Re: Help required - ignition coil Tesla

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Original poster: "James Howells" <james@xxxxxxxxxxxxxxxxxxxxxxx>

I have spent every day since Jan1 working on my tesla and can not get 
more than a 1" spark no matter what I do

To save my sanity - some help is requested - I WANT TO GET BIGGER SPARKS!
Power supply:- Twin Auto Ignition coils - 555 interrupter through two 
power transistors. A separate oscillator supply to main 12v 
battery-ball point pen case chokes - works well

Spark gap :- 6 mm copper tube fixed end to end but gap adjustable - 
best setting seems to be 0.1"
Primary : 4 series 390 pF 15kv caps , and 3 in series 390pf 15kv caps 
( should be 4 of each, but leg fell off one cap and no replacement yet)
the three  strings are in parallel
{4 x 390}
{4 x390}
{3x 390}

Primary coil wound on 4.3" plastic soil pipe ( sewer pipe) with .048" 
enamelled wire
Turns 18 at present but was 30 and reduced it and tested  one turn at 
a time down to 18 turns

Secondary: wound on 2.64" dia white ( abs?) plumbing waste pipe 
approx 450 turns of .019" enamelled wire to a height of 10.25 "

Various toroid top loads have been tried ... and non , which works best!

The present spark at the Tesla is about 1" which is about 20% of what 
I expected
I have not been able to improve on this - PLEASE HELP!"

  Haven't seen a response to this so will add my own.   I think your 
problem is much too small a primary capacitance - not enough stored 
energy.  I calculate 325 uufd, the resonant frequency of your 
secondary as about 1370 kHz without top load, and the primary circuit 
resonant frequency at about the same.  I have a similar coil (bit 
larger, bit lower frequency) which will produce 4" streamers to a 
screwdriver held in the hand.  Uses an 0.0047 ufd primary capacitor, 
single Exel "super coil" driven about as yours.  2.5 amps at 12 volts 
input power.  Try a lot more capacitance and adjust the primary accordingly.

Ed