Patent GB-584014-A (GB)
Title: Improvements in radio or like signal reproducers
IPC: H03J1/06
Filed: 1944-07-03
Abstract: 584,014. Volume control. McDONALD, E. F. July 3, 1944, No. 12613. [Class 40 (iv)] [Also in Group XL] Radio or like signal receivers have their output volume controlled by two independent means, which are spaced a considerable distance apart, one means being capable of transferring the control from one to the other. One of the means may be capable also of muting the loud-speaker and. changing the tuning. The controls are designed preferably for use in moving vehicles, and the control which includes the muting and the tuning may bo a pedal mounted to be accessible to the driver's foot, the other control preferably being mounted on the dashboard. In the example shown in Fig. 1, the power supply and the high-frequency stages 11 feed the transformer 20, the secondary of which is tuned by condenser 21 and connected to the diode detector section of the diode-triode valve 12. The output of the detector is fed through control potentiometers 71 or 37 to the control grid 25 of the triode section of the valve 12. The output from this amplifying stage is fed through resistance capacitance coupling to the power valve 13 and hence through the audio-frequency transformer 36 to the loud-speaker 14. The detected signal voltage appears between earth and the junction of resistances 28, 27. With the supply switch 34 closed (and switches 38, 53 as shown in Fig. 1), the output voltage across resistance 28 is also across potentiometer 37 contained in the driver's pedal control 46 and by changing the position of the moving contact 50 a variable amount of this voltage can be fed to the grid 25 by way of the switch 53 and the condenser 31. When switches 38, 53 are moved to the right, they cause the voltage across 28 to appear across the potentiometer 71, and so the voltage fed to the grid 25 may be varied by moving the contact 70. In this way there are two independent means of controlling the volume output of the receiver, the transferring from one control to the other being effected by the switches 38, 53. The pedal control 46 is associated with the radio receiver by multi-strand cables A, B, plug 41 and socket 42. One end of the secondary of the transformer 36 is earthed and the other is connected through the cable B to a movable contact 55. The pedal 54 is earthed and on bringing together the contacts 54, 55 by pressure on the pedal, the loud-speaker is muted. On further pressure, the contacts 54, 55 connect with a fixed contact 56 which energizes an operating coil 62 by battery 35, this coil controlling the mechanism for tuning the receiver. Figs. 4 and 6 are two examples of the control device 46. In Fig. 4 the control of the voltage from potentiometer 37 is effected by rotating the pedal 91. By depressing lightly the pedal 91 against spring 93, contacts 54, 55 are connected, and on further depression against the spring 94 these contacts are connected to fixed contact 56. In Fig. 6, a wheel 101 is mounted, within the housing 100, on the shaft of a potentiometer 102 which is in turn supported through a spring 103 from housing 100. Part of the wheel projects through an opening 104 in the housing so that the driver may depress or rotate the wheel by his foot. Rotation of the wheel adjusts potentiometer 102, depression causes the heading downwards of the free end of the spring 103 which carries two contacts 106, 107. Two co-operating contacts 108, 109 are mounted on insulation and are arranged so that as the end of the spring moves down the first effect is that contact 106 touches the contact 108 so muting the receiver, and the second effect is to make a connection between contacts 107, 109 which is effective to energize the operating coil 62. Fig. 7 is an example of the manual control device comprising a single switch 34 attached to the back of the volume control potentiometer resistance 71. Initial rotation of the shaft 81 closes switch 34,- further rotation causes a resilient member 112, fixed radially to the shaft 81, to engage the operating handle 111 of a double-pole, double-throw toggle switch 110 and move it to its opposite position. This switch performs the functions of switches 38, 53 in Fig. 1. Still further rotation of the shaft bends the member 112 over the handle 111 and then is effective to alter the voltage taken from across resistance 71 to be fed to the control grid 25. Figs. 9 and 10 show modified wiring arrangements and controls. Fig. 9 has the same pedal control system 46 as in Fig. 1, but the switch 34 is operated jointly with a tone control resistance 120. The volume control resistances 71, 37 are permanently in parallel of the resistance 28 which now forms, with condenser 130, a low-pass filter and the D.C. component of the detector output voltage appears across condenser 130 and can be used for automatic volume control purposes. In Fig. 10, the volume control resistance 140 is connected between earth and a point between resistances 27, 28, and is provided with two taps 141, 142. A multiple push-button switch 143 is used for the manual control. Button " O " is used in place of switch 34, " F " transfers control of the output volume from the manual to pedal control, " I " operates the receiver at full output volume independently of the setting of the tap 50 on resistance 37 ; 2 and 3 operate the receiver at lower volume by connecting control grid 25 to tap 141, 142 respectively. Resistance 37 is connected by conductors 63 and 172 across the input of the loud-speaker 14. The tapping 50 is connected to the cathode 24 of valve 12 and thus feeds back, in opposite phase, into the input circuit of valve 12 a portion of the output voltage. Adjustment of the tap 50 thus 'controls the output volume of the receiver.