Ran across a site called “sci-toys.com“, Science Toys. This site has a plethora of simple science toys you can build. For example, look at this article on building a three penny radio. I wonder if Bill knows about this site.
I’ve added it to the side bar. Lots of neat things you can build, magnetic heat engines, high voltage motors (different than Bills contraption, this one is not a Mazda), and much more.