US2318070A - Electrical condenser - Google Patents

Description

May 4, 1943. J. A. FLANZER ETAL 2,318,070

ELECTRI CAL CGNDENSER Filed Nov. 8, 1940 e2 MMF INVENTORS JOSEPH A. FLANZER PHILIP BEIN Y 9 W M ATTORNEYS Patented May 4, 1943 UNlTED STATES PATENT OFFlCn ELECTRICAL CONDENSER Application November 8, 1945), Serial No. 364,856

10 Claims.

This invention relates to electrical condensers, and more particularly to trimmer condensers such as are employed for push-button tuning of radio receivers.

The primary object of the present invention is to generally improve trimmer condensers of the specified character.

For broadcast station selection, it has been customary to provide a gang of trimmer condensers which are used in conjunction with a suitable switching arrangement controlled by push-buttons. Each trimmer condenser is adjustable by means of a suitable adjusting screw, thereby determining the station selected by its associated push-button. However, the widest range of any single commercially available trimmer condenser has not been large enough to permit the selection of a station anywhere in the broadcast frequency band. Thus, smaller condensers have been used for stations at one end of the band, and larger condensers for stations at the other end of the band. In practice, the gang of trimmer condensers would ordinarily have a progressive number of condenser plates, including three, four and five-plate condensers. As a. result, it has been necessary for the owner of the radio receiver to tune the push-buttons in the order of progressive broadcast frequencies, and to select stations reasonably well spread over the broadcast frequency band.

One primary object of the present invention is to overcome the foregoing limitations. For low cost and convenience, it is desirable that this be done while using only a single capacitor unit requiring only a single mounting and a single set of connecting wires, and devoid of a switch or the like for adding or subtracting the extra capacitance. Our object, therefore, is to provide a single inexpensive trimmer condenser having so large a range of adjustment as to be useable for tuning throughout the broadcast frequency band. The condensers in a gang of condensers may then be all alike, and any button may be set for the selection of any station in the broadcast band.

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

Fig. 1 is a longitudinal section through a condenser embodying features of our invention;

Fig. 2 is a. top plan view thereof;

Fig. 3 is a bottom plan View thereof;

Fig. 4 is a schematic diagram showing the metal condenser plates alone;

Fig. 5 is a graph explanatory of the operation and advantage of the improved condenser; and

Fig. 6 illustrates the manner in which the con denser may be mounted in gang formation.

So far as We are aware, no previously available trimmer condenser can be used with a pushbutton switch arrangement so as to cover the entire broadcast band, by means of a single adjusting screw. For example, an analysis of the capacitance range of a Well-known line of trimmer condensers reveals that the two-plate condensers of this particular manufacturer has a maximum capacitance of 100 mmf., and a minimum capacitance of 4 mmf. The three-plate trimmer has a maximum capacitance of 230 mmf. and a minimum capacitance of 6 mmf. The four-plate condenser has a maximum capacitance of 350 mmf. and a minimum capacitance of 20 mmf. The five-plate condenser has a maximum capacitance of 500 mmf. and a minimum capacitance of 35 mmf. On computing the ratio of maximum to minimum capacitance for each of these condensers, we find that the ratio for the two-plate condenser is 25 to 1; the ratio for the three-plate condenser is 35 to l; the ratio for the four-plate condenser is about 17 to 1; and the ratio for the five-plate condenser is about 15 to 1. Thus the greatest ratio between maxi mum and minimum capacitance is obtained in the case of the three-plate condenser.

But, while the ratio of maximum to minimum capacitance is large, the actual maximum capacitance is relatively small. However, by connecting two of these three-plate condensers in parallel, the maximum capacitance may be doubled to 460 mmf., and by so arranging the two con-- densers as to be adjusted by means of a single screw, the range of variation extends from 13 to 460 mmf.

More generally, the underlying concept of the present invention is to employ a plurality, ordinarily two, trimmer condensers, which have a large ratio of maximum to minimum capacitance, while having only a relatively small maximum capacitance, and then by connecting the trimmers in parallel and embodying the same in a structure such that they may be simultaneously varied by a single adjusting means, the resulting trimmer will be characterized by relatively large maximum capacitance and a large ratio of maximum to minimum capacitance, thus providing the desired large range of capacitance variation.

