US2197312A - Automatic broadcasting station selector and volume control - Google Patents

Description

April 16, 1940- c. o. NELsoN 2,197,312

I UTOIATIC BROADCASTING STTION SELECTOR bAND VOLUME CONTROL Filled Oct. 28, 1938 4 Sheets-Sheet 1 April 1s, 1940. l c o, NELSQ'N 2,197,312

AUTOMATIC BROADCASTING STATION SELECTOR AND VOLUME CONTROL Filed Oct. 28, 1938 4 Sheets-Sheet 2 eww@ tm @was ajlgyn iN ENTOR April 1s, 1940. o, NELSN' 2,197,312

AUTOIATIVIC BROADCASTING STATION SELECTOR AND VOLUME CONTROL Filed oct. 28. 195e 4 sheets-sheet :s

INVENTOR ATTORN EYS April 16, 1940. Q oa NELSON 2,197,312

AUTUIATIC BROADCASTING STATION SELECTOR AND VOLUME ,CONTROL Filed Oct. 28, 1938 4 Sheets-Sheet 4 T0 SET mZzls ajlfelmef' A ATTORNEYS Patented Apr. 16, 1940 UNITED STATES AUTOMATIC BROADCASTING STATION SELECTOR AND VOLUME CONTROL Curtis 0. Nelson, Belleville, Ill. Application October 28, 1938, Serial No. 237,563

4 Claims.

My invention relates to radio receivers and has among its objects and advantages the provision of an automatic broadcasting station selector and volume control.

An object of my invention is to provide novel means by which a radio receiving set may be automatically tuned to preselected broadcast frequencies at predetermined times and in which novel volume control means are incorporated.

The invention embodies novel selecting means whereby the apparatus is so designed as to automatically tune different stations in and out at predetermined times. The invention may be associated with a radio receiver of conventional design and is so associated therewith as not to interfere with the manual control of the receiver independently of the automatic feature. The station selector embodies means whereby selected stations may be tuned in and out more 20.A than once, for example, during a twelve hour period.

While radio waves received by a receiving set usually vary considerably in strength, the automatic volume control is so designed as to maintain the volume of sound from the receiving set substantially uniform. The volume control embodies means which may be precisely set or adjusted to the different broadcasting stations. Atmospheric conditions, distance and the like may weaken or strengthen signals. Precise adjustment is assured through the medium of a resistor which may be employed for correcting deficiencies in the automatic volume control.

In the accompanying drawings:

i Figure 1 is an elevational view of the selector drum and the automatic volume control;

Figure 2 is a top plan view of the structure of Figure 1;

Figure 3 is a sectional view along the line 3--3 oi Figure 1;

Figure 4 is a sectional view along the line 4-4 of Figure l;

Figure 5 is a perspective view illustrating the manner in which the selector pins are adjustably related to the selector drum;

Figure 6 is a view illustrating a switch;

Figure 7 is a view of the motor switch; and

Figure 8 is a diagrammatic view of the motor circuit.

50. In the embodiment selected to illustrate my invention, I make use of a radio receiver cabinet, a portion of which is illustrated at I8. Cabinet I0 is provided with a shelf I2 upon which I mount a selector drum I4. Drum I4 includes 55.y end flanges I6 and I8, see Figs. 1 and 3, con- (Cl. Z-20) nected with hubs 20 through the medium of spokes 22. Hubs 20are bored at 24 for the reception of a shaft 26 fxedly related to the hubs by means of set screws 28. Shaft 26 is rotatably journaled in bearings 30 formed at 5 the upper endsof brackets 32 and 34. Brackets 32 and 34 are Secured to the shelf I2 by screws 36.

Shaft 26 is connected with a shaft 38 through the medium of a iiexible coupling 40. Flexible 10 coupling 40 is bored for the reception of the ends of the shafts 26 and 38, and the coupling is made secure by set screws 42. Shaft 38 is driven by an electric clock 44 which may be of conventional design. The flexible coupling 40 15 dampens any vibration incident to operation of the clock. The cabinet panel 46 is bored at 48 for the reception of the clock so as to bring it substantially within the contour of the cabinet. The clock may include a. flange 50 lying 20 adjacent the outer face of the panel 46. In the present invention, the clock operates continuously so that the selector drum I4 is rotated Without interruption.

