US2163237A - Electrical condenser - Google Patents

Description

June 20, 1939. I J. FLANZER 2,163,237

ELECTRIC-AL CONDENSER Filed Aug. 13, 1956 7 l x I g 60 INVENTOR Q b JOSEPH A. FLANZEI? BY L84 W ATTORNEYS Patented June 20, 1939 ELECTRICAL CONDENSER Joseph A. Flanaer, Laurelton, Long Island, N. Y., assignor to Electro-Motive Manufacturing 00., Inc., New York, N. Y., a. corporation of New York Application August 13, 1936, Serial No. 95,751

9 Glaims. (Cl. 175-415) This invention relates to electrical condensers, and more particularly to small fixed-adjustable padder condensers commonly employed in radio receivers.

There are many uses for small fixed-adjustable condensers, an important one being for use as a padder condenser in radio receivers of the superheterodyne type. Such a condenser is connected in series with the oscillator of the super- ,heterodyne to help obtain the desired frequency difference between the oscillator circuit and the input circuit of the receiver in order to produce a desired intermediate frequency. These condensers have ordinarily been made with an insulation base or case against which the bottom plate of a group of bent condenser plates would rest, the capacitance being adjusted by a screw operating to compress the plates together to desired amount. Considerable diificulty has arisen by reason of undesired changes in capacitance of the condenser after it has been set to desired value. I have found that shrinkage or warping or deformation of the insulation, due to ageing or insuificient curing or the effects of high relative humidity, or any of numerous other factors which lead to slight change in dimension or shape, results in a change of capacitance which, in a superheterodyne receiver for' example, may throw theintermediate frequency entirely out of range and so make the receiver nearly or wholly inoperative;

With poorly cured synthetic resinous material, I have found that changes of the order of 30% may result at the elevated temperature which is found in the chassis of a radio set. This difficulty, caused by shrinkage or deformation-of the insulation, arises not only when using the synthetic resin or condensation product with a filler such as wood flour but even when using a much more expensive filler such as mica.

' The primary object of, the present invention is to overcome the foregoing difficulties, and to this end the insulation case is employed solelyto prevent relative rotation or lateral movement of the plates. The lowermost of the group of plates does not rest on the insulation case, but instead rests either directly or througha rigid metallic washer upon the end of an internally threaded bushingmwhich itself receives the adjusting screw. With this arrangement the adent of the molded insulation case. The wall of the metallic bushing passing through the case is made of suflicient thickness to take the load of the condenser adjusting screw, without depending upon support from the molded insulation. Shrinkage or warping or deformation of 5 the insulation therefore has no effect whatsoever on the critical spacing of the condenser plates and the capacitance of the condenser. In fact, with my improved construction the mechanical nature of the insulation material em- 10 ployed is rendered relatively unimportant, and while the material should be a reasonably good dielectric, it need not have extreme mechanical perfection. For example, a mixture of synthetic resin or condensation product with wood flour 15 may be employed with entire satisfaction.

Other objects of my invention center about the shaping and mounting of the plates, and are to so design the plates that all may be made exactly alike and may be completely formed in a 20 single die; to so support the plates in the case that variation or manufacturing tolerance in the manufacture of the case will not result in displacing the superposed plates from their desired-concentric relation; and to obtain a desired spacing 25 between the plates, with a minimum curvature of the individual plates. With these objects in view, the plates are supported by upper and lower tongues at diagonally opposite corners of the plates, these tongues being received in slots 30 cut through the side walls of the case. The plates are all alike and are curved or warped slightly during manufacture. Alternate plates are turned in opposite direction, this producing a desired spacing between the plates, with a minimum curvature of the individual plates. The manufacture thus stays well within the elastic limit of the material, and there is no danger of the material failing to spring back to curved position when the adjusting screw is tightened and then released. Variations in the location of the slots cut through the side walls of the case -may produce a slight oscillation of the J plates but does not displace the center holes from concentricity with one another and the bushing. vItis for this reason that the tongues are preferably located at diagonally Opposite corners.

