Welcome to Mars! (Sphere science fiction)

I first read this book 20 years ago and still remember it as one of my most memorable childhood reading experiences. The book concerns Dolph, a teenager who discovers that an anti-gravity field can be generated from simple electronics. Using further parts from army surplus stores he decides to outfit a simple spacecraft for a sojourn to Mars. He goes...and gets stranded due to the failure of a simple, but irreplaceable part.Sounds kinda dumb, but the book is well written, the characters are intelligent and believable in the face of adversity...and the ending is great. All in all its a fantastic kids book and a good intro to SF for kids...I wish I could get hold of a copy of this book...