Flange I6 is formed integrally with the'pe- 25 ripheral Wall 52-of the selector drum. Wall 52 is provided with a plurality of slots 54 and is formed integrally with the ange IIi.y These parts may be formed by diecasting from suitable material such as zinc, white metal, or alumi-.30 num. Flange I8 is provided with a circumferential ledge 56 which supports the opposite end of the peripheral wall 52, and the latter is provided with a ange 58 fixedly secured to the iiange `I8 by screws 60. Flange 58 extends com- 35 pletely about the peripheral wall 52 and is of somewhat larger diameter than the wall.

Peripheral Wall 52 includes forty-eight slots 54 which represent fifteen mi-nute periods of time for a twelve hour period. 'I'he selector drum is 40 positioned adjacent the cabinet side wall 62 and extends across an opening 64 in the wall. The opening in the wall may be provided with an ornamental liner 66, which liner is provided with division lines 68 to provide zones 10, 12, 45 "I4, 16, 18, 80, y82 and 84. Zone 'I0 is designated neutral, as at 86, while zone I2 is designated off, as at 88. Zone I4 is designated on, as at 90, while zone 84 is designated neutral, as at 92. Zones T6, 18, and 82 are designated dif- 50 ferent broadcasting stations, as indicated at 94.

The peripheral wall 52 of the selector drum carries a plurality of pins 96. The pins 96 are slidably related to the slots 54, and two pins are provided for each slot. Figs. l and 5`best 55 through the medium of conventional drives.

illustrate the relation between the pins 96 and the slots 54. The wall 52 is provided with longitudinal ribs 98 intermediate the slots or centrally of the ribs |00. Ribs 98 are considerably narrower than the ribs |00. Pins 96 have close fitting relation with the walls of their respective slots 54, and each pin carries a flange |02 which bears against the outer faces of their adjoining ribs |00. Each pin 96 also includes a bowed spring |04 which bears against the inner faces of their adjoining ribs |00. Springs |04 are bent back upon themselves at |06 so as to provide gentle curvatures facilitating relative sliding movement of the pins longitudinally of the slots 54. The springs |04 are fixedly connected with the pins 96 and are under tension so as to frictionally support the pins. However, the pins may be manually shifted.

Figure 2 illustrates the pins 96 distributed over the general area of the peripheral wall 52. The distribution of the pins 96 will depend upon the broadcasting station or stations to be tuned in at a predetermined time or times. The selector drum |4 is rendered inoperative for automatic tuning by shifting the pins 96 to positions on the selector drum |4 corresponding to the neutral zones 10 and 84.

Floor |2 carries two brackets |08 and ||0. Bracket |08 and the upstanding flange |2 of the bracket ||0 rotatably support a shaft ||4. To one end of the shaft ||4 I connect a worm gear ||6 arranged in mesh with the worm ||8 driven by the electric motor |20. Bracket |08 is made secure by screws |22, while the bracket ||0 is anchored to the oor by screws |24. I interpose a slip clutch |26 in the shaft ||4. The manually rotated shaft |28 for turning the condenser of the set extends through an opening |30 in the wall 46 in the usual manner, and the opposite end of the shaft is rotatably journaled in the flange |32 4of the bracket ||0. Shaft ||4 is Xedly connected with a flange |34 having a V-shaped lug |36 normally extending into the groove |38 in a disc |40 splined to the shaft |28 for rotation therewith but slidable longitudinally thereof. Between the disc |40 and the ange |32, I interpose a compression spring 42 which urges the disc |48 against the disc |34. Spring |42 causes the lug |36 to have such holding relation with the grooved disc ||4 as to impart rotation to the shaft |23 through rotation of the shaft ||4 when the motor |20 is operating. Shaft |28 may be provided with a gear or wheel |44 which may be operatively connected with the variable condenser To the outer end of the shaft |28, I connect a knob |46 so that the shaft |28 may be manually rotated for tuning purposes in the usual way. The variable condenser should be of the type in which the rotary section may be rotated continuously in one direction.

With the motor |20 inoperative, the condenser may be tuned manually through the medium of the shaft |23. Manual rotation of the shaft |28 will cause the lug |32 to cam the disc |40 toward the flange |32 against the tension of the spring |42. With the motor |20 inoperative, shaft ||4 remains stationary. For automatic tuning purposes, the motor |20 rotates the shaft |28 through the medium of the shaft ||4 for tuning the condenser.

