Jim in Idaho

yes...they break our hearts in the end, but all we can do is give them the best life possible, and then say "goodbye". then go get another. I'm on my 14th now. God, I pray they'll be waiting for me when I pass. Jim

Yeah...I have to be careful where I take Heidi, too. Last fall i wanted to prospect a particular canyon and ran into signs warning of potentially lethal traps in the area. They were trapping wolves, and the rancher told me the traps were non-lethal, but even a leghold for a wolf would probably break Heidi's leg, so I went elsewhere. I also try to never take her into snake country when the snakes are active. She's had the rattlesnake shots every year, but I'd rather not risk it. Limits where i can go, but not a big deal. I can't imagine a piece of gold big enough I'd risk Heidi to have it. Jim

Yup...Heidi, the rabbit dog. Wouldn't know what to do without her.

Permit? I don't need no steenking permit....LOL Jim......in Blackfoot.

Mark G. reminded me I hadn't posted the video link, to the comparison video, on here. So, here it is: sweep speed comparison

Many thanks, Mark. You did a nice job on it, and will be rewarded with many years of use, not to mention the increased depth1 Jim

Well, it's hard to gauge people's skill, Jim. You need a decent soldering iron with a small wedge tip, for starters. You also need some solder wick to absorb as much of the old solder as you can. It's also nice to have a really tiny drill bit, which I didn't have....the smallest I had was the one in my "number drill" kit, and it seemed it was too big, but might have been OK. (#60 .040") I ended up using a hardened steel wire, from a welding brush, heated with the soldering iron, to remove the last bit of old solder from the holes. Installing the new caps is easy, once the holes are cleaned out. The rest is just disassembly, and reassembly. A magnifying glass is a help, to check your resolder job on the new caps. The new caps need to be matched to 1%, too. The overall capacitance isn't critical, but whatever it is, they should be close to the same. I didn't see any difference in depth, but now wonder how much gold I've missed from sweeping too fast. Jim

Bit the bullet and did the sweep speed mod this morning. Made a huge difference in the acceptable SS. I ran the 1 grain gold bar past the 8 x 6 Sadie coil before doing the mod, and there was a relatively slow, specific sweep speed that gave the best signal. Too fast, and the signal completely disappeared. After the mod, the SS made almost no difference. Fast, slow, the signal was steady. No change in indicated depth in the air test. Threshold was still smooth. I'll post a video of the before/after tests later on. I changed the filter caps (C20, 21) from .47ufd, to ,22ufd. A friend in Florida, who is a civilian tech working for the Navy, was kind enough to send me a few matched pairs of the caps. Without his encouragement, and help, I probably never would have tackled this. Now I'm really glad I did. One tool I'm glad I had was my fly-tying magnifying light. My eyes don't focus like they did when I was young, and that magnification allowed me to see the soldered spots, to be sure I had done a thorough job. Jim

I did a quick test, with a quarter, on the 12"DF and it was about 11 1/2", Mark. The battery pack was purchased 3 years ago from a guy that goes by "Reidman" on Ebay. Last time I checked, he was no longer offering them, however. Now that I have one, I could build another pretty easily. I use a charger that the output voltage can be set to any desired voltage, so I can limit the final charge voltage to 16v. Standard chargers can't be adjusted, and don't stop until reaching 16.8v. The SL handles that OK, but you get more charge-discharge cycles from a pack by limiting the charge to 80%, or in the case of a 4-cell pack, 16.0v. Doing that will almost double the life of the pack. I think my SL is especially "hot". Just got lucky. It detects that 1 grain gold bar farther than my GM24K, or GMT. I think the reason the 12"DF is more sensitive than even the Sadie coil is the increased voltage. I'd bet, if I dropped the voltage to 12v, the 12"DF would not match the Sadie 8 x 6. I doubt the Sadie would decrease....the small coils don't benefit much from the added voltage. The SL is a good machine with the added voltage. Whites should upgrade the standard battery, IMHO. Or maybe re-design some components, and go all the way up to 21v. I was not impressed with the SP 350. I'd like to find a good 7 x12 mono for mine. LOL....that didn't cost an arm and leg. Jim

I finally had time to do some testing on the SL, regarding the Ground balance. Here's the result: TDI SL GB TEST 350 Super Pulse coil. battery voltage at start of test = 16.0v Freq. max., Switch in "ALL", Gain MAX, Pulse delay MIN. 1979 US nickel Sweeping side-to-side. The test setup was having the detector vertical, with the coil on top of a 5 gallon bucket to minimize the ground effects. I taped a yardstick to the shaft. I did NOT use headphones, but did repeatedly sweep the nickel to try and get honest results. GB off 13" GB on: 2 14 1/2" 3 15 1/2" 4 15 1/2" 5 15 1/2" 6 14 1/2" 7 to 11 15 1/2" Freq. set to minimum GB off same GB on: 2 14 3/4" 3 14 1/2 4 14 1/2" 5 14 1/2" 6 thru 11 15" Switch to 12"DF coil GB off 17" GB on: 2-5 17" 6-11 16" 12DF with 1 grain gold bar GB off 3 1/4" GB on: 2-11 3 3/4" Both coils with 6 gram men's gold ring: Both coils detected this very close to the same as they did with the nickel. But, turning the GB on and off had very little effect on the depth. It's apparent to me that on some items, my detector is definitely better with the GB on, but set to 2, or minimum. But on larger gold, the GB has little effect. But what effect there is favors having the GB on, but set to minimum. There was only one instance where having the GB off was an improvement. I also tested my NF Sadie 8 x 6, and was surprised to see it was LESS sensitive to the 1 grain gold bar, than the 12"DF. The Sadie struggled to make 3". For me the best coil is the 12"DF, where it can be used. Where it's too cumbersome, I'll go to the Sadie. The Sadie was better than the 7 1/2"DF, and the MJ 5 x 9. I sorta wish I hadn't sold the 7 1/2"DF...I'd like to test it more. I also tested a 1" thick x 4" diameter hunk of aluminum, with a 1 1/4" hole through the center. Neither coil could detect it near as well as they did the nickel. Jim

