US3783698A

US3783698A - Preset device for uhf tuner

Info

Publication number: US3783698A
Application number: US00218747A
Authority: US
Inventors: S Ogasawara; T Tamate; T Sonobe
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1972-01-18
Filing date: 1972-01-18
Publication date: 1974-01-08
Anticipated expiration: 1991-01-08

Abstract

A preset device for a tuner comprises a plurality of externally threaded tuning screws rotatably mounted in grooves on the periphery of a channel selector drum. Each screw is provided with a nut threadedly mounted thereon and movable within the drum grooves axially therealong in response to rotation of the screw.

Description

United States Patent 1191 Ogasawara et al.

[ Jan.8,1974

[ PRESET DEVICE FOR UHF TUNER 3,555,914 1 1971 Mase 74/10.s 5] Inventors: oj gasa a a; e uzo amate; 3,675,496 7/1972 Yasuda 74/ 10.6

Toshimits on all of yo, FOREIGN PATENTS OR APPLICATIONS Japan 662,025 4/1963 Canada 74/1o.2 [73] Assignee: Alps Electric Co. Ltd., Tokyo, Japan Primary Examiner-Allan D. Herrmann [22] Flled' Jan. 1972 Attorney-Maxwell James et a1. [21] Appl. No.: 218,747

[57] ABSTRACT [52] US. CL... 74/l0.2, 74/10.6, 74/10.8 [51] Int. Cl. H03] l/l4, F16h 35/18 A Preset devlce for a tune! P SeS a plurality of ex- [58] Field of Search 74/10.6, 10.2, 10.8; temally threaded Screws rotatably mounted in 192/141 grooves on the perlphery of a channel selector drum. Each screw is provided with a nut threadedly mounted [56] References Cited thereon and movable within the drum grooves axially UNITED STATES PATENTS therealong in response to rotation of the screw.

3,175,407 3/1965 Reinwall, Jr. 74/l0.8 5 Claims, 8 Drawing Figures 7 *2 !FF 'l' L :L'l'f'IT: 68 32 3 62 as 1% T65 I k. 175a. 84 I 2 F! 1 i 2/ .90 I4 97 /5 E a a 4 PATENTED 8 4 SHEEI 10$ 3 PRESET DEVICE FOR UHF TUNER The threaded members are driven by a fine tuning adjustment shaft adapted to be coupled to the selected tuning screw by means of a gear train normally maintained out of engagement with the selected screw but movable into such engagement upon depression of the fine tuning adjustment shaft. The movable gear train is provided with a frictional coupling mechanism adapted to yield when the nut on the selected tuning screw reaches its terminal position. That terminal position is defined by a stop mechanism comprising a pair of pins radially projecting from the tuning screw at either end thereof and adapted to engage the nut prior to its reaching the end plate on the drum.

The axial adjustment of the selected fine tuning nut is transmitted to a fine tuning rotor shaft via a rack plate provided at one end with a cam engaging the radial projection on the selected nut. The cam is curved to conform generally to the periphery of the drum and is provided with sloping cam surfaces adapted to smoothly engage successive nuts during channel selection, the drum being detented to predetermined positions corresponding to a predetermined engagement of each projection with the cam surface.

This invention relates to tuning mechanisms and more particularly to UHF tuners of the type having preset tuning devices.

For many years home television receivers have generally included preset detented tuning mechanisms for selecting any one of the 1 channels comprising the very high frequency (VHF) range. With the recent advent of a significant number of channels in the ultra high frequency (UHF) range, home television receivers are today generally adapted to receive such UHF broadcasts. Because the UHF range comprises seventy chan-' nels such receivers are generally provided with continuous tuning means, typically of the gang capacitor type. The many disadvantages of continuous tuning, both from the standpoint of the viewer and the manufacturer, have been recognized. Thus, the use of preset channel selection with a step-by-step detent action as used in the VHF band has already been suggested for the UHF band. Since it is not practicable to detent all seventy channels, prior art devices of this type generally subdivide the UHF band into groups of channels, typically twelve or 24 groups, providing a detent action for the selection of a group. It is very unlikely that more than one channel of a group will be active in any given geographic area. Thus, the individual control element associated with each detented position may be preset to the active channel within the group, such control elements being adjustable by a fine tuning mechanism.

