I have ran into a situation I was wondering if it was common or a fluke. I have both the Nox 800 and 900 and wanted a bigger coil to use with them. I decided to get the 15" Minelab instead of the 15" Coiltek. Price and weight were my two factors. Anyway...it came and I plugged it into the Nox 900 first, as it is my primary machine. I couldn't get it to detect anything. Nothing. I don't get any kind of error...the coil just doesn't work plugged into it. I was thinking bad coil...until I decided to try it on the 800. And wouldn't you know...it works GREAT on the 800. I can't find anything that says the 15" Equinox coil is only for the 600/800 but I wonder if it may be? That's what I am here asking about. The 6" Minelab coil works on both the 800 and 900....but that 15" one only works with the 800.