KC472M Capacitor ???


2007-10-06 6:29 am
Hello! I have a question for the pro,I have seen so many comercial amps that have a "Ceramic Blue Capacitor" it is round and flat and it is in the hot line of AC after or before the on/off switch.it is connected in line to the hot line.it looks like a filter for the "hot" line.
the other day I went to Radio Shack for some fuses and I saw these kind of capacitors and it said for "Spike".I have seen many "gainclones" but,I have never seen these "capacitors" been used in the AC "Hot" line.
my questions:

a) what are these for?
b) why "gainclone builders" do not use them?