Older Minelab Pi For Depth?

[Dutchman4]

I have a GPX6k that I have had good success with over the last few years.  I have found several patches that yielded in the range of 8 to 15 nuggets each with biggest ones at 1.7g and 2.5g.  I have considered going back to these patches and start layering off the surface to gain more depth but that sounds like a lot of work.  I have also considered getting the 17x13 coil for the 6k to gain more depth but the reported depth gain appears to be only about 1 inch over the stock 11 coil if that is true.  Another option I am considering is to purchase an older Minelab PI and combine it with the best coil for depth, so that I can use it to go over patches (that I have cleaned out using the 6k) to find larger (3-5g and larger) nuggets at depths deeper than the 6k is capable of.  So just to be clear I want a machine that is dedicated/configured for increased (at least 3+ inches deeper than 6k) depth on larger gold, has a stable threshold and the ability to handle ground mineralization and hot rocks better than the 6k.  It does not need to be an all around machine that can also find smaller shallow gold since I have the 6k for that, but if it can then that would be a bonus.  I want to limit my budget to a max of $1500. 

After some research and input from friends I have been advised to consider the following models:

SD2200D - Reported to be one of the deepest machines Minelab has made.  Apparently the extra depth is due to the detector power supply being unregulated and the full voltage from the battery is available to the coil.  Are Lithium battery packs, either commercial or home made, adaptable to this machine?  On an unregulated machine I would think that a lithium battery would be preferred.  At the same time I read that using mono coils on this detector is not practical because they generate too much ground noise and to use DD coils instead.  A DD coil cuts the width of the coil in half with an associated loss of depth so I am confused how this machine can be deep when only using DD coils unless very large DD coils are recommended.  I would like to limit max coil size to between 15-18" round.  I would prefer to limit cost to between $600 and $900 on such an old machine in case it dies and the faulty component is no longer available.  I have the skills to troubleshoot to the component level and make repairs on older "through hole" technology PCB's as long as the components are marked and available.  What is the best coil for depth on this machine?

GP3000, 3500 - I dont know much about these machines and if they would meet my requirements for depth, stability, etc.  Would this be a better choice than the SD2200D?  What is the best coil for depth on this machine?

GPX4500, 4800, 5000 -  A GPX4800 or 5000 with a NF 15" round evo mono coil (or similar) looks to be the best and the most expensive option.  I might have to look for a long time to get a below market value price on one.

Please advise,  regards,  Ceril

 

[Rob Allison]

Hi Ceril,

    Over the last 20 years, there has always been discussion on older PI's going deeper with larger coils.  Normally, someone would get a unit modded more for depth and use a large coil.  The 2 detectors I always heard were the best for overall mods were the Minelab GP 3000 and GP 3500, but there is much debate even on these.  

I'm not sure who stated the Minelab 17" elliptical would only get like 1 inch over the stock 11 inch, which I find that very hard to believe.  Also, there are so many depth exaggerations out there, I would say you would get a bit more depth on a sizeable nugget like 1/4 or better.  

Rob

[dig4gold]

I would have to wonder with using an older model ML PI or GPZ 7000 that the bigger deeper gold you are looking for has not already been found with them back in there day. Hence the GPX 6000 mopping up the crumbs these days. A very high chance that any ground you go over has already seen many a coil over it. The gold doesn't tend to grow back.

D4G

[kingswood]

1 hour ago, dig4gold said:

I would have to wonder with using an older model ML PI or GPZ 7000 that the bigger deeper gold you are looking for has not already been found with them back in there day. Hence the GPX 6000 mopping up the crumbs these days. A very high chance that any ground you go over has already seen many a coil over it. The gold doesn't tend to grow back.

D4G

Yeah i had the same thought too 🙂

If convinced its virgin ground, then would be interested to know the depth the larger bits found with the 6000 were found at.

[Dutchman4]

1 hour ago, kingswood said:

Yeah i had the same thought too 🙂

If convinced its virgin ground, then would be interested to know the depth the larger bits found with the 6000 were found at.

It is obvious to me that these patches are virgin ground since I am finding multiple nuggets up to 2.5 grams in size that should have been found by any PI machine and probably most VLF also.  

The average depth of these nuggets was 5 to 10 inches.

[Dutchman4]

3 hours ago, Rob Allison said:

Hi Ceril,

    Over the last 20 years, there has always been discussion on older PI's going deeper with larger coils.  Normally, someone would get a unit modded more for depth and use a large coil.  The 2 detectors I always heard were the best for overall mods were the Minelab GP 3000 and GP 3500, but there is much debate even on these.  

I'm not sure who stated the Minelab 17" elliptical would only get like 1 inch over the stock 11 inch, which I find that very hard to believe.  Also, there are so many depth exaggerations out there, I would say you would get a bit more depth on a sizeable nugget like 1/4 or better.  

Rob

Hey Rob,

So it appears you are saying that a stock GP3000, with the right coil, wont have a significant depth advantage over a 6000 with the 17x13 coil, on 3g+ nuggets.

[kingswood]

4 hours ago, Dutchman4 said:

It is obvious to me that these patches are virgin ground since I am finding multiple nuggets up to 2.5 grams in size that should have been found by any PI machine and probably most VLF also.  

The average depth of these nuggets was 5 to 10 inches.

Thats pretty cool.

A 3000 with a 24x12" ufo mono may be worth swinging over those areas.

[Dutchman4]

39 minutes ago, kingswood said:

Thats pretty cool.

A 3000 with a 24x12" ufo mono may be worth swinging over those areas.

Kingswood,

I see in your list that you own the GPX6000 and GP3000 so you would know if the GP3000 with the 24x12 ufo mono would have a depth advantage over the GPX6 on larger gold.  If this advantage is minimal then I will just get the 17x13 mono for the 6000 and hope it adds some depth over the stock 11.

[RONS DETECTORS MINELAB]

21 hours ago, Dutchman4 said:

Are Lithium battery packs, either commercial or home made, adaptable to this machine? 

I have had good success using lithium battery systems on all SD/GP/GPX series detectors. I use a step up boost converter on the SD’s to get the 7.3 ish volts to the coil. Only thing with lithium battery systems with an audio amplifier is that you really should have a bypass switch to reduce the distortion when using a Bluetooth transmitter or headphones.

Detacc brand & Jonathan Porter’s B&Z boosters had a bypass switch for a good reason. Detacc don’t sell them anymore though.

[RONS DETECTORS MINELAB]

DD coils really do not have the ability to get the performance in comparison to the Spiral wound coils. So the older detectors SD/GP’s that needed to run DD’s to handle the more mineralized ground are not going to help out in your situation with moderate to heavy ground mineralization.
 

Smooth timings are the way to go in heavy mineralized environments and the mods also do gain even more depth but these are expensive options to get the depth you’re looking for.

If you’re in less mineralization and can run normal or sensitive timings with a mono 15” Evo coil or equivalent then you could do will getting the depth that you have described wanting with the older models.
This is mainly due to the coil size being bigger than what is currently offered on the 6000 and if you went with the 5000 and ran Sharp it’s even 20% deeper yet but only in low mineralized conditions. 😳

I do a lot of comparisons videos and can send anyone a link if wanting to see different coils compared.