Simple way for tuning a tesla coil

[VNTC]

This way allows coil man will have very good observed on the oscilloscope because the output is strong and synchronized signals.
Accessory:
-A homemade square wave generator frequency range 30 kHz-- >400 kHz (555 IC’s circuit).
- 5 turns of wire (put around L2 or L1 coil, it will work as an exciter)
-100Ω resistor.
- An oscilloscope.
Proceed
Connect the output of the signals generator to 5 turns of wire through 100Ω resistor.
 Adjust frequency the generator and observed the sine wave signals at the top load or across C1 to find the highest amplitude at resonance frequency point.
Is way can used to tune L1 and L2 coil separately, include they was coupled together.
I have verified by Orcad Pspice simulation and got the result of this way is 98% -->99% accuracy.
To measure the resonance frequency of the primary coil, please make a jumper between 1 end of L1 and 1 end of C1 to closed the serial resonance circuit of the primary coil.( remember to take out the jumper before power on )
This way also helpful to make a practice AC sweeps a tesla coil as the Pspice simulation. By the way sweep a tesla coil without power supply to see what frequency it will run, we can let it run at what frequency we want to.
For example L1C1 resonance at 250 kHz and L2C2 resonance also at 250kHz But when coupling them together it will oscillation at 215kHz. By changing the values L1;C1;L2;C2 we will see in Pspice simulation, include by this practice way  we also see what frequency it will run exactly.   

[Mads Barnkob]

Hi and welcome to HVF

It is true that you can easily find the resonant modes with a signal generator and oscilloscope.

How well does it correspond with the calculated frequency from JavaTC?

Also there is still a need to detune the primary in regard to found resonant frequency of the secondary, in order to make up for spark loading pulling the resonant frequency of the secondary down at full load.

[Teravolt]

you can also add two back to back LED's in series with the tesla secondary earth ground or a ac cuurent meter

[VNTC]

Though we have formed a tesla coil with unique resonance frequency of primary and secondary, It will run at the third frequency different the first and the second. Javatc is perfect to show the first frequency and the second frequency but not show about the third.