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Considering a TDI
Posted by: Reg
Date: September 14, 2010 01:04PM
He guys and gals,

My response in a different thread is how I feel about the TDI. People should keep that in mind that what I have written is basically my opinion of the TDI and how it works for me. The way I wrote it is meant to try to assist all those who may be thinking about buying a TDI and not to try to convince people it is the only detector available that will work for them. I think I have mentioned the limitations of the TDI and why some people don't or won't like the detector and why others do. It all depends upon what a person is familiar with to begin with. In other words, I have tried to express the good the bad and the ugly.

As I said, it works for me but it took time to fully appreciate the capabilities. I can use it quite well to find silver, but it may take others a fairly long time to be able to do the same. Others may not like the extra noise that is inherent to PI's or the fact there is no Target ID feature. Still others may consider the audio feature to be quite primitive or the disc feature to be tool limited.

Had I not had a specific application besides coin hunting, I probably would have passed on getting one. Now, I have fun just trying to see what I can do to enhance the detector, or see if I can come up with a better coil design, let alone look for other hidden features.

Larry seems to think I am strongly defending the TDI and considers the subject closed. Well, this is a TDI forum so I never consider any discussion about it closed. That is why I moved it to a new thread for those who may have a question they feel I can answer. I assure you I will try to give as honest and thorough of an answer as I can.

No, I don't have all the answers. Heck, I don't even know all the questions yet but I have taken the TDI apart technically, have built coils for it, have tutored others on how to build coils, have offered suggestions to a few on how to enhance their detector and have participated in trying to find solutions to some of the limitations of the TDI. So, I do consider myself reasonably qualified to at least try to help.

Sorry if I have stepped on people's toes. That is or was not my intent.

Finally, I certainly don't want anyone to run out and buy one just because of what I say or what I can find with one. I feel a person should be sure they would be willing to take the time to learn this detector because it will take time. If a person isn't willing to do that, the TDI probably isn't the detector for them. After all, it certainly isn't a turn on and go type machine like so many others that are much friendlier to the coin hunters.

Quite some time back I wrote an article on understanding the PI. Here is a link to that article.

At the time I wrote the article, PI type detectors were rapidly becoming the preferred choice for nugget hunting. Personally, I feel a person should have a very good knowledge of how a PI type detector works to best know how to use the TDI or to even try to understand why certain things are not as easy to do on a PI as on a VLF. The article was written well before the TDI was even an idea but it does discuss some decent basic PI concepts for those interested in knowing more about this type of detector.


Re: Considering a TDI
Posted by: Jason in TN
Date: September 14, 2010 02:23PM
Reg the link does not work. I wish some one in ten know of how the Tdi works would make a good real world hunting video with relics coins and gold. Also tricks to I'd iron.
Took my pro relic hunting yesterday and dug some deep large iron and some bullets but had to dig every thing with it. I still can not tell small iron from good high conductor low tones.
It is deep but I still have to dig every thing to get the goodies may figure it out some time. I hunt in all my ground balances at around 8 1/2 and does not seem to have a lot of minerals when I have hunted it with a VLF detector. I may have to sell mine soon as work is slow but I do not want to feel I need to learn it better.


Re: Considering a TDI
Posted by: Reg
Date: September 14, 2010 03:38PM

Try this link.

Part 2 is at this link.


Edited 1 time(s). Last edit at 09/14/2010 03:40PM by Reg.

Re: Considering a TDI
Posted by: Mach1Pilot
Date: September 14, 2010 05:15PM
I'm a relic hunter that has been considering a TDI to compliment my Etrac. Now I'm not saying it will replace it or even get used more than the Etrac but there are a few sites at which I hunt that the soils are highly mineralized (think northern VA).... I'm thinking a PI will probably work better in those areas. So for me, the two machines would, in theory, compliment each other. Use the Etrac in the good soil (and highly trashed out homesteads), the TDI in the harsh soils... most of the time, anyway! :wacko:

Today I stopped by a White's dealer who let me walk outside and mess around a bit with the TDI. First thing I thought was this is lighter than the Minelab. :blink: It seemed to be well balanced. And when swinging it over my ring and some coins on the ground I could somewhat vaguely test its response and the two tone discrimination .... not sure what to think of it just yet but the first impression was fairly positive.