Upon the shaft ||4 I fixedly secure a plurality of stops |46', |48, |50 and |52. Stop |46' is aligned with the zone 16, while the stop |48 is aligned with the zone |18. Stop |50 is aligned with the zone 80, while stop |52 is aligned with the zone 82. In Fig. 2, I illustrate four station zones only, but the limited number is for the purpose of illustration only. More or less zones may be employed, since the construction of the selector drum 4 and its associated mechanism remains the same regardless of the number of the broadcasting zones.

Motor |20 operates to rotate the shaft |4 in the direction of the arrow |54, see Fig. 1. Brackets 32 and 34 support a shaft |56 which parallels the shaft |4. Upon the shaft |56, I mount companion stops |58, |60, |62 and |64. Companion stops |58 to |64 are aligned with the stops |46 to |52, respectively. Companion stops |58 to |64 are loosely mounted on the shaft |56 for rotation thereon. The stops are supported in spaced relation by spacers |66, and pins |68 extending through the shaft |56 restrain the assembled companion switch arms and the spacers |66 from relative movement longitudinally of the shaft |56.

Selector drum I4 is clock rotated in the direction of the arrow |10, see Fig. 1, and pins 96 are adjustable on the selector drum for camming the companion stops to positions for abutting relation with the stops |46 to |52. Fig. 1 illustrates the companion stop |64 pivoted to a horizontal position for bringing its end |12 into abutting relation with the stop |52 to prevent further rotation of the shaft ||4. Only one companion stop is pivoted to a horizontal position at a time, since each stop is associated with one broadcasting station only.

Motor |20 rotates the shaft ||4 for turning the condenser of the radio receiver. One pin 96 is aligned centrally of one of the zones 16 to 82, depending upon the broadcasting station selected, and the pin 96 selected depends upon the time at which the selected broadcasting station is to be tuned in. Flange 58 includes a diagonal face |14 upon which time indicia |16 are printed. The indicia are distributed to align with the slots 54 for representing fifteen minute periods of time. Fig. 1 illustrates one of the pins 96 in the |18 position as being in camming relation with the short end of the companion stop |64. The long end of the companion stop is characterized by an overbalancing weight in such a degree as to cause the long end to pivot downwardly as soon as the pin 96 in the |18 position has moved out of camming relation with the short end. Pin 96 in the |18 position has been aligned with the zone 82. Since the pin adjustment and other cooperating parts associated with each of the zones 16 to 84 operate in the same manner, the description of one adjustment will apply to all the zones.

With the stop |52 and the companion stop |64 positioned according to Fig. 1, the condenser of the receiver will be properly tuned to the demands of the broadcasting station represented by the zone 82. Referring to Fig. 1, the companion stop |64 reaches a horizontal position substantially at the time that the stop |52 is brought into abutting relation therewith. The stops |46', |48, |50 and |52 are cut away at |80 so as to provide cam faces of gentle angularity cooperating with the ends of their respective companion stops to prevent touching between the parts before the companion stops are moved completely to their stopping positions. However, the parts are so arranged that the companion stops are cammed to their abutting positions immediately before their respective stops are brought into abutting relation therewith. Means is provided for closing the circuit through the motor |20 at wire 268 through the medium of a wire 284.

such time as to bring the stop |52 into abutting relation with the companion Stop |64 at the proper time. Flange |58 is recessed peripherally at |82 to provide cam elevations |84 aligning with the slots 54. One such cam elevation is provided for each of the slots. The pin 96 in the |18 position has camming relation with the short end of the companion stop |66 for a considerable period of time. during the latter part of which time the cam elevation |84 in the |86 position is brought into pressure relation with the cam end |88 of a resilient spring conductor |99, see Figs. 1 and 7.

Spring contact |99 is anchored to an insulated support |92, and the contact is aligned with the ange 58. A conducting wire |94 is attached to a screw |96 having conducting relation with the contact |99 and anchored in the block |92. The latter is fixedly connected with the floor |2. Contact |99 carries a point |98 arranged to be moved into conducting relation with a contact 299 carried by a screw 292 to which I attach a conductor 294. The switch structure of Fig. 'l operates the electric motor |29.

