Sorry to interupt this very loooooong thread. I am years behind you guys(just trying to learn). I just started out to make a JT. The one I attempted is the simple one with the 2N3904, 1 k resistor, and Led. I bought all the parts needed at RS, but they don't have the ferrite toroid. So, I made my own! Anyhow, mine does not work with the 1K resistor but it will work without it. Is this normal? My DIY toroid was made from iron wire wrapped around a rubber grommet and then with about 20 turns each wire(30 gauge).

@leaningGreen, thanks for the reply! I will get back to reading some more.

Well done Mike2250, As you have seen this is a long long thread going way back in time, with some excellent ideas and contributions. Most of the JT type circuits I had put together I reclaimed from scrap,  as leaning green has already mentioned scavaging pays off...no need to spend money as most parts you can find for free. You will also get good results  using thin stranded hook up wire to wind you toroid...it's all experimental so results will vary. Kind Regards

i know this isn't a joule thief..
but the jt folks are more likely to use this than the desk jockeys.. out there..
if you use 9 volts and higher use a small 90v neon bulb with a diode to the battery..
if tuned right you can double your run time.. this is a ferrite core from a junk flyback coil..
i used a dual pot but it measures 2.2 k .. puts out a mod sine wave..
transistors or mosfets work.. fet have a cleaner sine wave..
the trick here is to not use the batterys voltage so use a diac , sidac , or even gas discharge tubes rated high than your battery volts.. just catch bemf back to the battery on the side that the transistor is in the off position so the volts feed back go in the battery and not the coil..

robbie

gas discharge I like sparks.... with high electrons avalanche
this concept is applicable to short muller motor coils?

http://www.youtube.com/watch?v=kvIUq9aCKIU&feature=autoplay&list=ULpQ0FyFaPqJQ&lf=mfu_in_order&playnext=2

  I just want to let the newcomers know that the advice of using junk parts will only get them meager result, as the toroids found in old Pc power supply are not "ferrite" nor will they work the same, just to save a couple of bucks.  I know, as I've built many of them. The picture below are mostly using the pc power supply toroids. Which is why I'm letting you know that they don't work as well as the real ferrite ones.
  These are Kooler style backward Jtc. or Hartley oscillators, which are generally more efficient than the regular JT.  Kooler had some of his BwJt last 7 months running non stop. That's quite a difference compared to just couple of days running when using Iron powder cores.
   Just trying to point some of the new guys in the direction of obtaining the best results.
 

@ mike2550

Since so many people seem to have difficulty getting toroids, I posted some videos showing a few "no toroid" Joule thiefs.  As you have access to Radio Shack, I recommend this one >>>   http://www.youtube.com/watch?v=D7CFkRLrtss

   Mike:
   The small toroids that come inside the cfl are ferrite, and they do work fairly well for their size. The picture of the smallest BwJt above on my last post is also from a cfl. It has a secondary, which can light several leds off of it.
   I am surprised that you were able to light the night light bulb, but it is probably because you have not used a resistor on the base of the transistor.  This can work, but the duration or running time will be much less. The point of the resistor is to control the amount of current that the circuit can use, otherwise is will discharge the AA battery in just one day, or less.
   I would recommend using the BwJt circuits as in the my pictures, it is a simple circuit and more efficient than the normal Jt. You pretty much can see how they are wired from just looking at the pics.
   You can also use the pancake coil idea made my Lidmotor, for a very efficient very low power draw circuit that does not use the toroid. There are many ways to go on this, but the neat thing is to have it last many days or weeks on an AA battery.
   Xee's circuit is also another good example of an efficient circuit. 
   If you use the 2700 mA AA rechargeable batteries they can last twice as long as a regular non rechargeable AA, and can also be recharged as well.

  Thanks Bill: 
   I've never seen the green toroids, but I have used the orange, and smaller black ones found in the cfls. They seam to work ok. As well as many different yellow pc types. Yes, they all work, I guess it all depends on what anyone wants to do. But, as I have used them, I still recommend not to use the iron powder ones even though they do work to a usable degree. I had a bunch of the yellow toroids around the house, so... I could not resist.
Pictures below of are iron powder cores, regular Jtc, and they are still working two years later.  Not bad for the price... Zilch!
                                                                                  NickZ