The lack of a VDI does not bother me, with the Etrac I go by sound 95% of the time anyway. I only use the visual display to confirm what I think it sounds like.

Your posts Reg are real informative - I've learned a lot from them. And I can see the points both you and Larry have to make in the other thread.

I guess the real decision will have to be made once I have saved enough cash to pick one up... :cool:

Re: Considering a TDI
Posted by: golddredgergold
Date: September 15, 2010 01:43PM
Bring on the tech and your settings Reg!!! As always I thank you for your insight and I know it is appreciated by many many guys/gals.
People are not being forced to buy a TDI they do that on there own. That is what a Whites dealer is for is to let you try one and give you a hands on run down on the machine to see if the TDI is for YOU or NOT. Guys use that service at the dealer and try to make a purchase based on your feel for the detector. TDI is a tool and not all tools work for all users. My son got handed his first detector when he was 9. He is now 14 and can run a detector better than just about anyone else I know. He can be handed an old Goldmaster 2 and he ground balances it perfect with slight positive and detects like a machine. He picked the TDI up and Ground Balance it with only a slight instruction from me and he uses it like a pro. My point is he has been taught the basics of GB since the first day. He took to the TDI due to this and he loves that detector. Reg shares a bunch of GB settings that use the GB more like a discriminator to set the TDI for a specific group of targets blocking out others. Take that info and try it. We have and it has really been useful but one must understand what is happening to get the most from the settings. George Tex shot me some great settings for DIV grounds and relics. It was very interesting to set up as when we hunt for gold here in Ca. the setting where litterally the opposite of what we do here for gold. Heck I learned a whole new angle to my TDI after that because guys like Reg and George are sharing the info. Is a TDI for everyone? Maybe maybe not that is up to you to decide. Take the info in...try it....use it....if it works great if not understand why and these guys will help you set it to YOUR conditions or targets of choice.

Happy TDI hunting!
Gold dredger

I am one...
Posted by: jbow
Date: October 29, 2010 07:38PM
I'm considering a TDI. I have been for a while. I am not sure whether the PRO will benefit me or not nut for the small differencein price if it's better i'll get the PRO.

I'm going to sell a few, get a GB PRO and a TDI. I am not a prospector, though I may take it up since there is gold in the SW quad of out county and I am a 30 minute drive from Dahlonaga, GA. Family legend has it that one of my ancestors found the first gold there when he stubbed his toe on a big nugget. I've heard that all my life. My grandmother was at Amalacola Falls, she was a Burt and it was Burt land before it was a park. Lots of Burts still around there.

It would be nice to find a big ol piece 'o gold... I tried the end of the rainbow... saw it in a field... leprechaun moved it before I got there... maybe do better with a TDI but I mostly hunt for civil war relics. There is a yard I have permission to hunt that is like some sort of veil... nothing there in the yard of a 150+ yr old Victorian... I even buried three coins at about 6" and they completely disappeared to every detector I had... the ground s absolutely black with cinder. It is across from the site of a really old RR depot site and I think the station master lived there way back... maybe the TDI will handle it, nothing else has so far and if it is virgin... it could be a relic gold mine due to its location.


Julien in Cartersville, Georgia...


I have CDO. It is like OCD but the letters are in order like they should be...

Re: I am one...
Posted by: bearkat4160
Date: November 09, 2010 12:16AM
You'd be better off with an Infinium in Georgia.

Minelab GPX 5000, Garrett ATX, Whites GMT, Fisher Gold Bug II, Garrett GTI 2500, Infinium LS, Ace 250, Scorpion Gold Stinger, Garrett AT Gold.

Re: I am one...
Posted by: togg77
Date: November 15, 2010 06:43PM
Hi Bearkat--I am looking to get either an Infinium or TDI Pro and would like the pro&cons of both doing relics and gold nuggets--any info you wish to share will be appreciated.

