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Whites tdi depth while prospecting for gold

Waterdog

Active member
I just recently bought a whites TDI sl and wanted to take it out while prospecting. Any ideas of what size coil would work better than others, or should I just stick with the stock 12 or 7.5 coil ? Is this a good Pulse machine to use ? Thanks for reading my post
 
I like my SL version a lot! From al the tests I've read, one of the top rated coils is the Nugget Finder Sadie 8 x 6. I use one myself. I also really like the Dualfield 12". I have a Miner John 5 x 9, and it works OK, but the Sadie is better. The Whites 7.5DF is just OK. I haven't found it to be any better, on small gold, than the 12"DF, and you lose some depth on bigger stuff. The Sadie is a pretty good compromise. I've also tested, and proved to myself, that the 4 cell 16.8v Li-ion battery pack gives a decent improvement on both depth and sensitivity. If you have the TDI, or Pro, you already have that pack. The SL comes with 12v pack.
Jim
 
The Sadie is a good compromise. You can't talk about depth without specifying the size of the target.On a bigger target, the bigger coils excel. But, they may not see a tiny target 2" below the surface. It's all about compromising. Also, what I said about the 16v battery pack applies to the larger coils as far as improvement goes. In my testing, I saw little improvement for the smaller coils...like the DF7.5, the Sadie, and the MJ5x9. Big improvement with the 12".DF. Air tests don't mean alot, but my SL can see a 1 grain...that's grain, not gram, nugget at 3" in an air test, using the 12"DF. However, because of terrain issues, I prefer to use the Sadie.
Jim
 

Waterdog

Active member
Thank you for the information on the sadie coils. I never heard of a sadie coil till you said something about it. I was looking at the 6x8 sadie for now. I think that might be a good starting point. One of my friends out here in the Sacramento Ca. area told me to get the biggest coil I could , but I don't have that big of a pick.:detecting:
 

roadapple

New member
+1 on the Nugget Finder "Sadie" coil as deep quality coil for gold . Just research this coil and you will find that "Karelian65" from Aus did some great testing with all size coils for the TDI and found the Sadie coil as the best overall coil. Best of luck in the field !
 
If you install a 16.8v battery pack, there's very little difference. Pulse detectors are current-driven, so upping the voltage directly improves the performance. The TDI's came with 16.8v packs. The SL came with a 12v pack, but will run with a 16v pack. A guy that goes by "reidman" sells the 16v packs for the SL's. I don't see tham listed on EBay anymore, however.
Jim
 

roadapple

New member
Jim in Idaho said:
If you install a 16.8v battery pack, there's very little difference. Pulse detectors are current-driven, so upping the voltage directly improves the performance. The TDI's came with 16.8v packs. The SL came with a 12v pack, but will run with a 16v pack. A guy that goes by "reidman" sells the 16v packs for the SL's. I don't see tham listed on @#$%& anymore, however.
Jim
Just a word of caution : If your SL is still under warranty, by exceeding the manufactures voltage, will void it for any future repairs !
 

Waterdog

Active member
In all the years of metal detecting the small coils have always been my favorite. Able to get on a target without the affect of another target masking it. I know that the smaller coils don't go a foot deep, but my best find was only five inches deep masked by another target only a few inches away.
 

karelian

New member
Must be said, the White's Tdi Pro and SL both love the Sadie coil, if you had to just have one coil then it is top of my list. The only other coil that comes close is the Detech 8" mono. Both coils balance well, run smooth and quiet with very good improvements over the factory coils.
 
To give the SL model all the performance of the Pro, and maybe even better, you want three mods. First is the 16v battery pack. Those are no longer being sold, so you have to make your own, or find somebody to make you one. I just finished my second, so I have a backup. Second mod is to remove capacitors C20 and C21, which are .47ufd, and replace with .22ufd caps. What that does is increase the allowable sweep speed on tiny nuggets. As sold the SL requires a really slow sweep speed to see the smallest nuggets. Sweep too fast, and you won't detect them. Sweep really slowly, and there they are.That's part of why the SL has such smooth threshold. By changing those caps, you get slightly more variance in the threshold, but a much larger range of sweep speeds without losing the sensitivity to small gold. The third mod is to remove capacitor C56. Also removing diodes D20, and D21, and installing a jumper across two of the three terminals on D21's location on the board.. These last mods also increase the sensitivity. For the squeamish...just removing C56, and leaving the diodes in, will help. Do all these and your SL:will be every bit as good as the PRO, with less weight, and a smoother threshold. One guy I know just pulled 44 cents at a depth of 24" from a beach in Florida. He was using an * X 14 coil. The Whites factory, on the new Special Edition TDI has done the third mod. They removed D20, D21, and C56, and put the jumper on D21's location. I've heard, but don't know for a fact, that all SL's made after 2015 have had the third mod done.Only way to know is to take a look at the circuit board.
Here's a video showing the effect of the second mod...swapping the sweep speed caps:SS mod effects
Jim
 

