Bell tap is a recognized telephone industry trouble term that has been around since the beginning of dial service. It refers to the fact that if the ringer and its associated network (and subscriber loop) are not set up correctly, when the switch hook is operated, or the rotary dial is used, the ringer will follow the opens/closures of the loop, making a tinkling sound. It can be cured by adjusting the bias spring, reducing the capacitance of the loop, and a few other things.
The other concept that seems to have gotten caught up in this discussion is the "straight line ringer vs common audible ringing" wiring schemes.
When used as a straight line ringer (bridged ringing) or used in a small "square" key system as a common ringer, the series capacitor (generally terminated on A and K of the network) is left in the ringer circuit. In the event that the installation gets so large and complicated that the ringing plan needs to be programmed for combinations and permutations of ringers and stations, a ringing matrix is installed. It uses diode logic to create multiple layers of ringers and lines. Since diodes pass DC and not AC, the DC-blocking capacitors are by-passed in each tel set. The resulting half-wave DC is then able to operate the ringers whenever generator is sent to a ringer or group of ringers, via the diodes. The ringers, which have bias, need to polarized properly for this scheme to work, so attention to the color code is essential when installing the system.
I believe that the "pulsating DC" referred to above is what's causing the confusion with bell-tap.
Arthur P. Bloom "30 years of faithful service...15 years on hold"
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