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Publication numberUS2747147 A
Publication typeGrant
Publication dateMay 22, 1956
Filing dateJan 4, 1954
Priority dateJan 4, 1954
Publication numberUS 2747147 A, US 2747147A, US-A-2747147, US2747147 A, US2747147A
InventorsCharles L Shull
Original AssigneeCharles L Shull
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Small capacity tubular adjustable condenser
US 2747147 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

May 22, 1956 c. L. SHULL 2,747,147


Application January 4, 1954, Serial No. 401,809

Claims. (Cl. 317-249) The present invention relates to a small capacity tubular adjustable condenser, and more particularly to a trimmer condenser for high frequency oscillating electronic circuits.

In order to secure accurate and stable adjustment and quiet operation of electronic devices incorporatingA oscillating circuits, it is necessary that the adjusting condensers operate smoothly, without either looseness or jamming; that lost motion or'backlash be prevented, and that continuous firm electrical connections be maintained at all times. Considerable difiiculty has heretofore been encountered in providing an economical form of trimmer condenser which meets these requirements.

It is an object of the present invention to provide a novel trimmer condenser which is adapted for accurate and stable adjustment, while being simple in structure and economical to manufacture.

It is another object to provide such a device which is free from lost motion during reversal of direction of adjustment. i

It is another object to provide such a device in which adjustment of the condenser is accomplished without breaking or disturbing the electrical connections of the movable element, firm electrical contact being maintained at all times.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a vertical substantially mid-sectional view of a preferred embodiment of the invention;

Fig. 2 is a detail in elevation of the inner electrode; and

Fig. 3 is a view similar to Fig. 1 of a modified form of the invention.

In Fig. 1 of the drawing there is illustrated a hollow cylinder 1 of suitable dielectric material such as glass or other ceramic material having an exterior metallic sheath 2 extending from one end of the cylinder for a distance somewhat less than half its length. The sheath 2 constitutes the outer electrode of the condenser and is formed with a cap 3 having an arm 4 for making electrical connection.

A hollow metallic mounting bushing 5 is rigidly connected in any suitable manner as indicated at 6 to the other end of the dielectric tube 1, said bushing being exteriorly threaded for the reception of a nut 7 by which the bushing may be rigidly mounted in a panel 8 or the like.

The bushing 5 is provided with an interior annular shoulder 9 having an outwardly facing concave spherical bearing surface 11. A screw shaft 12 is loosely mounted at one end in the bushing 5 and is provided with a head 13 rigidly mounted thereon as by means of a press-fit, and provided with a convex spherical surface 14 mating with the surface 11 of the bushing. The bushing is preferably provided with an annular ange 15 which is loosely constricted around a shoulder 16 on the head 13 to form a swivel connection for the shaft 12 in the bushing. The screw shaft 12 extends into the dielectric tube 1, and an inner electrode 17 having a sliding fit within the dielectric tube 1 is threaded on the shaft 12 for longi* tudinal adjustment by rotation of the shaft, as by means of a screw driver slot 18 formed in the head 13.

The inner electrode 17 is counterbored for a major portion of its length as indicated at 19, and the bushing S is provided with a similar counterbore 20. A compression spring 21 of electrically conductive material such as Phosphor bronze is received at its ends in the counterbores of the inner electrode and bushing and is assembled under pressure whereby it serves to hold the spherical surfaces 11, 14 of the bushing 5 and head 13 firmly in contact at all times.

The inner electrode 17 is provided with an axially extending socket 22, and the shoulder 9 of bushing 5 is provided with a similar socket 23. The spring 21 has its terminal portions bent axially and seated in said sockets 22, 23 whereby the spring resists rotation of the inner electrode and at the same time makes a rm continuous electrical connection to the bushing 5.

In order to stabilize the inner electrode in the dielectric tube and prevent loss of adjustment by reason of vibration or shock, it is provided with a chordal slot 24 which extends from its open end as best shown in Fig. 2, thus forming an arm 25 separated from the body of the electrode except at its lower end. The arm 25 is sprung outwardly as shown in dotted lines in Fig. 2 whereby, when the electrode is inserted in the tube 1, the arm bears frictionally in the tube and prevents lateral movement or vibration of the electrode and also resists its rotation in the tube.

