Patent GB-462475-A (GB)
Title: Improvements in or relating to radio receivers
IPC: H03J3/12
Filed: 1935-10-07
Abstract: 462,475. Wireless receiving circuits. COLE, Ltd., E. K., and BRADFIELD, G. Oct. 7, 1935, No. 27597. [Class 40 (v)] A radio-receiver is held in tune with a desired signal by a control current derived. from the signal circuit by means of a low frequency amplifying valve which acts to disable the tuning knob and automatically resumes its normal function when the receiver is in tune. In the drawing accompanying the Provisional Specification the output from the signal diode V3 of a super - heterodyne receiver is applied over a switch S2 to an audio - frequency amplifier V4, the output of which is connected either to the loudspeaker LS or over a rectifier G to a relay winding K by means of switches S3, S4. With S2 open, V3 is coupled to V4 over a transformer F tuned to 300 cycles. Between the output circuit of the I.F. amplifier V2 and the control grid of the octode mixing valve V is connected a feed-back circuit comprising a series circuit LC tuned to the intermediate frequency and controlled by switch S1. When the receiver is being manually tuned, switches S1, S3, S6 are closed. The valves V1, V2, reciprocally coupled over circuit LC oscillate at the true intermediate frequency ; the I.F. due to the incoming signal gradually approaches the true I.F. as the receiver is brought into tune, and beats set up between the two oscillations present in the input of V 3 consequently decrease in frequency. At 300 cycles the circuit F is energized, the amplified beats being rectified at G and energize relay winding K to pull up the relay arm B. This applies a brake to the shaft U of the tuning condenser on which the control knob is frictionally mounted, so that further operation of the knob has no effect on tuning. The pivoted arm B simultaneously operates switch assembly D which closes S5 to complete the relay holding circuit RK1, opens S and S3, closes S7, S2 and S4 to restore the receiver to normal reproduction condition. Closure of S7 lights an indicator lamp to show that the set is in tune. In a modification, Fig. 1, Comp. (not shown), a separate fixedtuned oscillator is provided instead of the oscillation coupling LC of V1 and V2. The switch S6 may be operated by pushing the tuning knob inwards to release the brake for another manual tuning operation. Fig. 2 shows an arrangement of the control knob A of the receiver, which is fixed to a bush G freely rotatable on the shaft K. A bush H is keyed to shaft K and a ball contact permits a friction drive between A and K by means of a spring member J. Inward pressure on knob A opens the contacts 15 corresponding to switch S6 ; B is a reduction gear and L the spindle of the tuning condenser. In a modified construction the switch may comprise a pair of spring contacts secured to slip-rings, and so arranged with respect to a third fixed contact that movement of the knob when the tuning shaft is braked opens one of the contacts, Figs. 3 and 4 (not shown). The brake may consist of a thin resilient segment which is clamped between the brake solenoid plunger and a stud on the chassis when the brake is energized, Fig. 5 (not shown). Specification 451,345 is referred to.