Still another object of the invention is to avoid the necessity for forming the thin sheets of mica dielectric with locating lugs or the like. Because of the provision of walls on all sides of the case, the mica may be given a plain rectangular or, even more preferably, square outline and is accurately located in place by the side 55 walls of the case. Moreover, the edges of the mica sheets'are protected by the side walls of the case. A still further object of my invention is to provide a simplified construction including the use of rigid cupped washers for effectively compressing a stack of condenser plates and for elevating the same from the bottom of the insulation case, while minimizing the capacitance to ground when the condenser is not grounded. Still another object is to provide convenient soldering lugs which are riveted or eyeletted together to make possible convenient testing of the capacitance of the unit before actually soldering the same in a radio set.

To the accomplishment of the foregoing and other objects which will hereinafter appear, my invention consists. in the electrical condenser elements and their relation one to the other, as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing in which:

Fig. l is a section taken in'elevation through a padder condenser embodying features of my invention;

Fig. 2 is a section taken in the plane of the line 2-2 of Fig. 1;

Fig. 3 is a section looking in plan in the plane of the line 3-3 of Fig. 1;

Fig. 4 shows the insulation case in perspective;

Fig. 5 illustrates one of the metallic condenser plates;

Fig. 6 is a section showing a modification;

Fig. 7 schematically represents the plate arrangement of a modified condenser having anodd number of plates and one side of which is grounded; and

Fig. 8 schematically represents the plate arrangement of a condenser having an even number of plates and one side of which is grounded.

,1 Referring. to the drawing and more particularly toFigs. 1 through 5 thereof, the fixed-adjustable condenser there illustrated is a padder condenser for use in radio receivers of the superheterodyne type. It will be understood that such condensers are relatively tiny in dimension, the drawing being approximately three times full size. The condenser comprises an internally threaded metallic bushing l2 which receives the adjusting screw [4 of the condenser. The particular condenser here illustrated has an odd number of metallic plates and is of the ungrounded type, that is, the top and bottom plates are insulated I from bushing I2 and adjusting screw I4 by large thin mica washers l6. Additional sheets 18 of mica dielectric are disposed between the successive condenser plates. The first, third, and fifth condenser plates are numbered 20, while the second and fourth condenser plates, which form the other side of the condenser, are numbered 22. These condenser plates are warped somewhat in order to initially space the same apart, the

capacitance of the condenser being increased by tightening adjusting screw I4 which operates to compress and flatten the condenser platesinto" close engagement with one another.

The condenser plates are located by a molded insulation case C having an end wall 24 mounted on one end of bushing l2 and having side walls 26 on all four sides. In accordance with the present invention, the'stack of condenser plates does not rest upon or even bear against the bottom or end 24 of the case. Instead the assembly of condenser plates rests upon a rigid metallic washer 28 which in turn rests directly upon the outwardly flanged or riveted inner end 30 of bushing [2. Because of this arrangement of metal on metal, the load of the adjustment screw I4 is applied directly to bushing l2 and is wholly independent of the molded insulation case C. The wall 32 of bushing l2, which passes through the insulation case, is made heavy enough to itself take the force applied by adjustingscrew l4, and themolded material at the center of the case immediately surrounding the bushing does not assist in supporting the inner end of the bushing. Consequently, shrinkage or other change in dimension of the case in no way'afiects the adjustment of the condenser.

The bottom or end 24 of the case is preferably recessed, as is indicated at 34, to receive and partially embed the metallic thrust washer 28. However, it will be understood and should be evident from the drawing, that although the washer is partially embedded in the insulation, it protrudes far enough to hold the stack of condenser plates elevated above the bottom of the case. It will alsobe noted that the rigid metallic thrust washer 28 is cupped or dished somewhat, it being convex downwardly. This is 'of advantage in order to insure obtaining the effect of the perfectly flat washer when adjusting screw I4 is tightened, that is, the washer is made somewhat concave toward the condenser plates, in order to make certain that it is not somewhat convex toward the condenser plates. Moreover,

this arrangement is of advantage when, as is here the case, the condenser is insulated from ground, for the capacitance to ground is minimized by reason of the fact that the washer Zllcontacts with the mica washer It at only the peripheral edge of washer 28, instead of contacting over the entire flat surface of the washer.

A rigid metallic thrust Washer 36 is also employed at the top of the condenserybeneath the head of adjusting screw M. This washer may be similar to washer 28 and is preferably cupped or dished somewhat for similar reasons. This washer provides a large area of pressure which serves to fully flatten the condenser plates for maximum capacitance when the adjusting screw is tightened. It will be seen that the assembly of condenser plates is supported between metallic washers 28 and 36, and that the pressure between the metallic washers is determined directly by the engagement of adjusting screw I4 in bushing I2, for the screw head bears on washer 36, while condenser.

