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AUDIO-FREQUENCY AMPLIFIERS COMPRISING ASSEMBLED UNITS FOR AMPLIFYING ELECTRIC SIGNALS, AUDIO-FREQUENCY TRANSFORMERS, CHOKE COILS, ELECTRIC PICK-UP TONE ARMS, ELECTRIC PICK-UP VOLTAGE CONTROLS, ELECTRICAL SOCKETS AND PLUGS, ELECTRICAL PHONOGRAPH PICK-UPS, POWER TRANSFORMERS, HIGH VOLTAGE IGNITION TRANSFORMERS, ENERGIZING TRANSFORMERS FOR ELECTRIC SIGNS, VOLTAGE AND CURRENT REGULATING DEVICES OF THE MOVING COIL TYPE, INTERCOMMUNICATING SOUND AMPLIFYING AND TRANSMITTING SYSTEMS AND PARTS THEREOF, COMPRISING SPEAKERS, AMPLIFIERS, MICROPHONES, INTERCONNECTING CIRCUITS, AND ENERGIZING DEVICES WHERE-BY CONVERSATION AT EITHER POINT MAY BE HEARD AT THE OTHER POINT OF COMMUNICATION