Joule Thief

[mike2550]

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]

Everyone has to start at some point if they are interested.
There is a lot of information to read. It is well worth your time to read some.
Trying to read it all at once, you would never start building. lol

Iron wire is diff than ferrite. Diff in such a way that you will get less ringing back from it(BEMF). The lower voltage on the base seems to have caused you have a working unit but the 1K resistor is holding back to much of the lower voltage. So, it works without it. If you can find an old computer MB, CFL base, power supply they have ferrite toroids on them. You should plan to have at least a 20ohm resistor on the base so you dont kill the transistor. Many use a 1K pot with a 20ohm to the base. That way you can adjust the pot but never be less than 20ohms on the base. Some prefer 100ohm minimum on the base. This is where the reading will explain a lot.

Best of luck.

[mike2550]

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

[LeaningGreen]

Congrats on getting it running with a little improv.
Most puter repair places will give you a few dead MB's & power supplies for free if you ask.
There is always dumpster diving after they close too.   lol

[crowclaw]

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