Can anyone explain how I can make a telephone ring without being connected
to the telephone line. This is for a play.
The phone company applies about 90Vac @ 20Hz to ring the phone during
ringing, but they also have special circuitry to remove the ringing voltage
quickly when someone picks up the phone ("goes offhook").
It's possible that a phone might ring if standard 120Vac @ 60Hz (i.e.,
household power) is applied to the phone (the green and red wires), but this
would be VERY dangerous. If there were no circuit to either limit the
current, or disconnect the high voltage if the phone were to go offhook,
then the person using the phone could be harmed.
The easiest way would be for you to get a real phone line, for the play, and
then just call it (and hope that no one else calls it at the wrong time).
There are also telephone line simulators that you may be able to rent. How
about a tape recording of a phone ringing? A cellphone? Teach someone to
make a sound like a phone ringing?
Be careful! You want to make sure all the actors are still alive in case
there's a curtain call.