Yup...that explains a lot, Mark...many thanks! If I can find the time, I'm going to have to rerun some tests to specifically target the GB settings, and see what's going on. JIm

That's an interesting question, but I have no idea if that's the case with the Whites TDI SL. Jim

It would be a help if the testers posted the year their SL's were built, along with the battery voltage at the time of the test. Jim

I picked up one good thing about this discussion, besides the overall stuff. That is, there's a benefit to running the frequency maxed out, as far as energy to the coil goes. I'll be doing that from now on, assuming it doesn't cause an excess noise problem. On mine, that's over an 8% gain in coil voltage. Nothing to sneer at. Jim

Sorry, John. I thought you'd said '14. So, it's possible the '13's are different somehow.

Sure looks that way, Mark. John (auminesweeper), and I both have machines built fairly early, and we get very similar results. His was built in '14, and mine in '13. So it looks like yours is different, for sure. What did you have a for a batterry voltage in that test? Jim

I'm measuring mine with a digital multimeter set on A/C volts. On the frequency, I'm seeing, with the 14.5v pack, 6.05v on the low, and 6.54 on the high. MIddle was 6.29. I'd be surprised if your coils have much difference in inductance, but it's possible. EDIT: I just did the inductance test on the 12"DF and got the exact same reading of 1.4 microhenrys. I assume that is the design inductance for the coils for TDI's. and probably the other brands of PI's. But, I don't know this to be fact. Jim

I just tested the voltage output on mine, and it tracks perfectly with the battery pack voltage. With the 4 cell pack at 14.53v, I got 6.29v of output to the coil, and with the 3cell pack at 12.03v, I got 5.3v of output. So the higher battery voltage does push more current through the coil on mine. Thus a stronger magnetic pulse going into the ground. I figured out the correct terminals by using my inductance meter to see which terminals showed a coil across them. Looking at the connector, with the gap at the bottom, the correct terminals are the second from the left, and the second from the right. Inductance on both the NF Sadie 8 x 6, and the Super Pulse 350 14 x 9 showed 1.4 micro-henrys. Jim

With the 12"DF, and 16.8 v battery, mine will easily see a 1 grain gold bar at 3" in an air test, John. Might do even better with my NF 8x6 Sadie, but I haven't tested that coil. Jim

I think, to use a voltmeter, you'd have to put a capacitor across the connections to get a true reading. I'm not sure about the capacitance needed...maybe 5mfd? Jim

I've never checked mine, but find that interesting. Mine was built in '13. Do you have a diagram for the coil connector? I'd like to check mine. Something's fishy, for sure, as the voltage clearly makes a big difference. It's possible, because the voltage pulses at 100kh, that you can't read the voltage difference, except with a synchroscope, or other similar device. Jim

Yeah...mine is a little more sensitive. But, it depends on the battery pack voltage. With the NiMH pack in mine, at 10.7volts, I was getting about 13.75" on the nickel, but with the fully charged Li-ion at 12.6 volts, I was getting 14.5, and with the 16.8v li-ion, I was getting 16.5". All these with the 12"DF. With that coil, the battery voltage is the difference, Mark. And, I gained about 1/2" by turning the GB on, but set at zero. By maxing the GB, I gained an additional 1/2". Jim

John, I couldn't agree more. I'd be happy with a TDI SL that ran from a 21v 5-cell Li-ion battery pack. Maybe with Reg Sniff's filter capacitor modification to ice the cake! Combine that with a Nugget Finder 12" round, spiral wound coil and you'd have a lightweight, really capable PI. Jim

The "deeper with GB on" is true with the SL, but apparently not the others. Auminesweeper is right, and my tests also bore it out. Regardless of the GB setting, as long as it's "on" the air tests show a definite improvement. Reg S. and I discussed this at length, and didn't come to any conclusions as to why, though Reg mentioned the GB circuit on the SL is different than the other TDI's. Jim

The PI detectors use a voltage regulator on the Receiver, but the transmit circuitry is current driven, so a higher battery voltage means a stronger pulse into the ground. My personal theory on why this mostly pertains to the larger coils is that the smaller coils are "maxed out", or saturated, at the regular 12v nominal, so don't benefit much from the higher voltage. Jim