Re: need help tuning my coil:

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

Original poster: Harvey Norris <harvich-at-yahoo-dot-com> 


--- Tesla list <tesla-at-pupman-dot-com> wrote:
 >  > Original poster: Pat Masterson <bat-at-grumman-dot-com>
 >  >
 >  >   I need some suggestions on the poor performance
 > of my first coil in
 >  > 20 years. The best I'm getting is 5 inch weak
 > streamers, but only when
 >  > tapped at turn 2 of my primary. Here are the
 > coil's components:
 >  > -primary is quarter inch refrigerator tubing
 > space a quarter inch. I have
 >  > about 10 turns on the board.
 >  > -cap is 5 geek 150 NFs in series, making 30 NF.
 >  > -HV is a 7500v/60 ma NST. (have RF chokes on both
 > sides)
 >  > -single static gap with a 4 inch fan blowing hard
 > on it. A larger gap
 >  > (around .06 in)
 >  > seems to give best performance.
 >  > -secondary is a 2.375 PVC with 1300 turns of 28
 > ga wire, about 18 inches
 > of
 >  > wire.
 >  > -Topload is a Freau 6 inch aluminum toroid.
 >  >
 >  >   I have adjusted the caps from 25 NF up to 33 NF
 > and didnt see much
 >  > difference.
Try using much less capacity and more turns of the
primary. If the inductance of LC is increased, C must
decrease, as LC is constant at the resonant frequency.
  The supply in your example is far below what the
straight demand of the capacity would be if the arc
gap did not function, so you are functioning many
times the LTR point. This problem is however thought
inconsequential since the the use of a narrow arc gap
determines the firing voltage from the transformer. I
still havent got my 1000 ft 4.5 OD/ 22 inch ht
secondary tuned, but I noted that if it resonated at
225,000 hz quater wave I would need 25 nf for
resonance with a 20 uH primary value. After
recalculating for a 50% higher resonant frequency I
intend to fire at half of this capacity, which Is what
I arrive at using 337 khz as a resonant value.
Since your secondary has a large H/D ratio, you might
try operating with less capacity and higher estimated
resonant frequency.
HDN