The condenser plates are all alike and may be formed in a single die. The configuration of the individual plates is best shown in Fig. 5 in which it will be seen that the plate comprises'a rectangular or preferably square area 40, with an oversized central hole 42. A locating tongue 44, stepped at 46, projects from one side of the condenser plate, while a locating tongue 48, stepped at 50, projects from the opposite side of the condenser plate. The tongue 48 is elongated and acts asa soldering lug. The plate is given a slight curvature during manufacture, and all of the plates may be shaped and curved alike.

The side walls 26 of case C are cut away to form locating slots 52, best shown in Fig. 4. The condenser plates are laid in case C, with the tongues 44 and 48 received in two of the-slots 52. Alternate plates are faced in opposite direction, the tongues 44 and '48 being receivedin the other two of the four slots. Thus, referring to Fig.3, the I into superposition, and similarly the soldering lugs of the even plates are brought into superposition. At the same time, the plates are spaced apart-by reason of the opposite curvature of the successive plates. It will be understood that the tongue 44 may, if desired, be located at the same side of the plate as soldering lug 48, but the present arrangement is considered preferable, among other things because any variation or tolerance in the location of slots 52 tends to merely oscillate the condenser plates about their center, rather than to displace or shift the same laterally away from concentricity.

The sheets l8 of mica dielectric need not be provided with locating tongues or projections, and this is of advantage because of the difficulty of working the mica and the increased expense when given a special shape. The sheets of mica are simply square and are accurately received within the side walls 28 of the case. The side walls thus accurately locate the mica sheets in proper position and protect the edges of the same against splitting and damage such as frequently result when these edges are exposed.

The top and bottom pieces of mica, numbered It, may be circular washers instead of square pieces, the circular form being standardized and even more inexpensive than the square form. These washers may be given a diameter equal to the internal dimension of the case, as is clearly shown in Fig. 3,. thus holding the washers in proper location. It will be noted that mica washers l6 are larger in diameter than metal washers 36, and that the square sheets of mica [8 between the plates are larger than the center or square portion of the metal plates. Similarly, the center holes in the mica are smaller than the holes in the metal plates.

It has heretofore been the practice to bend the soldering lugs upwardly toward the rear of the condenser, the lugs being left in superposed relation, but without securing the same together. This has proved inconvenient when testing the capacitance of the unit, and such tests are made not only by the condenser manufacturer but also .by the manufacturer of the radioreceiver in which the condenser is to be used. To obtain contact with all of the plates, it has been necessary to clamp the lugs together in a special fixture, for otherwise a correct reading cannot be obtained. In accordance with the present-invention, the soldering lugs are left flat, and round holes 54 punched therethrough thus come into true superposition. The lugs are riveted together, either by solid rivets or, more preferably, by eyelets 56 shown in Figs. 1 and 3. The lugs may also be soldered, but I flnd that the mechanical connection obtained by riveting the same together is adequate for good electrical connection. Where a solid rivet is used, a lead or pigtailmay be placed beneath the head of the rivet, whereas with eyelets, as shown in Fig. 3, it is contemplated that the leads to the condenser be slipped through the eyelet and soldered in place. with this riveted arrangement the capacitance may be tested by merely touching the terminals against a suitable contact'device, it being unnecessary to provide special clamps for the soldering lugs. At the same time, the soldering operation is made more convenient when the condenser is placed in a radio set or the like, for the lead wire may be plates has been insulated by the soldering flux,

or, for some other reason, has not been properly soldered to the main group of plates. The fault is not discovered until the radio receiver is finally tested, and even when the defective set has been found, it is exceedingly diflicult to locate the exact source of trouble. In some cases, contact with the lead is made but is poor, in which case the radio receiver may be operative but noisy, and this trouble is also a diflicult one to locate. None of these problems arises when, as is here the case, the soldering lugs are riveted together.

