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VTTC secondary coil winding direction

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RogerInOhio

Sun Apr 19 2009, 02:53PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

I never would have thought that it would matter witch way you wind the secondary coil on a VTTC but I recently found out by accident that it dose matter. With a tube coil Iâ€™ve been working on, I have been experimenting with different secondary coils and found that one coil I tried worked very poorly even though it was very similar to another coil I had used that worked very well. I got to wondering about this and noticed that the two coils where wound in opposite directions. Just for the heck of it I unwound the poor performing secondary and rewound it in the opposite direction (which happens to be the same direction as the primary) with the same wire (I hadnâ€™t varnished it yet). To my amazement it worked great.

The design of my VTTC is about the same as a lot of the 833 VTTCs people make . There is some information and pictures of it posted in the projects section under â€œjunk box tube coilâ€. I have read about everything on the web I can find about VTTCs including postings on this form, postings on the pupman email list, web pages and Wikapeidia and I havenâ€™t found much of anything that talks about this issue of secondary winding direction.

So now I have come up with my own theory as to why it is that if you wind your secondary coil the wrong way, your tube coil will still work but the performance will suck. Tube coils seem to work best if the tickler coil is about three of four inches above the primary. Presumably this is because the tickler coil will get feedback from the secondary coil whoâ€™s resonant frequency will change depending on loading.
If the feedback from the secondary is inductive then it still shouldnâ€™t matter which way it is wound. What Iâ€™m thinking is that the tickler coil is acting like the plate of a capacitor and therefore has capacitive coupling to the secondary coil . If this is the case, then the direction that the secondary coil is wound would matter. Also, because of this capacitive component to the feedback , the best value for the grid capacitor will likely be lower than one might expect. I have found that the grid capacitor value, number of turns in the tickler coil, and the height of the tickler coil above the primary are three variables you have to play with quite a bit to get the best performance and efficiency.

Roger

teravolt

Sun Apr 19 2009, 05:50PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

another thing that may afect performance is how far the tickler coil is up the tesla

...

Sun Apr 19 2009, 06:05PM

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

I did notice in my 811a coil that when I rewound the secondary I had wound it in the opposite direction, and to get the coil working I had to swap some combination of the primary/tickler polarities (I don't remember which).

I still am not quite sure why, but I expect it has something to do with the mix of capacitive and/or inductive coupling from the tickler coil.

Mads Barnkob

Sun Apr 19 2009, 06:33PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

My dual 811 VTTC uses a secondary wound opposit of the primary, giving 33 cm sparks.

My H bridge mini sstc was first made with secondary and primary wound in same direction but it would hardly make a breakout, so i reversed primary.

So my two coils only work with opposit winding direction between primary and secondary.

Arcstarter

Sun Apr 19 2009, 07:04PM

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

So my two coils only work with opposit winding direction between primary and secondary.

Maybe this is because you are on the other side of the earth? XD. Just kidding.

Anyway, this may be why i had such poor results on my 833C vttc. I would pull it out and mess with it, but there is STILL no space. I could do it, considering i have the bigger sgtc out, but there is not enough room to get around easily and i do NOT want to risk breaking a perfectly good 833C!

I have also noticed, that if you have a poor ground connection they do not like to work well, likely due to feedback not working well.

Also, i have had a coil that had a discontinuity in it, and it of course did not work well. I figured it would just arc, giving it enough continuity to not really matter. But again, it was likely the feedback, because the plate was turning red FAST.

About the capacitors in the circuit. I used a small 6 inch tall coil for an 811A coil, 1 inch diameter, and the tank capacitor as 650pf, as well as the feedback. I was still pumping 7 inch sparks through the tiny secondary, and the plate would stay black for quite awhile. With no topload the plate would not get red for a long time, while giving about 3 inch streamers. I add a topload and i got the 7 inches, but it heat up much much faster. Needed tuning of course.

RogerInOhio

Mon Apr 20 2009, 02:10PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

811s are a good tube for VTTCs. I built a tube coil that uses 3 of them about 12 years ago when I knew very little about VTTCs. It has the ticler coil below the primary, has very loose coupling and a big top load. It isn't great for long sparks but it is fun for illuminating light bulbs. It definitely didn't take advantage of feedback from the secodary coil.

Roger

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