US2149702A

US2149702A - Variable condenser

Info

Publication number: US2149702A
Application number: US88125A
Authority: US
Inventors: Elwood S Maris
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1936-06-30
Filing date: 1936-06-30
Publication date: 1939-03-07
Anticipated expiration: 1956-03-07

Description

March 7, 1939. E. s. MARIS I 2,149,702

' VARIABLE CONDENSER File'd June so, 1956 3nventor Patented Mar. 7, 1939 UNITED STATES VARIABLE CONDENSER Elwood S. Maris, Upper Darby, Pa., assignor to Radio Corporation of Delaware Application June 30,

3 Claims.

This invention relates to electrical condensers and particularly to variable air-condensers of the so-called trimmer type.

An object of the invention is to provide a capacitor, the operation of which is characterized (a) by a high degree of stability under extreme conditions of climate, (b) by ease of adjustment and (0) by absence of microphonic and other.

parasitic disturbances.

Another object of the invention is to provide a simple, inexpensive, compact, trouble-free capacitor and one which lends itself readily to mass production methods.

A more specific object of the invention is to provide a variable condenser having a fixed armature, a slldable armature and a guideway for the latter molded in, rigid permanent alignment with the fixed armature.

Other objects and advantages of the invention together with certain details of construction and assembly will be apparent and the invention itself will'be best understood by reference to the following description and to the accompanying drawing, wherein Figure 1 is a longitudinal sectional view of an air-type variable condenser constructed in accordance with the principle of the invention, Fig. 2 is an enlarged cross-sectional view taken on the line 2-2 of Fig. 1,

Fig. 3 is a longitudinal sectional view of certain of the parts of the condenser of Fig. I mounted on a mandrel and illustrating the manner of aligning these elements during assembly, and

Fig. 4 is alongitudinal sectional view of the condenser parts and mandrel of Fig. 3 inserted within a mold within which metal lugs are cast for maintaining the elements constituting the flxed parts of the capacitor in permanent alignment. r 1

Referring now to the drawing in which like reference characters represent the same or correspondingparts. The bodyof thevariablecondenser of Fig. 1 is constituted by a pair of conductive tubes' In and 20 arrangedin spaced end-to-end 5 relation and a hollow insulating member 30 spanning the space therebetween. Conductive tubes in and 20 each has a metal cup shape member designated at H and 2|, respectively, intimately joined thereto and in which the Opposite ends of the hollow insulating member 30 are immovably seated.

Conductive tube Ill constitutes one armature or electrode of the condenserpthe diameter of its bore is greater than that of conductive tube 20. Armature tube I0 is provided with'an' outwardly America, a corporation of 1936, Serial No. 88,125

extending peripheral rim l2. A wire lead to looped about tube I0 is clamped between the outer wall of this rim [2 and the adjacent circumferential edge of the insulating tube 30. The

other conductive tube 20 is provided with a pair of rims 22 and 22a, the inner side wall of the first rim 22 contacts the opposite circumferential edge of insulating tube 30. Rims l2 and 22 preferably have non-circular peripheries (see Fig. 2), or they may be knurled to prevent movement with respect to the cup shape members H and 2l in which they are embedded. The other or second armature comprises a conductive rod 40 having a diameter corresponding substantially to that of the bore of the smaller conductive tube 20. Armature 40' slidably contacts the inner wall of conductive tube 20, which tube is of sufficient length to constitute a support capable of maintaining that part of rod 40 which extends therebeyond against undesired lateral movement with respect to the inner wall of the tube-like armature- III. The diameter of the rod-like armature III is less than that of the bore of the armature Ill whereby an air gap is established therebetween. The terminal end of that portion of rod III which is presented to the interior of tube Ill carries an insulating annulus ll of a diameter sufficient to close the air space s between these two armatures against moisture and dust. Annulus 4| further prevents displacement of armature 40 with respect to the inner walls of armature In. The end portion 42 of the rod-like armature 40 adjacent the annulus 4| is preferably beveled, as shown in .Fig. 1 to provide a receptacle for such dust and minute metal particles as may result from abrasive contact between 4| and the inner wall of tube Ill. The opposite terminal end of rod I0 is provided with a key-hole 43 adapted to receive a key (not shown) which may be used to facilitate movement of rod ll, whereby to achieve a desired capacitance by altering the effective armature area presented by (0 to the inner walls of conductive tube Hi.

