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[TCML] Repairing a Coil - Please Help

Hail to the great TCML geniuses, I am in need of help.

The National Center for Atmospheric Research is hosting a Super Science Saturday this weekend and has previously done a lightning demonstration with a Tesla coil.  However, it is not working well today and I have been asked to help because of my limited coil experience from high school.  Any suggestions to get it working again for the kids would be most appreciated.

My understanding is that the transformer went bad and was replaced.  I was told the coil needs a 60KV, 120mA transformer but that it currently had "only" a 60KV, 60mA installed.  We later discovered that the installed transformer was actually 15KV and 60mA.  I suspect the original transformer was 15KV and 120mA but I am not certain.

The coil itself is modest.  The secondary is about six inches in diameter and three feet tall.  The primary is about seven turns of .25 inch tubing.  The capacitor is an array of 16 high voltage DC caps with a total capacitance of 19.2 nF.  Two nice inductors (about 500 turns around 2 inch plastic pipe) protect both poles of the transformer.  The spark gap is enclosed in square metal plates sandwiched together in a way that made me originally mistake the whole unit for another capacitor.  4 long nylon screws hold the whole thing together so I wonder if the gap is adjustable.

Right now, when the coil is turned on, the spark gap fires and the secondary coil gets a bit of charge, I would describe it as fuzz when you get a ground wire close.  It is nothing like the 6 foot sparks I understand it is normally able to produce.  I suspect the coil is well tuned as the clip location for the primary is very well marked, although again, I could be mistaken.

My main question - is it possible that switching out the transformer with one with half the amperage could make the difference between fuzz and 6 foot sparks?  Would the voltage have to change or would there need to be another problem?

And my followup - does anyone have any suggestions that might make this coil function for the kids, even if at a lower capacity?

My thanks in advance,


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