US2878356A

US2878356A - Hole mounted resistor

Info

Publication number: US2878356A
Application number: US547102A
Authority: US
Inventors: Risk George
Original assignee: Dale Products Inc
Current assignee: Dale Products Inc
Priority date: 1955-11-16
Filing date: 1955-11-16
Publication date: 1959-03-17
Anticipated expiration: 1976-03-17

Description

March 17, 1959 G. RlsK 2,878,356

HOLE MOUNTED RESISTOR Filed Nov. 16, 1955 2 Sheets-Sheet 1 INVENTOR.

GEORGE RIS K VN uw w, QN QQ N\ G. RISK HOLE MOUNTED RESISTOR March 17, 1959 2 Sheets-Sheet 2.

Filed NOV. 16, 1955 United States Patent O HOLE MOUNTED RESISTOR George Risk, Columbus, Nebr., assignor to Dale Products, Inc., Columbus, Nebr.

Application November 16, 1955, Serial No.547,102 6 Claims. (Cl. 201-67) y This invention relates to resistors for electronic circuits and more particularly it is an object of the inven tion to provide a resistor adapted to be mounted through a wall of the chassis of such a circuit, the resistor being of miniature size for the conservation of space.

It has heretofore been recognized as desirable to construct a resistor in a way adapted to be mounted through a hole in a wall of a chassis. However, it has been thought impossible to construct a resistor for such mounting and which would further be of miniature form to conserve space without sacrificing the power rating of the resistor. This has been because resistors have been constructed heretofore with their heating elements in the shape of small cylinders with terminal wires extending outwardly from each end.

In a wall-mounted resistor it is necessary for both terminals or leads to extend outwardly from only one end of the resistor. Obviously this would necessitate causing one of the leads to be doubled back along the outside of the resistor. In such a construction the lead would have to be insulated from the remainder of the resistor and would also have to be spaced from it a considerable distance in order to prevent dielectric breakdown of the insulation between the two leads.

An objective 'and concept of my invention is to make it possible for the resistor to be made of small size through attaching one of the leads to the inner side of its cap, rather than the outer side as is customary, and extending this lead down through the center of the hollow cylindrical resistor coil supporting member.

A particular object is to provide a resistor as described the housing of which is adapted to be drawn tightly against a wall of a chassis for contact therewith over a substantial and large area for the use of the wall to dissipate heat from the resistor, further making practical the use of a very miniature size of resistor without: sacrificing the power rating thereof.

Still another object is to provide an aperture in that end of the housing which is opposite the leads for permittng the escape of fluid insulating material therethrough during insertion of the resistor core, the fluid. insulating material then filling the space between the core and resistor housing as is common in the prior art.

' Still further objects of the invention are to provide a resistor as described constructed in a fashion for main-- taining the leads in positions sufficiently spaced apart asto prevent dielectric breakdown of insulation disposedV between the leads.

A further object is to provide an improvement upon the wall-mounted resistor described in my earlier copending patent application titled Wall Mounted Resistor filed March 21, 1955, Serial No. 495,726, this application being a continuation-in-part thereof.

Objects of this application invention which are addi-- tional to the application No. 495,726 are as follows:

vAn object of this invention is to provide a wall-mounted resistor having a housing provided with a greater mass for heat conduction and dissipation adjacent the hot spot 2,878,356 Patented Mar. 17, 1959 of the resistor, which is normally at the center of the coil.

A further object is to provide a wall mounted resistor as described having a greater mass opposite the hot spot at the center of the wire coil, the outer shape of the housing being such as to dispose one side of the portion of greater mass adjacent a threaded portion of the resistor whereby it engages and dissipates heat to a panel or wall through which the resistor is mounted.

It is therefore an object of this invention to provide a resistor, the resistance of which is relatively uneifected by changes in panel thickness or area. This is important in the simplifying of the determination of the rating of the resistor for calculation relating to its use in electronic circuits, also greatly insuring that a person does not accidentally use a resistor rated for one panel thickness in another situation where a panel is smaller or thinner, as would overload the resistor or shorten its life if it didnt have the construction of this invention.

A further object of this invention is to provide the housing of the resistor with at portions for receiving a wrench.

Still a further object of the invention is to provide a modification of the housing of my resistor in which ribs extend vertically up the sides of the resistor with the ribs spaced apart providing vertical grooves therebetween through which air can circulate, rising upwardly for Ventilating and cooling the resistor.