In operation, when the condenser is incorporated in an electrical circuit, one connection is made by means of the connector arm 4, and the other connection by grounding the bushing 5 or in any other suitable manner. Rotation of the head 13 and screw shaft 12 causes longitudinal movement of the inner electrode 17 to bring it more or less into registry with the outer electrode 2 whereby the capacity of the condenser is varied as desired. During this adjustment, and at all other times, the spring 21 performs the three functions of holding the thrust bearing surfaces 11, 14 in firm contact, preventing lost motion between the threads of the screw shaft 12 and inner electrode 17, and resisting rotation of the inner electrode so as to insure its traversal when the screw shaft is rotated. At the same time, the pressure of the spring arm 25 against the interior of the dielectric tube 1 insures a firm sliding fit of the electrode in the tube and further assists in preventing rotation of the inner electrode. The spherical shape of the thrust bearing surfaces 11, 14 permits the screw shaft to adjust itself angularly in the bushing 5 to compensate for any slight misalignment of the dielectric tube 1.

Fig. 3 of the drawing shows an embodiment of the invention in which stabilization of the inner electrode is accomplished by means of the stabilizing spring disclosed in applicants prior application Serial No. 263,540, filed December 27, 1951. As there shown an elastic spider member 26 is rigidly mounted on a reduced terminal portion 27 of said electrode as by means of a spinning operation as indicated at 28. The electrode has a tapered section 29 adjacent the reduced portion 27, and the spider 26 is formed with a plurality of divergent spring arms 30 which embrace said tapered section when compressed by introduction of the electrode into the dielectric tube 1.

The pressure of the arms 30 against the interior of the dielectric tube has been found in practice to stabilize the electrode against all but destructive shocks.

Although structure has been shown and described in detail, it will be understood that changes may be made afnam? in the precise form and arrangement of the parts without departing from the spirit of the invention.

I claim:

1. In a tubular trimmer condenser a dielectric tube having an 'exterior metallic sheath for a portion ofits length forming the outer electrode, a hollow metallic mounting bushing -iXedly attached to one end of the tube, a screw shaft swivelled in the bushing with freedom for limited universal movement, an inner velectrode threaded on the screw shaft and slidable in the tube into and out of registry with the outer electrode, said bushing and inner electrode having coaxial facing coonterbores, and means including a'm'etallic compression spring loosely surrounding the screw shaft seated in said counterbores and nonrotatably anchored at its ends to the bushing and inner electrode respectively, for exerting axial pressure thereon to compress the universal connection, to resist rotation of the inner electrode, and to form a rm stationary continuous electrical connection between the bushing and inner electrode.

2. A trimmer condenser as set forth in claim l in which the swivel connection between the bushing and screw shaft comprises a head on the screw shaft having a convex thrust surface, said bushing having a mating concave thrust surface, the pressure of said spring Servf ing to hold said thrust surfaces in contact.

3. A tubular condenser as set forth in claim l in which said bushing and inner electrode are provided with axially extending recesses, `and said spring is provided with outturned ends seating in the recesses and resisting rotary movement of the inner electrode in the dielectric tube.

4. A tubular condenser as set forth in claim 1 including further expansive spring means on said inner electrode bearing frictionally against the inner surface of the dielectric tube to stabilize said 'electrode against vibration.

5. A tubular condenser as set forth in claim l in which the inner electrode is in the form of a hollow cylinder having a chordal slot forming an elastic arm which is sprung out to press against the interior of the dielectric tube to resist lateral movement and rotation of the inner electrode in the tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,810 Sander Nov. 26, 1946 2,607,826 Barnes Aug. 19, -1952 FOREIGN PATENTS 263,948 Great Britain 1an. 10, 1927 496,315 Great Britain e Nov. l29, 19.38 628,499 Germany Apr. 6, 1936

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2411810 *Sep 20, 1943Nov 26, 1946Rca CorpAudio reactor
US2607826 *Jul 25, 1950Aug 19, 1952Llewellyn T BarnesTrimmer capacitor
DE628499C *Jun 1, 1934Apr 6, 1936Porzellanfabvrik KahlaKondensator unveraenderlicher Kapazitaet willkuerlich regelbaren dielektrischen Temperaturkoeffizientens
GB263948A * Title not available
GB496315A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3153753 *Jan 25, 1961Oct 20, 1964Erie Technological Prod IncTrimmer condenser
US3166695 *Oct 12, 1960Jan 19, 1965Charles T BarnesTrimmer capacitor
US3731165 *Oct 4, 1971May 1, 1973Jfd Electronics CorpTrimmer capacitor with slotted piston
US4209819 *Mar 13, 1978Jun 24, 1980Key Tronic CorporationCapacitive keyswitch
US4472759 *Sep 9, 1983Sep 18, 1984Murata Eria North America, Inc.Air trimmer capacitor
US4851961 *Nov 14, 1988Jul 25, 1989Funk Alexander LEndless reactor
U.S. Classification361/295
International ClassificationH03J1/08
Cooperative ClassificationH03J1/08
European ClassificationH03J1/08