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PI And Small Gold

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I find the discussion about using a PI to find small gold and whether it can be done somewhat amusing.  Ask a lot of PI users and they can tell you they have seen a PI in use many years ago that could do just that. 

How do i know this?  Well, many years ago  a lot of the invisible gold being discussed at that time was gold found around Greaterville AZ.  John Blennert had found lots of the stuff and used to have fun challenging PI owners to try to detect it or build a detector that could.  In some cases, the gold tried to be detected was several grains in size.  In fact, there were a couple of the "invisible" nuggets weighing about 8 grains totally frustrated a lot of PI owners.  Lots of owners tried to detect those nuggets and lots of owners failed. One detector could detect those nuggets even for a couple of inches in distance with a nice strong signal.

John B. used to joke how some owners would pound the gold and the ground trying their best to detect this gold. Some said it couldn't be done.  He used to laugh and say they couldn't pound it flat enough to detect it. 

Well, many years ago John Blennert challenged people to build a detector that would detect this gold known at that time he called invisible gold as well as gold down to a grain or less in size.  Well it was proven it could be done and was.  The detector operated at about 8 usec and could detect a lot of those nuggets not detected by the present PI's of that day and most made today PI's made today still failed.  Discussions and displays were held in places such as at the old 24K club  and many of the well known PI users in AZ saw it happen either there or somewhere else including at least one other member of this forum.  This member saw a demonstration at Greaterville.  How about it Fred, remember when you were at Greaterville along the well known AZ twins that frequent the Nuggetshooter forum and saw a demo?

The truth is, the question of whether it can be done and at what delay was answered many years ago. So, to me this discussion is old stuff but still fun to hear all the speculation of what needs to be done.


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  What needs to be done? Just find a place where there is larger gold and use a P.I. detector. Please don't misunderstand me -I'll take any gold I can find but for me it's all about accumulating as much gold weight with as little time (and effort) invested as possible. At times I will put on a 6" coil for cleaning out exposed bed rock and find unweighable specs and then question weather it was worth the time.

  I would like to see a detector that can be switched between VLF and PI.


I've never been to Arizona. Would I need a Passport?

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Hi Reg -

It's an interesting line of discussion. I was not at the Greaterville meeting you mentioned, but have had long discussions about this with John B. He took pounds of gold off the mine dump that yielded the bulk of invisible gold that John used to show around. I have a sample of it in my collection.

I am curious of the PI detector you mentioned but did not name. I have no doubt of the accuracy of your statements, but am curious about the name and maker of the detector. I am not sure which it was. Can you tell us?

Of course when John used to do this, it was back in the days of the SD detectors which were notorious for inability to detect small and wiry gold (John's invisible gold is wiry). The later GP and GPX Minelabs have made incremental improvements but still have difficulties with the smallest and most wiry gold. As John B sometimes jokes, when they finally get the Minelabs perfected, it will be a Goldmaster (John's VLF of choice for prospecting). It one of those jokes that is funny because it does have a certain element of truth. I suspect the new ML detector will represent another incremental improvement in the ability of the ML detectors to see small and wiry gold, but we shall see exactly what it is when it comes out.

Its good to see you posting, I hope you are doing well.

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Building a PI that detects small gold is not new. I know you have done it Reg as have others. The issue is - where does a person get one? As far as I know Eric Foster hand building units is as close as we have got to such a detector commercially. 5uS At The Beach Link deleted since Findmall update broke all old links

Getting something like this into mass production is the issue at hand. Even then price is going to be a barrier to entry without serious competition. White's could easily do it if they wanted to. Just put out a TDI that adjusts to shorter delay lengths. But they won't.

From your perspective why is that Reg? What is the hardest part in producing a hot PI? The coils? Something else? I assume the efficiency of the ground balance circuit gets more critical the hotter a PI gets? You have covered this all very well in the past at http://forums.nuggethunting.com/index.php?/topic/3802-oxymoron-pix-of-invisible-nuggets/?p=25910

This statement you made there would seem to illustrate an issue with the ATX and coil falsing when bumped:

"If the sample is taken right at the edge or just when it will allow the circuit to work, generally, the coil becomes hyper sensitive. The upside is the coil will detect smaller stuff, seems extremely sensitive, etc. The down side is it will also be noisy, usually generate false signals if bumped, and will generate much stronger ground signals to deal with."

The ATX obviously has a fairly short delay but Garrett is not saying what it is.

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As Reno Chris said Reg, it is good to see you posting as I have followed your postings over many years from here in Australia.

As I mentioned in Steve’s thread in regards to the new Minelab PI my main interest in this SDC / MPF detector would be IF it can produce any extra depth on small gold that lies beyond the GPX’s Fine Gold timing. I feel where I detect small nuggets in the 1 to 2 gram range are still at depths that are out of reach for Fine Gold even with a smaller coil. 

I am NOT interested if the SDC is targeted at micro size nuggets but hey if it did away the need for a Wash Plant or a Dryblower than would I have a change of mind.

