Hi all, I'm new here so bear with me if this is all old hat.
I've been building my recreation of the schoolgirl and she's not behaving very well. I've already burned out two transistors, one by trying to solder the coil wire to the case--
way too much heat!--and the other? Not sure what happened there. At any rate, trying to chase down magnet wire around here (Austin, TX area) has been difficult to say the least. Sure, you can get it at Radio Shack or Fry's, but only in ridiculously small quantities like 40 ft. (for #22) and 75 ft. (for #26). You can get a whopping 200 ft. of #30, but that's probably way too small.
So, the problem is most likely in my coil--I was only able to get 388 turns out of that 75 ft. of #26 which was wrapped bifilar with #24. In checking the coil with a voltmeter and spinning the rotor near it only around 5 mV max comes through as induced current. I'm guessing that this is not nearly enough current to bias the transistor on.
When sending current through the coil, though, it generates a good kick. If I pulse current through it by hand, I can get the rotor to turn fairly well.
Anyway, a few questions come to mind about this circuit. First, I notice that there's a ground connection shown--is this strictly necessary? I saw on
this page (near the bottom) that the circuit is almost identical (the only difference is the diode going to the recharge battery), but they caution that if there is no load that a neon bulb is
required to keep the transistor from burning out. Is that the purpose of the ground in this circuit?
The other thing is I notice a lot of bifilar windings have the wires twisted around each other. Is that really necessary to get this to work? Perhaps the better question would be does it confer an advantage over winding the wires side by side (the way I did my coil)?
I'll post some pictures once I get this thing going. I'm almost 100% sure that the problem is that there's just not enough turns on my coil to induce enough current to bias the transistor. I've got some longer magnet wire lengths on order, so once those arrive we'll see what happens.
