By Jim in Idaho
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.
I'm looking at penetration through schist / slate type bedrock and quartz vein medium mineralized on a 70 deg vert plane, so the end grain is detectable. Fair amount of fracturing from the use of explosives I believe leaving hairline to 1/32 cracking here and there and some larger along the rock wall with 60 or so years of CA. High Sierra weathering on it. . But I'm also looking at what the penetration depth would be for the same material in solid condition further in from the rock face. Anyone have any experience with these conditions? Target is a leafy up to .5 mm thick ribbons and crystalized pockets of gold in, umm, not sure what they're called but they look like flattened bubbles in the quartz coated with crystalized gold inside, the only visible "bubble" is .70" w x 1.7" or so deep, at least according to my fillet knife.
I know that most of you guys are not using TDIBH for underwater hunt. TDI is actually horrible for this task 'couse it floats.
Youare really suffer to hold it under water.... Horrible, you have to spent a lot of energy to sink down the detector. Somebody uses the coil weight, but in my opinion it is not so good solution as it provokes extra wear on the washers and makes the coil not so hydrodynamic....
My solution is to use lead shots in the 3d printed plastic case as a weight. It works great. The weight is just clipped on the shaft and that's it. No modifications whatsoever are needed. If you hunt on the dry send, just take a weight off.
Here are some pictures:
By Jim in Idaho
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.
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
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"
12DF with 1 grain gold bar
GB off 3 1/4"
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.
By Steve Herschbach
I have never experienced this on any version of the TDI. The “ground balance off” mode should be the pure unfiltered signal. Engaging the ground balance engages a filter which reduces the air test results in a properly functioning TDI. The only reason the TDI has the ability to turn off the ground balance is to get this extra depth back, as has been highlighted in numerous online posts and videos. The manual says air test depth increases with the ground balance shut off. What you are saying simply makes no sense from a pure electronics standpoint and how the ground balance functions. If a TDI loses depth in air tests when the ground balance is shut off then in my opinion it is not working properly.