In a typical device of this type a detented rotary turret or drum is provided with a plurality of adjustable tuning projections spaced about its periphery and movable axially into and out from the drum. The operative projecting length of each tuning projection is preset by means of the fine tuning adjustment mechanism so that as the drum is rotated through its several detented positions, the projections of different lengths are adapted to adjust the impedance of a variable impedance tuning element, thereby to tune the oscillator to a preselected frequency. This is generally accomplished by means of a complex linkage mechanism operatively connected between the adjustable tuning projections and the variable capacitance turning element, which linkage is effective to transmit the axial positioning of the selected projection into a rotary positioning of a fine tuning rotor shaft adapted to adjust the impedance of the tuning element. More particularly, devices of this type typically employ a pivotal arm or the like which is spring biased into engagement with the selected tuning projection whereby adjustment of the axial position of said projection is effective to rotate the contact arm about its pivot point.

One of the important considerations in the construction of such mechanisms is size. Thus, particularly in UHF tuners, where there is an additional VHF tuning mechanism incorporated in the same receiver chassis, the tuner mechanism must be made as small as possible so as not to take up space which could otherwise be utilized for the operative circuitry. This is particularly important in view of the current popularity of compact portable television receivers.

In the past, tuning mechanisms of the type described have employed rather complex and space consuming linkages for fine tuning adjustment. Thus, the operative tuning projections sometimes have been in the form of adjustable screws movable axially into or out of the channel selector drum, the movement of those screws being transmitted to a line tuning adjustment shaft via mechanical linkages such as pivotal arms, pins, etc. which as a result of their construction and path of movement require considerable space within the tuner chassis. Moreover, because the elements themselves extend out from the drum and are adapted to engage the linkages involved, considerable space, in the axial direction of the drum must be provided to accommodate such movement.

In addition to the above, the accuracy and wear characteristics of previous mechanisms of this type leave much to be desired.

More recently, UHF preset tuning mechanisms have been proposed in which fine tuning adjustment is achieved through the axial movement of a stud or nut along one of a plurality of threaded members each associated with a UHF channel, in response to the rotation of the selected threaded member. While mechanisms of this character typically represent a significant improvement over previous structures, there are several significant drawbacks associated with such devices. Thus, there is a tendency for the adjustable nut to tighten against or frictionally engage the end plate at either end of the threaded member, thereby impairing smooth operation, reducing accuracy and substantially increasing wear. Also, in prior art devices of this type the mechanisms for converting the axial movement of the selected tuning nut in rotary adjustment of the fine tuning rotor shaft are typically cumbersome} and require considerable space within the tuner chassis. Finally, the complexity of these mechanisms results in increased cost of manufacture and reduced reliability.

It is a primary object of the present invention to provide an improved preset device for UHF tuners which substantially eliminates all of the above mentioned drawbacks of prior art devices of this type.

More particularly, it is an object of the present invention to design a preset mechanism for UHF tuners in which the space requirements within the chassis are reduced to an absolute minimum.

It is another object of the present invention to provide a preset tuning mechanism of the type described in which smoothness and accuracy of operation have been enhanced to a degree unattainable in prior art structures.

It is yet another object of the present invention to provide an improved preset device for UI-IF tuners which is simple in construction and operation and inexpensive to manufacture.

It is still another object of the present invention to design a preset device of the type described incorporating a linkage mechansim which exhibits improved wear characteristics resulting in an operating life substantially longer than that of prior art constructions.

To these ends, the present invention comprises an improved construction of a preset device for UHF tuning mechanisms of the type wherein a rotary drum is affixed to a channel selector shaft. The drum is provided with a plurality of fine tuning adjustment screws mounted along its periphery, one screw for each channel. Mounted for movement axially along each screw is a fine tuning projection, the selected one of which engages one end of an axially extending rack plate. The other end of that plate is provided with a gear surface operatively drivingly engaging a gear fast on a fine tuning adjustment rotor shaft, that shaft being adapted to adjust one or more variable impedance elements within the tuning circuit housing.

The fine tuning projections are in the form of small cylindrical members extending from noncircular nuts threadedly mounted on the adjustment screws. The nuts are guided axially in noncircular grooves cut in the periphery of the drum, the cylindrical members extending radially outwardly from those grooves.

