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Minelab 705


HagenT

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Thanks Mike Furness, & Bill for the welcome!

I only have the DD 18.75 Khz coil. Is that still considered VLF?

I'm able to pick up pretty small stuff, but I'm probably limited on depth.

Do you have a favorite coil to shoot nuggets with?

Thanks,

Hagen

Edited by HagenT
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Hagen ... The 'VLF' refers to the technology in the way the detector sends/receives signals from a target more so than the frequency that it operates on. If the coil you have is the 10x5 eliptical DD you have the best all round coil for that machine. There is also a 10" round DD for a little more depth. Don't get confused by the 10" round Concentric coil which is also available ... The Concentric is more of a treasure/beach/jewelry/coin coil. Stick with the DD coils for gold on this machine.

Mike F

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Hagen ... The 'VLF' refers to the technology in the way the detector sends/receives signals from a target more so than the frequency that it operates on.

Mike F

FYI Mike F---

Frenquency

The number of complete alternating currency cycles produced by the transmit occillator per second.

VLF-Very low frequency=3-30 KHz

LF-Low requency=30-300 KHz

MF-Medium frequency=300-3000 KHz

HF-High frequency=3-30 MHz

Mike C... :200:

Edited by Mike C...
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Mike C ... I was referencing the "general" technology of the "VLF" detector in my reply ... I didn't want to confuse the issue with the different levels of oscillation ... BUT ... Thanks for the additional input. The 705 is still considered "VLF" technology compared to the other common technology "PI" aka "Pulse Induction". Most prospectors could care less about the different levels of oscillation and consider the information superfulous and useless ... all they want to know is is it VLF or PI ... and which is better to use when.

Mike F

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That 6"round coil is sweet!

The xTerra is a great unit for hunting the trashy areas.

In my understanding the term for the way (most) VLF's operate is TR, transmit receive.

Other methods that are "old school" are IB and BFO, Induction Balance and Beat Frequency Oscillation.

Hope this is not too "superfulous and useless" :)

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FYI Mike F---

Frenquency

The number of complete alternating currency cycles produced by the transmit occillator per second.

VLF-Very low frequency=3-30 KHz

LF-Low requency=30-300 KHz

MF-Medium frequency=300-3000 KHz

HF-High frequency=3-30 MHz

Mike C... :200:

Mike C,

That info says LF=30-300 khz. So why is a gold bug 2 running at 71 khz called a VLF detector?

Rim

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Thanks everyone for your responses. Much appreciated.

Mike, You mentioned the 10" DD gets a little more depth compared with my 10x5 eliptical DD.

Can you quantify that for me? I know it's a hard question because of all the varibles involved.

And of course my next question, is how much better at depth is the GPX 5000 for the same size target?

The last nugget I found was 0.13 grams quite small, and I think was about two inches deep. Still had a good signal though.

Oh and for all you dry washers out there. I found it because it was still encased in clay. It had gone right through someones machine.

It might be a good idea to come up with another gadget that can break up the clay from the gold before it get into the dry wash.

Cheers,

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Mike C ... I was referencing the "general" technology of the "VLF" detector in my reply ... I didn't want to confuse the issue with the different levels of oscillation ... BUT ... Thanks for the additional input. The 705 is still considered "VLF" technology compared to the other common technology "PI" aka "Pulse Induction". Most prospectors could care less about the different levels of oscillation and consider the information superfulous and useless ... all they want to know is is it VLF or PI ... and which is better to use when.

Mike F

Oh but frequency does matter Mike-The higher the KHz the more sensitive it is to smaller gold-Thats a fact Jack :4chsmu1: -When looking for small gold or beepin mine tailing piles I will take a 50 - 71 KHz detector over a lower KHz beeper any day :head: Useless I dont think so :old: -Superfulous-WTF :nutty: Mike C... :200:

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Mike C ... You're missing my point ... I was talking generalities ... you're talking specifics. I am fully aware of oscillation rates to sensativity ... just didn't want to make a mountain out of a mole hill when a simple question was asked. Nuf said on this pissing point my friend!

