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In the middle of my attempt get my GP Extreme working I purchased a second coil off Craigslist. The original was a black model 110 that came with the GP. The Craigslist coil was white Minelab Goldscan DD for SD series. I fixed the detector and the original coil now works great. But the white Goldscan doesn't work well at all. A quarter is detected only within 2 or 3 inches from the coil vs over a foot with the black standard coil.
Measurements taken off the coils:
Using LC102 LCR meter (L):
Goldscan TX 291uH RX 483uH both in series 760uH
Black 1100 TX 290uH RX 403uH both in series 673uH
Using B&K 875B (resistance):
Goldscan TX .39 ohms RX 17.62 ohms in series 18.02 ohms
Black 1100 TX .42 ohms RX 17.34 ohms in series 17.78 ohms
Not much difference between TX/TX RX/RX if I run them off a Surf PI clone output and look with a scope. RX on 1100 is a bit faster.
So is this an intentional design difference and the Goldscan is not appropriate in some way for the GP? In a few days I'll try frequency resonance and capacitance tests...
Measurements taken off the coils:
Using LC102 LCR meter (L):
Goldscan TX 291uH RX 483uH both in series 760uH
Black 1100 TX 290uH RX 403uH both in series 673uH
Using B&K 875B (resistance):
Goldscan TX .39 ohms RX 17.62 ohms in series 18.02 ohms
Black 1100 TX .42 ohms RX 17.34 ohms in series 17.78 ohms
Not much difference between TX/TX RX/RX if I run them off a Surf PI clone output and look with a scope. RX on 1100 is a bit faster.
So is this an intentional design difference and the Goldscan is not appropriate in some way for the GP? In a few days I'll try frequency resonance and capacitance tests...
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