To facilitate transition from one channel to the next, the rack plate is formed with a cam portion adapted to engage successive tuning projections, the cam being curved to conform to the periphery of the drum and being provided with sloping cam surfaces extending at either side by an amount equal to the full range of axial movement of the tuning projections. The rack plate is spring biased away from the fine tuning rotor shaft. Accordingly, as the drum is rotated from one channel position to the next, one tuning projection slides along one sloping surface of the cam until the next projection engages the opposite sloping surface thereof, whereupon the next projection slides along that surface until the drum reaches it detented position, the rack plate moving against the bias spring to adjust the fine tuning rotor shaft to a preset condition corresponding to the axial position of the projection in question.

The adjusting screws are journalled in (but not threadedly engaged with) the drum and are provided at one end, extending axially from the drum, with gear surfaces The gear surface of the selected screw is adapted jto meshingly engage with a crotch gear rotatably mounted on a resilient pivotal bracket and is normally maintained by said bracket out of engagement with the crotch gear. The crotch gear is frictionally driven by an intermediate gear which in turn is adapted to be driven by a fine tuning drive gear fast on a fine tuning adjustment shaft. The fine tuning adjustment shaft is mounted concentrically of the channel selector shaft and is biased outwardly. Upon depression of the fine tuning adjustment knob, the fine tuning shaft is moved inwardly, the fine tuning drive gear drivingly engaging the intermediate gear and pivoting the bracket to bring the crotch gear into meshing relationship with the gear surface on the selected tuning screw. Rotation of that screw by means of the fine tuning shaft is effective to move its associated nut axially along that screw whereby the cylindrical projection moves the rack plate to adjust the rotor shaft.

A unique stop mechanism in the form of a stop pin radially projecting from the adjustment screw engages the adjustment nut at either end of its travel and serves to prevent any tightening or frictional engagement of the nut on the drum. This feature together with the frictional drive mechanism provides an unusually smooth and accurate fine tuning adjustment with a minimum of wear.

The device is constructed of a minimum of inexpensive parts combined in a surprisingly compact and efficient manner.

To the accomplishment of the above and to such other objects as may hereinafter appear, the present invention relates to a preset device for a UHF tuner as defined in the appended claims and as described herein with reference to the accompanying drawings, in which:

FIG. 1 is a plan view, partly in section, of a preset device constructed in accordance with the preferred embodiment of the present invention;

FIG. 2 is a cross-sectional view taken generally along the line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view, partly broken away, taken generally along the line 3-3 of FIG. 1;

FIG. 4 is an enlarged perspective view of the movable tuning projection, rack plate and rotor shaft of the tuner of FIG. 1;

FIG. 5 is a fragmentary plan view of one of the fine tuning adjustment screws and associated nut of FIG. 1 showing its range of travel;

FIG. 6 is a fragmentary sectional view taken generally along the line 66 of FIG. 1;

FIG. 7 is a fragmentary cross-sectional view taken generally along the line 7 7 of FIG. 1 and showing one embodiment of a frictional coupling arrangement for driving the selected tuning screw; and

FIG. 8 is a cross-sectional view similar to FIG. 7 showing a second frictional coupling arrangement for driving the selected tuning screw.

Referring to the drawings, wherein like reference numerals designate like parts throughout, and particularly to FIG. 1, the illustrated tuner comprises a chassis or main housing 10 enclosing the operative mechanical and electrical components of a UHF tuner. More particularly, a mechanical tuning drive mechanism generally designated 12 is disposed at the left hand side of main housing 10 adjacent a subhousing 14 within which the operative electrical tuning circuit components are disposed. The electrical components within housing 14 comprise a variable impedance tuning circuit and need not be described here in any detail as those components may be conventional and form no part of the present invention.

The operative variable impedance element or elements within subhousing 14 are operatively adjustably connected to a rotor shaft 16 journalled within one wall of the subhousing and adapted to provide rotatable adjustment to the operative tuning elements (i.e., capacitors or inductors) thereby to adjust the frequency to which the circuit is tuned in known manner. Rotor shaft 16 is spring biased counterclockwise (as viewed from the bottom of FIG. 1) by means of a tension coil spring 18 affixed at one end to a collar 20 fast on shaft 16, wound about that collar and affixed at its other end to the main housing 10. Shaft 16 is further provided with a gear 22 mounted fast thereon and meshingly drivingly engaged with a gear surface 23 on a longitudinally extending rack plate 24 which extends through a slot 26 in subhousing 14. Accordingly, as best shown in FIG. 4, the tuned frequency of the tuning circuit depends upon the extent to which the shaft 16 is rotated clockwise against the bias of spring 18 in response to the movement of rack plate 24 to the right as viewed in FIG. I. That movement of rack plate 24 is controlled by the mechanical tuning adjustment or drive mechanism 12 which provides for both preset channel selection and adjustable fine tuning for a given channel.

