Re: tuning primary and harmonics

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

Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 1/29/03 4:36:38 PM Pacific Standard Time, 
tesla-at-pupman-dot-com writes:


>Original poster: "Justin Wright by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <justin-at-tracesofnut-dot-com>
>
>Hi All,
>
>I tuned my primary coil using a freq generator and scope.  I used the
>frequency that suited the secondary.  It was about 180khz.
>
>I didn't have a freq meter, so I just left the generator running and
>used the same frequency on the primary.
>
>As I tuned the primary by moving the tap around, I found the amplitude
>on the scope rising and falling at different tap points.  I guessed
>these were harmonic frequencies?
>
>Anyway, I found a tap point that made the highest single on the cro and
>used than.  It was at 9.5 turns.  The coil works fine with this.
>
>When I later keyed in the figures into WinTesla, it reported the tap
>point as being just over 11 turns.
>
>I didn't try this far out when tuning the primary, so I am wondering if
>I had just found another harmonic at 9.5 turns.
>
>Are there a lot of places around the primary that will create a large
>signal on the scope?  Has anyone else found multiple tap points that
>make a coil work ok?
>
>I plan to test this when the weather improves.
>
>
>My coils specs are...
>
>
>Secondary:
>110mm (4.33") pvc
>860mm (33.85") of 0.63 enamelled copper
>150x300mm (6"x12") topload - 450mm (18") total diameter
>
>Primary:
>11 and a bit turns of 6mm (0.236") copper tubing at 6mm spacing
>19.4 nf MMC (0.33uf x 17 -at- 1600v)
>
>Static Spark Gap
>15kv at 60, 90 and 150ma


Justin,

I ran some calculations on your coil.  I made a couple of assumptions that 
may or may not be correct.  I assumed that your primary inside diameter was 
6.3" and that your wire diameter was .63mm which is close to #22 guage 
wire.  I calculate a tap point on the primary of about 10.4 turns for 
proper tuning.  I have found these calculations in the past to be within 
one turn and often one half turn of the actual best tap for longest 
sparks.  This was calculated at 38 turns per inch on the secondary and 
produced a secondary resonant frequency of 191 khz.

Changing the turns per inch to 39.4 yields a secondary resonant frequency 
of 184 khz - close to your measurement.  Now the best primary tap point is 
right at turn 11.

Ed Sonderman