That portion of the outer wall of the conductive supporting tube 20 which extends beyond insulating tube 3! and its supporting cup 2| is provided with a D-shape screw-threaded portion 23 and a bifurcated cylindrical end section 24 which terminates in a beveled edge 25. The screwthreaded portion 23 receives a nut 26 for clamping the device to a panel or base p of the radio apparatus (not shown) to which the condenser lead 10 extends. Screw threads 23 also receive a second nut 21 which has a beveled collet or shoulder portion 28 which engages the beveled edge 25 of the bifurcated portion 24 of the conductive armature supporting tube 20, and compresses it tightly against the siidable rod-like armature, whereby to clamp it securely against movement in a desired relative position.

One very important feature of the condenser 01 the invention is that the parts iii, 2d and 3d constituting'its main body portion are Joined one to another in permanent fixed alignment by molding first fitted on the mandrel and thepre-formed looped end of conductive lead w placed about the outer surface of tube iil'in contact with-its peripheral rim 12. The hollow insulating shell is then slid into position with its inner end overlapping a portion of the armature tube l0 and its inner edge against the wire lead 10. Conductive tube 20 is then placed over the reduced diameter portion 52 of the mandrel 50 with its inner end fitted within the insulating shell 30 and its inner rim 22 in contact with the edge of this shell 30.

With the armature l0, lead wire w, insulating shell 30 and conductive tube 20 positioned in the described manner on mandrel 50 the assembly is inserted in a moldBll (Fig. 4) with the lead wire to projecting through a hole 5|, provided for the purpose, in its lower section 62. The upper section v.63 of the mold is provided" with two holes 64 and'65 to permit the introduction of the molten metal which eventually forms the cup-shape members H. and 2| (Fig. 1) which surround the terminal edges of the insulating shell 3|]. Preferably the shell 30 is provided with semi-peripheral grooves 3|, 3la adjacent its ends and into which the metal flows. These grooves 3i, like the non-circular peripheral contour of metal rims i2 and 22 prevent the possibility of relative axial movement of the parts after themetal cups Ii and 2| have been'cast. Y

When the casting operation has been completed and the assembly removed from the mold, the mandrel 50 is withdrawn and .the rod-like armature 40 slidably inserted into the conductive supporting tube 20 so that a portion of its surface extends within, but out of contact with, the tube-like armature Ii].

It is to be understood that the foregoing description of a preferred embodiment of the invention is to be interpreted as'illustrative and not in a limiting sense except as required by the prior art and the spirit of the appended claims.

' What is claimed is':

l. {i variable condenser comprising a pair of hollow conductive tubes arranged in spaced ,coaxial relation, a hollow insulating member spanning the space therebetween, means including said insulating member for maintaining said tubes in rigid insulated alignment, said tubes having bores of difierent diameter, a terminal end of the tube of smaller bore being bifurcated to render it resilient and the tube of larger bore constituting an armature of said condenser, a second armature for said condenser comprising a conductive rod extending into both said tubesfor.

relation, one of said tubes constituting an arma-.

ture of said condenser, a hollow insulating member spanning the space between said tubes, 2. pair of said insulating member are immovably seated, and a rod-like armature extending through one of said tubes in slidable contact with the inner wall thereof and into, but out of contact with the walls of, said armature tube.

3. A variable condenser in accordance with claim 1 and wherein a terminal connection for said armature tube extends outwardly therefrom through the body of one of the cup-shape members in which said hollow insulating member is seated.

ELWOOD S. MARIS.

- of cup-shape members intimately joined respectively to said tubes and in which the opposite ends