US2665919A

US2665919A - Pickup arm for phonographs

Info

Publication number: US2665919A
Application number: US1399A
Authority: US
Inventors: Donald J Baker
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-01-09
Filing date: 1948-01-09
Publication date: 1954-01-12
Anticipated expiration: 1971-01-12

Description

Jan. 12, 1954 D. J. BAKER PICKUP ARM FOR PHONOGRAPHS Filed Jan. 9, 1948 g m 0H 5H a? H NH nd Q it I QM r. m 3H P IN VEN TOR.

an OLNfS-LD J. BAKIQR ATTORNEY Patented Jan. 12, 1954 UNITED STATES PATENT OFFICE PICKUP ARM FOR PHONOGRAPHS Donald J. Baker, Los Angeles, Calif.

Application January 9, 1948, Serial No. 1,399

Claims.

This invention relates to pickup arms for electric phonographs.

A broad object of the invention is to devise a pickup arm structure in which some of the weight of the arm and the attached pickup is counterbalanced by means of a spring element enclosed within the arm.

Another object is to devise a structure in which the counterbalancing spring cooperates with the enclosing arm to form a friction brake to damp out any resonant efiects which may otherwise develop in the arm itself or in the spring.

Other objects will become apparent from the following description of the invention.

The preferred form of the invention is illustrated in the accompanying drawing in which:

Figure 1 is a plan view of the pickup arm;

Figure 2 is an elevational view of Figure 1 showing part of the pickup head and the forward end of the arm in section, and the arrangement for pivotally mounting the rear end of the arm is also shown in section; and

Figure 3 is a side elevational view of the arrangement for pivotally supporting the rear end of the arm.

Referring to the drawing, 1 indicates the baseboard for supporting the usual turntable 2 carrying a record 3 which is engaged by the stylus of the pickup head 4 carried by a tubular arm 5. The pickup head is secured to the free end of the arm 5 by means of a screw 6 passing vertically through the forward end of the tube and being threaded into the lower removable part of the casing of pickup head 4.

The rear end of the arm 5 is secured to a hollow casing 1 which is pivotally mounted to permit the arm 5 to be moved in any direction about both a horizontal axis and a vertical axis. The rear end of arm 5 enters a bore formed in the front wall of casing I, and the wall portion Ia below the bore is slotted in a vertical plane. A clamping screw 11) passing through the slotted wall portion clamps the end of arm 5 in the bore.

The arrangement for supporting the casing 1 for swinging movement about a vertical axis involves a vertical pivot tube 8 journaled in a sleeve 9 which is secured to the baseboard I by a nut Ill. The upper end of sleeve 8 carries a U-shaped bracket H, and easing 1 is pivotally supported on the bracket II by means of a horizontal pivot pin l2 passing through the easing I and through the upstanding arms of the bracket H. Bracket H is mounted on the upper end of tube 8 in the manner shown in Figure 2, that is, the upper end of tube 8 has a reduced portion which enters a hole formed in the yoke section of the U-shaped bracket, and the outer end of the reduced portion of tube 8 is turned over or flared outwardly to rivet the bracket to the tube. By means of the arrangement just described, the arm 5 may be swung horizontally about a vertical axis provided by sleeve 8, and may be swung vertically about a horizontal axis provided by pivot pin I 2. Casing 1 is provided with an abutment 1c arranged in spaced relation with an abutment Ila carried on one or both arms of the bracket H to limit the downward movement of the arm 5. As shown in Figure 2, these abutments are normally spaced apart when the pickup is in operative engagement with the record on the turntable, and the spacing of the .abutments is sufiiciently close to prevent the stylus of the pickup from engaging the base board I when the pickup is lowered beyond the outer edge of the turntable.

The counterbalancing spring I3 is arranged within the tubular arm 5 and is connected at its forward end to the screw 6. The rear end of the spring I3 is connected to a flexible cable or string [4 which passes rearwardly over a pulley I5 journaled on an axle |5a within the casing 1. The cable I4 is provided with a loop [4a at its rear end which engages a hook portion of an anchor element l6 removably secured to the end of a rearwardly extending arm llb of bracket H. The spring I3 is under tension when mounted as shown in Figure 2, and the arrangement is such that the pull of the spring on the bracket arm I It tends to counterbalance the weight of the arm, and thereby reduces the pressure of the stylus on the record. By properly designing the spring and its connections, the pressure of the stylus on the record can be fixed at any desired value.

As shown in Figure 1, the tubular arm 5 is bent in a reverse curve in the horizontal plane. By this curved arrangement, the longitudinal axis of the pickup head 4 is properly oriented with respect to the radius of the record 3 at the point where'the stylus engages the record. Also, the curved form of the arm 5 causes the spring [3 to frictionally engage the walls of the arm on one side in the zone 5a and on the other side in the zone 51), see Figure 1. The frictional engagement of the spring against the sides of tube 5 serves to damp out any resonance eiTect which may be inherent in the arm itself. Also, it serves to damp out any local vibration which might otherwise be set up within the spring itself. It will be understood that the same damping action will be secured with a single bend in the arm 5 and a reverse bend is not essential.

