DD coil information and questions

[Teemore]

Thanks,
May have a fiddle with the ML 11" DD that came with the 4800 before deciding on possibly a larger version.
Any recommendations???
Thanks Tom.

 

[user 4485]

I've used a Coiltek 14" DD pro elite on both a SD2200D & GP3500 (different coils) & have found it to be a good size, stable coil, good depth etc. I haven't used a bigger DD coil, only smaller, so it's really the only bigger one I can recommend. Seems to be a favoured coil especially on the older machines & I would assume it works as good or better on the GPX series?

 

[condor22]

I picked up an almost new 15 x 12 Commander DD 2nd hand at the Coiltek Gold centre in Maryborough last year for $200 (bargain) had only been used once on a beach.

Very stable and good in open ground. Like any large coil, a pig in scrubby patches. My thoughts are that you need a selection of coils depending on usage.

I broke it down to size and type, calling the 11" Commanders medium sized. So I got a small mono (8") for mullock heaps and a larger mono (18x12 Coiltek which came with the 5000 as a deal) and as said a larger DD.

Simply put, the general rule is, if you want small gold, shallow you need a smallish coil, if you want larger gold, deep, you need a larger coil. Conversely in thicker scrub more often than not a small elliptical is all that you can swing and in noisy, trashy ground a DD still has its uses.

I would suggest that if you go over open ground with a large coil, go over it again with a small coil especially if you find something with the large coil.

 

[Ridge Runner]

Can't complain about recent success with the SDC or the 4800 with the 14x7 NF or the new 14" Mono Elite but have a couple of locations where the screaming of what I'm assuming is rusted metal is keeping me away (at least I hope it's just junk).

Been thinking of using a DD with Iron Reject but ...... I'm assuming with a trade off of some loss in depth .......
So just how much depth do I lose????

If using a 11"mono how much does loss is there if using a 11" DD (1", 3", 6" ???) or to put it another way how large a DD would be needed to get the same depth that a Mono would give (14", 18" ????).

If using say the Coiltek 14" Pro DD what depth equivalent in a mono coil would that be (11", 8" ???).

Hope those questions make some sense and more so that someone has some tech knowledge to provide a guide.

Cheers Tom.

Seeing as No Two Nuggets are the Same I am going to Use Coins as An Example, Ok.

From what I have seen, A DD can see it's width In depth, IE a 10" coil will see 10 and 12" will see 12 inches Deep,

But with Mono's and Concentric's they can see about 1.5 X their width Deep in the Ground and Sometimes even more, BUT on Average ground The Norm is about 1 and a 1/3rd Times its Width So A 12 Inch Coil can see about 16 inches deep and A 15 inch coils can go to about 20 inches deep, And when the Mineralization goes up above Medium levels on a scale of 0 to 100--- Say about 65 to 70 they are equal to A DD and when the ground gets up around 75 to 80 ish you are losing Depth So your 15" Mono is more like a 10/12 inch DD,

Mono's and Concentric's Are A Lot Hotter on Small/Tiny Gold, But When the Mineralization Goes up Some of that Sensitivity Gets Lost Depending on the GB settings.

DD's Don't Like EMI compared to other Coils But as the Ground Get Hotter DD's Loose Less Depth than Mono's and Concentric's,

If you want to maintain Sensitivity you can still use a Mono or a Concentric Coil in Hot Ground But you have to use a smaller Coil in Order to Reduce the Picture of the Ground that the Detector See's, although A smaller coil will loose some depth they will still punch deep compared to an equal size DD,

A 15 inch DD can see 15", A 15 inch Mono or Concentric Can see 20", A 10 x 15 DD can see 12.5 Inches In Theory. A 15" DD is equal to a 12" Mono/Concentric, The Difference between the two Types of Coils is a DD has to be about 3 inches Bigger to match a Mono or Concentric, After 15" you have to use the 1 and A 1/3rd Maths to get the Answer Because 15" Coils are where the Formula Changes,

But if Big or DEEP Nuggets are your Goal Then A DD is they way to Go In Hot Ground,

Hope this helps,, John

 

[Teemore]

Tks for your input, will take my ML 11" DD and do a few trials with some sample nuggets.
May then consider a larger DD to use in trashy areas.
Cheers T.

 

[old hand]

A friend of mine is having the most success he has ever had using a DD standard black gp extreme coil on a extreme ,he is using it in mono mode there are not many days when he does not return with 1,2or 3 pieces of gold all small but they add up regards john

 

[bbrook]

Hi all , I have a gp3000 with the original 11dd and the lead is disintegrating !
Trip before last I got it out and the lead covering had split in one spot across and then lengthways I assumed I had snagged it getting it out of the backpack somehow and taped it up ,but when I got it out again this weekend ,its gone the same way in two other places (and started to split the inner covering ) ...back to the tape!

