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How small can a VTTC be?

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uzzors2k

Wed Jun 07 2006, 04:58PM

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

Just how small can a VTTC be? Could one be made from a low power triode, with a say, 2 inch tall secondary? I don't see why its not possible, but for some reason I've never seen one before. (Maybe there's still room for a smallest TC award!) Or are they just too impractical at such small sizes?

Dr. Shark

Wed Jun 07 2006, 05:17PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I have seen a rather small VTTC on the web somewhere, and aparently it did not produce enough voltage for break-out, even though it was well-designed. So aparently there are some practical difficulties.

From the theoretical side it looks pretty good, since tubes are available in all sizes and for frequencys up to the GHz for radio transmission.

Really small is relative though: Even a guitar amp with only 100W of power has four rather big power tubes in it, so you might well end up with a 2" secondary driven by a 4" tube. Maybe that's what is putting people off.

Plasmaniac

Wed Jun 07 2006, 05:41PM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
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Posts: 72

A VTTC can be veryvery small, compared to how small a SSTC can be. Tubes dont care if you drive them at some 30MHz. As far as I remember, some plasmatweeters work at something around 36MHz using vacuum tubes.

Marko

Wed Jun 07 2006, 07:36PM

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

I would really like a coil operating at several tens of MHZ and giving significant breakout!
Capacitive coupling effect would be enormous...

...

Wed Jun 07 2006, 11:02PM

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

I think the problem is that at the insane frequencies breakout just doesn't work like we want... EVR has a (not so publicised) sstc that he built running at 10mhz in excess of 1kw and he only got like 3" sparks out

Even if we disrupted it at ran like a drvttc I still think the sparks would be so puny for the size of the power supply/tube/cap/etc

It should work well for power transfer

Plasmaniac

Thu Jun 08 2006, 06:16AM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

But som 10s of MHz would be great for a plasma speaker because the output is more like flame than some streamers, so you have a better sound quality.

ragnar

Thu Jun 08 2006, 06:43AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

I'm already working on a small, very high frequency SSTC... and I'll send you the board artwork if you want. =P

Won't do much good for a VTTC though, hehe

uzzors2k

Thu Jun 08 2006, 01:49PM

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

So much for the mini VTTC. It would be pretty awesome though, a real vintage tiny-tesla coil. Oh-well, they're no fun if they can't even achieve a breakout.

blackplasma wrote ...

I'm already working on a small, very high frequency SSTC... and I'll send you the board artwork if you want. =P

Won't do much good for a VTTC though, hehe

I'm a t00b-n00b anyway, hell, I haven't even built a SGTC yet. But I'd like to see your SSTC project, I'm on such a budget I don't know when I'll be able to make full-sized TC. I really need to get a job....

Dr. Shark

Fri Jun 09 2006, 08:46AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I am pretty sure you _can_ achieve breakout and good sparks. Just that it hasn't been done before, doesn't mean it's not possible. I suppose the key to sucess would be do drive it pulsed, i.e. with an DRSSTC-like interruptor. This ought to work much better with tubes than with IGBTs, since you cannot easily damage a tube in a transient. Everything that can be done solid state can be done with tubes, without all the complications like low-inductance layout, zener and TVS protection and so on. You just need to cover some new ground here, maybe use some non-traditional tubes like thyratrons... Whatever you can come up with.

Marko

Fri Jun 09 2006, 09:31AM

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

Pulsed VTTC's are called staccato and they use to generate somewhat longer sparks, they draw much lower current and tube heating is minimal. See steve w. site :)

But what we want here are big, CW, utra-high frequency sparks for a reasonable power input (means not using few kW for few cm of spark.

Tube isn't a real problem here (they can transmit at very high powers at 100's of MHz anyway)
At several tens of Mhz worst losses happen because of skin effect, especially at secondary.
When we want to make it small we use thin wire wich turns into a huge resistor killing Q of resonator, overheating the coil and blowing it up quickly.

Primary and primary cap dissipation also increases dramatically.

Now we would need to make secondary out of some ill-thick wire (or maybe multifilar, BP style) wich would make it huge moving ourselves away from ''world's smallest VTTC'. And again spark length would now be puny compared to secondary size.

I think there were also some experiments with tyratrons, but they didn't work too well.
Check the archives...

We would probably need to build a huge secondary

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