Mike F

Edited by Mike Furness
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Hagen ... In generalities ... so I don't get stepped on by to many long time forum members ... a round coil of similar size to an eliptical tends to get better depth. For example a 10" round versus a 10" eliptical ... assuming the elipitical is 10x5 for example ... a rough equivalency to convert an eliptical would be: length added to width divided by two. so for the 10x5 it would be 10 + 5 =15/2 = 7.5 or approximately the size of an 8" round coil. Now you can make a comparison ... rough that it is ... between the 10x5 and the 10 round. The actual depth that the round will be able to do versus the eliptical has a lot to do with conditions but I don't think any would argue that for the same size target the 10" round would beat out the 8" round. Clear as mud now? LOL

Anyway hope that helps you a bit.

Mike F

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gallery_26507_15_16098.jpg

Hey I just figured out how to upload a picture!

My first two gold nuggets and the dark one I think may be platinum.

I found the upper gold one last Friday. The gold are both around 0.1 and 0.13 grams each. Enough for gas money?

Cheers,

Edited by HagenT
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OK. Going back to the Minelab 705...

I like to dable in electronics and make some fun projects. So I do know a thing or two...

I have an idea for a new coil arrangement that I would love to try on my 705.

Does anyone have a pinout for the coil connector, and any information that might be helpful?

I seem to remember from the manual that the 705 Knows which coil has been connected and adjusts it's frequency to match. How is this done?

I did measure a resistance of about 15.87k ohms between pins 2 and 6 and that is kind of close to the the 18.75k ohms that the 705 uses for this coil.

Any help would be appreciated!

Hagen

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The XTerra coils have a microchip in them.

Nice Nuggs !

Try a magnet on the dark one looks like slag to me.

A chip? That sucks... I guess that means no after market coils. I may have to build a very simple detector from scratch then and see if the coil is any good.

The dark one is non-magnetic. :arrowheadsmiley:

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There is 1 aftermarket coil, The 7.5 kHz 15" WOT by Coiltek.

Its best used for beach, coin and relic.

Is the dark one malleable? Will it cut with a pocket knife? Could be native silver based on the oxidation.

Platinum is a noble metal, typically when found as placer its untarnished.

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Thanks for all the tips!

What about some Sodium Hydroxide & water? I have some of that around...

It's very hard and wont cut with a knife and looks silver in color when I scrape off the oxide layer.

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OK. I'm exited. The only weak acid I had lying around was from my acid blend for wine making. Citric, malic and tartaric acid. I put some in a test tube and I can see some gold spots!

I can't wait for it to get all clean and see what I have. May have to get some stronger stuff. Thanks for the tips.

I hope it's not brass... that would suck... Seems a little too heavy for brass though.

Edited by HagenT
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I think many of us here have seen gold with black coating... in person or in pics.

I do hope that's a gold nug in blackface :)

As for that ~15 K Ohm reading... that value won't equate to the 18 KHz in the statement :)

I have an odd question in talking about different frequency ranges... shouldn't a young person with good hearing be able to hear an 18 KHz oscillation? That is within the far upper range for humans. I would imagine it would drive a dog nuts?

I only had the GMT when I had a VLF, so I wouldn't be able to say from experience. That, and I've never stuck a GB coil to my head :)

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Well you might hear something if ya got some gold fillings!

Your right, a young one should hear 18KHz. I remember those old fashion green monitors would drive me nuts with their squeal.

If the coils are potted and is not acting up as a speaker then it may not be putting out much of a sound.

I think I need to go by some muric acid... I've tried vinegar, then ammonium chloride but it's taking forever to eat away the oxide.

Maybe I should try some Coke a Cola :)

Hagen

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Hagen ... Go to your local hardware store and ask for some Whink in the original formula. A dip in that stuff for a few minutes will probably take care of it. Wear gloves and don't breath directly over the GLASS container you use to clean it.

Mike F

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