Fig. 8 illustrates the motor and selector circuit. Line wires 298 and 2 9 lead to a source of current, withfthe wire 2|9 electrically connected with the clock 44 and the wire 298 connected with the clock through the medium of a wire 2|2. vWire 298 is connected with the terminal 2 |4 of a double pole switch 2|6. Terminal 2|8 of the switch 2|6 is connected with the wire 229 through the medium of a wire 224. Wire 229 leads to the receiving set not illustrated. The second wire to the receiving set is illustrated at 226 and is connected with the terminal 228 of the switch 2|6. A wire 239 connects the terminal 232 of the switch 2|6 with the wire 2|9. Switch element 234 may be moved into conducting relation with the terminal 232 at which time the switch element 236 will be electrically connected with the terminal 228 through the medium of the element 238. Under suc-h conditions. the circuit to the set will be closed asI follows: from the wire 208 to the terminal 2|4, switch element 236, element 238 and wire 226; from the wire 2|9 to the wire 239, terminal 232, switch element 234. wire 224 and wire 229.

To the wire 2|9, I connect a wire 249 leading to a contact 242 of a selector switch 244. The switch element 246 includes a contact 248 arranged to be brought into electrical relation with the contact 242. Switch element 246 is electrically connected with a wire 259 connected with the wire 229. The primary coil 252 of a transformer 254 is connected with a wire 256 leading to a contact or terminal 258 arranged to be electrically connected with the terminal 228 through the medium of the element 238 when the switch 2|6 is positioned according to Fig. 8. Coil 252 is connected with the wire 259 through the medium of a wire 269. Switch 2|6, of Fig. 8, is in the selector position.

The secondary coil 262 is connected with a wire 264 leading to a contact 266. Coil 262 is also connected with a wire 268 which leads to the motor |29. The wire 219 connects the motor |29 with a contact 212 carried by a relay switch `arm 214, which is pivotally mounted on a suitable support for movement about the airis `216. Wire 294 is connected with an on relay 218, while a wire 289 connects the on relay 218 with the off relay 292. Wire 289 is connected with the Off relay 282 is connected with a wire 284' which is switch 2|6 is positioned according to Fie connected with the bracket 34. Shaft |56 is of conducting material, which is also true of the bracket 34 so that the wire 284 will be electrically related to the shaft |56. Companion stops |59 to |64 are also of conducting material and are electrically related to the shaft |56.

Wire |94 connected with the spring contact |99 is connected with the wire 264 at one end and at its other end with the bracket ||9. Bracket ||9 is of conductive material so as to 'ce electrically related to the shaft ||4. Stops |46 to |52 are of conducting material and are arranged in electrical relation with the shaft ||4. Motor |29 is of sufficient capacity to handle the shaft ||4 as well as the receiver condenser through the medium of the shaft |28 and the drive between the latter and the condens-er. The motor operates with a low voltage which low voltage current is supplied because of the transformer 254,

Motor |29 can be energized only when the contact 248 is moved into electrical relation with the contact 242. Switch element 246 is pivotally connected at 299 with a bracket 292 secured to the blocks |92 by `a screw 294. Wire 259 is anchored to the screw 294, and the bracket 292 is of conductive material. A tension spring 296 has one end anchored at 298 to the bracket 292 and its opposite end anchored to a pin 399 .xedly connected with the upper end of the switch element 246. Referring to Fig. 8, the pivotal connection 299 is so located as to be positioned to one side of the tension spring 296 when the switch element 246 is pivoted in either direction. Switch element 246 carries cam surfaces 392 and 394 so arranged as to be engaged by certain of the pins 96 when properly located on the selector drum |4. Cam surface 392 is aligned with the zone 12, while cam surface 394 aligns with the zone 14. A pin 96 when shifted to align centrally with the zone 12 will be brought into camming relation with the off cam surface 392 for pivoting the switch element 245 to the position. of Figs. 3 and 6. Similarly, when one of the pins 96 is shifted on the selector drum i4 to align centrally with the zone 14, that pin will be brought into engagement with. the cam surface 394 for pivoting the switch element 246 to the on position. In the on position. the contact 24B on the switch element 246 will contact the contact 242 for electrically connecting the wire 249 with the wire 259.

With the switch 244 closed, assuming that the 8. the circuit to the radio receiving set will be closed as follows: from wire 2|9 through wires 249 and 259, to wire 220. Wire 2.98 will` then be electrically connected with the wire 226 through the medium In operation, switch 2|6 is positioned accordf ing to Fig, 8 for selector tuning purposes. The circuit to the receiver will then. be closed whew ever the switch 244 is closed. Closing and opening of the switch 244 is consummated through the medium of two pins 96. One pin is aligned with the on zone 14. while the second nin is aligned with the off zone 12. Fig. 2 illustrates such alignment. Pin 96 in the 399 position in advance of the pin 96 in the 3|9 position. The two pins are fifteen minutes apart in that they are associated with adjacent slots 54. With the t on and. off pins operating in adjacent slots. the

switch 244 will be closed at the preselected time. which time is determined by proper selection of the pin 96 to be aligned with the on zone 14. Indicia |16 correspond to the time reading on the face of the clock 447 so that the switch 244 will be closed at the proper time.

