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and very rarely ever needs repairs, once you fix them." - Dan/Panther

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Wiring a 500-type telephone for ringing on modern telephone lines

Started by unbeldi, March 12, 2016, 01:37:44 PM

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Historically, telephone companies used a variety of wiring schemes for connecting telephones to the public switched telephone network. In particular, many telephone lines used a mode of sending ringing current to a telephone that involved a ground (earth) connection.

Western Electric 500-series telephones, such as the 500-type desk set and the 554-type wall telephone can easily be converted from any of the historical schemes to one that works today on lines either from the telephone company or when connected to voice-over-IP (VoIP) adapters.

The following diagram shows the top of a 425-type network which contains the connection screws of the telephone.

The telephone line always connected to L1 and L2. The polarity is not important anymore today, but for some Touch-Tone pushbutton telephones of the 1960 and 1970s it still is, because of the transistor used in that dial.  For proper operation of those, the L1 (green) conductor should be the positive side, and L2 (red) should be negative with respect to L1.

If a third wire (yellow usually) is present in the line cord, then it may be connected to terminal G, but this is not required for proper functioning anymore.  The G terminal is connected to nothing else. It was used to bring the earth ground into the telephone set.

The C4A ringer has two wire windings in the coil of the electromagnet, and therefore it has four wires emerging:  black, red, slate, and slate-red.   These should be connected to terminals L1, L2, K, and A, respectively.

The circuit diagram on the right-hand side of the image shows a properly connected ringing bridge, with the line cord wires in color.

A common problem of old sets when found in their original condition is that the ringer does not work, because the black ringer wire is still connected to the G terminal. It should be moved to the L1 terminal.


An example of a typical ringer problem is discussed in this topic.

The black ringer wire was still on its original connection terminal, G.

Moving the spade of the black wire to terminal L1 solves the problem.  This indicated by the the blue arrow in the picture.