Other and further objects and advantages of the present invention will be apparent from the following detailed description, drawings and claims, the scope of the invention not being limited to the drawings themselves as the drawings are only for the purpose of illustrating a way in which the principles of this invention can be applied.

Other embodiments of the invention utilizing the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawings:

Figure 1 is a cross-sectional view taken diametrically through the hole-mounted resistor of this invention, a portion of a heat-conductive wall to which the resistor is attached also being shown in cross section in Figure l.

Figure 2 is an exploded view of the hole-mounted resistor of this invention.

Figure 3 is a side elevation of a modification of the resistor of Fig. 1 shown as mounted on a section of heatconductive wall.

Figure 4 is a top plan view of the resistor of the modiication of Fig. 3.

The hole-mounted resistor of this invention has an outer housing generally indicated at 10.

The housing 10 is formed of a suitable heat-conducting material and has a first end portion 12 preferably of an outer dimension relatively smaller than the remainder of the resistor housing 10. The smaller housing portion 12 is adapted to be disposed through an opening 16 in a wall 18. As the opening 16 is normally round, the portion 12 is preferably of cylindrical shape as seen from its outer side in Figure 2.

The outer surface of the smaller iirst housing portion 12 is threaded for the purpose of receiving a nut 20 thereon. The nut 20 is preferably formed of a suitable heat-conducting material.

The wall 18 shown in Figure l, represents a section of a wall forming a part of the chassis of an electronic device of any kind, such walls are ordinarily formed of metal and are therefore highly heat-conductive. For this reason the mounting of the resistor housing 10 on the wall 18 causes a dissipation of heat from the resistor housing 10 through the wall 13, which has advantages in maintaining the housing 10 cooler, whereby the resistor housing 10 can be made of a more advantageously miniav ture size than would be otherwise possible, for the same resistor power rating.

,A The resistor housing 1t) also has a second and larger end portion indicated at 24 which is disposed on the opposite side of the wall 18 from'the smaller housing portion 12.

The larger housing portion 24 has a central body section 26 which preferably is of a cylindrical shape. Around the body portion 26 are a plurality of outwardly extending circular, annular ribs 3). The ribs 3i) can be relatively thin in comparison with a larger rib 32. The larger rib 32 is disposed the wall 18 and adjoins the smaller housing portion 12. The larger rib 32 is preferably over three times Vas wide as the thinner and smaller ribs .30, whereby in effect the rib 32 is actually not a rib at all but forms a large mass of heat conductive material which is in a sense more a part of the main body portion 26 of the housing than it is a rib.

The mass of material 32 extends circumferentially around the resistor housing 10 and has the effect of delivering heat to the wall 18 much more readily than would be the case if the mass of material 32 were thin, as are the ribs 3i?, and as all of the ribs of the resistor housing were in applicants earlier co-pending patent application heretofore referred to.

The interior of the resistor housing l is hollow and opens 'at the terminal end of the portion 12 thereof. The cylindrical sidewall 42 of an outer and larger-diametered rst hollow portion 40 of the hollow-interior of the resistor housing is parallel to the substantially cylindrical outer surface of the smaller housing portion 12, and the housing 10 has a second inner hollow portion 46 disposed farther inwardly and having a preferably cylindrical sidewall 48. The sidewall 48 of the inner hollow portion 46 is of a lesser diameter than the wall 42, the difference in diameters being small but substantial. The inner hollow portion 46 is disposed substantially completely in the larger housing portion 24 of the resistor. An annular ledge 52 extends transversely between the wall 42 and the wall 48.

The inner and smaller-diametered hollow portion 46 of the housing 10 has an inner wall 49 which is disposed transversely tothe wall 43, the wall 49 forming an end portion of the resistor housing 10 whereby the hollow portion 46 is in eifect a recess, although an opening 55B extends through the end wall 49 of the resistor for a purpose later described.

The hollow interior of the resistor housing 1t) is for the purpose of receiving a coil of resistance wire 60, best seen in Figure 2, the coil being wound around the outer side of a resistor core 62, formed of an electrically in sulating material, such as the ceramic material, commonly used in the manufacture of resistors.

The core 62 preferably has a* cylindrical shape on its outer surface and has a hollow interior, being open at each of its ends. The core 62 is disposed inside the outer and larger portion 46 of the hollow interior of the housing 10 protruding outwardly therefrom to a small degree into the larger-diametered housing portion 10.

