The talking circuit uses DC. The ringing circuit uses AC. You can use them separately just to test the functions of the phone.
DC = talking, sidetone, transmission, reception, dial pulses or DTMF tones
AC = ringer
You need to study up on how telephones work. Google is the best way to get started. My fingers would wear out if I were to try to teach you everything you need to know about this subject. I figured you already were conversant with the basics and just needed to know how to test old phones for proper operation.
