SERIES LOOP ACCESS SYSTEMS FOR PROVIDING ACCESS TO SERIES LOOP CIRCUITS COMPRISING SERIES LOOP ACCESS PANELS AND SERIES LOOP INSTRUMENT PANELS, SOLD AS A UNIT; JACKFIELDS; LOOP BACK TEST SYSTEMS FOR MONITORING AND TESTING TWO-WIRE COMMUNICATION LINES COMPRISING A TRANSMITTER AND A RECEIVER, SOLD AS A UNIT; RECEIVERS USED IN LOOP BACK TEST SYSTEMS FOR MONITORING AND TESTING TWO-WIRE COMMUNICATION LINES; COMMUNICATION COMPONENTS AND DEVICES-NAMELY, TERMINAL BLOCKS, CONFERENCE BRIDGES, JACK PANELS, JACKS, CUTOVER SWTICHES, PATCH CORDS, PLUGS, LAMP SOCKETS, LAMP CAPS, TELEPHONE COILS, REPEAT COILS, CONNECTORIZED CABLES; SOLID STATE TELEGRAPH RELAYS; BATTERY CHARGERS-NAMELY, AIRCRAFT BATTERY CHARGERS AND INDUSTRIAL AND LEISURE VEHICLE BATTERY CHARGERS; DIRECT CURRENT AMMETERS; TRANSFORMERS; PRIVATE LINE TEST FACILITIES FOR PERFORMING TESTS ON COMMUNICATION SYSTEMS COMPRISING ACCESS MODULES, LINE SELECT MODULES, DIAL/SIGNAL MODULES, TEST MODULES AND OHMMETERS, SOLD AS A UNIT; CURRENT SENSORS; MAGNETIC AMPLIFIERS; BROADCAST FILTERS; MOTOR SPEED CONTROLS FOR CONTROLLING THE SPEED OF ELECTRIC MOTORS; POWER SUPPLY UNITS FOR SUPPLYING POWER TO ELECTRICAL APPARATUS-NAMELY, COMPUTERS