Referring again to FIG. 1 that drive mechanism comprises a channel selector shaft 28 joumalled in an end wall of housing and extending outwardly of that housing to terminate in a flattened end 28a upon which a channel selector knob may be conveniently mounted. Within housing 10 channel selector shaft 28 is adapted to provide step by step preset channel selection. For this purpose, mounted fast on channel selector shaft 28 within housing 10 is a rotatable turret or drum generally designated 30 provided with a plurality of axially adjustable tuning elements generally designated 32. Drum 30 comprises a cylindrical main body portion 31 extending between two end plates 33 and 35.

Tuning elements 32 are in the form of axially extending threaded members or screws 34 each disposed within a groove 36 formed in the periphery of the main body portion 31 of drum 30, those grooves 36 being generally equally spaced around the circumference of drum 30. As best shown in FIG. 5, screws 34 are journailed in end plates 33 and 35 by means of nonthreaded portions 37 of reduced cross section. Each screw 34 is provided outwardly of end plate 33 with a gear surface 40, each adapted in a selected position of drum 30 to be rotatably driven through a gear drive mechanism generally designated 42 (described in detail hereinafter).

Each screw 34 is provided with an internally threaded nut-like member 44 mounted thereon for axial movement relative thereto. As best shown in FIG. 3, each nut 44 comprises a main body portion 46 which is generally square in cross-section, slidably received within one of the generally square grooves 36 in the periphery of drum 30. A generally cylindrical projection 48 extends radially from the body portion 46 of each nut 44 beyond the circumference of drum 30, the projection 48 of the selected nut 44 being adapted to engage the rack plate 24 to move same to a preset condition corresponding to the preset frequency of the associated channel.

As best shown in FIG. 4, projections 48 are generally circular in cross section, the circumferential surfaces thereof being adapted to engage a cam portion generally designated 50 provided integrally on the left-hand end of rack plate 24. Cam 50 is generally triangular in configuration, having a generally V-shaped cam surface 52 with a rounded apex 52a and gently sloping side surfaces 52b and 520. Accordingly, as best shown in FIGS. 3 and 4, as drum 30 is rotated, for example, in the clockwise direction (as viewed in FIG. 3) the projections 48 on successive nuts 46 engage the cam 52 at its leading sloping surface 520, slide along that edge over. the rounded apex 52a and thence along the trailing sloping surface 52b. Since the axial positions of nuts 46 on screws 34 are preset, the engagement of cam 52 by a projection 48 and its movement along surface 52c thereof, effects a predetermined movement to the right (as viewed in FIG. I) of rack 24.

Drum 30 is detented to positions corresponding to the engagement of each projection 48 with the rounded apex 52a of cam 52, by means of a detent mechanism, generally designated 54 (FIG. I). As best illustrated in FIGS. 1 and 6, mechanism 54 comprises a cam plate 56 mounted fast on channel selector shaft 28 adjacent subhousing 14 and provided with a plurality of equally spaced triangular projections 58 corresponding in number to the number of adjustable nuts 44 carried on the periphery of drum 30 (here shown as eight). An elongated resilient member 60 is anchored at one end on a wall of housing 10, extends parallel to channel selector shaft 28 past drum 30 and is provided at its other end with a depending spring portion 62 which is provided with a bent part 64 adapted to snugly fit into the crevice 66 defined between successive projections on cam plate 56. As shaft 28 is rotated from one detented position to the next, a projection 58 slidingly engages the bent part 64 of spring portion 62 to move same radially outwardly to the left as viewed in FIG. 6 until the point of the projection passes the point 68 of the bent part 64, whereupon the spring snaps back into the next crevice defining the next detented position. Each time the channel selector shaft is rotated from one channel position to the next, as described above, the associated tuning projection 48 engages the sloping cam surface (52b or 520 depending upon the direction of rotation) and moves to the apex 52a of cam 52 as shown in FIG. 4.

As best shown in FIG. 3, cam plate 52 is curved to conform generally to the periphery of drum 30. The reason for this is twofold. First, it insures that the cam is accurately aligned with projections 48 along its entire operative surface including the full length of sloping surfaces 52b and 52c (see FIG. 3). Since the sloping surfaces 52b and 52c preferably extend, in the axial direction of drum 30, the full adjustment length W of nuts 48, each nut will engage the cam surface regardless of its axial position. Second, the curvature of cam plate 52 contributes significantly to the compactness of the mechanism.

