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.
> _______________________________________________
> Tesla mailing list -- tcml@xxxxxxxxxxxxxxx
> To unsubscribe send an email to tcml-leave@xxxxxxxxxxxxxxx
>