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Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
You are absolutely right in that there is a limit somewhere, and we cannot make a TC running at 1GHz But if you look at Richie Burnetts HFTC, 4MHz is perfectly possible, and he was running comfortably at 400W CW. The coil did not produce very long sparks, and I think the reason might be that is was driven SSTC-style rather than DR. With tubes it would be possible to run DR at those frequencys, because tubes can take more abuse current-wise. I am not a tube-person myself, but I think there is a lot that could be done.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
You can easily make a VTTC running at 2.45GHz, by putting a quarter wave long piece of copper wire in a microwave. If you want a bipolar "coil" then get a half wave of wire and bend it into a loop with the ends close together.
Dunce. Registered Member #28
Joined: Fri Feb 03 2006, 03:29AM
Location:
Posts: 76
Look on my really old hot-streamer page. I made a "vttc" out of a miniature pencil tube, and a small coil of wire. It ran at like 30mhz off a camera flash inverter, and could light up fluorescent tubes from a distance. Not enough power to break out, however.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
Just made one with a 6SN7 (twin triode, 2.5W each) with the triodes in parallel, running off doubled 120VAC (~335V). I can get it to oscillate, and with a non grounded screwdriver on one end of a xenon strobe tube and the other end connected to the secondary, It lights up. I cant get breakout though. I made a feedback winding with more turns, and that helped a little, but still no breakout. Im using a 20k grid leak resistor, and a 2nF grid leak capacitor, and i've tried tank caps marked "390" and a 1nF one. Suggestions welcome if you want to see breakout
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Yup, my suggestion is still standing: Dont drive it as a classical VTTC, pulse it and make it a DRVTTC. hit it with some really high peak power, keeping the duty-cycle low. The key might be to have a primary circuit with a very low surge impedance, since tubes can take a lot more current than IGBTs.
This might be a heap of b***sh** since I have never been near a VTTC myself, but I really dont see why it should not be possible to build a DRTC with the switch, the primary and the tank cap all in series. Someone correct me if I'm wrong, otherwise I guess I have to buy a tube and try it
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
It's not true that tubes can take more current than IGBTs. They usually run out of emission at an amp or two for big power tubes, and proportionately less for small tubes.
Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
Thanks for pointing that out. As I said, I am a tube-noob. Replacing the tube by a hydrogen thyratron would probably cure the problem, but would be getting uncomfortably close to an ordinary spark gap coil again. I think what I was getting at was a half-bridge of tubes, since DRSSTCs seem to work so well, and that requires being able to turn the switch off. I am not so sure if any tube-like devices exist that sustain high peak currents and have turn-off capabilities.
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How small can a VTTC be?
But if you look at Richie Burnetts HFTC, 4MHz is perfectly possible, and he was running comfortably at 400W CW. The coil did not produce very long sparks, and I think the reason might be that is was driven SSTC-style rather than DR. With tubes it would be possible to run DR at those frequencys, because tubes can take more abuse current-wise. 
If you want a bipolar "coil" then get a half wave of wire and bend it into a loop with the ends close together.
