A hundred years ago this month, the January 1917 issue of Boys’ Life magazine carried the plans for constructing this wireless sending set. The author, A. Frederick Collins, had written the previous month on how to construct a receiver.
He notes that five parts are required: A spark coil, a tuning coil, a telegraph key, a spark gap, a battery, and an aerial switch, hooked up as shown here. The spark coil, the same type used for gas engine firing, was available for about five dollars. For those who wished to build their own, he directed readers to his own Book of Wireless, which contained more complete plans.
The tuing coil could also be procured for about five dollars, but he notes that a boy could easily make his own, and provides details.
A wireless telegraph set will give you all the apparatus you need for you to experiment with and theory to rack your brains over and on for the rest of your life, and it will also give you a liberal education in a highly specialized field of electricity.