What purpose does a series capacitor on the output of the secondary side of transformer serve?

Question

I have a 110VAC to 14VAC AC/AC power supply that is broken - it feeds an audio amplifier. On the secondary side of the transformer in the supply there is a series capacitor (ceramic, small thing, probably 10's of nF) connected to on of the two pins from the output of the transformer. Is this likely for dc suppression or noise suppression? Since it is AC i assume the polarity is not important as to which pin the series capacitor is connected to?

Oops:-
connected to *ONE* of the two pins from the output of the transformer

14Vac----l l----s| |p-----240/110Vac
e| |r
c| |i
0ac--------------o| |m------0 ac

looks like i can't to ascii drawings. yahoo stuffs it up...

14Vac-----| |------------------Tx pin1 (sec.)
0Vac-----------------------------Tx pin2 (sec.)

Answer 1

It is almost certainly not a capacitor (work out Xc at mains frequency.)

It's more likely to be a thermistor, perhaps in lieu of a fuse.

Answer 2

A capacitor in series with the output of a transformer would block the AC from the transformer. Not good.

Where is the other leg of the cap connected? Ground? If so, it is almost certainly for noise/spike suppression.

Answer 3

The capacitor is most likely part of an AC to DC converter circuit since the circuitry inside the amp is probably DC.

It charges and discharges, at a rate determined by the size of the capacitor, and along with some other components it can create the equivalent of square wave AC - which can be used as the equivalent of DC in most circuits.

Answer 4

There is probably a voltage regulator IC in the power supply -- either a linear or switching regulator. The (relatively low value ceramic) capacitor is used to help stabilize the voltage regulator, to help the transient response of the regulator, and to help prevent oscillation.

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