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"Electric flame" HF VTTC

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LAN_403

Dr. Dark Current

Fri Aug 28 2009, 12:25PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

This is more of a theoretical question because I don't own a vacuum tube yet, I'm just curious.
I'd like the TC to make a small candle-like flame discharge, mainly to amaze people ("where does the fire come from?")

What frequency, how much power and how powerful tube would I need for this? Is this doable with semiconductors without some extreme tuning and/or expensive parts/equipment?

HV Enthusiast

Fri Aug 28 2009, 12:43PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Any SSTC will do this so long as you provide a ground arcing path. It will create a flame-like arc.
However, if you don't ground the arc, then you end up with your standard blue coronal discharge.
Frequency is irrevelenant.

Dr. Dark Current

Fri Aug 28 2009, 01:06PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

I know when I arc to ground, I'll get a flame arc, but flyback can do just the same. I wanted the discharge to look like a flame without any ground nearby, like with those VTTC plasma speakers.

I know that with a high enough frequency (several MHz?) and CW operation, I can get this. So the questions remain, how high frequency and how much power to create a candle-like flame. I saw a "lighter" VTTC which created just that, a HF plasma flame.

Smlizz

Fri Aug 28 2009, 02:13PM

Registered Member #129 Joined: Fri Feb 10 2006, 07:55PM
Location: Austin Texas
Posts: 9

I have a plasma speaker that has an output just as you have described.

I used a 8032 pentode tube and my coil ran at 27 MHz. It used about 50 watts and had a flame like output that was about 20mm tall and 5 mm thick and very hot. It weighted about 10kg with the plate transformers and RF chokes but I also had a modulating circuit as well.

Sorry I don't have better documentation at the moment I am away from home. If you want when I get home in a few weeks i might be able to get it off the shelf and dust it off and go over it in more detail.

GeordieBoy

Fri Aug 28 2009, 03:09PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Hi Jan,

My 8MHz and 18MHz Class-E SSTCs produced discharges that were reasonably flame like. Certainly more like a candle flame than the traditional hissing purple corona discharge you see from most SSTCs running at lower frequencies.

As for power, I would say the more the better. Even at 18MHz the discharge initially starts out as a purple jet of corona but that gets engulfed in a glowing mass of surrounding air as the power level is increased. It's just the same as how low current NST arcs look purple and weedy, and high current arcs look like roaring flames. HF CW coils are just better at producing flames because they can achieve a high current density into a relatively small volume of conducting air surrounding the discharge electrode.

Both of these pictures were taken with a coil running only a couple of hundred watts CW at 8MHz. This is easily achievable with a device like the IRFP460A tuned to run in Class E if you want to go down the Solid State route.

-Richie,

...

Fri Aug 28 2009, 05:10PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

To give you an idea of the 'lower end' my coil runs about 500khz, and when running CW has some hiss (not a ton), and gives white core with purple brances coming off. This effect can be seen in some of the pictures toward the end of the thread.

Arcstarter

Fri Aug 28 2009, 05:25PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Vacuum tube i'd say is the way to go. Semiconductors switching some 50 watts of power don't really like 30mhz :P.

YOu need a tetrode or pentode for the 'plasma tweeter' schematics. I started a tiny one just days ago, in fact. I never did get it to work, perhaps we can help each other out if we figure something out :P. You can probably find a way around the tetrode or pentode power amp, maybe a triode main amp and a smaller pentode for a preamp for higher gain. Not sure. Yay base-fed!

Schematic in the middle. You can just remove the audio section and give the screen some sort of voltage (whatever it is rated).

Once again, you can just give the screen the rated voltage instead of audio.

No audio mod schematic, for tetrode.

cduma

Fri Aug 28 2009, 06:33PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

I dont know if this will help at all but, I have noticed that when you place foil around the store bought plasma bulbs and provide a path to ground you get a nice red arc that is kind of fat too. I dont recommend you use your hand as the path to ground since it leaves lots of tiny little burn marks and it really hurts.

Arcstarter

Sat Aug 29 2009, 12:46AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Also, i would like to point out that the base fed 'vttc' is not really a Tesla coil, i don't think. Would it be called one? The reason i ask, is because it is not a transformer. Just an oscillator and a resonator. Would it still be a Tesla coil? I don't think so. Resonance is the mechanism it operates with, but it is not a transformer.

Also, the output is not that high. Maybe 30kv or something for a small one. But, at such high frequency, low voltage will break down air. Cool :D

EDIT: Here is the translated link for Reachings 'plasma speaker'. It is the most simple and straight-forward schematic.

If i had any TV sweet tubes i would make this (the pentodes supressor is normally grounded internally, otherwise you just ground it yourself).

uzzors2k

Sat Aug 29 2009, 02:03PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

This VTTC might interest you.

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