21 ELECTRICAL APPARATUS-NAMELY, AUDIO AND RADIO-FREQUENCY GENERATORS, OSCILLATORS, DETECTORS, AMPLIFIERS, CATHODE-RAY LIGHT PICK-UP AND DISPLAY APPARATUS INCLUDING SCANNING AND RELATED CIRCUITS, PRE-AMPLIFIER BOOSTERS, CONVERTERS, MIXER SEPARATORS, AND WEATHERPROOF AND RADIATION-PROOF HOUSINGS FOR THE SAME; POWER-SUPPLY SYSTEMS; ELECTRICAL CONNECTORS, PLUGS, CABLES, TRANSMISSION LINES, LINE AND CABLE COUPLERS, OUTLETS, TAP-OFF CONNECTORS, MOUNTING PLATES,CONTROL BOXES, ISOLATION AND OUTLET NETWORKS, LINE SPLITTERS, IMPEDANCEMATCHING DEVICES, FILTERS, ATTENUATORS, ATTENUATION EQUALIZERS, DUPLEXERS, DIRECTIONAL COUPLERS, WAVE TRAPS, FILTERS, RELAYS, AND CABLE STRIPPERS