The bell's coil resistance is around 1000 ohms. Placing the bell coil across the phone line, the central office would probably think you had the telephone off-hook because of direct current flow. The capacitor prevents the flow of direct current. Because of the capacitor's ability to pass alternating current (90-130 VAC, 20-30 Htz), the bell rings without the central office thinking you have the phone off-hook. However, capacitors have AC resistance, called impedance. Capacitors can fail or degrade 3 different ways 1. Short and electrically appear to be a wire. 2. Open and electrically look like nothing. 3. Slowly degrade, becoming a lower and lower value making their impedance rise. Ringer capacitors, as an example, start at .47uf-.5uf. As they degrade to, as an example, .22uf, their impedance, or AC resistance, increases. All other things being equal, a rise in Impedance, or AC resistance, will result in a lower current flow. In the case of ringers, not as much 'power' is available to ring the bell. Hence, the bell is not as loud as it used to be. I know, TMI!
John C.
