Re: Instrumental TC tuning

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

Hi Chris,

On 28 Oct 2003, at 12:39, Tesla list wrote:

 > Original poster: "Mudford, Chris" <chris.mudford-at-agresearch.co.nz>
 >
 > Hi everyone
 >
 > Since installing a new secondary to my coil, problems have been
 > occuring.  I think my caps were having problems due to a poor connection
 > between my ground and the secondary coil.  However, with the grounding
 > connection cured, my safety gaps are firing constantly.  I have tuned as
 > well as I can by maximising spark length.  I have reset my safety gaps
 > to fire at 105% and my main gap is always firing (although I am going to
 > measure the breakdown voltage).
 >
 > I want to tune using measurements and am checking that I've got it
 > right.
 >
 > Have a 50 ohm impedence scope and will use a 100k resistor in series.
 > For secondary resonance I disconnect the ground from the secondary and
 > connect the resistor to the ground in series with my generator (what
 > voltage and waveform should I use) I will place my scope across the
 > ground of the generator to the base of the secondary.  I alter the
 > frequency and look for a drop in output.

Leave the resistor out and simply connect the hotwire of the
generator to the bottom of the secondary. The more resistance you
introduce in that part of the circuit, the less accurate the
measurements will get. Rather than probing the base of the coil,
connect a few inches of wire to the scope probe, set the scope input
back to hi-Z and dangle the probe a few feet away from the top of the
secondary to pick up the electric field coming off it. You sig gen
should have a low-Z output. A sinewave is fine. Ensure the secondary
is either clear of the primary or that the primary coil is totally
open-circuit for this measurement.

 > For primary resonance.  I disconnect my filter and bridge the spark gap.
 > I connect the function generator with the 1k resistor in series to the
 > tapping point on the primary and with the scope between the function
 > generator ground and the tapping point I measure the voltage looking for
 > a voltage rise.  I set the generator to the resonant frequency of the
 > secondary and move the tapping point.  Can I alter the tapping point
 > with everything running?

A 1k resistor is OK, a 10k one is much better. No problem changing
the tap point with the sig gen but not a good idea while the coil is
powered up.

 > Any other areas to look at for why my safeties are going constantly?  My
 > topload is small, I am running at near resonant capacitor and my ground
 > could benefit from some attention, BUT, it was all OK when I had my old
 > secondary.

What type of filter are you using between the gap and transformer?
The best approach is ensure a minimum of lead length between these
two items.

Malcolm

 > Cheers, Chris. (NZ).
 > ==========================================================
 >
 >
 >