See my earlier posts for details. John Freau's TT-42, which is still one >of > > >the most efficient coils ever, has Zo=44k. John found that adding a >bigger > > >toroid to his TT-42 (which would lower the Zo towards 36k) increased the > > >spark length. > > >And, Richie Burnett found that a coil with Zo=22k performed poorly, but > > >changing to a resonator with Zo=~50k gave much bigger sparks with the >same > > >bang energy.
Steve,
My old research coil was somewhat more efficient than the TT-42 coil when the TT-42 is fitted with the normal 4" x 13" smooth toroid. The TT-42 coil requires a "robust" NST to obtain the 42" sparks using the normal toroid, but the old research coil produced 42" sparks using a normal NST. The TT-42 gave 44" sparks using a 6" x 24" smooth toroid which barely permitted breakout to occur. I ran the research coil using a potential transformer for better efficiency at times. I often used a 6.5" x 24" secondary wound with 28awg formvar magnet wire. At other times I used a 4.2" x 23" secondary also wound with 28awg wire. In both cases the toroid was a 5" x 20" ducting toroid, for producing the 42" sparks using about 620 watts (wallplug). I seem to remember that both secondaries gave about equal spark lengths. So it may be interesting to calculate the Zo for those two secondary/toroid combos.
Cheers, John