TWO & FOUR WIRE CAPACITORS (CONDENSERS)
as Applied to Telephone Circuits
The following explains why phones like the #302 have a 4-wire capacitor, and
older phones have a 2-wire capacitor:
The Yellow and Gray leads are the Ringer Section. You have to have a capacitor
in series with the ringer, or it will cause the line to lock in at Central and
make a busy signal. Also, without the capacitor, the ringer will draw a lot of
current and will prevent other phones on the line from ringing.
So, when you look at a typical #302 telephone, you will find that the yellow
wire is hooked to "L2," and the gray wire to "K." Normally, the black ringer
wire is on "K" and the red ringer wire is hooked to "L1."
The other section of the capacitor is the "talk" circuit, or "secondary." The
induction coil boosts the speech voltage and sends it out on the telephone
line. The receiver doesn't work very well if line voltage is present on it, so
there has to be a means of removing direct-current and letting speech sounds
through (alternating-current). This is where the capacitor comes in.
If you look, the black capacitor wire is attached to Line Two via the
transmitter (terminal "BK") in a #302. From "BK" you can readily trace the
circuit to "Y" in the dial and through the brown/yellow switch wire to the
solid yellow switch wire which is hooked to "L2."
The other wire from this capacitor section is red and is hooked to "C" on the
induction coil. "C" is the end of what is called the Secondary Winding. If you
take the wire off of "|C" the receiver will still operate, but very
inefficiently because it will only be hooked up via what is called the
You will note in older phones that there is only one condenser that shares
duty with the ringer and the induction coil. This is called a Side-Tone
circuit and if you disconnect the condenser in these older phones, the
receiver will not work.
This is why older phones have only a two-wire capacitor and newer,
Anti-Sidetone phones have a 4-wire capacitor.
Provided as a
Service of VTS Industrial Company
Thanks to Mike
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