material comprised of solid particles, and filling the housing with a potting material.

21. The method of forming a semiconductor ignition system including a support and having the components mounted on the support comprising the steps of covering at least a portion of the support with a liquid adhesive, inserting selected components into the adhesive to secure the components to the support.

22. The method of claim 21 including making all internal connections to complete the pulse forming circuit, and covering the support and circuit With a potting material to completely encapsulate the circuit.

References Cited UNITED STATES PATENTS 1,424,705 8/1922 Abell 123-195 10 Kiekhaefer 123198 Rose 11518 Hetzler et a1. 317101 XR Adams 317'101 XR Watkins 11518 Kaehni 123-148 Byles 317101 XR Kahn 31710'1 Ransom et al 317-101 Judson 123-448 Stibbe et a1 11518 LAURENCE M. GOODRIDGE, Primary Examiner.