A number of stations may be pretuned to operate the receiver in successive fifteen minute periods, or the fifteen minute periods may be spaced at selected intervals. Similarly, one station may be pretuned and the receiver operated continuously for thirty minutes, forty-five minutes, an hour or longer. The length of time is determined by the location of the on and off pins 96 associated with the on and off zones 14 and 12. The off pin breaks the circuit to the receiver at the end of the pretuned period so that the set will require no attention other than proper setting of the selector mechanism.

Selector drum I4 is rotatable manually to facilitate selection of the pins 96. Opening 64 lends access to the selector drum. After the pins have been selected, drum I4 is manually rotated for setting the clock at the proper time after which the clock vn'll rotate the selector drum at the speed of the hour hand of the clock. Rotation of the selector drum will bring the pin 95 in the |18 position, for example, into camming relation with the companion stop |64. At the same time, spring contact |98 is depressed for closing the circuit through the motor |20. Motor |28 rotates the shaft H4 for bringing the stop |52, for example, into abutting relation with the companion stop |64 in its horizontal position to restrain further rotary movement of the shaft. Stop |52 is flxedly related to the shaft and is adjusted so as to stop further rotation of the shaft at the moment that the variable condenser of the set has been precisely tuned.

Referring to Fig. 8, when the spring contact |90 is depressed for bringing the contacts |98 and 280 into conducting relation, the circuit will be closed through the on relay 218, at which time the arm 214 will be pulled in the direction of the relay for establishing conducting relation be tween the contacts 266 and 212, Thus current will be supplied to the motor |26. Arm 214 is connected with one end of a spring 3|2, the other end of which is flxedly anchored to a suitable support. AXis 216 is located to one side of the spring 3|2 when the arm 214 is in either of its two positions so as to be yieldingly supported in such positions. Companion stop |84 does not engage the stop |52 until the moment that the cam elevation |84 in the |86 position passes over the cam end |88 of the conductor |88. As the conductor |98 is freed it separates the contacts |88 and 288, at which time the stop |52 lies in contacting relation with the companion stop |64 which immediately closes the circuit through the off relay 282. Relay 282 will then attract the arm 214 to the position of Fig. 8, at which time the spring 3|2 is rendered effective for yieldingly holding the arm in the position illustrated until such time as the on relay 218 may again be energized.

In Figs. 1, 2 and 4, I illustrate my automatic volume control 3|4. The volume control includes a bracket 3|8 having a threaded shank 3| 8 extending through the opening 328 in the wall 46. A nut 322 clamps the bracket to the wall. Bracket 356 carries a bar 324, an upright post 326 formed integrally with the bar and a second bar 328 paralleling the bar 324. Post 326 interconnects the bar 324 and 328 at one end, while a cross piece or post 330 interconnects the opposite ends through the medium of screws 332. Bars 324 and 328 are grooved at 334 for slidably receiving a rack 336 arranged in mesh with a pinion 338 fixed to a shaft 340. Bars 324 and 328 are provided with openings 342 for rotatably supporting the shaft 348, while the shank 3|8 is provided with an opening 344 loosely receiving the shaft. A knob 346 is fixed to the shaft 340 to permit manual rotation thereof.

Upon the rack 336, I mount a resistor 348, which resistor is insulated from the rack through the medium of a suitable strip 353 anchored to the elevations 352 on the rack 336 through the medlum of screws 352.

Post 338 is provided with an opening 354 for slidably receiving a shaft 356 having a square reach 358 slidable in the square opening 38|) in the post 326. A collar 362 is adjustably connected with the shaft 356 through the medium of a screw 364. Between the post 338 and the collar 362 and upon the shaft 356, I interpose a cornpression spring 366. The wire 368 of the volume control of the receiver is electrically connected with the post 330. Post 330 is in conducting relation with the shaft 356, while the collar 362 is also in conducting relation with the shaft. A feeler wire 318 is connected with the collar 362 at one end and has its other end contacting the resistor 348 and arranged to slide therealong. The other wire of the volume control circuit of the set is illustrated at 312 and is connected with the resistor at one end. The other end of the resistor is dead.

