I am trying to repair a 2500 Touch-tone phone from 1981. One side of the ring coil is open. Alternately, can a 2 - wire ring coil from a rotary dial 500 phone be used? Does it affect the REN adversely? Any help is greatly appreciated. Ciao. Ray

Absolutely, you can swap in the 500 ringer. The ringer capacitor is A and K on the network. One side of the ringer goes to L1, the other side of the ringer goes to K, and a jumper wire from A to L2 will complete the circuit.