Patent GB-501370-A (GB)
Title: Improvements in or relating to tuning devices for radio receivers
IPC: H03J5/14
Filed: 1937-09-01
Abstract: 501,370. Electric control systems. MITCHELL, F. A. Sept. 1, 1937, No. 23864. [Class 40 (i)] The tuning device of a radio receiver is set under the control of a rotary member having conducting and insulating zones engaging contacts, one of which is selected to determine the setting, an electric motor for rotating the member being controlled over the contacts in such a manner that the direction of rotation depends on whether the selected contact is engaging a conducting or insulating zone. If contact is with an insulating zone, the drive continues until the contact leaves the zone and is then reversed until it is insulated again. The contacts may be selected as described in Specification 416,775, or by a sliding contactor or push-buttons. Several such contact selectors may be associated with one receiver. A lead from a push-button switch 12, only one of which is shown in Fig. 1, may be plugged into sockets A-N of panel 11 connected with the contacts A-N engaging with the rotary control member 6, the push-buttons being fewer in number than the contacts so that any desired tuning positions may be provided for. The rotary member 6 has an insulating zone 8, Fig. 2, with stepped edges to stop the motor after an angle of rotation determined by the selected contact, the angle being limited to 180‹. Assuming first that the member 6 is in its extreme anticlockwise position, 'the selected contact being engaged with the insulating zone, full depression of button 12 until the lower spring 13 contacts with a grounded plate, operates relay 31 and magnet 21 from a source comprising rectified A.C. from transformer secondary 25, potentials for the receiver being supplied over other secondary windings. Magnet 21 operates a common latch 20 to hold the button, when released, in an intermediate position, and the magnet and relay 31 remain held. The windings 28-30 of the motor are fed from the primary 27 of the transformer, the circuit of winding 28 and also of winding 30 being closed by relay 31 so that member 6 is rotated in the clockwise direction. When the selected contact reaches the conducting zone, relay 32 pulls up from ground on member 6 over the depressed key and replaces motor winding 30 by winding 29 to reverse the direction of rotation, the holding circuits of relay 31 and magnet 21 being transferred to the ground on member 6. Thus, the member rotates back until the selected contact runs off the conducting zone, whereupon relay 31 and magnet 21 are de-energized and the motor stops, relay 32 being released when the button 12 restores. If, however, the selected contact is in engagement with a conducting zone, relays 31, 32 and magnet 21 are all operated substantially immediately the button is pressed and the motor will rotate counterclockwise as will be understood from the above description. If due to ordinary manual control, the member 6 had been rotated clockwise through 180‹, selection of a contact engaged with the insulating zone' would, with the' circuits so far described, tend to further clockwise rotation, whereas counterclockwise rotation is required. This is effected by the portion 56 of the conducting zone which in the extreme clockwise position engages contact G to operate relay 32 when relay 31 is operated by any depressed button. Switching-off the' receiver, and other controlling arrangements. A switching-off button is connected to contact 0 which, when the receiver has been tuned, is always on the conducting zone. The member 6 is thus rotated counterclockwise until part 57 of the insulating zone engages contact 0. In this position, a striker on member 6 operates contacts 50 to switch off. When tuning is taking place, it is arranged that the loud-speaker plugged into sockets 59 and fed by secondary 56 of the output transformer, is muted over contacts of relays ,31, 32. A potentiometer 55 provides volume control. Adjusting the relative positions of the contacts and member 6. The contacts A-N may be mounted to move up and down in grooves in the support 9. As shown in Fig. 8, the contact 111 is V-shaped and engaged by a lever 124 rotated by a disc 128 and worm' gearing, or the lever may be rotated directly. Modified adjusting arrangements, Figs. 6 and 9 (not shown), are also described and a further adjustable arrangement, Fig. 11, is described below. Modifications. The press-buttons may be replaced by a sliding contactor, Fig. 10 (not shown) used in conjunction with a single pressbutton to complete the various circuits controlled by the press-buttons in Fig. 1. In the modification shown in Fig. 11, using separate press-buttons 230, the rotary member 207 comprises an insulating disc with an inset semicircular conducting zone 208. The contacts 212 are adjustably mounted in slots in a fixed plate 211 and are set by manually tuning to a desired station and moving a corresponding contact up to the edge of the conducting zone. A press-button 230 is first completely depressed to close springs 218, 220, 223 and 225, 220A, springs 220, 220A being connected to the A.C. supply and the upper group of springs being held and ultimately opened by a latch 229 released on depression of another key. If the selected contact is on the insulating zone, winding 221 of 'the motor is supplied over condenser 224 and the lower pair of springs, winding 222 being supplied over the upper springs. The motor runs counterclockwise, closing contacts 227 controlled by a disc 226, thereby operating magnet 228 to hold closed the lower pair of springs. When the contact 212 reaches the conducting zone, condenser 224 is short-circuited and the resulting phasechange in winding 221 reverses the motor so that contacts 227 open to release magnet 228, to open the motor circuit over condenser 224, the other motor circuit being opened when the contact again engages the insulating zone. If the contact were on the conducting zone, condenser 224 would be short-circuited and the motor driven clockwise until the contact reached the insulating zone; magnet 228 would not be energized. The insulating zone may have portions corresponding in function to 56, 57, Fig. 2.