I suppose what size gold do we class as small, is it up to 1 gram, up to 5 gram or even up to 10 gram ?  

Also I expect there is only so much you can do to a PI detector that it will only ever hit a certain size nugget at a certain depth and any extra depth on that nugget is up to using machinery or whatever means to remove the surface to another level.

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On 5/22/2014 at 9:30 AM, Steve Herschbach said:

White's could easily do it if they wanted to. Just put out a TDI that adjusts to shorter delay lengths. But they won't.

Yikes, I wish it were so easy. The TDI running at 10us is pushing the absolute lower limit of that circuit. It won't go lower, that requires a new design.

I got beat up on a pretty regular basis by certain people who wanted iron ID added to the TDI. As in, "Just take the TDI and add iron ID to it!" Yup, that's all you gotta do

Ironically, I was working on a new design that went down to 6us, and had iron ID, and ground balance with no target hole. I suspect that is a Dead Horse now.

- Carl

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Hi Carl,

Really good to see you here, maybe your change of circumstances will allow you to hit the forums more?

I do believe Reg was running a TDI modified down to about 8uS which is the reason I made that comment. Sadly, it probably is a moot point now.

Reg commentary on 8uS TDI -

Link deleted since Findmall update broke all old links


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Hi Carl,

When you get a chance, drop me an email.  I am hearing the project you mentioned has sort of been resurrected. Also, I have some software questions. 

BTW, how in the heck are things going for you now?  Hope all is well and everything is working out..

On a different note, the PI I mentioned was considered a low powered unit and that is part of why it could go down to a shorter delay.  Also, one big trick was to use a DD coil .  With that combination, I could hit the 8 usec delay well and pretty well match the big boys on a typical 1 gram nugget for depth and clearly beat them on the smaller stuff while using AA batteries that would last a couple of days of hunting. 

The cute part of this non production model was the fact that a DD would alter the signal from reasonably large iron relatively close to the coil, so it could be ignored.  The really small iron such as bits of tin cans or shavings off the blade of a cat would give an abrupt response that was easy to recognize.  Gold responses were always smooth and clear. 

I even had a couple of LEDs, one blue and one red to let me know the probability of the metal.  The part of the design did need some improvement but it worked.  Unfortunately, I was using an extremely compact housing and had no room for further modification.

I remember one trip to the 24K club where I got there about a week after one of their pushes.  I swear the entire push area was stomped down with footprints, leaving no spot that hadn't been hunted hard.   Well, i was using something new and never seen on a PI before, a 12" by 3" rectangular coil that I could slip into the mild trenches left by  the cat during the push. 

To shorten the story, within an hour I picked out a half gram nugget from the worked out area out of one of those trenches.

As for the long narrow rectangular coil design, I had Bill Hays make the initial housings for me and today, they are quite popular.

One more thing, a couple of things mentioned recently gave me some ideas to try that just might allow a means of detecting smaller gold on the TDI.  Now, I need to work on that project.


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Hi Steve,

I see you resurrected a couple of my posts.  Yes, the original TDI's could operate at close to 8 usec and that did allow them to find smaller gold.  Unfortunately, it could cause problems for the owners if they didn't know what they were doing since large coils may act like they are working correctly but really are not.  Ultimately, failure to operate properly could cause problems for White's so I was quite careful as to who received the info on how to adjust the detector. 

The 8 usec adjustment works with smaller coils that are properly built.  Miner John who is the new owner of Razorback coils is doing things right.  The key on the original 200 TDI's is to keep the coil size down if you want it to work right at the 8 usec and even then, the ground signal is extremely strong and can cause problems. 

Eric used to make a 10" coil he used on some of his non ground balancing high power PI's and that was about the biggest size coil I knew of that worked consistently at the shorter delay.  I certainly don't recommend trying anything bigger.

Now, getting back to the old posts, one guy really did called me a liar and went on to say I never hunted but all I did was I spouted off about detectors.  I still have his email on my old computer.  I do need to get that old computer set up again so I can retrieve a lot of valuable info.  No, that email is NOT part of that valuable info.

I thought I had copied the info onto a usb drive but for some reason that info wasn't on the drive once I moved over to my new computer I got to avoid problems that might arise because of lack of support for my old favorite XP system.

The truth is, what I advocated was a TDI could use a DD coil to help an owner recognize ferrous objects if those objects were close enough to the coil.  What would happen would be the iron signal would cause a transition to a low tone if it was close enough.  Now, what I didn't tell the "wizard with all the answers" was if the iron signal was already a low tone, it couldn't make the transition because it was already there.  DUH!!!

The key is to set the GB setting such that ferrous objects generate a high tone.  This is usually around 4 on the GB of a TDI.  With the GB off, all signals are high tones.  Now, when using a DD coil, close iron generally would give a low tone.  Raise the coil and it will revert to a high tone.

I used this ferrous signal transition for years on my low powered PI and it worked well. 


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