Re: Coupling constant for 4.25" secondary

In a message dated 99-03-14 04:46:59 EST, you write:

<< Original Poster: Gary Lau  12-Mar-1999 2058 <lau-at-hdecad.ENET.dec-dot-com> 
> Hello All:
> One of the few things I have yet to optimize on my coil is the pri/sec
> coupling, though from what I've read, it can make a big difference in
> performance.  I've not had problems with racing sparks on the secondary.


It makes more difference on some coils than others.  Sometimes, if
a coil is producing two simultaneous streamers, reducing the coupling
might cause the coil to produce only one streamer, which might then
be longer.  Too tight coupling can hurt the quench and maybe reduce
the sparks that way, but there's a lot of doubt whether fast quench is
really important.  Whether racing sparks occur will also depend on
power input, break rate (in some cases), and secondary insulation
type, secondary length, toroid size, etc.
> I've measures the coupling coefficient "k" two different ways with
> identical results:  0.139.  I just tried raising the primary up by 0.25"
> and that changes it to 0.144, but it doesn't seem that the start of the
> primary should be above the start of the secondary.  

I run my 4" secondary 1" below the primary, but I have to do this
because the primary inside dia is 8" or so.  (My coupling is still
loose at k = .08 or so, but any tighter gives me racing sparks at
high powers.)
> I know that there are so-called magic values of k that make for the
> cleanest quench, the nearest one to my coil being 0.153.  

I haven't seen much difference with fine changes is k to try to hit
these magic values, but certain coils might react differently.
> What I would like to ask is, for other coilers using 4.25" secondaries,
> what values of k have you achieved?

I use loose k, but I use thin wire (#28awg) on the short 24" 
secondary with 25kV or so on the primary with a 6" by 26" topload.
at 1500 watts input, for 64" max length streamers.  

When I use my 6" secondary (same wire dia and secondary length),
with the same primary, I do use a tighter coupling at k = .11 or so.

John Freau  
> Gary Lau
> Waltham, MA USA >>