Improving the Static Spark Gap

[dannybeckett]

Hi guys,

I'm considering to build a simple spark-gap tesla coil, but I have two qualms with tesla spark gaps. They are:

• Painfully loud
• Not easily adjustable

I wonder if there's a way to make a quiet spark gap by enclosing a normal spark gap inside a bell jar and pulling a vaccum? Then you could alter the spark gap breakdown voltage by varing the amount of vaccum...

[MRMILSTAR]

I wouldn't worry about the noise from the spark gap. The sound from the streamer usually overwhelms the sound of the spark gap. Even DRSSTCs, which don't have a spark gap, have very loud streamers.

[klugesmith]

Let's discuss the quietness and adjustability goals separately.

For sure, you can greatly reduce the noise by enclosing the spark gap in a rigid enclosure.  Of course that will make it harder to cool the gap electrodes.

Also for sure, you can adjust the breakdown voltage by reducing pressure.  This is not about high vacuum; I hope you are thinking of pressure range going no lower than 1/2 atmosphere.  A sealed chamber would have no vacuum pump noise, and could have pressure adjusted by a sliding piston.   But it might be easier to control voltage by moving a gap electrode. 

Pressure measurement and control can be remote, via a hose.   Consider pressures above nominal instead of below.   Either way, there are simple hand-operated pumps for applications with no continuous gas flow.  e.g. vacuum pump for bleeding brake lines.

[dannybeckett]

Thanks guys for the input!

I've heard that the spark gap wailing is a considerably loud audio source so I'd really like to design as much of that noise out, leaving only streamer noise.

A rigid enclusure is also feasible as a more conventional sound reducing technique. This coupled with a moving gap electrode is probably an easiler way to go in all honesty. I also really like the idea of a sucker gap as a way to keep thinks cool and the breakdowns consistent:


http://www.hvtesla.com/sucker_gap.html

In fact, yes I was considering pulling a high vacuum. Notice the Paschen curve for N2 is linear all the way from 1000 Torr to 1 Torr (1.3 to 0.0013 Bar)! I do agree this would be a royal PITA to design with adequate cooling, so perhaps some kind of remote adjustable sucker gap would be the way to go!


https://en.wikipedia.org/wiki/Paschen's_law

[MRMILSTAR]

I see PVC pipe in your picture. Be aware that ultraviolet light will degrade standard white PVC. Spark gaps emit a lot of ultraviolet light. If you can provide a shield or keep the PVC out of line-of-sight then it should be OK. I'm not sure what the effect of ozone will be, if any.

[dannybeckett]

Thanks for the heads up, that isn't my gear - but will design with this in mind