On the outer end of the resistor core 62, which is the left end thereof as seen in Figure l, a metal band 70 is provided, which extends circumferentially around the core 62 and fits tightly thereagainst.

The wire coil 60 has one end xed to the band 70 and the band 70 is formed of electrically conductive material.

The inner end of the coil 60 of resistance wire terminates a short distance from the inner end of the core 62 for the purpose of permitting a cap 74 to be placed over the inner end of the core 62, the cap 74 having a recess on that side'thereof which faces the core 62, the recess being of a cylindrical shape for receiving the resistor. The cap 74 has another portion extending transversely across the end ofthe core.

The inner end of the coil 60 is electrically connected to the cap 74 and the latter is formed of electrically conductive material.

The purpose of the electrically conductive cap member 74 is to permit the attachment of a first and longer lead member thereto in accordance with this invention. The lead member 90 is provided with an innermost portion 92 which latter extends through the hollow interior of the resistor core 62 and is disposed adjacent one side of the core 62 and is spaced only a short distance therefrom. The longer lead 92 has an end portion 94 which is disposed at a right angle to an inner portion 92 of the lead 9i) and which latter is electrically connected to the inner side of the cap member 74.

The inner portion 92 `of the lead member 90 extends outwardly to a point at the outer end of the core 62 and is there connected to a central or connecting portion 96 of the lead 9d, which latter is relatively short with re'- spect to the portion 92 and extends outwardly toward the side of the resistor and also outwardly toward the open end of the resistor housing at approximately a 45 degree angle with respect to the axis of -the cylindrical smaller resistor housing portion l2. l

The connecting or central portion 96 of the resistor is attached to an outer portion 98 of the lead 90, and the portion 98 extends parallel to the axis of the resistor and is disposed spaced a short distance from the side wall 42 of the outer hollow portion 40 of the resistor housing 10.

The outer portion 98 of the lead 90 is disposed approxi mately in alignment with and opposite the coil 60 and Yis odset to the side and farther from the axis of the resistor housing 10 than the inner portion 92 of the lead90.

The purpose of the metal band 70 is for the electrical connection thereto of a second andr shorter lead 110, which latter extends parallel to the axis of the resistor housing portion 12 and from the outer end thereof through the hollow portion 40 and up to a point adjacent the band 76.

The second lead is connected to the band 70 by a connecting member 112 which has a cylindrical portion lying parallel to and electrically connected to the band 70 and xed to the outer side of the band 70 with the connecting member 112 having another portion attached to the outer end of the cylindrical portion thereof, and extending inwardly toward the axis of the resistor, and a terminal portion of the connecting member 12 extends outwardly parallel to the axis of the resistor at approximately the same distance from the axis of the resistor as the outer side of the core 62.

The inner end of the second lead 110 is connected to the `outer terminal end of the connecting member 112, and the connecting member 112 is formed of electrically conductive material for electrically connecting the lead 110 to the band 70.

The second and shorter lead 110 is disposed spaced a short distance from the opposite side of the wall 42 of the smaller hollow portion 4t) from the lead 98 for a wide spacing between the leads 98 and 110 Vto avoid.

shortage of electrical current between the leads 98 and 110.

The

leaders

90 and 110 are maintained in separated positions by a header which is preferably formed of ceramic material and is necessarily formed of some electrically insulating material. The header 120 has a cylindrical outer wall for snugly tting into the cylindrical outer wall 42 of the hollow portion 40, and has two parallel openings therethrough, as seen at 122, which latter are parallel to the axis of the header 120, and are disposed adjacent the outer edges thereof for the purpose of receiving the respective leads 90 and 110 therethrough.

Inwardly of the header 120 a spacer member 130 is provided which latter is of a cylindrical shape on its outer' side and is provided with a hollowinterior having a wall also of cylindrical shape. The spacer member is relatively thin between its inner and outer walls, although it has a substantial width from side to side. The spacer member 130 has an inner end resting against the ledge 52 and its outer end is disposed against the inner side of the header 120.

