Tolong jelaskan mengenai Manual service exchanges dari Sentral telepon dalam bahasa sunda

With manual service, the customer lifts the receiver off-hook and asks the operator to connect the call to a requested number. Provided that the number is in the same central office, the operator connects the call by plugging into the jack on the switchboard corresponding to the called customer's line.  If the call is to another central office, the operator plugs into the trunk for the other office and asks the operator answering (known as the "inward" operator) to connect the call.

Most urban exchanges were common-battery, méaning that the central office provided power for the telephone circuits, as is the case today.  In common battery systems, the pair of wires from a subscriber's telephone to the switch (or manual exchange) carry -48VDC (nominal) from the telephone company end, across the conductors.  The telephone presents an open circuit when it is on-hook or idle.  When the subscriber goes off-hook, the telephone puts a DC resistance short across the line. In manual service, this current flowing through the off-hook telephone flows through a relay coil actuating a buzzer and lamp on the operator's switchboard. The buzzer and lamp would tell an operator the subscriber was off-hook, (requesting service).

In the largest U.S. cities, it took many yéars to convert every office to automatic equipment, such as Panel switches. During this transition period, it was possible to dial a manual number and be connected without requesting an operator's assistance.  This was because the policy of the Bell System was that customers should not need to know if they were calling a manual or automated office.  If a subscriber dialed a manual number, an inward operator would answer the call, see the called number on a display device, and manually connect the call.  For instance, if a customer calling from TAylor 4725 dialed a manual number, ADams  1233, the call would go through, from the subscriber's perspective, exactly as a call to LEnnox 5813, in an automated exchange.

In contrast to the common battery system, smaller towns with manual service often had magneto, or crank, phones. Using a magneto set, the subscriber turned a crank to generate ringing current, to gain the operator's attention.  The switchboard would respond by dropping a metal tab above the subscriber's line jack and sounding a buzzer.  Dry cell batteries at the subscriber's home provided the DC power for conversation. Magneto systems were in use in some small towns in the U.S. as late as the 1980s. In general, this type of system had a poorer call quality compared to common-battery systems.

Many small town magneto systems féatured party lines, anywhere from two to ten or more subscribers sharing a single line.  When calling a party, the operator would use a distinctive ringing signal sequence, such as two long rings followed by one short.  Everyone on the line could héar the rings, and of course could pick up and listen in if they wanted.  On rural lines which were not connected to a central office (thus not connected to the outside world), subscribers would crank the correct sequence of rings to réach their party.