The outer end of the squared reach 358 is slotted at 314 to receive a Wheel 316 rotatably mounted on a pin 318. Wheel 316 has pressure relation with the periphery of a volume cam 380 Xedly connected with the shaft |28. Spring 366 urges the shaft 356 in the direction of the volume cam 380. Volume cam 38D is provided with peripheral recesses 382, 384, 386 and 388. Recess 382 receives the wheel 316 when the stop |52 is positioned according to Fig. 1. Movement of the feeler wire 310 along the resistor 348 in the direction of the wire 312 thus giving more power output. Recesses 382 to 388 are of different depths so as to vary the power output. One recess is provided for each of the stops |46' to |52. Recess 382 is operatively related to the stop |52, which stop is aligned with the zone 82 so that the power output value of the recess .Y

382 will be in accordance with the demands of the broadcasting station represented by that Zone. Recess 388 is associated with the stop |48, while the recess 386 is associated with the stop |46. Recess 384 is associated with the stop |58. It will thus be seen that the volume cam 380 functions as a volume control for each of the broadcasting stations represented by the zones 16, 18, 80 and 94. The number of recesses in the periphery of the volume cam will depend upon the number of the broadcasting station zones incorporated in the station selector.

Frequently atmospheric conditions, distance and the like may weaken or strengthen signals. I provide means whereby the automatic volume control may be precisely adjusted. Rack 336 may be shifted longitudinally through the medium of the gear 338 manually actuated through the medium of the' knob 346. Such adjustment of the rack 336 moves the resistor 348 relatively to the feeler wire 310. Adjustment of the resistor through the manual control increases or decreases the ratios of the recesses 382 to 388 in corresponding amounts. It will thus be seen that the manual control incorporated in the automatic volume control permits refinement to be made in the power output of the automatic control.

I claim: 1. An automatic tuning mechanism for radio receivers including a rotatable condenser shaft adapted to be turned to predetermined radio station tuning positions, a rotary station selector drum, a time device for rotating the selector drum, a motor including a circuit for turning the condenser shaft, a motor switch in said circuit including momentary switch closing means carried by the selector drum, an on, and` o switch including a circuit for connection with the receiver circuit, selector pins shiftable on said drum for actuating the on and ofi` switch at predetermined times, stops corresponding to different broadcasting stations fixed to the condenser shaft, shiftable companion stops, selector pins shiftable on the selector drum for moving the companion stops into abutting relation with said stops, to stop further rotation of the condenser shaft when rotated to respective tuning positions, said stops and said companion stops being electrically related and comprising a part of the circuit associated with the motor, and electrical means energized through contact of said stops with their respective companion stops, to maintain a broken circuit through the motor only.

2. An automatic tuning mechanism for radio receivers including a rotatable condenser shaft adapted to be turned to predetermined radio station tuning positions, a rotary station selector drum, a time device for rotating theselector drum, a motor including a circuit for turning the condenser shaft, a motor switch in said circuit including momentary switch closing means carried by the selector drum, an on and off switch including a circuit for connection with the receiver circuit, selector pins shiftable on said drum for actuating the on and off switch at predetermined times, stops corresponding to different broadcasting stations fixed to the' `condenser shaft, shiftable companion stops, selector pins shiftable on the selector drum for moving the companion stops into abutting relation with said stops, to stop further rotation of the condenser shaft whenrotated to respective tuning posil tions, said stops and said companion stops being electrically related and, comprising a part of the circuit associated with the motor, and electrical means energized through contaotkof one of said stops with its respective companion stop, to maintain a broken circuit through the motor only, all of said selector pins being shiftable to neutral positions on the selector drum.

3. The invention defined in claim one wherein the selector drum is provided with bar-like members p-aralleling the axis of rotation of the drum, with the bar-like members spaced to provide slots lfor the selector pinssaid bar-like members having flanges and each selector pin having a flange slidably engaging one flange of two bar-like members, and a spring connected with each pin and frictionally engaging the opposite sides of the two fianges engaged by the flange of that pin to frictionally secure the pin in its different positions.

4. The invention defined in claim one wherein the stops fixed to the condenser shaft are in the nature of arms projecting radially from the condenser shaft, said companion stops being in the nature of bars pivotally connected to a fixed support intermediate their ends and arranged to be pivoted by their respective 'selector pins to position the bars in the path of their respective stops fixed to the condenser shaft.

` CURTIS 0. NELSON.

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