Joule Thief - What's The Frequency, Kenneth? (4K)

The most frequent question about the joule thief is "what frequency does it operate at?" I've got 2 that were made from the same batch of parts and today I finally got the set up to measure it, so let's find out!
MATERIALS
O-scope
Joule Thief (x2) (2n2222 NPN transistor, black core, 22 and 11 windings, red LED)
The common "black" core used has a range of 1kHz to roughly 200 kHz, however they can go into the low MHz range. The 2n2222 has an hfe of 30-35, Emitter Base volt of 5 (I killed my no toroid JF by ignoring this), max op freq 250 MHz....
Note: Technically this is not a joule thief as is commonly made on the internet. It's a modified circuit from an antique transistor tester.

[@gumpster6]

Interesting video - thanks for sharing. Did you have a x10 probe on there? The Vpp was showing around 200-300mV most of the time and the LED shouldn't be lit at that voltage.

[@tsbrownie]

Thank you. Good question. Yes probe was set to 10x.

[@gumpster6]

@@tsbrownie That makes sense - thanks.

[@craignehring]

You always have some interesting videos

[@tsbrownie]

Thank you for that.

[@t1d100]

Yes, a very interesting investigating. Thank you.

[@tsbrownie]

Glad you enjoyed it.

[@andrewel5383]

What happens if you add a ceramic capacitor across the coil connect from power to collector? Would that possibly form an LC resonant tank circuit? If so would that cause said joule thief to oscillate at said frequency?

[@tsbrownie]

Remembering that all components (even a straight wire) has 3 properties: resistance, capacitance and inductance, adding capacitance to the natural capacitance of the inductor would change the frequency at which it resonates, mostly likely lowering it.

[@andrewel5383]

@@tsbrownie thank you! Would it be possible to raise the resonant frequency? Let’s say to 3mhz? Like if a capacitor which was lower than the parasitic capacitance was hooked up

[@tsbrownie]

@@andrewel5383 Yes, lower inductance and capacitance gives you higher frequency. So you need to use a higher frequency toroid coil and fewer turns.

[@andrewel5383]

@@tsbrownie okay thank you!!