Coil selection 4 soil type

[Jackpine Savage]

I gotta believe a DD that size for the C V & T will be a killer coil for dense iron/trash. The big question will be how well it handles the iron at low disc settings. While good at seeing mid to low conductors in iron the 5.75 concentric is only an "average player" on the Cibola and Vaquero compared to some other small coil combos, my opinion only. Sweep speed, angle of approach and the ability to user higher settings should all be improved with a DD (I hope).

Tom

 

[plugger]

Bob, Monte can write a book on a bunch of detectors and I would be the first line to get one! I have printed out a bunch of his answers and laminated them and carried them with me until I "got" it.

Bill

 

[Mick in Dubbo]

Great post BT.
It's good to have you on board. I look forward to reading your posts.
They will add some extra dimension to the forum.
Mick Evans.

 

[Mick in Dubbo]

Just a thought in regards to the round DD coil being a bit nose heavy.
I don't know how tall you are, but if you of average size or smaller, then the lower shaft is probably too long for you, putting the coil too far from your feet. Think about it like how heavy a small weight can feel when you hold it on a long pole that is away from your body. I found this with the standard coil.
Solution. cut a few inches off the lower coil (or buy the short shaft). Bring the coil as close to your feet as you feel comfortable. Doing this will relieve at least some of that feeling of the coil being nose heavy. I have cut several inches off my lower shaft and found that the detector feels a lot more comfortable to swing.
Mick Evans.
PS. I don't own the DD coil yet and have applied the above to the standard coil, but the same principal should apply to the DD coil.

 

[nugget71]

There is nothing better then reading a simple and direct answer to a question, nice one BT. I too use the elliptical 18.75kHz coil and haven't taken it off my detector since putting it on. I live in far north Queensland and have access to many gold-fields in my area and cant wait to head out after the wet season is totally over. The 18.75kHz DD coil is very sensitive and perfect for all the areas I am detecting at the moment. The maneuverability is fantastic and love how light it is. I advise anybody who owns an XT-70 to get one of these coils you will not be disapointed.
Cheers!

 

[Monte]

can't be shortened enough for many people of even the upper-end of 'average.' That's one thing I noted from their release. The bigger coil does get nose heavy a bit, and if both the lower and middle rods were just each a little shorter it could be ideal.

You're right, however, in that too many people tend to hunt with a lot of excess rod out there.

Monte

 

[parrott]

Maybe cutting (hacksawing)the lower shaft close to the clip will give enough shortner... it did for me. Actually the lock nut seems to be adequate w/o the need of the spring clip.

 

[B.T]

Good stuff Nugget. I lived in Yeppoon for a couple of years before returning to VIC about 15 months back. I envy you being up there.
It was the most incredible place I have ever lived QLD.
Im a mad fisherman too, mad being the operative word the misses reckons, and do I miss those speedster mackeral and monster flatheads.
Mate do I miss that place full stop.
Great goldfield Victoria but dry as!
That little 18.75 is deadly and I couldnt believe how much of a difference it made when I put it on.
Good luck when you get out.

 

[nugget71]

Cheers mate I'm sure I will have a great time. Your right about the fishing up here you just cant beat it. When I was a kid the beach was literally my front yard as my parents own beach front property and still do today. Before and after school fishing was my religion, man those were the days no responsibilities just fishing ,sport and hanging out with ya mates bragging about the massive one that got away.....lol not much has changed in that department I must admit. Anyway if you ever decide to head up this way in the future maybe we could meet up and do some damage on the reef and out bush.
Cheers!

 

[Mick in Dubbo]

I took to mine with an angle grinder.
First of all. I put the the lower rod in so that it was locked into the top hole to give the shortest length. Then after prechecking that I had the right drill size for the holes in the middle shaft, I drilled another hole into the lower shaft, using the middle shaft as my drill guide. I drilled down 2 holes from the top hole (could have gone 3). I removed the lower rod and cut off several inches with the angle grinder. My only regret. I just nicked the internal spring enough to wreck it. Should have pulled it out first. Replaced it with one that I bought from a camping shop.The same sort of spring goes into the extendible poles for tents. I did have to trim it a bit to work though.
The end result. The detector is a lot more comfortable to swing now.
Guess if I buy the 70, I'll have to do it all over again.
Mick Evans.

 

[Mick in Dubbo]

That is why it is less sensitive to mineralisation (less ability to see it). This is also why a concentric coil will hit smaller gold targets eta than a DD coil.
My knowledge is fairly limited in regards of all this, but I hope that it's enough to help you.
Mick Evans.

 

[Piero franchi]

Just a thought, if it has less windings, why is it heavier???????

 

[Mick in Dubbo]

That's a very good question. When I asked the same question to the local Minelab dealer, the answer I got, had to do with keeping the windings stable within the coil. More material had to be used to achieve this. Apparently, if less was used, then there is an increased chance that the coil could start giving you false signals ( due to some sort of movement). It doesn't sound particularly scientific; but that is the answer that I got, and all that I can give you.
Mick Evans.

 

[Digger]

By design, DD coils have smaller diameter windings for the transmit and receive coil, compared to a concentric coil using the same size housing. In a concentric coil, the receive coil is located within the circumference of the transmit coil. This donut design provides a symmetrical detection field and provides the best results in low to moderately mineralized sites. And with the concentric design, you can wind the coils as large as possible, to fit within the coil shell. The bigger the windings, the deeper the detection field. In a DD coil, the transmit and receive coils are arranged like to capital letter D

 

[bfodnes]

I have cut my lower pole to absolute minimum and it fits both my 11 year son and me, i am 6 foot.

I just laid the lower rod beside the detector to the point where the locker nearly came in contact with the plastic at the tip of the lower rod. Then marked the upper section of the lower rod exactly where where it meets the bend of the middle rod.

Cut it there and pushed it all the way in to mark the point to drill a new hole for the clip.

Before you cut the rod, mark an exact line down the lower rod from the original hole for the clip so you can see where the center of the drillbit should enter when drilling a new hole.

Its very difficult to drill a new hole so that it will hold the coil in perfect angle, thats why you should do that.

I have burned myself on that, dont want anyone to do as me. When you have cut it at exactly minimun length, there is no second chance.

 

[Mick in Dubbo]

Drilling a round pole could be tricky. To make the job a real cinch,
Place the lower pole back all the way into the detector and drill a few holes down from the locating pin, using one of the holes in the middle shaft as your drilling template. This should guarantee a perfect angle and location for the hole. It takes all the guess work out of the equation.
Mick Evans.

 

[Mick in Dubbo]

That is a great heads up Randy.
These last few threads may be a bit on the long side, but a huge amount of very good info. I'm sure a lot of people have benefited from it. It's a great reason to ask questions.
Mick Evans.

 

[parrott]

Mick in Dubblo... You did good. All I did was to put the shaft
in a vise and with a hacksaw cut the end off tight to the spring
clip. With the end off it became shorter and the shaft could be
slid in further as it now did not extend into the upper rod curve.

Also, the lock nut can be tightened to hold the lower rod w/o
the need for the spring clip.

But I really like your way of shorting the lower rod... Thanks for
sharing...

 

[Mick in Dubbo]

Thanks for the compliment Parrott.
A lot of people seem to have issues with the length of the shaft. Hopefully these posts shows one way of overcoming it.
Mick Evans.

 

[parrott]

I believe that those such as I am who are not tall (grin) find that
the shaft even in the smallest notch too long... However, it is easier to cut a little off rather than the opposite and need to rig a longer one.