@carbonzit
Nice. Can't have too many web pages out there about JTs. Couple comments:
1. Your site unfortunately doesn't lend itself to actually finding stuff within it. Any chance of adding some index pages, or some navigation aids, so one can find posts by topic? As it is, the only links are to archives by date.
Google is your friend. If you google watsonseblog and then the joule thief topic you're looking for, google will generally sort out the blogs and give a line or two from the beginning, which hopefully will give you what you're looking for.
2. Heh; I like your little tag line: "My favorite programming language is solder."
Yeah, I stole that from Steve Ciarcia.
By the way, regarding DIY transformers used in JTs, I notice that you seem to favor toroidal windings. I'd just like to point out that all my JTs use a simple transformer wound on a single small bar of ferrite, as I described above. The bar is about 1/8" square by about 3/8 to 1/2" long, with the primary wound first, the secondary wound on top of it. They seem to work as well as any toroid, and are a lot easier to wind (no threading wire in and out of the doughnut). Just a note that there are several ways to skin this particular cat.
Yeah, in my blog you'll find some JTs made with air core coils, ferrite bars and bobbins, etc. The Joule Thief started out with the pioneers using toroids, but there is nothing that says you have to use them. The 'right' toroid has the big advantage of a high permeability, which means you can get enough inductance with as few as 10 or a dozen turns. Winding one is easier than a bobbin. but the wrong toroid, a low permeability one, will require a lot more turns and a lot more time winding it. Of course the same goes for ferrite bars and bobbins. I took some cylindrical bars from the board of a dead PC power supply, the ones that have a few turns of very heavy wire wrapped around it. I unwound the heavy wire and wound 28 AWG magnet wire on it, and measured it with my LC meter. The inductance was still only a few microhenrys, so those bars don't make a good coil for a JT.