, It is not essential to employ a bottom washer 28 which is separate from the bushing of, the condenser. Thus, referring to Fig. 6, I show a bushing 60 the inner end of which is enlarged to .form a flange or plate 82 which replaces the bottom washer 28 heretofore described. In this case the bushing is applied to the end wall 64 of the insulation case by means of a nut 68 threaded on the outside. of the bushing. A second nut. corresponding to the nut 88 shown in Figs. 1 and 2, is, of course, employed to mount the condenser in place, The remaining details of the condenser need not be described and may be like those heretofore described. In the claims, in referring to a washer, I mean to include an integral flange, as in this Fig. 6, as well as a separate washer, as in Fig. i.

In the condenser of Fig. 1, both sides or both sets of plates are insulated fromground. In many cases this precaution is not necessary, and one side of the condenser may be grounded. In such case it is preferable to employ an odd number of plates, for then the top and bottom plates may bear directly against the top and bottom washers. This arrangement is schematically indicated in Fig. 7 in which it will be seen that the odd plates I necessitate the use of an even number of plates while dealing with'a condenser in which one set of plates may be grounded. The plate arrangement of such a condenser is schematically illustrated in Fig. 8, in which the odd. plates 88 are insulated from bottom washer 82 by means of a mica washer 84. The even plates 88 are grounded by direct contact to the top washer 88. The odd and even plates-are, of course, separated from one another by mica dielectric 88.

It is believed that the construction and operation, as well as the many advantages of my im- 8 proved fixed-adjustable condenser will be apparent from the foregoing detailed description. It will also be apparent that while I have shown and described my invention in preferred forms,

many changes and modifications may be made in terms are used in only a relative or instantaneous sense for the condenser is used in a high-irequency alternating current circuit.

I claim:

1. A small flxed adjustable condenser comprising a metallic bushing which is externally.

threaded to receive a nut for mounting the condenser in place, and which is internally threaded to receive an adjusting screw, an insulation member mounted around the bushing, a rigid metallic washer disposed at the inner end of the bushing,

a plurality of condenser plates over said washer,

said washer operating to keep said plates away from said member, said insulation member being provided with means to support the plates against relative lateral movement, thin sheets of mica diele tric disposed between said plates, said plates be ng so relatively bent as to normally space the same apart, and an adjusting screw passing through said plates and threadedly received in said bushing for compressing the plates together and thereby determining the capacitance.

of the condenser, the arrangement. being such that the adjustment is determined solely by metallic and mica parts and is independent of the insulation member. 7

2. A small fixed-adjustable condenser comprising a metallic bushing which is externally threaded to receive a nut for mounting the condenser in place, and which is internally threaded to receive an adjusting screw, a molded insulation case mountedaround the bushing, a rigid metallic washer disposed within said case at the inner end of the bushing, a plurality of condenser plates in said case over said washer, said washer supporting said plates above the subjacent. wall of the case, said case being open at the top but provided with side walls which supportthe plates against relative lateral movement, thin sheets of mica dielectric disposed between said plates, said plates being so relatively bent as to normally space the same apart, a rigid metallic washer above said plates, and an adjust-.

ing screw passing through isaid plates and threadedly received in saidbushing for compressing the plates together and thereby determining the capacitance of the condenser, the arrangement being such that the adjustment is 'determined solely 'bymetallic. and mica parts and is independent ofthe molded insulation case.

3. A small fixed-adjustable condenser comprising an internally threaded metallic bushing;

a molded insulation .case havingan end wall mounted on said bushing and having side walls,

said side walls being cut away to form locating slots, condenser plates and mica dielectric plates disposed-in said case and bearing against the inner end of said bushing and being supported thereby in such manner as not to bear against the end wall of the case, said condenser plates having tongues projecting therefrom and so dimensioned and located as to be received. in the aforesaid slots, said plates being bent during'manufacture and being thereby spaced apart, said mica dielectric plates having a simple rectangular configuration devoid of locating tongues and dimensioned to be received within and located by the side walls of the case, and an adjusting screw passing through said plates and bushing for compressing the plates to desired capacitance, the adjustment depending solely upon the relation of the metallic plates and mica dielectric and being independent of the molded insulation case.