In the specific case discussed above, the range of our improved trimmer condenser is from 13 to 460 mmf. It is true that this is not as large a range as has heretofore been provided. It has been customary for set manufacturers to use the three, four and five-plate trimmers, thus providing a capacitance range of from 6 /2 to 500 mmf. However, on investigation, we find that this has been done largely because the extra range was anyway inherently available in the commercial trimmers which were required for push-button tuning. The broadcast band has a frequency ratio of approximately 3 /2 to 1. The capacitance needed for this purpose varies as the square of the frequency, and therefore the capacitance ratio would have to be 12% to 1. Assuming that the rest of the circuit being tuned has distributed capacitance of 20 mmf., this figure added to, say, 15 mmf. as a working minimum for the trimmer condenser, would give a total minimum of 35 mmf. The maximum therefore would have to be about 430 mmf. Obviously, a trimmer having a working range of 15 to 430 mmf. should prove entirely satisfactory. This working range will be safely covered by the trimmer condenser disclosed herein with its range of 13 to 460 mmf., the maximum preferably being somewhat excessive because the capacitance values obtained near the fully tight position of the adjusting screw, are too critical in adjustment, and therefore not conveniently useable.

Referring now to the drawing, and more particularly to Figs. 1, 2 and 3, our improved trimmer condenser comprises a first trimmer condenser generally designated l2, and a second, generally designated l4, these being connected electrically in parallel by means of the tubular member l6 and screw 18, at one side of the condensers, and by means of a flexible, multiple-strand wire 20 at the other side of the condensers. One of the condensers is provided with an internally threaded bushing 22, and a single adjusting screw 24 passes through both condensers and bushing 22. As is usual with these condensers, the plates tend normally to open or spread apart, and tightening of screw 24 tends to close or bring the same together, thereby increasing th capacitance. It will be evident that the single screw functions to simultaneously increase or decrease the capacitance of both of the component trimmer condensers.

Considering the arrangement in greater detail, each of the condensers here employed is a threeplate condenser, and may be constructed partly along lines such as those set forth in Flanzer Patent No. 2,209,546, issued July 30, 1940, and entitled Condenser. Specifically, the condenser I2 comprises a suitable insulation base 26 which may be made of a molded ceramic. The bottom plate 28 is a fiat plate resting directly on the top surface of base 26, and is eyeletted thereto at one end of the base by means of the eyelet 31!. A mica film 32 is disposed above plate 28, and is also held in position by the eyelet 30. The intermediate plate 34 is a curved plate which is secured at the opposite end of base 26 by means of an eyelet 36. A mica film 38 is disposed above plate 34, and is also held in position by the eyelet 36. The top plate 49 is made of heavier gauge metal, and is bent upwardly at 42, downwardly at 44, and inwardly beneath the base of the condenser at 46, where it is secured to the base by the eyelet 30 previously referred to. The center part of the "plate is cut away at 42 and 44, thus leaving two spaced arms Which increase the yieldability of the movable plate 40. Some of the waste metal struck from between the spaced arms may be bent outwardly, as is indicated at 48, thus forming a means for both electrical and mechanical connection to the condenser l 4. A contact strip 50 may be bent outwardly above the support 48 to insure connection to the bottom plate 28 as well as the top plate 40. The actual wire connection may be made to a suitable soldering lug 52 projecting sidewardly from the condenser. 7

At the opposite side of the condenser the interme-diate plate 34 may be extended outwardly, as indicated at 54, to provide a soldering lug, and inasmuch as the metal of the intermediate plate is quite thin, this extension 54 is preferably backed by a support piece 56 made of thicker metal and secured in position by the eyelet 36 previously referred to.

The upper condenser I4 is somewhat similar to the lower condenser l2, but is preferably disposed in inverted position, that is, the condensers I2 and I4 are preferably arranged face to face. The outside configuration of the ceramic base 60 may be similar to that of the base 26. A flat metal plate 62 rests against base 60, and is eyeletted thereto, together with a mica dielectric insulation film 64, by means of eyelet 66. A curved intermediate plate 68 is secured to the opposite end of base 60 by means of an eyelet Ill, and this eyelet preferably also holds a mica dielectric film 12. The outer plate 14 is a thick plate bent and secured in position much as was described in connection with the plate 49, the inwardly bent part 16 of plate 14 being fastened by eyelet 66.

The extension 13 of fiat plate 62 and the extension of late 14 are held together and are spaced from the extensions 48 and 53 of condenser i2 by means 'of tubular spacer 16, the assembly being held together by screw l8 and nut 82. The extensions 18 and 80 are sufficiently flexible to permit movement or change in angularity of the base 60 relative to the base 23. For this purpose, the extension 80 may be weakened or necked, as indicated at 81 in Fig. 2.

Conductor 20 extends from the middle or intermediate plate 68 of condenser l4, to the intermediate plate 34 of condenser l2. Thus the condensers are connected electrically in parallel, and the only external connections needed are to the soldering lugs 52 and 54.