Referring to FIG. 5, it will be seen that screws 34 are threaded along the entire length of drum 30 from end plate 33 to end plate 35, thereby affording nuts 44 a maximum span w of axial fine tuning adjustment. However, it will be appreciated that if nuts 44 are allowed to engage end plates 33 and 35 at the extremities of their axial travel, excessive torque on gear surface 40 would effect a frictional engagement between nut 44 and the end plate, thereby tightening or jamming the nut against the inner surface of the end plate. As a result disengagement would be difficult and smooth operation would be severely impaired.

To prevent such occurrence, means are provided to prevent further rotation of screws 34 prior to the engagement of their respective nuts 44 with end plates 33 and 35. As best illustrated in FIG. 5, that means comprises a pair of stop pins 68 radially projecting from threaded screws 34 at either end thereof adjacent but slightly spaced from end plates 33 and 35. Nuts 44 are formed with oppositely extending shoulders 69 defining oppositely facing ledges 70 adapted to engage pins 68 as the nut 44 approaches an end plate, as illustrated. Once thus engaged, nut 44 is locked against movement in one direction relative to screw 34. However, it will be apparent that rotation of screw 34 in the opposite direction is unimpeded by the locking pin, there being no frictional engagement to overcome. The angular and axial location of pins 68 must be carefully designed to correspond to the mating angular and axial position of nut 44 in order to insure against the frictional engagement of the pin 68 with the end surfaces 72 of nut 44.

Referring again to FIG. 1, the fine tuning drive mechanism 42 comprises a fine tuning adjustment shaft 74 mounted concentrically on channel selector shaft 28 and movable axially and rotatively relative thereto. Within housing 10, shaft 74 is provided with a fine tuning drive gear 76 fast thereon. Shaft 74 and gear 76 are biased outwardly to the left as viewed in FIG. 1 (solid line position) by means of a flat spring bracket 78 anchored at one end on housing and normally extending downwardly to the left (as viewed in FIG. 1). Mounted on the lower end of spring bracket 78 is a gear drive mechanism 80, adapted in its broken line position to effect an operative driving connection between gear 76 and the gear surface 40 of the selected tuning screw 34. As best shown in FIG. 7, in a preferred embodiment, gear mechanism 80 comprises a shaft 82, journalled in spring bracket 78 and formed at one end with a gear surface 84. Mounted fast on shaft 82 at either side of spring bracket 78 are stop plates or

collars

86 and 88. An intermediate gear 90 is freely rotatable mounted on shaft 82 between stop ring 86 and spring bracket 78 and is urged against stop ring 86 by means of a spring washer 92 compressed between stop ring 88 and spring bracket 78. Accordingly shaft 82 is frictionally driven by gear 90 via stop ring 86. Shaft 82 extends through an enlarged aperture 93 in a bracket 97 fixedly mounted on housing 10, collar 88 engaging bracket 97 when shaft 74 is moved in the direction of arrow 96.

An alternative frictional drive mechanism is illustrated in FIG. 8, like reference numerals designating like parts. As there shown, shaft 82 is provided with a circular disc 94 mounted fast thereon, that disc being urged into frictional engagement with gear 90 by means of a coil spring 96 compressed between gear 84 and gear 90. In order to provide good frictional drive without unnecessary slippage, the engaging surfaces of disc 94 and gear 90 may be appropriately roughened as shown at 95.

While the frictional coupling is here shown in both FIGS. 7 and 8 between

gears

90 and 84, it will be apparent that this coupling may be provided at any other point in the drive mechanism 42 such, for example, as between fine tuning adjustment shaft 74 and gear 76. In any case, the frictional coupling should be sufficient to transmit the rotation of fine tuning adjustment shaft 78 to the selected tuning screw 34 during normal operation without slippage. However, upon the nut 44 engaging a stop pin 68 at the end of its axial adjustment span that frictional coupling is adapted to yield to prevent any damage to the mechanism.

The operation of the fine tuning adjustment mechanism will now be apparent. Upon the depression of fine tuning adjustment shaft 74 inwardly (to the right) in the direction of arrow 98, spring bracket 78 moves to the right bringing collar 88 into engagement with bracket 97 and gear 84 into engagement with the gear surface 40 of the selected tuning screw 34, drive gear 76 engaging intermediate gear 90. Rotation of shaft 74 accordingly is transmitted via gear 76 to gear 90,

through the frictional coupling to gear 84 and thence to the selected tuning screw 34 via its gear surface 40.