karelian

New member
While I moved to the Tdi Pro from a SL, after a year I missed that smooth SL threshold and super light weight and beautiful balance. The new handle and pretty desert tan paint work saw a Special Edition SL back in my arsenal of machines. I now still have my Tdi Pro, but also enjoy the new SL, mostly as an urban/beach machine and as a loaner when out prospecting with family and friends. Using both machines I must say I enjoy both. Image shows the Special Edition with Miner John made 14 x 8 mono coil, aka Jimmy Sierra Digger coil. Used on the beach it is a easy to swing rig, light and nicely balanced. Yes is does appear to be less swing speed sensitive than the earlier SL models. That works well with larger coils for beach work. My love affair with the High, All and Low conductivity switch means the water proof version will not be considered. We are spoiled for choice.
All the best,
Karelian
 
karelian said:
While I moved to the Tdi Pro from a SL, after a year I missed that smooth SL threshold and super light weight and beautiful balance. The new handle and pretty desert tan paint work saw a Special Edition SL back in my arsenal of machines. I now still have my Tdi Pro, but also enjoy the new SL, mostly as an urban/beach machine and as a loaner when out prospecting with family and friends. Using both machines I must say I enjoy both. Image shows the Special Edition with Miner John made 14 x 8 mono coil, aka Jimmy Sierra Digger coil. Used on the beach it is a easy to swing rig, light and nicely balanced. Yes is does appear to be less swing speed sensitive than the earlier SL models. That works well with larger coils for beach work. My love affair with the High, All and Low conductivity switch means the water proof version will not be considered. We are spoiled for choice.
All the best,
Karelian
According to Howard at Whites, they changed the sweep speed caps on all SL's made after 2015. But, the Special Edition that a friend in Florida bought had the same .47ufd caps as the original TDI SL. So, no change in sweep speed. That wouldn't make much difference on the beach, however, but would impact gold prospectors. The second mod that Reg Sniff recommended...the removal of diodes D20 and D21, and a jumper across two of D21's three connections, and the removal of C56, was done on his Special Edition, however.
Jim
 

karelian

New member
Jim in Idaho, the use of higher voltage batteries is an area I am willing to explore. It may give the SL a bit more depth. Thanks to a local poster in Australia, XLOOX. I have blatantly copied his design for a higher powered battery holder using 4 x 18650 cells. Again full credit goes to him. When we explore the depth of the Tdi SL it is seems well established by users that 16 volts is both safe and highly sought after.
Just one image to show you where I'm at.. not finished yet, waiting for carbon fibre sheet etc. But everything fits and it works.. Dremel the guts out of a White's battery tray, use flat 18650 cells, the nipple ones don't fit. Keep the front connects and use a copper connection at the rear. Very tight fit with solid connections. A picture tells a thousand words.
All the best,
Karelian
 
Nice work. That's identical to the one I built a couple of months ago. I installed the battery management board right between the batteries. Works good. I now have two of these....the first was purchased from Reidman. You're going to be surprised at the results of the added voltage. I use a buck converter as a charger. That allows me to set the max voltage on the charge. I generally limit it to 16.0v, rather than the typical max of 16.8v. By doing that, the pack will last longer, and it protects the detector from a possible over-voltage situation. You should also do the two mods that Reg Sniff suggested. Really makes the SL come alive.
Oh yeah....you'll have to find a THIN material for the cover on your new pack. I used a section of plastic milk jug, but a piece of vinyl notebook cover works OK, too.
Jim
 

karelian

New member
Power upgrade is certainly very interesting, there is an increase in depth. I did a quick are test between the Orange pack with 3 x 18650 cells at 12.38 volts and the 4 x 18650 pack at 16.48 volts. Then compared them to the results with a Tdi Pro. TDI SL MAX gain, 10us, GB off. Tdi Pro had gain at 5. Gb Off, 10us.

12.38 volts give 6cm on a 1 grain ingot, 24cm on a half gram gold coin, 32 cm on a gold Half Sovereign, a US Quarter came in at 27cm.
16.48 volts give 8cm on a 1 grain ingot, 26cm on a half gram gold coin, 35cm on a gold Half Sovereign, a US Quarter came in at 30cm.
Tdi Pro gives 8cm on a 1 grain ingot, 27cm on a half gram gold coin, 36cm on a gold Half Sovereign, a US Quarter comae in at 33 cm.

So with 16.48 volts and at max gain, the SL is close to the Pro when is is on gain of 5.. in the air.. at least. I'll need to go out and play some more.

All the best,
Karelian
 
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