The spacer member 130 is preferably about three times the width of the band 70, and is of a size for holding the header member 120 a substantial distance outwardly from the outer end of the core 62. The purpose of the spacer member 130 is to prevent the header 120 from being pushed too far inwardly during assembly, whereby a space is created between the header 120 and the core 62 for receiving the inclined connecting portion 96 of the lead 90. y

An insulating sleeve 150, which is preferably formed of fiberglass is disposedaround the outer side of the coil 60 and extends from the inner end of the cap 74 to the opposite end of the core 62, overlapping the outer side of the band 70 and connecting member 112.

The spacing of parts is such that the fiberglass sleeve 150 is disposed spaced apart from the side wall 48 of the inner hollow portion 46.

Also, the cap member 74 is maintained spaced apart from the inner end wall 49 of the resistor housing 10 by means of an electrically insulating washer 160 of annular shape, the washer 160 being disposed between the cap 74 and the inner wall 49. y

All open spaces of the interior of the resistor are preferably lled with a suitable electrically insulating material such as Silastic, which is a liquid when rst applied, then later gets solid and has a capacity to withstand heat, retaining its electrically insulating qualities even after long periods of use. The Silastic material can be seen at 170, and lls the space between the header 120 and the core 62, lls the interior of the core 62, and lls the space between the sleeve 150 and the spacer 130, and between the sleeve 150 and the side wall 48 of the inner hollow portion 46 of the resistor housing. Silastic material 170 also lls the interior of the washer 160 and fills the aperture 50.

In the manufacture of the resistor, the Silastic material is rst placed in the housing to fill the opening 50 and the interior of the washer 160. Then the washer 160 is put in place, and next the core 62 with the attached coil 60 and fiberglass sleeve 150, and with its attached leads 90 and 110 are put in place. Then the spacer 130 is put in place and the interior of the core 62 and the interior of the washer 130 are filled with Silastic material. Lastly, the header 120 is placed over the

leads

90 and 110.

The purpose of the opening 50 is to permit escape of a vapor which exudes from the Silastic material 170 during baking of the resistor. This is of advantage because if such vapor is trapped inside the resistor then pockets are formed which give the -"Silastic insulating portion of the resistor bad insulating qualities.

As distinguished from the applicants earlier co-pending application, the mass of housing material found at 32, which is so large as to be in eifect not a rib at all, is disposed almost opposite or approximately opposite the center of the coil 60. The center of the coil 60 is the hottest part of the resistor, and the part that needs the most cooling for the greatest efciency.

Therefore, it is my conception to have the greatest mass of resistor housing material, which latter is highly heat conductive, disposed almost directly opposite the hottest part of the resistor or between the hottest part or center of the coil 60 and the heat conductive wall 18 for conducting heat thereto. AThis has the eect of conducting heat away from the hot part of the reistor for delivery to the air and more particularly for eticient delivery to the wall 18 of the chassis of the electronic device in which the resistor is used.

The wall 18 conducts the heat away from the resistor providing a very efficient cooling surface and functioning for purposes of cooling, much like a giant resistor housing would.

As distinguished from the applicants original resistor of this type, as dened in his earlier co-pending application previously identied herein, the hollow interior of this resistor has two hollow portions 40 and 48, the outer portion 40 being of a larger diameter for providing more space for receiving the outwardly protruding connecting member 112 of the lead 110, thus spacing the connecting member 112 apart from the head conductive resistor housing 10 as provides the resistor with much better qualities for preventing di-electric breakdown and shortage of current between either the connecting member 112 or the lead 122 and adjacent portions of the housing 10 of the resistor.

Also, as distinguished from the earlier application, the spacer header is provided. The header 130 makes possible more rapid and accurate assembly.

Referring to Fig. 3 a modication of the resistor of Fig. l is there shown in which the internal construction is the same as the resistor of Fig. l but in which the ribs extend vertically and for that reason are given the numeral 30 rather than 30 as was that 30 was the number used for the ribs on the housing in Fig. l. All other parts bear the same numerals as they are a modification of Fig. l.

It will be seen that the ribs 30 are each of approximately an inverted U-shape as seen in side elevation with grooves also of inverted U-shape between each two ribs 30'. The terminal surfaces of both the ribs and the grooves are preferably rounded.

The side portions of the ribs 30 are disposed vertically so as to permit air to circulate upwardly in the side portions of the grooves 31 between the ribs 39 and in the direction of the arrows 33 shown on Fig. 3.

As thus described it will be seen that this specification provides a resistor adapted to fulfill the objects of this invention.

