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Offline Paul ATopic starter
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« on: November 12, 2010, 05:50:29 am »
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Hi,
If anyone has built the Mark Stuart P.I. (or Trevor Hills "goldpic" clone) here's a good mod!
I was going to swap out the IRF840 mosfet for a IRF740 to try and wring a little more depth out of it.
Someone gave me a couple of "HUF75337P3" "super mosfet" to try out so I used one of those to see what would happen....
Wow......... the increase in depth is amazing!
A good couple more inches over the 840!
Seems more sensitive to silver now too strangely...........


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Offline ram
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« Reply #1 on: November 12, 2010, 09:52:10 am »
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hello, paul a, powerful mosfet! how about incorporating mosfet driver, ex. sc1301 non inverting.maybe more powerful?

regards, ram,

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Offline japanese
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« Reply #2 on: November 12, 2010, 12:06:13 pm »
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Hi paul a
          IRF840- 8A ,500V , 0.850 ohm---- R1=56 ohm in the diagram.
      HUF75337P3-75A ,55V  , 0.014 ohm-----R1 must Less to 47 ohm or less than to       Running the g of the mosfet.
 best time
j.
         

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Offline GoldDigger1950
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« Reply #3 on: November 12, 2010, 11:24:36 pm »
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Paul, Japanese is right. Your gain is down to the resistance which changes the circuit timing. That also accounts for the sensitivity increase in the silver range. You'll find that also correlates to gold sensitivity. A MOSFET is a DC switch, not an amplifier. The pulse passes through the MOSFET but is not enhanced in gain by it. There is also a current limiting resistor in most circuits which limits the input current to keep the part cool. Be sure not to change that. They are normally 1/2 watt or larger rather than the smaller 1/4 watt.

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Offline Paul ATopic starter
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« Reply #4 on: November 13, 2010, 03:49:03 am »
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Thanks GD!
Really useful stuff!
Yep - it's a 2 watt job 330r from memory.
Really pleased with this little detector now!
It also seems to have cleared up an issue I had with it being a little "unstable".
 Great

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« Reply #5 on: November 28, 2010, 04:33:42 am »
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i have built a mark stuart pulse induction. I a recently built a clone PI (chance) pulse induction and i thing the clone pi is better, and can discriminate

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Offline jeyjey
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« Reply #6 on: June 01, 2011, 12:44:59 am »
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tanks Japanese very goods for mosfet
please most help me about replase irf840 with HUF75337P3 in schematic

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Offline electrosoft
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« Reply #7 on: June 01, 2011, 02:30:13 am »
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Quote:Posted by fmtemp
i have built a mark stuart pulse induction. I a recently built a clone PI (chance) pulse induction and i thing the clone pi is better, and can discriminate


hi were you find the mcp3201 chip in france / salut ou vous avez trouve le mcp 3201 en france j ai bien cherche sur internet mais en vin si vous pouver me donne un non de fornisseur dans la region parisienne merci

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« Reply #8 on: June 01, 2011, 09:50:24 am »
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Hi jeyjey
   as befor HUF75337P3-75A ,55V  , 0.014 ohm-----R1 must Less to 47 ohm or less than to       Running the g of the mosfet.
 rang r1  47 ohm---27 ohm-----12 ohm-----4.7 ohm  ,1/2w {i Suggested 10 - 12 ohm }

 as  Paul A say the increase in depth couple more inches , more sensitive to silver , too strangely...........
best time
j.


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« Reply #9 on: March 12, 2022, 11:30:06 am »
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New here but was looking for experiences with the Mark Stuart ver 2 using the Picmicro many of the components are becoming extinct so i though I would try and upgrade it, also intend using a higher power Mosfet and a Mosfet driver IC.
The original used a 16pin pic although only 2 outputs were used, so am going to reprogram a later 8pin Pic to base the original program on, probably won't be until early summer before I know the results. Wink


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