4. Asmall fixed-adjustable condenser comprising an internally threaded metallic bushing, a

-molded insulation case having an end wall mounted on said bushing and having four sidewalls, 'said side walls being cut away to form four 10- eating slots, condenser plates and mica dielectric plates disposed in said case and bearing against the inner end of said bushing and being supported thereby in such manner as not to bear against the end wall of the case, said condenser plates being identical in construction and having tongues projecting therefrom said tongues being so dimensioned and located as to be received in the aforesaid slots, alternate plates being turned one way to be received in two of the slots, and the other plates being turned the other way to be received in the other two slots, said plates being similarly bent during manufacture and being thereby spaced apart when alternate plates are turned to opposite position as aforesaid, and an adjusting screw passing through said plates and bushing v for compressing the plates to desired capacitance, the adjustment depending solely upon the relation of the metallic plates and mica dielectric and being independent of the molded insulation case.

5. A small fixed-adjustable condenser comprising an internally threaded metallic bushing, a molded insulation case having an end wall mounted on said bushing and having four side walls, said side walls being cut away to form four locating slots near the corners of the case, condenser plates and mica dielectric plates disposed in said case and bearing against the inner end of said bushing and being supported thereby in such manner as not to bear against the end wall of the case, said condenser plates being identical in construction and having tongues projecting at diagonally opposite corners thereof, said tongues being so dimensioned and located as to be re-- ceived in the aforesaid slots, alternate plates being turned one way to bereceived in two diagonally opposite slots, andthe other plates being turned the other way to be received in the outer two diagonally opposite slots. Said plates being similarly bent during manufacture and being thereby spaced apart when alternate plates are turned to opposite position as aforesaid, said mica dielectric plates having a simple rectangular configuration devoid of locating tongues and dimensioned to be received within and located by the side walls of the case, and an adjusting screw passing through said plates and bushing for compressing the plates to desired capacitance, the adjustment depending solely upon the relation of the metallic plates and mica dielectric and being independent of the molded insulation case.

6. A small fixed-adjustable condenser comprising a metallic bushing which is internally threaded to receive an adjusting screw, an insulation member mounted around the bushing, a rigid metallic plate disposed at one end of the bushing, a condenser plate over said first plate, said first plate operating to keep said condenser plate away from said member, said insulation member being provided with means to support the plates against relative lateral movement, a thin sheet of mica dielectric disposed between said plates, said plates being so relatively bent as to normally space the same apart, and an adjusting screw passing through said plates and threadedly received in said bushing for compressing the plates together and thereby determining the capacitance of the condenser, the arrangement being such that the adjustment is determined solely by metallic and mica parts and is independent of the insulation member. i

7. A small fixed-adjustable condenser comprising a metallic bushing which is internally threaded to receive an adjusting screw, an insulation member mounted around the bushing, a rigid metallic plate disposed at one end of the busha thin sheet of mica dielectric disposed between said plates, and an adjusting screw passing through said plates and threadedly received in said bushing for compressing the plates together, the arrangement being such that the adjustment is independent of warping of the insulation member.

8. A small fixed-adjustable condenser comprising a metallic bushing which is internally threaded to receive an adjusting screw, an insulation member mounted around the bushing, a first condenser plate disposed at one end of the bushing, means at the end of the bushing operating to keep said condenser plate away from said insulation member, a second condenser plate over said first plate, said insulation member being provided with means to support the plates against relative lateral movement, a thin sheet of mica dielectric disposed between said condenser plates,

said plates being so relatively bent as to normally space the same apart, and an adjusting screw passing through said plates and threadedly received in said bushing for compressing the plates together and thereby determining the capacitance of the condenser, the arrangement being such that the adjustment is independent of warping of the insulation member.

9. A small fixed-adjustable condenser comprising a metallic bushing which isinternally threaded to receive an adjusting screw, an insulation member mounted around the bushing, a first condenser plate disposed at one end of the bushing, means at the end of the bushing operating to keep said condenser plate away from said insulation member, a second condenser plate over said first plate, said insulation member being provided with means to support the plates against relative lateral movement, a thin sheet of mica dielectric disposed between said condenser plates, said plates being so relatively bent as to normally space the same apart, and an adjusting screw passing through said plates and threadedly received in said bushing for compressing the plates together and thereby determining the capacitance of the condenser, said adjusting screw functiming to compress the plates together between the head of the screw and the end of the bushing, whereby the capacitance of the condenser is determined by compressing the plates between metal parts and without compression oi'the aforesaid insulation member,-so that the adjustment of the condenser is independent of shrinkage and cold flow of the insulation member.

JOSEPH A. FLANZER.

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