Re: Tuning a tesla coil without high voltage power

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Mccauley, Daniel H by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
> 
> Is there a method of tuning a tesla coil at low power using a signal
> generator or something?  I've tried searching the archives, but didn't find
> anything useful.

Get a square wave generator with low output impedance and connect it
across the spark gap (high-voltage power supply removed, of course).
Observe with an oscilloscope the waveform across the primary capacitor
or inductor. When the coil is properly tuned you will see, at every
transition of the low-frequency square wave, something like this:
http://www.coe.ufrj.br/~acmq/tesla/vc1c1ct.jpg
http://www.coe.ufrj.br/~acmq/tesla/vc1910.jpg
The deep notches indicate that the coil is tuned. What you see is
the primary energy moving from the primary tank circuit and the 
secondary resonator and back, At the notches all the energy that 
was initially at the primary is in the secondary.
For the square wave generator, an oscillator with a 555 IC, followed
by a resistive divider with 100 Ohms and 1 Ohm can be used. In a
low-power coil, the 555 output can be connected directly across
the gap. The desired waveform will appear in every negative
transition. In a high-power coil with very low primary impedance, 
a more elaborated buffer can be required.
The best tune is usually when you get the notches when you approach
your hand to the secondary terminal. This allows for some detuning
due to streamers.

Antonio Carlos M. de Queiroz