All ringers must be isolated from the telephone line by means of a blocking capacitor (or "condenser" in telephone terms). If not, the Direct Current (DC) from your Central Office will find a short circuit across the ringer coils and will register a "false Busy."

A Condenser blocks DC, but it allows Alternating Current (AC) to pass through. The ringer in your old telephone operates on 20 to 30 Hertz (HZ) AC ( electric appliances in your home operate on 60 HZ). This frequency was derived by the average output of a hand-cranked magneto. Magneto telephones were once the most common form of telephone. Since the batteries were usually to be found inside of a magneto phone, or close by, the older form of telephone is called a Local Battery Set. When battery power was located in the Central Office, telephones were reconfigured to Central Energy, or Common Battery style.

With battery voltage ever-present on the telephone line, there could be no path through the telephone set if it was not being used, or On Hook. Only if the set were Off Hook would there be a current path that would signal Central to alert an Operator or bring in Dial Tone. By means of a Condenser, the problem of leakage through the ringer coils was solved.

The most common analog telephones in use today are Western Electric Licensed Style. They are patterned after Bell Laboratories equipment developed after World War II, starting with the #500 set. All of the Networks in such apparatus will have the same letter codes, and most will have a 4-wire ringer. Common models are: #500 desk, #554 wall, #2500 touch tone desk, and #3554 touch tone wall (larger). The Condenser in any modern analog network will always be identified by the letters "K" and "A." The ringers will always have a Black, Red, Slate, and Slate/Red wire. Here is the correct way to wire the ringer in your analog phone:

Black Ringer Wire connects to terminal "L1."

Red Ringer Wire connects to terminal L2"

Slate Ringer Wire connects to terminal "K"

Slate/Red Ringer Wire connects to terminal "A"


In many telephones, one ringer wire was connected to "ground," usually via the Yellow line cord wire. If you have a phone with an older cord, and the ringer isn't working, try connecting both Yellow and Green wires to the same post in your jack or adapter plug. If this doesn't work, try connecting the Red and Yellow wires to the same post in your jack or adapter plug, in case the wiring was reversed.


Another complimentary service of VTS Industrial Company

Steve Hilsz, Technician

Two- and 4-Wire Capacitors (Condensers)

A Discussion of Party Line Ringers

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