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Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Yes, I do have a big Audio coil on the Horizon. I wanted to understand what it requires to ensure audio is clear, so played with this one for a year or so.
Hard switching these FET’s really is no big deal; just ensure you can get the heat out of the die.
The issues I had was the gate drivers. I ended up having use eight drivers to keep the signal from clipping. Big focus on next coil is trying to use newer FETs with lower gate drive requirements. Also try putting an Equalizer, Subwoofer Amp and cassette player under a coil, talk about RF issues, wheeeeeeeeeeeeeeeeeeeeee!
But we want 1-2 foot audiomodulated arcs, not these tiny ones, right?
Hard switching is not exactly a killer alone, massive reactive current (because of poor primary to secondary coupling) is a killer. You probably figured out to what can you push those ''too small'' 50 amp mosfets.
I'd really want to see a big-sparking audiomodulated SSTC (not DRSSTC!) - that's one of things that need to be acheived yet.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
2 foot of CW spark needs like 5kVA+, its surely no easy feat.
Ive developed a high quality class D amp for a semester project, and with that experience id say its certainly possible to use a class D front end on a SSTC, but the real question is why? The SSTC itself closely resembles a "clocked" class-D amp, so i dont see the point in adding another switching stage. From what ive learned with my self-oscillating class D design, i wonder if a similar operation could be implemented with self-oscillating SSTCs to modulate them.
Registered Member #639
Joined: Wed Apr 11 2007, 09:09PM
Location: The Netherlands, Herkenbosch
Posts: 512
Steve Ward wrote ...
2 foot of CW spark needs like 5kVA+, its surely no easy feat.
Ive developed a high quality class D amp for a semester project, and with that experience id say its certainly possible to use a class D front end on a SSTC, but the real question is why? The SSTC itself closely resembles a "clocked" class-D amp, so i dont see the point in adding another switching stage. From what ive learned with my self-oscillating class D design, i wonder if a similar operation could be implemented with self-oscillating SSTCs to modulate them.
Guess what I was planning to build next month, a self oscillating class-D teslacoil.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
The SSTC itself closely resembles a "clocked" class-D amp, so i dont see the point in adding another switching stage. From what ive learned with my self-oscillating class D design, i wonder if a similar operation could be implemented with self-oscillating SSTCs to modulate them.
Steve, and that *was* the point of my post!
5kVA and an achievement, hmmmmmmmmmm please send contributions by paypal to my email account, hee hee!
Still think a SSTC magy with primary and first secondary in oil housed by plexy with some big fat FETs at 240 volts @ 50 amps on doubler would make some really nice CW audio……………………..! Of course the oil is lit up with LED’s like my Quad MOT’s @ .
Cheers, Ch
Chris, I don't think you'll achieve anything with air-cored transformer magnifier, simply because your coupling gets too low and magnetizing current way too high.
You can have many times the input DC current circulating through your mosfets and with hard switching, fr that power level, things just don't look good.
That's where large ferrite transformer skips in - at least in my theory, it should ensure efficient energy transfer, and although audio-modulation would cause hard switching, keep the mosfets happy.
That is, necessarily a ferrite transformer.
I don't think that should be any harder than designing a class D amp for the same power level, but I'm no expert.
That's probably something that would need some ugly prototyping before plexing it up.
I'd really like to see Steve W.'s thoughts on that!
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
I did indeed accept the gracious offer of Dr. Spark to witness this and many other projects several months back in the "garage of wonder".... It was the final seed to get me hooked.
The meticulous nature of the gentleman's construction was really what sealed the deal for me. I love seeing something DONE RIGHT!
Plexiglas is not too difficult to "clean-up" if a scratch exists, etc and it really allows an element of creativity to a project that makes the piece a keeper. I have made a few little toys here and there but they didn't "look" attractive; regardless of the clean solder points, layout, or what have you.
There is a Hell of a lot of creativity in the good doctor's work - but there is also style. And that can make the difference between working on a project and then let it go after a great amount of effort - And KEEPING that project alive! In my opinion, that has great impact in the HV hobby.
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Small Bi-polar SSTC
