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Thank´s a lot baum. I think i will rework my chance.
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Chance Rebuild
Best of luck and happy hunting! I believe that you could wind your spider coil with a value anywhere from 350uh to 400uh and get good results. My next spider coil will be wound with the teflon insulated wire I mentioned several posts back. This should yield even lower capacitance and result in a faster coil. By the way I flood insulate my spider coil with self expanding urethane foam. I sand it to a shape that results in a minimum 6mm spacing from the coil to the graphite shield. Then I fiberglass the coil for protection.
DanComment
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Dan is this the spider coil design picture you are talking about ?
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Spider coil
No, that is the original basketweave design of the Russian author. My spider coil is pictured in one of the earlier pages of this thread. It is in the form of a ring with shallow slots on the inner and outer edges of the ring.Comment
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Spider Coil
The image I'm referencing that my coil is patterned after can be found on the first page of this thread in a posting by 6666 GURU. He indicates it is a recommendation of the Russian author too. Mine differs in that the width of the ring is 2.5 cm and is cut from 4.5mm Lexan with slots cut 3mm wide and 6mm deep. Hope this helps.
DanComment
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OOPs!!
Sorry GURU didn't realize it was you who posted that on page 1 and asked about the original coil. My mistake...I'm gonna have to pay better attention!
Regards
DanComment
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The coil on the picture is my coil similar to the autor´s coil. But it was out of spect´s. So I have built it now with 350 uH and 1,5 Ohm with coil-cable. I have no shield because i search not for gold, only for silvercoins.
I can run the coil on Guard Interval 28.
Now i have changed NE5534 to OP 37 so i can run at Guard Interval 23
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My choke was broken
(only 5 uH). I have built one with 305 uH. The Chance run´s now quieter.
Dan thank´s for the hint´s with OP and choke.
First test´s are ok. Iron is jumping from left to right without Iron Mask.
But with iron mask on 2 there is almost no signal for iron but i found silver with almost the same deep as with iron mask off.
Sorry for my bad english
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Chance coil and fixes
I am very pleased that you were able to get your Chance PI operating. The coil you have is just fine for silver coins. I think the silver coins register on the discrimination scale about 3 divisions from the right end. Your English is great...no problem here!
Happy Hunting!
DanComment
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Dan let me start again
is this the coil you made as shown below
if so how did you mount it in a housing or whatever ?
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When I print the pattern for the mandrel or former it comes out at about 193mm outside dia
is that what everybody else gets ?????Comment
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Spidercoil
Yes that is the general geometry I used but my Lexan form was 2.5cm wide. That is wider than the one shown. I shielded it using Dave's graphite process and then wrapped over the graphite with thin self adhesive cloth hospital tape. Then I put one layer of fiberglass fabric on, let it cure , and added a second layer of fiberglass resin and fabric. I used RG-62 coax for it's low capacitance characteristics.
DanComment
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Coil dimension
Yes, my coil is 8" or 20cm OD. ID is 6" or 15cm. The cross section of the finished coil is approximately 1.150" in width and height. This includes the windings, 6mm urethane foam shield spacer, graphite shield, tape wrap, and two layers of fiberglass fabric/resin skin. This is a 412uh coil.
DanComment
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Thanks Dan
that was a lot of time and effort that you put into that coil
if I alter the margin on the printer I may be able to get it to eight inches wide.
cheers
6666Comment
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Coil dimension
Yes it was a lot of work but worth it as it is fast enough to detect small amounts of gold flakes and the authors original coil is not. My only regret is that I did not use teflon insulated wire to wind it which would have helped to lower the capacitance even further.
I'm planning to wind another coil using teflon insulated wire with an inductance in the 350 uh range. Building coils is a lot of fun for me as I'm still learning how to make a good coil for placer gold detecting. This forum is a magnificent resource of information with lots of people working on the cutting edge of detector development. I can't wait to see where it is in a few years.
Regards,
DanComment
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Thanks Dan
When time permits will give that one a try, i need to study how the windings are layed out.
All the best
DaveComment
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