I read this story in the late 80's or early 90's, but I suspect was written much earlier. It was about a precocious boy, about 10-12 years old, who was always getting into mischief.
One day he decides to experiment with the family TV with a soldering iron. While he is doing this there is an alien invasion force coming towards Earth because we are an easy target.
Due to this boy's experiment he creates a shield/weapon which drives the aliens away and then promptly burns out.
I say this was probably written much earlier because the family has only one TV and the author talks about vacuum tubes and such in describing the inside of the TV.
What is the name of this story?