[Al (astral highway)]

Originally Posted by Viewmaster

Al, my rig isn't plasma now but square wave modulated sparks.

Hey Albert!

Pix of your coil operating, please?

If you cathode modulate the two transmitting valves with a digital audio signal, you're simply switching them on and off at the frequency of the note, as you observe.

That doesn't change the nature of what pops out at the antinode of the secondary coil. It's still ionised gases - AKA plasma - including nitrogen and oxygen. It's hot! On my first valve Tesla coil, I had a 2mm brass wire as the break-out point. It vapourised the metal.

The audio is not put into a plasma flame to give that very high freq tinny noise but turns a tesla spark on/off at the frequency of the musical note.

I think this is just a (harmless) confusion of terminology. I don't know what a 'Tesla spark' is...

I prefer to make it clear the huge difference between 1) mild corona 2) the spark you might get out of an ignition coil or a LOPT, and 3) the spectacular discharge from the antinode (top of the tesla secondary) that is going into free space and not to a grounded object -- but that's just to emphasise how high the voltage at the antinode of a Tesla coil is. And also there's an aesthetic component...

Here's a good example of 2 tesla coils playing Beethoven together !

Those are big old coils, with a distinctive, unusual topload (it's normally a toroid, as you've likely seen repeatedly elswehere.) They are probably (from what I know of the typical size of the electronics encased under the primary) 1.5 metres or more tall.

Most digital coils this big use a 3-phase power supply, 10kW in isn 't unusual, although it's not possible to see in this case if those cables draped along the ground plane are thick enough to be three phase. It takes a lot of skill to build a solid-state coil that can survive repeated ground-strikes like this. It puts a gigantic amount of current through the switching devices.

Some people like to cycle these sorts of spectacular, solid-state exhibition coils through various modes - 'burst', with a repetition rate between 40-400Hz or so, and audio modulated, and sometimes (much, much more rarely) CW

I do find the typical, prominent, very 'buzzy' sound that accompanies this kind of modulation (you can hear it clearly in the clip you've posted) a bit of an unwanted distraction and full of distinct harmonic impurity. But that's probably because I play the piano/keyboards, and prefer the complex resonant properties of notes produced this way. Also, I find that when there's a moment of intentional, obvious polyphony with an orchestra, this doesn't develop with sounds produced this way.

But it sure makes for a spectacular display if people haven't heard it before!

I'd love to see more of your coil, so yes, pix of it in operation, please!