(Found) Short story? Heinlein? Plans for diy brushcutting laser capable of destroying the planet made public on worldwide media. Read in the 70's

Nemesis Looms

I remember your name but your face escapes me.
Jul 28, 2018
57deg.54'01"N, 5deg.9'41"W
Set principally in the US with a definite Heinlein feel to the politics involved, a major part of the plot was the development of a cheap and easy redneck diy brushcutting laser which had the potential to be scaled up to be able to destroy the planet. Eventually after various alarums and excursions, the plans are broadcast to the world via a hijacked news broadcast ( or something else vaguely analogous to the internet ).

It's for an article I am putting together - about the internet. Dystopia anyone?

Many thanks in advance for any help.