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Need some advice...

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LAN_403

raff

Sun Mar 14 2010, 02:37AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

ooopss this was an SGTC..

I was thinking of DR LoL...

Sun Mar 14 2010, 05:50AM

Registered Member #2736 Joined: Sat Mar 13 2010, 03:48AM
Location:
Posts: 5

we know that there is a high amount of primary coil. we figured once we tune it we'll cut off any extra. it was better to over shoot than under. since we made another one that was 3/8" pipe with about 9 turns and that didn't seem like it was enough. I guess I'll try to redo the spark gap and make sure that its in the right spot. and retry the tuning.

Hazmatt_(The Underdog)

Sun Mar 14 2010, 06:35PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

1. Make sure your cap value is 1.5xCres. If you want the whole story check my Calculating LTR thread.

2. Don't hang the tap lead on top of the primary. The primary IS AN AUTOTRANSFORMER, which means that your clip is probably arcing underneath and you're losing power as a result.
When you get deeper into RF stuff you'll learn that those un-used windings are actually costing you power too! It's interesting stuff.

3. Think of every inch of wire in the primary tank as your whole tank circuit, Especially the connecting leads! You will have on average 9-12uH of connecting lead inductance that is not part of the "transformer", which is costing you your power throughput. These leads need to be as short and heavy as possible for best performance.

You're almost there. Best I got from a 7500/30 was about 18", so with a little work you will be there soon.

dex

Sun Mar 14 2010, 06:56PM

Registered Member #2566 Joined: Wed Dec 23 2009, 05:52PM
Location:
Posts: 147

Also make sure your NST isn't damaged. About "half a dead" NST behaviour I've learned the hard way .

oucivileng

Mon Mar 15 2010, 01:01PM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

You could attach a computer fan so that it blows air across the spark gap. You can pick one up for a few bucks at radioshack and buy a simple 9V battery connector to power it. Just make sure you position it so that you get a good amount of airflow right at the gap.

Fri Apr 16 2010, 07:41AM

Registered Member #2736 Joined: Sat Mar 13 2010, 03:48AM
Location:
Posts: 5

wanted to give everyone an update on this. Was finally able to work on it and to tinker with it. So what I checked the spark gap and tried retuning it. What we found out from our physics teacher was that we needed the surface of the toroid to be smooth and the moisture in the air to be gone. So what we did was attached aluminum tape around the whole thing and turned on the AC to about 57 degrees. There was actually a discharge from the toroid with out the light bulb. But it was coming off of the edge of the tape that had a bit of a gap. but we only got a few inches off of it. But at least we got something out of it. Plus we added a small fan too.We gotten an electric field of about 45" since monitors was flickering and the light bulb turned on at that distance. Thanks for everyone with their advice. and is there anything else we can do to really make it shine?

Mads Barnkob

Fri Apr 16 2010, 08:31PM

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

=P wrote ...

wanted to give everyone an update on this. Was finally able to work on it and to tinker with it. So what I checked the spark gap and tried retuning it. What we found out from our physics teacher was that we needed the surface of the toroid to be smooth and the moisture in the air to be gone. So what we did was attached aluminum tape around the whole thing and turned on the AC to about 57 degrees. There was actually a discharge from the toroid with out the light bulb. But it was coming off of the edge of the tape that had a bit of a gap. but we only got a few inches off of it. But at least we got something out of it. Plus we added a small fan too.We gotten an electric field of about 45" since monitors was flickering and the light bulb turned on at that distance. Thanks for everyone with their advice. and is there anything else we can do to really make it shine?

The long distance of EMI indicates that your coil is so detuned that the energy is transmitted as waves through the air instead of going into producing sparks from your secondary coil, tuning should solve this matter.

The sparks coming from a sharp corner of your tape is similar to using a breakout point, since electrons dont really like to stay on a surface they will seek away, sharp points is where they will go, but there is not enough space for them, hence a spark discharge will occur.

Herr Zapp

Fri Apr 16 2010, 08:58PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

=P

Your coil is actually pretty nicely constructed, and I think a few enhancements and improved tuning will get you at least 12" - 14" streamers, without any breakout point or grounded target needed.

Here are a few tips and questions.

1. Increase the value of your primary capacitor to .013 - .015 uF. This will be a better match for your 9-30 NST (it will increase the "bang size", the amount of energy dumped into the primary coil every time the spark gap discharges).

2. Change your primary spark gap from a single-segment to a multi-segment, with at least 3 or 4 individual gap segments in series. This will improve quenching, and better quenching can help reduce the amount of energy being "lost" in the spark gap. For a 30ma power supply, you don't need tungsten electrodes. Try building a simple 4-segment gap out of 3" or 4" long sections of 1/2" or 3/4" diameter rigid copper pipe, spaced ~.020 - .030" apart . Make sure that you add some sort of fan or blower to cool the electrodes and sweep out ionized air; the greater the air velocity, the better.

3. Isolate your spark gaps from anything remotely conductive, which plywood is. Mount ALL the spark gap components on a piece of plastic, or on plastic or ceramic standoff insulators. You have through-bolted both ends of your spark gap to a piece of plywood, the bolts are only a few inches apart, and the peak voltage across the bolts is at least 12,700 volts (probably higher). You almost assuredly have some current "leakage" through the plywood. This goes for your safety gap also.

4. Make sure that ALL your connections between the MMC, spark gap, and primary coil are as short and direct as possible, and use relatively heavy gage wire (minimum #12 or #10 AWG). For lowest resistance, solder all crimp terminals.

5. Shorten the cable to your primary tap, and run it under the primary coil, not on top. Your photo of your primary tap doesn't show much detail, but make sure it's copper on copper, and not a cheesy copper-plated-steel "alligator clip" arrangement. You want a good, solid, high-contact-force, low-resistance connection between the tap and your primary tubing.

A few questions:

1. What is the dielectric used in your MMC capacitors? I'm not familiar with the manufacturer's trademark "iC", so I wasn't able to look up a datasheet. Got a link to the manufacturer's website?

2. What is the value of the bleeder resistors used in your MMC?

3. How many of the 2kV rated capacitors do you have connected in each series "string"?

NOTE: 8-12 turns on your primary coil is just fine. If, after you perform all your enhancements and tuning tricks, you find that you have multiple unused turns, you can simply remove them. A conical primary may end up with too high a coupling value ("K" factor), or my be physically too close to your toroid when you get longer streamers, so ultimately you might end up with rebuilding it into a "flat" sprial.
Regards,
Herr Zapp

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