Patent GB-526886-A (GB)
Title: Tuning control device for radio receivers and the like
IPC: H03J5/32
Filed: 1939-03-18
Abstract: 526,886. Wireless receiving sets. PHILCO RADIO & TELEVISION CORPORATION. March 18, 1939, No. 8713. Convention date, April 13, 1938. [Class 40 (v)] Wireless sets with pushbutton control have one group of pushes arranged to select particular wave-ranges for manual tuning, and a second group arranged for station selection, the pre-set elements for station selection being associated with a common conductor which is connected through the contacts of the first group of pushes to the grid of the first valve so long as those pushes are inoperative, but is disconnected when these pushes are pressed. The tuning-dial lamp may be extinguished when a station-selection button is pushed, and a further pushbutton may be provided for switching off the set. As shown in Fig. 1, the circuit comprises a frequency-changing valve O with a short-wave coil SW and a medium-wave coil BC on the input side, and with similar coils SW<SP>1</SP>, BC<SP>1</SP> in the oscillator section. The output feeds an amplifier IF, detector D, and audio amplifier AF. The first group of pushes Ps, Pb are arranged, when operated, to connect a manually-operated tuning condenser TC across the respective input coils SW, BC and a condenser TC<SP>1</SP> ganged with TC across the corresponding oscillator coils. The second group of pushes P, ... P. select a particular pre-set condenser C, ... C 5  for connection to the conductor d and a corresponding condenser C 1 <SP>1</SP> ... C 5 <SP>1</SP> for connection to the conductor d<SP>1</SP>. When the pushes P 5 , P, are unoperated the conductor d is connected through their contacts to the grid lead e and to the medium-wave lead b, so that operation of any of the pushes P 1  ... P 5  connects the corresponding condenser C 1  ... C 5  both to the coil BC and to the grid of valve O, and makes corresponding connections for the oscillator circuits. The lead d is however disconnected from the grid lead e when either of the buttons P 5 , P 3  is depressed. A dial damp L is cut off from the supply transformer T when any of the pushes P 1  ... P 5  is pressed, and a second lamp or lamps L, illuminate the pushbutton indicators whenever the set is in operation, preferably as in Specification 521,812. The mains plug is connected to the supply transformer T through the contacts of a push P, depression of which disconnects the supply, and by means of a latch bar LB common to all the pushes, releases any operated push. Operation of any of the other pushes releases the push P and thus connects the power supply to the set. The pushes may extend through an inclined panel along the upper front edge of the cabinet, and the tuning- dial may extend in a straight line above the pushes with the tuning-knob movable longitudinally beneath the pushes. The moving contacts of the push-switches comprise spring fingers 15 carried above and below insulating blocks 16 attached to the plungers 38 as shown in Fig. 4. The stationary contacts are formed by flexible metal strips 14, Fig. 3, bent and threaded through holes stamped in insulating strips 10, 11. A slightly modified circuit arrangement of the push switches and their contacts is described, Figs. 6 - 8 (not shown).