1) I was wondering what determines the frequency of the super simple tesla coil?
2) Is the 300 turns that determines the frequency?
3) Does changing the 3 turns on the primary change the frequency?
4) What's the simples way to adjust the frequency of this circuit on the fly?

 

https://www.instructables.com/Simple-Tesla-Coil/

1,2,3 all influence the frequency of oscillation. https://www.teslascientific.com/products/coil-resonant-frequency-calculator/
4. You don't usually, in a reliable manner, it will change all by itself as it it moved, components warm or cool and with the phase of the moon.

 

Lol I take it you are kidding about the phase of the moon? Gravity has an effect on a tesla frequency?

And in the circuit you posted, why use a potentiometer? Is it to adjust coil output power?

 

Lol I take it you are kidding about the phase of the moon? Gravity has an effect on a tesla frequency?

And in the circuit you posted, why use a potentiometer? Is it to adjust coil output power?

I'm only kidding by a small bit about the moon as the circuit is unstable (and likely not to work at all) to say the least. The pot adjusts the transistor bias for somewhat stable operation, the coil output power won't vary by much.

 

I am missing the diode in that circuit? Besides that it looks like a Slayer Exciter, though it should have a diode between ground and the transistor base, facing kathode toward the base. A LED can be used there to also serve as an indicator of the circuit working.

The trick here is that the circuit leaves out an invisible component. There is parasitic capacitance between the high end of L2 and ground. So L2 plus that C is what determines the frequency.

And since C is dependent on a lot of parameters there may be some moon phase in it too

 

So having a wiper arm like in a radio on the secondary to change # of L2 windings would dramatically change the frequency?

 

So having a wiper arm like in a radio on the secondary to change # of L2 windings would dramatically change the frequency?

What would this wiper arm actually do? GIve us a circuit.

 

A wiper would more likely make your secondary coil burn. The voltage difference between the windings can be significant, having no insulation on them is not a good idea.

 

Interesting post, BUT first, the circuit shown is not a TEsla coil. It is a very poor version of an oscillator driving a step-up transformer.
In polite circles it may be called a "Blooper" oscillator because if you examine the circuit you find NO FEEDBACK CONNECTION.
Any possible feedback is from the way the different parts are positioned relative to each other. And probably there was no mention of that fact in any text that may have been associated with the circuit. The only physical feedback connection is from the collector to the base, feeding back the voltage developed by the effective internal resistance of the battery.
The only possible resonance would be due to the capacitance between the turns of coil L3.