Casing 1 is provided with an internal abutwhen the pickup arm is raised fromthe record.

is relatively small, with the result that the counterbalancing force exerted by the springrema ins substantially constant in all verticali positions of the pickup arm.

A pair of connecting leads I! [for thepickup' 4' extends rearwardly through the spring l3 in the arm: 5: into the hollow casing I and then verticallyr downward through the pivot tube 8' to the usual amplifier not shown. With this arrangement, the connecting leads H are shielded throughout their length by the pickup arm assembly, and these leads may be formed of unshielded: conductors up to the point where they emerge from the sleeve 8.

The pull. of spring; I3 on the forward end of arm 5 is. along: the axis of tube 5 which passes above the horizontal pivotal axis l2 and thereby exerts. a counterbalancing pull on the arm. The pulley l5 could be omitted if the arm H'b were extended upwardly and rearwardly to a point approximately where the cable I l engages the pulley.

Lolaim:

1.. In a pickup arm fonphonographs, the. combination of a tubular'arm supporting a pickup at one: end and rigidly'secured to a hollow casing at the" other-end, a pivot pin mounted for turning on a. vertical axis, means mounting said casing on. said pivot pin for swinging: movement about said vertical axis 'andifor pivotal movement about a horizontal axisan arm rigidly secured to said pivot pin within said casing and extending rearwardly from said pin, a coiled spring located within. said tubular arm: between said casing and said pickup and having its. forward end secured to said tubular arm, an idler pulley journalled in said casing, and a flexible connection extend ingfrom the rear end of said spring and passing overpaid pulley and being connected to said rearwardly extending arm for maintaining said spring under tension, said connection passing into-said casing, above said horizontal axisw'hereby the pull of said spring, counterbalances part of the weight of said pickup arm.

2'. A pickup arm assembly comprising a. tubular arm pivotally mounted at one end and: adapted to carry a pickup head on. the other: end, a coiled spring within said arm and maintained under tension, said arm being curved in a horizontal. plane: to; cause frictional engagement of said spring withthe wallof; said arm over-a substantial: portion of the length of" said arm wherebythefrictional engagement between said spring and the wall of 'said arm clamps out resonant effects within said arm.

'3. A. pickup arm assembly comprising a tubular arm adapted to carry a pickup head on one end, pivotal means at the other end 01f said arm for supporting the arm for swinging about a vertical axis; a coiled spring within said arm, means attaching one end of said spring to the free end of said; arm,,.m1eans: securing the. other end of said spring under tension to said pivotal means to counterbalance part of the weight of said arm, said arm being curved in a horizontal plane to cause engagement of said spring with the wall of said arm over a substantial portion of the length of said arm, whereby resonant effects within said. arm willbe. damped. out.

4-..- A. pickup arm for. phonographs comprising a U -shaped bracket pivotally mounted for rotation about a vertical axis, said bracket having a rearwardly extending arm formed thereon, a hollowcasing pivotally mounted on said U- shaped bracket by means of a horizontally disposed pin passing through said casing and through the legs of said bracket, a reverselycurved. tubular arm having one end mounted in said casing at a point above said horizontally disposed pin, a pulley mounted for rotation in a vertical plane within said casing and. in alignment with said tubular arm, a: pickup head mounted on the other end of said tubular arm by means of a single screw extending. transversely through said tubular arm, a tensioned. coil spring disposed internallyof said tubular arm and; hav-- ing one end attached to said transverse screw, and a flexible cable attached to the other end of said spring, said cable extending over. said. pull'ey' and being attached to said rearwardly extending arm of said U-sharped' bracket, whereby said spring will counterbalance. part of. the weight of said pickup arm and tends; to damp out resonance eiiects within; said am by frictional contact with the: walls of said arm.

5. In apickup arm forphonographs, the combination of a tubular arm supporting a pickup at one 'end' and rigidly secured to a hollow casing at the other end, a pivot pin mounted for turning on a vertical axis; means mounting said casing on said pivot pinior swinging movement about said vertical axis. and for. pivotal movement about a horizontal axis, an arm rigidly secured to said pivot pin within said casing and extending rearwardly from said pin, a coiled spring 10'- cated within. said tubular" arm between said casing. and said pickup and having its forward end secured to said tubular arm, and a. connection from. the rear end of said' spring to said rearwardly extending arm for maintaining said spring under tension, said connection. passing into said casing above said horizontal axis whereby the pull of said spring counterbalances part of the weight of said. pickup arm, said tubular arm being curved in a horizontal plane to cause said spring to have frictional contact with the wall of said tubular arm.

' DONALD'J. BAKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,866,403 Elmer July 5, 1932 2,174,156 Guedon Sept. 26, 1939 2,295,905 Kurkjian Sept. 15, 1942 2,484,570 Johnson Oct. 11, 1949 2,545,652 Dann-et' a1; .Mar. 20', 1951 2,551,506 Rockwell May 1. 1951 2,600,914 Palo et al'. June 17, 1952 FOREIGN PATENTS Number Country Date 61 78/32 Australia Feb. 20, 1933 590,514 Germany Jan. 5, 1934 621453 Mar. 5, 1936