My NST is buzzing- how do I stop it?!?!?

Hello, I am in the final steps of perfecting a Tesla Coil that I started a few months back. I only got the spark gap to fire in one test run. Every other time, the circuit does nothing, and my new 10 kv neon sign transformer buzzes loudly and ominously. I'm really worried that I'll burn it out.
Why is it malfunctioning? How can I fix the problem?
Update: After a little experimenting, and checking all connections, I've found that the one time that the spark gap fired happened because of a wiring error (i connected the gap in series to the transformer instead of parallel); this resulted in a spark across the gap, but no oscillation. I'm starting to think that the capacitor's are the problem. I originally believed that the required capacitance was .003 uf, but I recalculated that and found that it was actually .0079 uf. This could explain why a spark couldn't jump. I'll order some more, and see how that goes. Thank you all.

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codex6537 years ago
yeah, you have the spark gap way way too wide for anything to even happen. my nst does the same thing. you'll find that if you test out homemade capacitors without any spark gap, it hums also. it's no big deal, just put the gap closer together
kjbaran8 years ago
Make sure you triple check all of your connections! Your primary circuit is what you need up and running before anything else. If you can get that spark gap to start firing off then we're good. If all connections are good and your capacitors havent burned out and your gap isnt too wide THEN I would start to worry about the NST. Dont let it run like that for too long while you're checking out where the problem lies. If it burned out there is still hope! Check around for a sign supply shop. I just got back today from one and they gave me two 15kv NST for free! The guy said they cant re-sell them after they take em out of old neon signs so they just use em as weights and doorstops!
ElectricUmbrella (author)  kjbaran8 years ago
Weights and doorstops? An outrage!!! lol :)
Thank you for the advice,
The gap isn't actually set very wide - I'm using a (admittedly kinda flimsy) home-made rotary spark gap with two stationary electrodes. I wouldn't think that the distance would be the problem (especially since the one time it did work, the distance was the same), but I'll mess around with it anyway to see if it helps.
The connections are definitely likely to be causing it, now that you mention it - I was only using those connector-nut things. My best option, I guess, would be to solder, but if possible, I would prefer something less permanent. Any ideas?
Again, I can't thank you enough!
You don't really need a rotary gap at this power level (and two electrodes probably aren't enough in any case). Go back to a static gap. or a multiple electrode gap. See the one I made at https://www.instructables.com/id/SF5D28MFVS7L7BF/.

The buzzing is a sign the spark gap is too wide, and not firing.
Xellers8 years ago
The spark gap is the problem. Even if you are using a rotary spark gap with close electrodes, if it isn't synchronized with the frequency of the transformer (usually 120bps), then the capacitor may not have enough energy to jump the gap at each beat. Also, you should check all of your connections. When I put my small Tesla Coil back together after months of no use, I accidentally connected the capacitor incorrectly and got intermittent sparking through the cap and a bunch of bad noises. Another problem that you might encounter is a half burnt out transformer. If this is the case, then you will need to compromise for 5kV from only one half. You can check for a half burnt out transformer by seeing if each high voltage output arcs to the case. Good luck.
kjbaran8 years ago
Soldering doesnt really matter as far as connections go. If electricity can go from point A to point B, then you have a connection. Just make sure your circuitry is right. When I set my spark gap too wide, my capacitors hum. lol.