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10MHz high power VTTC test

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Tonskulus

Thu Feb 19 2009, 11:52AM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Ok, we made some modifications for tube induction heater. It is that commerical "plasma tweeter circuit" using 15-30turn resonator coil. Results were surprising.
Ok, here is powersupply section:
http://sooda.dy.fi/fpaste/index.php?1qS&avase

It is using 7kW air cooled transmitting tetrode from UHF broadcast amplifier.

And then, video:
http://www.youtube.com/watch?v=6qQwhC0wNSY&feature=channel_page

Has someone made similar teslacoils before?

Marko

Thu Feb 19 2009, 12:52PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi tonskulus...

Wow, so I'm beaten to attempting something like this first. I have a nice 3.5kW transmitting tetrode but never even got to lash up stage due to lack of tube socket, general funding, and balls. What tube do you have in action?

..So is that streamer indeed consuming over 5kW alone? (not kVA input?)

And you're actually using an antenna for feedback just as with regular tweeter? I had problems with this scheme and didn't think it could be scaled up like that.

Any more pictures of the amplifier insides for me?

Marko

GeordieBoy

Thu Feb 19 2009, 01:24PM

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

Verrrry Impressive!!! That flame-like discharge is what I saw with my Class-E Tesla Coils operating at 10MHz and above. I never pushed more than a kW of power though, so nothing as dramatic as this!

Marko: Although not very long compared to a conventional TC, the discharge is fat like a flame and incredibly hot. You can feel a tremendous current of hot air rising above the arc by convection.

-Richie,

Tonskulus

Thu Feb 19 2009, 01:54PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

Yes, discharge is really hot. But i noticed something weird..Im using copper as discharge needle but it starts melting in about minute. I also tested steel but it melted immediately! Why is that? steel has higher meltingpoint than copper..

Anyway, I think this kind of circuit can be scaled up to any size. I dont have any pics inside of tube oscillator.
Component values are:
grid leak resistor=27k/100W
grid leak capacitor=1nF/15kV
tube= 7F71
There is no capacitor beetween resonant coil and plate.

In my video: Plate voltage 4kV, plate current 1.5-2Amp.

Phillip Slawinski

Thu Feb 19 2009, 02:02PM

Registered Member #1732 Joined: Thu Oct 02 2008, 02:34PM
Location: Huntsville, AL
Posts: 112

The reason the steel melted immediately could be due to hysteresis. Very cool coil by the way.

Steve Conner

Thu Feb 19 2009, 02:51PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Steel also has much poorer thermal conductivity than copper, so the heat can't get away from the electrode tip.

The antenna feedback thing should work with any size of tetrode. They need much less drive than triodes, giving lots of power with no control grid current at all.

When you say "grid leak" do you mean the resistor is from antenna to ground, and the capacitor in series with the antenna? (Do you think a capacitor in series with the antenna is needed?)

Very nice btw

Tonskulus

Thu Feb 19 2009, 04:59PM

Registered Member #1223 Joined: Thu Jan 10 2008, 04:32PM
Location:
Posts: 133

yes, "gridleak" resistor is beetween grid and ground. grid capacitor is not necessary but it seems to be more stable with capacitor.

I also tested some audiomodulation (screengrid modulation), using output transformer from tubeamp as modulation trafo.
Oh yes it was really loud. At full volume, it hurted my ears! Modulation amplifier was commerical 50Watt hifi amplifier.
It was indeed surprise how loud can arc flame be playing some music, even bass frequencies were noticeable.

vasil

Thu Feb 19 2009, 07:06PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

Wow, beautiful output.

The single vttc seen until now of this kind was on the hcrs site:

http://www.hcrs.at/HFSCHW.HTM

http://www.hcrs.at/BILDER/HFSCHW7.JPG

I remember that I was amased by the power of the flame, but never didnt have the luck to play with such a toy.. :))

Proud Mary

Thu Feb 19 2009, 07:55PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The magnetic permeability of steel means that its skin depth will be about five times less than that of copper. The wire melting can not be due to hysteresis, as the Curie temperature of steel is about 700 deg. C, at which point it loses its magnetic properties, so any heating above that temperature must be caused by skin-effect eddy currents alone.

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