The insulation base 26 of condenser 12 is provided with the threaded bushing 22 previously referred to, but the base 60 of condenser I4 has no such bushing, and instead, the adjusting screw 24 passes with considerable clearance through base Bi! and the upper and lower condenser plates. A pair of washers B4 are preferably disposed between the outer plates 40 and 14 of the condenser, and these washers preferably have arcuate surfaces where they contact one another, and fiat surfaces where they contact the condenser plates, thus helping compensate for angularity as the condenser adjustment is changed.

It will be understood that the disposition of a single curved condenser plate between two relatively flat condenser plates, one of which seeks normally to open to an angular position relative to the other, helps produce a maximum opening of the condensers, and therefore the desired .largge ratio of maiximum-to-minimum capacitance. This will be clear from consideration of Fig. 4, which schematically illustrates the metal condenser plates alone, the lower condenser comprising a curved plate 34 between flat plates 28 and 40, and the upper condenser comprising a curved plate 68 between flat plates 62 and 14.

The condenser may be mounted in any desired manner which will afiord relative movement of the condensers during adjustment of the same. We find it convenient to treat one of the condensers as a stationary condenser, so that the desired relative movement takes place in connection with the other condenser. Specifically, the lower condenser I2 is here treated as a stationary condenser, and it is preferably provided with a staple-like mounting 86, the flat or bridge portion of which is secured to the bottom of ceramic base 26 by means of the bushing 22 previously referred to. The staple is provided with spaced downwardly bent legs 88 which may subsequently be bent when securing the condenser to a mounting strip. A gang or bank of condensers may be mounted side by side on a single mounting strip, and this is indicated in Fig. 6, showing a fragmentary portion of a mounting strip 90 on which condensers 92, 94 and 96 are secured by means of staple mountings 86 (Fig. 3). The strip 90 (Fig. 6) is provided with holes 98 for the bushing and adjusting screw, and with associated pairs of holes I00 for the staple legs 88, the latter being passed through the holes I00 and bent over or clinched.

as indicated in the drawing. The soldering lugs 52 and 55 of the condensers project sidewardly from the strip 991 and are accessible for wiring. Figure 6 is, of course, a bottom plan view, and shows the gang in inverted position.

The construction and operation, as well as the advantages of our improved trimmer condenser, will be apparent from the foregoing detailed description thereof. The operating advantage of the condenser may be further illustrated by reference to the graph shown in Fig. 5, in which the dotted line I02 represents the capacitance characteristic of a five-plate trimmer condenser, while the solid line curve I04 represents the capacitance characteristic of our new trimmer condenser. It will be observed that whereas the capacitance of the five-plate condenser levels off at a relatively high value of about 35 or 40 mmf., the capacitance of the special twin three-plate condenser of our invention diminishes to a very much lower value of,

say, 13 mmf. The capacitance has been represented on a logarithmic scale because of the importance of showing the results at the low end of the scale.

It will be understood that while we have referred to quantitative capacitance values at various points in the foregoing description, these values have been given solely by way of exemplification and not in limitation of the invention.

It will be apparent that while we have shown and described our invention in a preferred form, many changes and modifications may be made in the structure disclosed, without departing from the spirit of the invention as sought to be defined in the following claims.

We claim:

1. A wide-range trimmer condenser comprising two trimmer condensers arranged one above the other in face to face or inverted relation, each of said condensers comprising an insulation base having a plurality of normally openable metallic plates, the lower base being provided with an internally threaded bushing and having a mounting staple secured to the bottom of the base by said bushing, a single adjusting screw passing through the upper base and the plates of the upper and lower condensers, to the threaded bushing, whereby rotation of said screw simultaneously adjusts both condensers, means movably mounting the upper base for movement relative to the lower base, and means connecting said condensers in parallel.

2. A wide-range trimmer condenser comprising two trimmer condensers arranged one above the other in face to face or inverted relation, each of said condensers comprising an insulation base having a plurality of normally openable metallic plates with mica film dielectric insulation therebetween, alternate plates being eyeletted at opposite ends of the base, the lower base being provided with an internally threaded bushing and having a mounting staple secured to the bottom of the base by said bushing, a single adjusting screw passing through the upper base and the plates of the upper and lower condensers to the threaded bushing, whereby rotation of said screw simultaneously adjusts both condensers, means movably mounting the upper base for movement relative to the lower base, and means connecting said condensers in parallel,

3. A wide-range trimmer condenser comprising two trimmer condensers arranged one above the other in face to face or inverted relation, each or said condensers having a comparatively small capacitance but a large ratio of maximum-tominimum capacitance, each of said condensers comprising an insulation base having a plurality of normally openable metallic plates with mica film dielectric insulation therebetween, alternate piaies bein. eyeletted at opposite ends of the base, the lower base being provided with an internally threaded bushing and having a mounting staple secured to the bottom of the base by said bushing, a single adjusting screw passing through the upper base and the plates of the upper and lower condensers and the threaded bushing, whereby rotation of said screw simultaneously adjusts both condensers, means movably mounting the upper base for movement rela tive to the lower base, and means connecting said condensers in parallel, thereby providing a con denser of relatively large capacitance and a high ratio of maximum-to-minimun: capacitance.

