You've got some N-gons on the top there! I am always a little confused about N-gons. Some people tell me to avoid them like the plague but online I sometimes see really good models made of entirely triangles. Whats the reason to work in all quads- and why did you leave some Ngons in the big circle in the middle of the model?
Thank you for the video!
Here watch this ngons and low poly myths - YouTube
Should explain it for you.
Video thanks to ctbram.
Dave 
From a readers' Q and A column in TV GUIDE: "If we get involved in a nuclear war, would the electromagnetic pulses from exploding bombs damage my videotapes?"