Holmes Engineering Free Harp Stuff
Ron Holmes, the creator of the Holmes Commander and other feats of engineering, has a page with a load of free downloads. There's Soldering 101, Harmonica Player's Guide to Getting Heard and Harp Player's Questions About their Gear. It's all interesting stuff and the price is right. While you're there check out the Homes Commander and the other interesting stuff on his pages.
I hesitated telling you about this link. The pages do not work in Firefox, so Ron's pages are useless to nearly 25% of the surfers who land on the page. If you have Firefox open the link in IE. The links bring you to LuLu.com and require an account even if you the files are free. The LuLu interface is annoying and difficult, but I was able to do it with a little head scratching.
The Harp Player's Questions About their Gear pdf has some interesting articles. It is only about 30 pages and is not a comprehensive discussion, rather a series of questions and answers. Some don't really affect me, some do. I picked up a few good ideas from the booklet.
Free Harp Stuff