From the foregoing description, it is thought to be obvious that a hole-mounted resistor constructed in accordance with my invention is particularly well adapted for use, by reason of the convenience and facility with which it may be assembled and operated, and it will also be obvious that my invention is susceptible of some change and modication without departing from the principles and spirit thereof, and for this reason I do not wish to be understood as limiting myself to the precise arrangement and formation of the several parts herein shown in carrying out my invention in practice, except as claimed.

Iclaim:

l. A resistor for mounting in a hole in a wall of the chassis of an electronic circuit having: a housing, an end portion of the exterior of said housing being threaded and disposable through said hole, and means comprising a securing member engageable on said threads for connecting said housing to said wall, said resistor housing having a first end portion disposed opposite said threaded end portion and of a size for not passing through said opening and said larger sized end being disposed against one side of said wall at said opening at a time when said threaded end portion of said housing is disposed extending through said opening, said securing member ,being disposed upon said threaded portion and on an opposite side of said wall for tightly receiving said wall between said securing member and said larger sized housing portion for tight engagement with said Wall for the use of said Wall for the dissipation o-f heat from said resistor, said resistor having an interior coil, means insulating said interior coil from said housing, and leads extending outwardly of said threaded end of said housing and means connecting said leads to said coil.

2. A resistor for mounting in a hole in a wall of the chassis of an electronic circuit havingz. an outer housing having a portion adapted to be disposed through an opening in a wall o-f a chassis of an electrical circuit, said housing having a hollow interior open at one end, a hollow resistor core disposed in said interior, said core being open at two opposite ends thereof, a resistor coil disposed around said resistor core, a first lead extending through the hollow interior of said resistor core, a cap disposed extending over the inner end of said resistor core, said cap being electrically connected to the adjacent end of said resistor coil, a first lead attached to the inner side of said cap and extending through the hollow interior of said resistor core and outwardly through the other end of said resistor core and outwardly through the open end of said housing adjacent one side of said open end of said housing, means connecting the inner end of said first lead to the inner end of said coil, a second lead disposed extending through said open end of said housing adjacent the other side of said open end of said housing from said first lead and vextending into the hollow interior of said housing, means connecting the inner end of said second lead to the outer end of said coil, insulating means filling the interior of said housing in the space between said coil and the interior wall of said hollow housing, said insulating .means being of a type capable of holding its insulating properties operably during operation of the resistor.

3. A resistor for mounting in a hole in a wall of the the chassis of an electronic circuit having: an outer housing having a portion adapted to be disposed through an opening in a wall of a chassis of an electrical circuit, said housing having a hollow interior open at one end, a hollow resistor core disposed in said interior, said core being open at two opposite ends thereof, a resistor coil disposed around said resistor core, a rst lead extending through the hollow interior of said resistor core, a cap disposed extending o-ver the inner end of said resistor core, said cap being electrically connected to the adjacent end of said resistor coil, a first lead attached to the inner side of said cap and extending through the hollow interior of said resistor core and outwardly through the other end of said resistor core and outwardly through the open end of said housing adjacent one side of said open end of said housing, means connecting the inner end of said first lead to the inner end of said coil, a second lead disposed extending through said open end of said housing adjacent the other side of said open end of said housing from said first lead and extending into the hollow interior of said housing, means connecting the inner end of said second lead to the outer end of said coil, insulating means filling the interior of said housing in the space between said coil and the interior wall of said hollow housing, said insulating means being of a type capable of holding its insulating properties operably during operation of the resistor, the hollow interior `of said resistor housing having an outer portion disposed said first housing portion and opening at the terminal end of said first housing portion and also having an inner hollow interior portion disposed inwardly of said outer hollow interior portion and larger in cross-sectional area than said outer hollow interior portion of said housing, whereby a ledge exists connecting the walls of said inner and outer hollow interior portions, one end of said coil extending into said outer hollow interior portion, a spacer member of annular shape disposed in said outer hollow interior portion of said resistor and having one side resting against said ledge, and a header member having slots therethrough for receiving said leads therethrough respectively, said header being disposed on said leads and being disposed in said outer hollow interior portion, and said header being disposed against said spacer.

