Hello unnamed person :)
Thank you for your feedback. I'm unfamiliar with winding my own chokes.
That is, I'm unclear on how to design my own chokes for a particular
specification, and I lack an LCR meter to determine I have enough
inductance. If I use my existing 500ohm/100W resistors to form a RL lowpass
filter, I will need two chokes of approximately 0.25mH each.
> The real key to not burning out your NST is proper tuning.
Yes, I'm not quite sure what other tuning I need. Changing the tap position
has not made an appreciable difference. I have tried a smaller topload; a
1" torroid vs a 4" torroid, and did get increased spark length, but not
significantly. (Obviously I had to change the tap point).
> I always meter off the ground connection of secondary with a shunt
resistor.
What type of resistor do you use? I would really like to not destroy an
oscilloscope! Do you require differential probes for this?
Thanks again.
Joshua Thomas
On Sun, Nov 21, 2021 at 7:59 AM <pupman.com@xxxxxxxxxxxxxxxxxxx> wrote:
> Hi,
>
> I just use large air cored chokes and a spark gap. It's simple, and
> impossible to burn out. There's no need for some rube goldberg setup. HV
> capacitors are expensive and like fuses can only be abused once. The last
> set I made was probably on 2" PVC with 6" of #28 windings or something
> similar to that. Protection spark gaps should be pointy and just on the
> verge of firing. If they arc at full line voltage and no load, even
> better. You don't get full nameplate voltage on a NST at full load
> anyways, so don't expect that with a coil running. It's a not that
> different from how you should never run a microwave oven empty. They must
> have a load to prevent arcing.
>
> The solid state ignition transformer sounds fun. I ran my coils off DC,
> rectified from NSTs or even unshunted transformers.
>
> The real key to not burning out your NST is proper tuning. I could tell
> from the video you posted a week or so ago that the coil was still not
> tuned correctly, or other adjustments are still needed. The sound of the
> spark gap and how the arcs looked was the key. You should be able to get
> streamers that grow in length and do not not look like DC arcs from a
> power pack or electrostatic generator. Even for a coil the size of yours
> the tuning will change due to the proximity of objects nearby, even your
> arm or a ground lead. For maximum fun, tune the coil to you and the ground
> wand you draw arcs off.
>
> If you can look at the waveform for the coil with an oscilloscope, that
> helps too. I always meter off the ground connection of secondary with a
> shunt resistor. It's the safest place to obtain a low voltage with respect
> to ground for taking measurements or attaching instrumentation.
>
> Congrats of the first light!
>
>
> On Sat, 20 Nov 2021, Joshua Thomas wrote:
>
> > Hello all,
> >
> > I've been struggling to build a lowpass ("Terry") filter to protect my
> NST
> > from RF feedback. The first one suffered arc-overs because
> > the capacitor leads were too close together, and the second one had the
> > capacitors fail - apparently only 9kV per rail wasn't enough. It's a 12kV
> > NST so I assumed 18kV > 12kVx(sqrt 2) and therefore would be sufficient.
> > Apparently not.
> >
> > What suggestions are available for those who have made a NST filter that
> > was successful? Particular capacitor types/brands would be welcome, as
> well
> > as how the physical layout was accomplished. I use two 500ohm/100W
> > wire-wound resistors for the R half of the RC filter.
> >
> > On a different topic I got a used OBIT for $35, but it appears to be a
> > solid-state one running pulsed DC. The model is Allanson 2275-628G.
> 17.5kV
> > "peak", 45mA, at 20khz. I mainly bought this for curiosity to see how it
> > might perform on a coil. I'm a little suspicious of the voltage and
> > amperage, as the total VA rating is only 87.5VA - which is a fraction of
> > the 560VA that would be expected from 12.5kV RMS (17.5kV peak) at a full
> > 45mA!
> >
> > What experiences has anyone had with one of these?
> >
> > Cheers,
> > Joshua Thomas
> >
> >
> >
> >
> >
> >
> >
> >
> > --
> > Joshua Thomas
> >
> > My new email address is: joshuafthomas@xxxxxxxxx
> > Please update your information if you have not already done so.
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--
Joshua Thomas
My new email address is: joshuafthomas@xxxxxxxxx
Please update your information if you have not already done so.