I have had this stored in my building for about 15 years. I found it again when I was going through boxes of stuff to find things to display in my new shack. I originally bought this from a SK's estate. I wish I could remember his call sign. This is a very interesting piece of history. It is a home-brew set that I have no idea when it was built. Was it built as a demo or is it an early spark gap transmitter? I am not sure, but I wish I knew. If there are any experts out there, I would love to have some more information.