Hi John, Joe,I think the ID is fine. It depends on the vertical position of the primary in respect to the secondary, and I didn't see those numbers listed (unless I missed them?).
One thing I noticed is that for this coil (even with plenty of ht changes with the primary), for the coil to tune in at the 12 to 13 turn range as stated, then the primary total tank capacitance is nearer to 0.027uF. Likely the plate caps are calculated values and I expect that all these caps are in series.
For myself, it's difficult for me to figure out what spark length you should expect. Granted, the easy calculation is 7.5kV at 180mA. We would normally expect about 50" length at best, and given your gap setting, I would even expect 60", but I'm sure there are losses causing the lower spark length. Where those losses reside can be difficult to find. The obvious spot is the gap (this is the #1 player with losses). The stacked NST's may also have some losses as well as the caps.
The only way to find losses is by component intervention. For the caps, the MMC route is ideal, but you may want to move the capacitance up a little to 0.045uF to take advantage of some resonant charging (this would cause tuning at about 10 turns). For the transformers, I would leave them as they are. The gap is of course the "looker". Add more volume of air flow over the segments. You might even want to reduce the segments to 5 and increase the individual segment spacings for an equivalent breakdown voltage (if practical).
Take care, Bart johnbrooks@xxxxxxxxxxx wrote:
hello bigjohn,the first thing I notice is the primary ID is about an inch or so too big. joe On Sat, 10 Jan 2009 23:39:50 +0000, b.jbohn@xxxxxxxxxxx said:Hello everyone, first time here (great site!). I've built a coil that refuses to put a streamer past 36" to a grounded plate suspended vertically at the top of the secondary. Occassionally I'll get one 41-42". I'm using NST's 1@60Ma 7.5kv 4@30Ma 7.5kv all hooked together. I think they're all okay because if I remove any one of them from the system performance diminishes. The secondary coil that I've had the best luck with is wound on a 5-1/4" varnished paper tube winding length 22-1/2" the wire is .014 or #27 magnet it's 1,607 turns 2,208 feet.My capacitors are a mixed batch of homemade HDPE plate type.Caps #1 & 2 each contain aluminum plates 10 x 12" 16 plates each .090 HDPE between each plate Caps #3 & 4 each contain aluminum plates 4-1/2 x 9" 40 plates each .060 HDPE between each plate Cap #5 rolled type in oil .01583 MFDAll capacitors are in oil.My spark gap is a segmented type with 10 copper tubes 7/8 OD 5" long total space between gaps is .150" just enough so the transformers can break.The gap is also blown with a fan.My primary is a 1/4" copper tube conical 15 degree 14 turns 23" OD 7-1/2" ID seems best tapped at 12 to 13 turns. I'm using a spun toroid it is 4-1/2 x 18" that size seems to work the best although if I put a 6" sphere on top pretty cool stuff happens (the streamers jump around the toroid and ball). I have other secondaries that I've tried but this one is the best. I have looked at other coils on this listing and other websites and I think mine should be doing better than 36". Any input appreciated! Bill _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla
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