coil building 11 DD gp extreme and questions

[porfirio]

Hi to all of you lovers of this fantastic passion for the search!

I live in italiy, Rome and me I have this passion for the search from more than 25 years.
I have little experience of electronics and I would like to build a coil 11 DDs for my gp extreme. In italy there are some grounds very mineralized and the gp extreme as the others of the serious sd/gp/gpx, are insuperable. But unfortunately these detectors have some problems of discrimination. I could never use a mono coil, I would become crazy!
I have a coil of the coiltek from 11DD and I have modified some things (for my small experience) and I have to say that it is all right in discrimination and established .
I have opened the coil and I have replaced the two sheets of paper that have the varnish of screening in graphite, that measures ohm 200, with some new sheets of paper with varnish of pure graphite to 95%, the graphite is in dust a lot of goal, mixed with some glue for wood in relationship 1 to 10, that is a part of glue and 10 parts of water. I have made four passages of varnish of graphite and I list you the various measurements for every passage of varnish:

First passage, measurement with the tester to 20k 18,50, measure taking on the most external part of the cardboard

according to passage, measurement with the tester to 20k 10,00, measure taking on the most external part of the cardboard

third passage, measurement with the tester to 20k 6,50, measure taking on the most external part of the cardboard

fourth passage, measurement with the tester to 20k 5,00, measure taking on the most external part of the cardboard

Perfect job! Very important thing I have prolonged the thread of the screening of the coil of 4 inches, (10 centimeters), in the inferior part of the coil, (copper thread that is to contact with the varnish of graphite).
In this way the detector has improved of very its discrimination and his established in the grounds very mineralized, the depth has remained the same one.
Other thing that I have modified is the small resistance that is connected among the two terminals of the smallest wrapping of the coil that it measures ohm 6,3/6,4.
This small resistance of the coil original measure ohm 619 and me I have replaced this resistance with one from ohm 280.
I think that this small resistance regulates the voltage of the coil and in this way it passes more current to the coil, I have to say that the detector is faster in the search, as if the detector had more gains, the depth is increased of two inches (5 centimeters).
This for me has been a great satisfaction, but unfortunately there is always some problem, when in use the detector in the grounds strongly mineralized, the detector is not stable and feels the mineralized rocks.
I ask you if you have the possibility to resolve this problem, and to understand what he is able to modify for maintaining this depth of the detector, also in the grounds strongly mineralized!!!

The measures of the two wrappings of the coil 11DD of the coiltek measure ohm 6,3/6,4 and ohm 0,9/1,0

I over this problem, would like to build a new 11DD coils, even with your experience, to be able to realize a 11DD coil that is superior of this coiltek coil!

Excuse for mine bad language English and me I hope that you what I have written you!!!

Thanks of your patience and courtesy.

Bruno.

[porfirio]

2 photos original coiltek coil and 1 photo with new graphite

[Kev]

Hi Bruno,
I'm unsure what happened to your original DD, but it sounds a bit like my setup when using Nickel paint...Eric Foster advised me of the problem in my case, it was that the detector could see the Nickel screen...no good

Maybe in your case the graphite layers have become so thick that it's interfering with the ground balance, like mine, or the sheild is somehow acting like a shorted turn and generating eddys ???

As for building a new one from scratch there is already a lot of information posted in the archives, so do a search, for things like "Minelab coil" or "Minelab coil Q" and you should dredge up some results.

Cheers
Kev.

[porfirio]

Hi Bruno,
I'm unsure what happened to your original DD, but it sounds a bit like my setup when using Nickel paint...Eric Foster advised me of the problem in my case, it was that the detector could see the Nickel screen...no good

Maybe in your case the graphite layers have become so thick that it's interfering with the ground balance, like mine, or the sheild is somehow acting like a shorted turn and generating eddys ???

As for building a new one from scratch there is already a lot of information posted in the archives, so do a search, for things like "Minelab coil" or "Minelab coil Q" and you should dredge up some results.

Cheers
Kev.

Hi Kev,

I thank you for your information, but the true problem is if I replace that small resistance from inside ohm619 to the coil that is connected to the wrapping of smaller measure of thread.
This resistance should limit the voltage to the coil, me my dish now works with an ohm280 resistance and the depth of the coil it is increased and the coil is more precise in to notice the objects. The discrimination is improved a lot, I have prolonged the thread that is connected to mass to the varnish of graphite of inch5, you can see it in the photo of right, and in this way the discrimination is excellent. You have to consider that I use the detector where unfortunately there a lot of is I fit with iron ancient, therefore is I fit with iron type I steel and for me the discrimination is important!
If I replace the ohm619 resistance with ohm280 and the sheets of paper with the graphite original of the coiltek, the coil is not stable to the ground middly mineralized, it is not even rather stable in the grounds a little mineralized, this because the original graphite has little power of screening, alone ohm200.
Conclusions, the graphite is a good material to screen and more it is pure and more it has power of screening, the graphite of the coiltek has a low power of screening, this because it is not pure. I don't believe but the varnish of nickel is not proper to screen the coil, and I believe that gives some troubles to the coil, really for her characteristics that it is a metal.
If I could lower even more this ohm resistance 619 to + / - ohm 100, the detector becomes a killer but the problem of established it increases notably, my small experience of electronics now stops here him, unfortunately.
I also believe that there am a relationship among between detector and coil and I am sure that a competent person of eletronica knows where the problem is and even is able him to resolve, is perhaps really the coil that should be referred with new wrappings of I spin and new technology!!!
Do you know if some person of the forum has realized a coil 11DD weries best????
I would be happy to try to realize a new coil!!!


Cheers

Bruno