Long story shorter , I think its time to retire this coil so , what is out there in 11 dd that may be a better performer than the one that came with the 3000 . I have a 14 dd but I like the 11 for weight and poking round the grass .any recommendations ? commander , detech , coiltech ?

thanks Brett

 

[user 4485]

Keep an eye out on eBay etc. There's been a few new GP Series 11" DD's that are supplied with the re-released GPX4500 come up & sell for $100-120.
I reckon the 11" is as good a coil as you can get for all-round detecting. I had a Coiltek Joey DD 10"x5" & the 11" DD wasn't far off it for sensitivity but obviously better on deeper stuff. The 10"x5" was better in tight spots.

 

[bbrook]

Hi mbasko , yes , there was one not long ago that went pretty cheap , I was watching it but that was before I knew I needed one!!
are they an improvement on the stock 3000 coil ?
thanks , Brett

 

[user 4485]

Being a new/newer coil it should be an improvement i.e. stability, better winding wire etc.
I'm a believer in coils being matched to the detector series though I.e.
Goldsearch series coils - SD series detectors
GP series coils - GP series detectors
Commander series coils - GPX series detectors
Detech are going to release some supposed new technology DD coils soon & I think they will have some at the Laanercoorie Gold Bash but it is 15".
http://www.detectorprospector.com/forum/topic/1281-new-detech-coils/#entry14496
Other than that I reckon a DD coil is a DD coil no matter how you paint it & any reputable brand should be ok.

 

[PhaseTech]

Hi mbasko , yes , there was one not long ago that went pretty cheap , I was watching it but that was before I knew I needed one!!
are they an improvement on the stock 3000 coil ?
thanks , Brett

That was probably one of mine

 

[PhaseTech]

There's an 11" DD pro currently on ebay. Might go for a good price

 

[Davent]

Ok, thinking about adding a DD to my coils, for days when I cant tame my evo, s.
I have a commander 11"dd, but am not confident with it, as a mate pulled a .5 gm from under me, and even it was exposed, the DD couldnt see it.
so im thinking about getting a really good dd, it must be able to see sub grammers at about 2 inches (better if possible)....am I dreaming?

I like the sound of the detech, 15 but sounds a bit heavy. Anyone recomend a red hot dd?
wish detech did an 11 or 12d.d

 

[PhaseTech]

The stock 11" DD should rip in a 0.5g at shallow depth unless it is an unusual piece. Do you remember what timing you were in?

Detech do a range of DD's: 8" DD, 12.5" DD, 15x8" DD, 15x12" DD etc. but the only one that is spirally wound is the 15" Ultimate. There is no magic bullet, use smaller coils for small gold and bigger coils for big gold. The 15" Ultimate is the exception where it has very good sensitivity considering its size.

 

[Digginholes]

I found my first nugget using the dd commander supplied with the 4500 using close to factory preset and it was 3" deep under a nice size rock so in actual fact was more like 6-8" below my coil and she was loud n clear signal on a .56g

 

[Davent]

The stock 11" DD should rip in a 0.5g at shallow depth unless it is an unusual piece. Do you remember what timing you were in?

Detech do a range of DD's: 8" DD, 12.5" DD, 15x8" DD, 15x12" DD etc. but the only one that is spirally wound is the 15" Ultimate. There is no magic bullet, use smaller coils for small gold and bigger coils for big gold. The 15" Ultimate is the exception where it has very good sensitivity considering its size.

I was in factory preset, DD.

 

[AuWanderer]

Had great luck with the 15x8" dd eleptical...in trashy areas disc works good. A bit heavy for its size...but a great mid size E coil...smallest piece found so far is 3.5 grains 1-2" deep. Anything smaller on your detector you will feel like your not covering ground.

 

[muzz]

So what do you run the discrimination at in a trash area using the dd Coils guys

 

[Davent]

Been playing around with the idea of adding a biggish dd to my coils. Having pretty good success with a 14x9 evo mono on small gold, but bigger gold is eluding me, and I know there must be some bigger bits still around.
Ground is pretty hot, and comming up to the wet season proper now, so ground noise is increasing. I can NEVER get my machine to normal or sharp (4500) so spend nearly all detecting time in enhance.
So, thinking that to get more depth, I need a dd, in normal, pump up the gain, wind the stab back and search the deeper areas where im finding my sub grammers.
Now, which dd do I need?
I like eliptical coils, for the reason of being able to carry them easier in my pack, and also weight savings. Now I kinda understand how a dd works, as in rather than a cone like a mono, it sends down a sheet, so side to side is a must, where I sometimes find myself pushing fwd with a mono. So how does being eliptical effect a dd depth, say a 17x11 platypus dd compared to a 17 round dd, much depth loss on the elip?

Also, will the 17 platypus elip in normal, grt much more depth than a 15" mono in enhance and tuned down a bit, gain around 6-7 ?

cheers

 

[Heatho]

Hey Dave,the Detech 15" Ultimate Spiral DD Coil is probably the one you want, I think Nenad has done some vids on these, he will recommend it I'm sure and I think he sells them too.

http://www.detech-metaldetectorsaustralia.com.au/ultimate-dd-spiral-coils

If you search for some info on them you'll see they are getting bits down under .1 of a gram.

Another good one would be the 15x12 commander DD but if I were buying a new DD it would be the Detech.