Not to be left in the dust with all the white LED single AA cell experimenting going on here, I decide to have a go. Scavenged wire from the coil of an old speaker and wound some of it on the only toroid I could lay hands on, 0.75". Not having a proper xstr, I used the venerable 2N3904. Got oscillation right away, much to my amazement.
But the thing needs a proper transistor. Also, the magnet wire I used is
*tiny*. More like hair than wire. I have some 20# magnet wire, but only 50-60" of it I'd guess. Does that sound like enough?
I gotta get some proper white LEDs. The several cheapos I have are more blue than white.
Don't want to search for - much less buy - the perfect wire. I'm just puttering around here. Toroid and wire are "found stuff". Would like to use the 20# enameled, if the piece I have is long enough to give the needed inductance when wound on the .75" toroid.
Silver plated wire wrap wire ... interesting. I must have wrapped miles of wire in my technician days but never knew any of it was silver plated. Apparently some was, because several years ago, while canibalizing a digital clock I built back in 1973, I found all the wraps were black as coal!
I faced a wire acquisition dilemma back in my college days. I had built a bench variable DC supply and needed several yards of heavy enameled wire to carefully wind (non-inductively, knock-on-wood) and put in series with the supply output, for current sensing. A prof. suggested a particular motor shop close to campus, so I went and asked how much they'd charge for some (wire size) wire. "How much do you need?" I thought, oh nuts! the guy expects me to buy miles of the stuff. When I told him I wanted only 10-15 feet he snorted, walked over to a spool and whipped off yards and yards for me. Even coiled and taped it for me. And he didn't charge a cent. I walked back to my apartment on a cloud.
I ripped the hair wire off my toroid and re-wound it with 21 turns of the 20# stuff. It works but of course it's impossible to compare operation of the two circuits now. I'm gonna take another look through mountains of "junk" and mebbe find a SWPS with a small toroid that I can rip out.
And I'm definitely gonna buy a Zetex low Vce xstr to play with. But first I'll check with photo shops in the area and ask for disposable cameras!
that doesn't necessarily mean it was silver though. I used to live in Rotorua NZ, a geothermal hot-spot. It plays absolute hell with electronics in general, and crimped connections in particular. Back when I was a videogame tech I used to have to re-wire entire cabinets after 2 years or so - the coloured PVC insulation all went a murky brown colour (just like the inside of PAs mouth) and the crimps corroded to hell. We had to scrape back the insulation just to tell what colour the damned wire was. We also soldered every crimped connection, to make it last longer. un-tinned Cu wire would disappear very rapidly.
Later on in life I helped service some AC motor controllers that had been in a fertiliser factory, and they were just as bad; most of the pcbs were written off - tracks gone completely etc. Here's another nasty gotcha with crimps - when using PVC insulation, if you heat it to about
70C it outgasses chlorine, which eats away at the crimp, making it get hotter and outgas more.....voila, positive feedback. It was a *huge* issue in a 400A motor controller (at least it was back when they were built with cables and crimped connections). Yay for X-linked polymer sheathed cables like Radox.
Those Zetex trannies *are* lovely, but meanwhile you can get a large improvement just using a heftier jellybean. The 2n2222a's Vce(sat) is much better than that 2n3904 you're using. MPSA06 and 2n4401 are others to consider.
As for disposable camera strobe, those transistors saturate, but gain is often (or at least was, a few years back) horrible.