Loudspeaking telephone using transistors

Abstract

Abstract 858,678. Substitution circuits. GENERAL TELEPHONE LABORATORIES Inc. Dec. 30, 1957 [Jan. 15, 1957], No. 40317/57. Class 40 (4). A loud-speaking sub-station has a pair of transistor amplifiers powdered from the exchange battery for amplifying incoming and outgoing speech currents. The apparatus can be used in normal manner, making use of a normal transmitter 133, receiver 134, and impulse springs 21. If, however, the subscriber wishes to use the loud -speaking facilities he turns control knob 40<SP>1</SP> so closing contacts 41, 43 and opening 42, Fig. 1. The circuit shown in Fig. 2 is now brought into use. A silicon-carbide resistor 31 maintains the voltage applied from exchange battery substantially constant, as described in Specification 849,530. A full-wave rectifier 32-35 supplies power through filters 151-156 to a microphone transistor amplifier with two stages 110, 120, a transistor oscillator 130, and a loud-speaker transistor amplifier 160, 170, 180, the filters ensuring that voice frequencies do not disturb the power supply. The signal output from the microphone 55 and the input to the loud-speaker 65 pass through induction coil 56 and resistance bridge 140, whereby interference is prevented. While the loudspeaking equipment is in use the oscillator 130 flashes a neon tube 62. If the subscriber wishes to cut-off the microphone he depresses button 40<SP>1</SP> so closing contacts 44 and shunting the microphone 55. The volume of the loudspeaker is controlled by knob 60<SP>1</SP>. The components shown inside the dashed lines 80 and 90 are mounted on printed-circuit cards inside the set, Fig. 6, and loud-speaker box, Fig. 8, respectively. The card 80 is of plug-in type. To answer a call the subscriber either lifts the handset or turns knob 40<SP>1</SP> to the loud-speaking position. Specifications 693,137 and 795,620 also are referred to.

Inventors

No inventors recorded.

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