4. A wide-range trimmer condenser comprising two trimmer condensers arranged one above the other in face to face or inverted relation, each of said condensers being a three-plate condenser having an insulation base, the lower base being provided with an internally threaded bushing, a single adjusting screw passing through the upper base and the plates of the upper and lower condensers to the threaded bushing, whereby rotation of said screw simultaneously increases or decreases the capacitance of both condensers, means movably mounting the upper base for movement relative to the lower base, and means connecting said condensers in parallel.

5. A wide-range trimmer condenser comprising two trimmer condensers arranged one above the other in face to face or inverted relation, each of said condensers being a three-plate condenser having an insulation base, a flat bottom plate adjacent the base, a curved intermediate plate, a resilient normally open outer plate, and insulation mica films between said plates, alternate plates being eyeletted at opposite ends of the base, the lower base being provided with an internally threaded bushing and having a mounting staple secured to the bottom of the base by said' bushing, a single adjusting screw passing through the upper base and the plates of the upper and lower condensers and the threaded bushing, whereby rotation of said screw simultaneously increases or decreases the capacitance ofv both condensers, means movably mounting the upper base for movement relative to the lower base, and means connecting said condensers in parallel.

, 6. A single wide-range trimmer condenser comp-rising two trimmer condensers coupled together and arranged one above the other, each of said trimmer condensers having its own insulation base with a set of condenser plates attached thereto, means connecting said trimmer condensers in parallel, one of said condenser bases having a threaded part, and a single adjusting screw mating with said threaded part and passing through the condenser plates of both condensers and through the base of the other condenser and bearing against a part of said other condenser, whereby rotation of said screw operates to move one condenser relatively to the other and to move the plates of both condensers to simultaneously increase or decrease the capacitance of both condensers.

'7. A single wide-range trimmer condenser comprising two trimmer condensers coupled together and arranged one above the other, each of said trimmer condensers having its own insulation base with a set of condenser plates attached thereto, each said set consisting of a, bot tom plate adjacent the base, an intermediate plate, and a top plate, meansconnecting said trimmer condensers in parallel, one of said condenser bases having a threaded part, and a single adjusting screw mating with said threaded part and passing through the condenser plates of both condensers and through the base of the other condenser and bearing against a part of said other condenser, whereby rotation of said screw operates to move one condenser relatively to the other and to move the plates of both condensers to simultaneously increase or decrease the capacitance of both condensers.

8. A single wide-range trimmer condenser comprising two trimmer condensers coupled together and arranged one above the other, each of said trimmer condensers having its own insulation base with a set of condenser plates attached thereto, each said set consisting of a fiat bottom plate adjacent the base, a curved intermediate plate, a resilient-normally open top plate, and insulation films between said plates, means connecting said trimmer condensers in parallel, one of said condenser bases having a threaded part, and a single adjusting screw mating with said threaded part and passing through the condenser plates of both condensers and through the base of the other condenser and bearing against a part of said other condenser, whereby rotation of said screw operates to move one condenser relatively to the other and to move the plates of both condensers to simultaneously increase or decrease the capacitance of both condensers.

9. A single wide-range trimmer condenser comprising two trimmer condensers coupled together and arranged one above th other in face to face or inverted relation, each of said trimmer condensers comprising an insulation base with a set of normally openable condenser plates attached thereto, means connecting said trimmer condensers in parallel, one of said condenser bases having a threaded part, and a single adjusting screw mating with said threaded part and passingthrough the condenser plates of both condensers and through the base of the other condenser and bearing against said other base, whereby rotation of said screw operates to move one condenser relatively to the other and to move the plates of both condensers to simultaneously increase or decrease the capacitance of both condensers.

10'. A single wide-range trimmer condenser comprising two trimmer condensers coupled together and arranged one above the other in face to face or inverted relation, each of said trimmer condensers comprising an insulation base with a set of normally cpenable condenser plates attached thereto, means connecting said trimmer condensers in parallel, one of said condenser bases having a threaded part, and a single adjusting screw mating with said threaded part and passing through the condenser plates of both condensers and through the base of the other condenser and bearing against said other base, whereby rotation of said screw simultaneously adjusts both condensers and moves one condenser relatively to the other, thereby providing a con denser of relatively large capacitance and high ratio of maximum-to-minimum capacitance.

JOSEPH A. FLANZER. PHILIP BEIN.

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