I just received my C-500s. Got them working with the K3. Had to use the little battery box, since I am thinking that the mic on the headset was an electret and requires some DC voltage to work.

The headset is very comfortable and according to W6LAB whom I worked on 20M phone this evening I had a great audio signal. Best $45 I ever spent!! Thanks to all who provided input.



73 
Rich Arland, K7SZ
Bent Dipole Ranch, Dacula, GA
"Cogito Ergo CQ" ("I think therefore I HAM")
Author: "The ARRL's Low Power Communications, the Art and Science of QRP" (all 3 editions)
Editor: "QRP POWER", QST Magazine (Jan 2000 to Dec 2003)
Editor: "The Learning Curve", CQ Magazine