Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi Curt,Coupling itself won't be affected. It's purely a function of individual inductances and their proximity to one another. The currents and voltages do not affect the ratio, and that is all coupling is, a ratio. However, your gap is greatly affected by a higher current transformer as is your cap size performance.
The high current NST will charge the caps faster, bps will be affected, and I would bet performance drops unless you use a variable voltage input to the NST like a variac, at which point, you'll probably fine that there will be a lower voltage which gives about the same performance your seeing now.
Something important changes with the 120mA NST. Your resonant cap size changes as does the LTR value (they both double from their current 60mA sizes). If you double your cap size, then you will achieve a higher bang energy. At that point, there will be a spark length increase which you will certainly notice. This will be twice the current at the gap and it will likely require more cooling than your now using. If not, performance will increase briefly, then drop off after a few seconds of run time. There's also the possibility of smoking the secondary on such a small diameter coil. If you let the smoke out, it won't work any more. You must keep the smoke in. ;-)
Personally, I wouldn't do it. Kind of a waste for a 120mA NST. Build a nice 6" or 8" coil with such beast! You'll be happy you did! Build something that is runable in the garage, gives excellent spark lengths, yet doesn't require a lot of the hassle which goes along with big high powered coils (there are many hassles!). Big coils are great a few times a year, but a midsize coil is great all year long.
Take care, Bart Tesla list wrote:
Original poster: "C. Sibley" <a37chevy@xxxxxxxxx> I've pretty much pushed my 60mA 2" secondary coil to it's limit, getting 30" sparks. I adjusted the primary-secondary coupling and am running coupling just below where I see running sparks. I have a 120mA transformer that was originally planned for another project, hat I'm now considering throwing into the little coil for giggles. Question, will this throw me over the edge and make it over coupled, or is coupling purely a function of the geometry of the primary and secondary? If I make the swap and need to raise the secondary to reduce coupling, will the higher current of the transformer help my spark length more than decreasing the coupling will decrease it? i.e. is it worth doing? I'm in the process of building a PT powered 6" coil, not sure I want to expend the effort on the little coil unless it would be cool :-) Thanks, Curt.