Tweet
Originally posted by dingbatca
View Post
-
If you have a local dealer call them and see if they have any surplus coils. You can sometimes get them on eBay for $10-20. -
Thanks for the info Carl-NC. A 9" Minelab X-Terra 7.5kHz coil just popped up on eBay, for cheap. It's got a broken mount, but my 3D printer can easily fix that.
https://www.ebay.com/itm/124153685268
Thoughts?Comment
-
Originally posted by dingbatca View Post
I think they have a chip inside not sure what effect that will haveComment
-
Correct, X-Terra's have a pre-amp circuit and a copy-protection security IC built into them. The security IC is not important, as you're not using it, but the pre-amp is going to make producing your own copy troublesome.
And (from memory ) the TX tuning capacitor is in the coil too, restricting what changes you can do. IE: you could maybe drop the freq a bit by adding capacitance, but in general, it's not ideal.Comment
-
dingbatca,
don't buy, it's not what you need for.Comment
-
It's also clearly a concentric coil. It's far easier to reverse-engineer and copy a DD-coil.Comment
-
-
Again, thanks for all the good info/warnings.
I am not so much interested in directly copying their design, as reverse-engineer and improving upon it. I need a "known good" coil to see if I can make something better. Still stalking eBay, nothing yet. No local shops around me to ask for surplus. :-(Comment
-
Next DD coil, Minelab 10 1/2" FBS 1050 Explorer 2 Coil.
https://www.ebay.com/itm/352930655126
Again, trying to use this as a "known good" coil, and also something to rip apart and understand what they did.
Thoughts?Comment
-
Unsuitable.
Has pre-amp internally, and has a low-inductance TX coil designed to be force-driven with a square-wave signal, not used as a resonant tuned circuit with sinusoidal drive.Comment
-
Where are you getting this info?! Thanks so much for all the input.
Lets try this one:
Nokta Makro Impact Metal Detector7.5 X 4" IM19 Black Waterproof DD Coil
https://www.ebay.com/itm/313060810240
Alternatively, there is always Aliexpress... But stuff out of China always scares me, and it's a bit out my price range for a brand new sacrificial guinea pig.
ACE250 Metal Detector MD6250 Search Coil 8.3x11''
https://www.aliexpress.com/item/4000220449863.htmlComment
-
The Nokta Impact is so new that no-one knows anything about it yet. The machine is selectable frequency, most likely by switching in additional parallel capacitors, located in the control box .... so the coil itself may be just a plain TX coil, or may have some capacitance in parallel with it, tuning it to the highest frequency. You could then lower this freq with added caps, and probably adding a parallel resistor too, to maintain the Q-factor. But in principle, it should suit your desired freq range.
Don't use an ACE coil, they are tuned to 6.6kHz, probably lower than you really want. Nothing wrong with 6.6k, it will find plenty of stuff, but won't be that good on the lower-conductivity targets.Comment
-
I would look for a tesoro widescan. As far as I know there's no capacitors inside, just the two windings.Comment
-
Wow, $30 for a busted coil? Plus shipping? I'd pass.
I know the Sovereign coils had preamps, I thought the Explorer coils did not. The TX coil is 500uH which is perfectly fine for a resonant system, White's uses 540uH in most of their SF coils.Comment
-
Still in a holding pattern. If any one happens across a good coil for my use case, please send me a link. Or if you happen to have a spare coil that you don't mind sacrificing for the pursuit of knowledge, send me a PM.
I still want to both build my own coil, and understand how said coil works. But I need a reference coil as a comparison.Comment
Comment