4. A resistor for mounting in a hole in a wall of the chassis of an electronic circuit having: an outer housing having a portion adaptedto be disposed through an opening in a Wall of a chassis of an electrical circuit, said housing having a hollow interior open at one end, a hollow resistor `core disposed in said interior, said core being open at two opposite ends thereof, a resistor coil disposed around said resistor core, a first lead extending through the hollow interior of said resistor core, said cap disposed extending over the inner end of said resistor core, said cap being electrically connected to the adjacent end of said resistor coil, a first lead attached to the inner side of said cap and extending through the hollow interior of said resistor core and outwardly through the other end of said housing adjacent one side of said open end of said housing, means connecting the inner end of said first lead to the inner end of said coil, a second lead disposed extending through said open end of said housing adjacent the other side of said open end of said housing from said first lead and extending into the hollow interior of said housing, means connecting the inner end of said second lead to the outer end of said coil, insulating means filling the interior of said housing in the space between said coil and the interior wall of said hollow housing, said insulating means being of a type capable of holding its insulating properties operably during the operation of the resistor, said insulating means comprising a material which is before curing .a liquid of low viscosity and which is of an electrically non-conductive nature during operation of the resistor, said material giving off a vapor during curing, said housing having an outlet opening through the end thereof opposite the said open end, said opening in said opposite end vbeing for the purpose of permitting escape of said vapor to prevent traping thereof inside the resistor.

5. A resistor for mounting in a hole in a wall of the chassis of an electronic circuit having: an outer housing having a portion adapted to be disposed through an opening in a wall of a chassis of an electrical circuit, said housing having a hollow interior open at one end, a hollow resistor core disposed in said interior, said core being open at two opposite ends thereof, a resistor coil disposed around said resistor core, a first lead extending through the hollow interior of said resistor core, said cap disposed extending over the inner end of said resistor core, said cap being electrically connected to the adjacent end of said resistor coil, a first lead attached to the inner side of said cap and extending through the hollow interior of said resistor core and outwardly through the other end of said Vresistor core and outwardly through the open end of said housing adjacent one side of said open end of said housing, means connecting the inner end of said first lead to the inner end of said coil, a second lead disposed extending through said open end of said housing adjacent the other side of said openend of said housing from said first Ylead and extending into the hollow interior of said housing, means connecting the inner end of said second lead to the outer end of said coil, insulating means lling the interior of said housing in the Ispace between said coil and the interior wall of said hollow housing, said insulating means being of a type capable of holding its insulating properties operably during operation of the resistor, and a header disposed plugging the open end of said housing, said header being of an electrically insulating nature and having two openings therethrough receiving said leads respectively.

6. A resistor lfor mounting in a hole in a wall of the chassis vof an electronic circuit having: an outer housing having a portion adapted to be disposed through an opening in a wall of a chassis of an electrical circuit, said housing having a hollow interior open at one end, a hollow resistor core disposed in said interior, said core being open attwo opposite ends thereof, a resistor coil disposed around said resistor core, a first lead extending asrsse through the hollow interior of said resistor core, said cap disposed extending over the inner end of said resistor core, said cap being electrically connected to the adjacent end of said resistor coil, a first lead attached to the inner side of said cap and extending through the hollow in terior of said resistor core and outwardly through the other end of said resistor core and outwardly through the open end of said housing adjacent one side of said open end of said housing, means connecting the inner end of said first lead to the inner end of said coil, a second lead disposed extending through said open end of said housing adjacent the other side of said open end of said housing from said rst lead and extending into the hollow interior of said housing, means connecting the inner end of said second lead to the outer end of said coil, insulating means tilling the interior of said housing in the space between said coil and the interior wall of said hollow housing, said insulating means being of a type capable of holding its insulating properties operably during operation of the resistor, the inner end portion of said first lead extending through said core closer to the respective side of said core than to the other side of said core, and said first lead having a central portion disposed adjacent the opposite end ot said core from said cap and connected to said inner end portion and extending outwardly toward the adjacent side of said resistor housing, and said iirst lead further having an outer end portion connected to said central portion and offset to the side of the resistor from the inner portion of said first lead, said outer end portion of said iirst lead extending outwardly through the open end of said resistor housing on that side of said resistor housing which is opposite said second lead.

References Cited in the le of this patent UNITED STATES PATENTS 1,708,961 Abbott Apr. 16, 1929 1,741,265 Warppler Dec. 31, 1929 1,922,150 Beresh Aug. 15, 1933 1,929,446 Ogg Oct. 10, 1933 2,310,325 Smith Feb. 9, 1943 FOREIGN PATENTS 958,021 France 1949