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Re: [TCML] A New Kind of Valve Coil
Phillip -
Thanks for the response. All good information, but of course it triggers more questions:
1. If the good performance obtained by the elevated position of the feedback coil was just because it reduced the grid drive voltage, could you get the same effect with a low-mounted feedback coil shunted with a variable resistor (plus your series inductor) so you could adjust grid voltage "on the fly"?
2. In a VTTC with a conventional feedback coil, do you think the most significant magnetic coupling is between the feedback coil and the primary, or between the feedback coil and the secondary?
3. Do you have any idea of the value of the inductor that you placed in the grid circuit?
4. Is this inductor in close proximity to the primary coil (and possibly affected by the primary's magnetic field), or is it located remotely, closer to the tube itself?
Scott
--- On Wed, 6/22/11, Phillip Slawinski <pslawinski@xxxxxxxxx> wrote:
From: Phillip Slawinski <pslawinski@xxxxxxxxx>
Subject: Re: [TCML] A New Kind of Valve Coil
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Date: Wednesday, June 22, 2011, 5:52 AM
Scott,
I never took scope shots of the grid when I had it pushed down further
on the form. I didn't get my HV probe until after it was pushed
pretty far up the form. I think the reason it works better up higher
is just because it puts less drive on the grid. Earlier this year I
rewound my my grid coil with more turns, thinking that I wasn't
driving the grid hard enough. When I put the new feedback coil on
with more turns, the results were dismal. So I pushed the grid coil
up higher, and the results got better. The sparks still weren't
satisfactory, so I started unwinding turns. I probably removed around
5-8 turns. I wasn't sure if removing the turns would help any, so I
didn't cut off the excess wire, but instead I just put it in a
cardboard box next to the coil (to keep it from arcing to the ground).
Well, when I started the coil up again, the results were pretty
spectacular, and I had about a 50% increase in spark length or
something like that. I attributed this to the removal of turns at
first, but later when I cut off the excess wire, the performance
dropped again. The best I can tell is that the inductor lessens the
dip in voltage right after the grid turns on. You can see this in my
scope shots.
http://www.flickr.com/photos/pslawinski/5530682808/ ; -> Without Inductor
http://www.flickr.com/photos/pslawinski/5530098141/ -> With Inductor
Unfortunately it's no longer possible for me to reposition the grid
coil easily. When I rewound the coil, the grid coil form shrank a
little bit, and because of this it's not loose enough to move over the
entire primary form. Perhaps I'll get motivated one day and make
another one. This being said, I don't see any development happening
with the 833C coil anymore. I'm quite satisfied with the performance
I achieved, as far as I know that's the best performance ever obtained
from an 833-based coil. If someone knows otherwise, please let me
know! My intent is to move away from the feedback coil completely
with the new 3CX2500H3 SSVC I'll be constructing. I'm working on a
solid state grid drive, which should be far more reliable than the
grid feedback coil.
-Phillip Slawinski
On Tue, Jun 21, 2011 at 16:16, Quarkster <quarkster@xxxxxxx> wrote:
> Phillip -
>
> I was perplexed by the "extreme" grid feedback coil location when you first built your 833 VTTC, and I see that you have stuck with that location while adding further improvements. On your Flickr page there are some scope shots of the grid drive with and without the added inductor, but no shots of the grid drive obtained at different feedback coil elevations.
>
> Do you remember if you looked at the grid drive signal at different feedback coil positions, and if there was anything that stood out as far as amplitude, pulse shape or pulse timing?
>
> Scott
>
> --- On Sun, 6/19/11, Phillip Slawinski <pslawinski@xxxxxxxxx> wrote:
>
>
> From: Phillip Slawinski <pslawinski@xxxxxxxxx>
> Subject: Re: [TCML] A New Kind of Valve Coil
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Date: Sunday, June 19, 2011, 4:44 PM
>
>
> Roger,
>
> I had to do a lot of things to push the 833 that hard. Driving the
> coil via grid feedback is really finicky. The grid coil is pushed up
> as high as it can go, and that's the only place where it works. I
> also added some inductance in series with the grid. When I added the
> inductance I almost doubled the spark length that I could get. I'm
> not sure these results are very repeatable. The tube I have seems to
> be more rugged than the standard 833. I'm able to push about 20kV
> peak on the plate.
>
> http://www.flickr.com/photos/pslawinski/5530682878/in/photostream
>
> I also overdrive the filament to 10.8V. There may be some more
> performance to be extracted from an 833C based system, but I'm ready
> to move on. I'm trying to find a larger tube now, so I can make
> longer sparks, and run a higher PPS rate.
>
> -Phillip
>
>
>>>
>> Hi Phillip, Thats quite a remarkable setup there. Is there anything
>> special you had to do to the 833 tube coil so that it could handle this
>> pulsed mode operation. I noticed that the tickler coil was up kind of high
>> but I'm guessing that that's where you keep it for CW operation as well.
>>
>> Roger
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