This phone is loud ringing tone circuit for generating the electricity bell in the old telephone. This circuit is relatively loud. so can use to replacement the same ringer or the original telephone may be lost. We do not need a new phone. This circuit is easily to build, because it uses a single IC as shown in figure below. How this circuit works The called signal from the telephone lines is entered through C1, R1 Come to the bridge diode circuit D1-D4, D5 is the positive voltage at 20V supply to pin 1 of IC1 that KA2411 or CS8205 as the Telephone Bell Replacement IC. When IC1 is given the supply volt as I said, it will generator a ringing signals through the R5, to drive the Piezoelectric transducer BZ1 be a bell tone out to hear. The ringing tone light, we may reduce the R5 for low down. [...]

read more: Loud ringer for phone using KA2411