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VTTC first light!

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James

Mon Apr 04 2011, 11:22PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

You know, if I hadn't seen the video of Arcstarter's coil, I'd probably be satisifed with mine :)

I ordered a 1000pf doorknob to try, as I think mine are a bit large and it would be nice to have only one cap to deal with. Hopefully the combination of smaller capacitor and more turns on the primary will reduce the loading on the tube a bit. Once I get the thing running acceptably I can remove some turns from the MOT secondary so that it doesn't run it too hard plugged straight into the wall. Time permitting I'll wind a few more secondaries to play with too.

I do rather like the soft rumble and straight pointy sparks this thing makes a lot better than the deafening raspy lightning bolts produced by the interruptor driven and SG coils I've seen.

Arcstarter

Tue Apr 05 2011, 12:41AM

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

Another reason i had little heating considering the spark length on my coil is because of the small grid leak cap. This keeps the duty cycle of the tube lower. It did change the sparks a little bit but not too much.

You should also calculate the primary resonant freq and make sure it resonates with the secondary.

James

Tue Apr 05 2011, 05:59PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Hmm I thought a smaller grid leak cap would make the duty cycle longer?

I did calculate everything, I suppose I should measure the resonant frequencies rather than just basing everything on calculations though.

Dr. Drone

Tue Apr 05 2011, 06:31PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
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Posts: 1673

James

Tue Apr 05 2011, 09:03PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

If my calculations are correct, mine runs at about 930 kHz, but I haven't made any measurements yet. I like the straight sparks, although I don't have enough experience yet to know the effect of different frequencies.

PhilGood

Fri Apr 08 2011, 12:17AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Gratz James on your 1st coil !

BTW I wonder if a VTTC would be a good solution for me (I can't have a real RF ground)

Is everything grounded to mains ground in a VTTC ?

James

Fri Apr 08 2011, 12:23AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I don't think the topology makes any difference, you still need to have the coil grounded. I've used a mains ground for all of my high voltage experiments, I haven't had any issues with it.

Spark gap, vacuum tube or solid state are just different methods of driving the primary. The secondary works pretty much the same either way.

PhilGood

Fri Apr 08 2011, 12:46AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

Well, I'm quite new to this hobby....

But from what I understood so far, VTTC's rather work in CW mode, when SGTC's and DRSSTC's work in pulse mode, thus drawing huge amount of power / bang and generating lot more EMI...

Concerning RF ground you can have a look at this thread to undersatnd why I'm afraid of having troubles with my neighbors....

PhilGood

Fri Apr 08 2011, 05:00AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

@Arcstarter: your single 811A VTTV is really impressive, gtz on it !

It seems quite close to Steve's circuit, available here except your uses only one VT

I'd like to build something similar as my first TC, your video is very well made, but there are still a few things I'm wondering...would you please give me some more infos about your circuit ?

- Are you powering your circuit directly with the MOT output (2KV AC), rectified with the MO Diode (2KV "DC") or using MO Diode and Cap as level shifter (4KV "DC") ?

- I'd like to know coils specs (AWG and number of turns for the 3 coils)

- Isn't your grid leak resistor (R2) overheating ? According to steve's circuit it should be 50W, I can see you used 3 in parralel (maybe 2-5W each?)

- Where can you find these nice 550pF red capacitors, where do they come from ?

- Is your secondary bottom hooked to the rest of the circuit ground ? In case yes, is the circuit ground connected to mains ground or do you use any kind of dedicated RF ground ?

- Eventually anything else that is different from Steve's circuit and would help run this nice device smoothly...

Your help would be greatly appreciated, congrats again on the great reasults

James

Fri Apr 08 2011, 07:55AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I think he and I both used Steve's circuit as a reference and then improvised based on what we had or could get easily. I can't speak for him, but I used the mains ground on mine. I also used only one tube after hearing of several people getting just as good or better results than with two.

The 1000pF doorknob cap I bought arrived today so I fiddled with my coil some more. Added some turns to the primary and did some further tuning and now I can run indefinitely with the MOT plugged straight into the wall with very little reddening of the plate. I bought some 650pf doorknobs on ebay so when those arrive I'll give one a try and see if I can improve performance further.

Experience so far tells me that it's very easy to get something that works. The real work is getting it optimized so that it works well.

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