Rotation of the selected screw in turn effects an axial 5 adjustment of nut 44 which is transmitted via projection 48, cam 52 and rack plate 24 to rotor shaft 16, thereby to adjust the impedance of operative electrical tuning elements within subhousing 14.

It will be appreciated from the foregoing that we have provided a preset device for a UHF tuner of simple construction which is inexpensive to manufacture and takes up a minimum of space within the receiver chassis. The preset device herein described provides improved accuracy and wear characteristics thereby substantially enhancing its effective operating life. The unique stop mechanism herein provided insures against sticking or frictional locking of the operative fine tuning adjustment nuts at either end of their full range of travel thereby to provide surprising accuracy and smoothness of operation combined with a minimum of wear. The operating life of the device is further enhanced by the provision for a frictional coupling engagement adapted to yield upon reaching the terminal position of the adjusting nuts.

While only a limited number of embodiments of the present invention have been herein specifically disclosed, it will be appreciated that many variations may be made therein without departing from the scope of the invention, as defined in the following claims.

We claim:

1. A preset device for a tuner comprising rotatable channel selector means, a rotatable fine tuning adjustment shaft, adjustable tuning means, a plurality of externally threaded elongated members rotatably mounted on said channel selector means and extending in a direction substantially parallel to the axis of said channel selector means, frictional drive coupling means movable between first and second positions and effective in its second position to operably frictionally drivingly connect said fine tuning adjustment shaft and a selected one of said externally threaded members, a resilient bracket means mounting said drive coupling means in said first position, said fine tuning adjustment shaft being movable axially and when so moved operably engaging said resilient bracket means to move said drive coupling means to said second position, a plurality of internally threaded members each threadedly mounted on one of said externally threaded members and adapted to move axially along said externally threaded member in response to the rotation thereof, each of said internally threaded members being provided with a fine tuning projection extending in a direction radially outwardly of said axis of said channel selector means, and means movable axially along the channel selector means and engaging a selected one of said fine tuning projections, said movable means being effective to adjust said tuning means in accordance with the position of said fine tuning projection, and means projecting radially from said externally threaded member and adapted to engage said internally threaded member in a direction transverse to the axis of said externally threaded member as said internally threaded member approaches the end of its axial adjusting span, thereby to provide a nonfrictionally engaging stop means for said internally threaded member.

2. The preset device of claim 1 wherein said drive coupling means comprises a first gear operably engaging said fine tuning adjustment shaft, a second gear adapted to operably engage said selected externally threaded member, and means frictionally coupling said first and second gears.

3. A preset device for a tuner comprising rotatable channel selector means, a rotatable fine tuning adjustment shaft, adjustable tuning means, a plurality of externally threaded elongated members rotatably mounted on said channel selector means and extending in a direction substantially parallel to the axis of said channel selector means, frictional drive coupling means movable between first and second positions and effective in its second position to operably frictionally drivingly connect said fine tuning adjustment shaft and a selected one of said externally threaded members, a resilient bracket means mounting said drive coupling means in said first position, said fine tuning adjustment shaft being movable axially and when so moved operably engaging said resilient bracket means to move said drive coupling means to said second position, a plurality of internally threaded members each threadedly mounted on one of said externally threaded members and adapted to move axially along said externally threaded member in response to the rotation thereof, each of said internally threaded members being provided with a fine tuning projection extending in a direction radially outwardly of said axis of said channel selector means, and means movable axially along the channel selector means and engaging a selected one of said fine tuning projections, said movable means being effective to adjust said tuning means in accordance with the position of said fine tuning projection.

4. The preset device of claim 3 wherein said drive coupling means comprises a first gear operably engaging said fine tuning adjustment shaft, a second gear adopted to operably engage said selected externally threaded member, and means frictionally coupling said first and second gears.

5. The preset device according to claim 2 wherein said axially movable means comprises a member axially movable along said channel selector means, said axially movable member having a cam portion engaging a selected one of said fine tuning projections for movement in accordance with the axial position thereof and a rack portion integral with said cam portion and rectilinearly movable in the same plane therewith, and wherein said adjustable tuning means comprises a rotary shaft, and gear means operably drivingly connected to said rotary shaft, said rack portion drivingly engaging said gear means to rotate said rotary shaft in accordance with the axial movement of said axially movable member.