Re: Considering a TDI
Posted by: calibil
Date: November 23, 2010 08:11PM
How about a mine field test with the TDI and brands xyz
Let's try an old Cambodia minefield , it would be a suitable location for a do or die real world test

Re: Tdi mod?
Posted by: tvanwho
Date: April 08, 2011 09:28PM

How hard would it be to add a dual GB control to a stock TDi for fine and coarse GB adjustments? I see they have these on the Fisher Goldbug 2. Is a new pot required or is it a dual knob thing that attaches directly to the existing pot shaft? I dunno much about electronics actually...can't even work a Voltmeter yet..just was curious?


Re: Tdi mod?
Posted by: Reg
Date: April 08, 2011 10:38PM
The difficulty would depend upon a person's skills. The easiest way to add a second ground balance pot would be to install another pot, maybe a 10K in value. We will call this a vernier GB pot. Then one would simply add this pot in series with the one already installed. The setup would give you two pots, with the new pot having the full adjustment that would have an effect of about one number on the coarse pot.

By just adding this pot in series, if the vernier is set to min resistance, there would be no change at all and it would be like the vernier pot wasn't there. So a setting of 9 would still need a setting of 9. Set the vernier pot to max and the setting of the coarse pot would be about 8 for the same results as one pot by itself.

I would recommend installing the vernier GB pot as close as possible to the present pot so wiring won't be much of a problem.

Obviously, the detector would have to be taken fully apart so the case could be drilled without fear of drilling into the pc board. The location of the second pot would have to be carefully selected to assure there would be no mechanical or electrical interference once everything was installed. As for wiring, one would simply have to move one of the two wires on the present GB pot over to the new vernier pot and add a jumper from the coarse to the vernier to complete the circuit.

The actual project shouldn't be that difficult if care and patience is applied. However, when in doubt, such a project should be left to those people like Mr. Bill who is already familiar with making such mods.

Again, this final design as mentioned would change nothing with the vernier at minimum and add a little more GB when the setting was at max on the vernier. The additional GB would add a little more noise when set to maximum but would do a little better job of balancing out some basalt that might be difficult now.


Re: Tdi mod?
Posted by: tvanwho
Date: April 08, 2011 11:08PM
So Mr Bill could do this for me? How do I contact him about it? I'd rather pay an expert some money than to mess it up myself. What were your thoughts on the single dual knob GB control from the Fisher Goldbug 2 in comparison to 2 separate GB knobs as you just described?? Can the Fisher dual knob GB control be used to replace the Whites Tdi GB pot without any issues?


Re: Tdi mod?
Posted by: Reg
Date: April 09, 2011 08:46AM

You should contact Mr. Bill personally and check with him. You can do this by going to the PI forum and clicking on the Surfscanner banner at the top to get his number.

As for whether you can use any dual setup such as that on the Fisher, I doubt it could be used. The pots would have to be the right resistor value and be able to fit in the allocated location. I highly suspect neither would be true.

There is very little room on both the original TDI and the newer surface mount TDI between the pc board and the top part of the metal case. The newer design has the least of the two if I remember correctly.

A person might be able to remove the original GB switch and add a pot that contains a switch in that hole. I can't tell you for sure if this could be done since I haven't looked inside either TDI version for a long time. This would make the mod easier if it could be done this way.

As for the actual value of the additional POT, that would depend upon how minor of an adjustment one might want. As I said, a person could use a 10K pot. This would make the entire pot adjustment equal to about the same GB adjustment as moving the original pot one division. I don't recommend going lower in resistance value. If a person used the next more common pot size, a 20 or 25K value, then the vernier would adjust about 1/4 to 1/5 of the range of the present GB pot. Again, the amount of these adjustment measurements are approximate.

If for some reason Mr. Bill no longer does mods, you might contact Colorado Gold Man since I believe he has done the mods on his detector. He might be willing to help.


Re: Considering a TDI
Posted by: Neil in West Jersey
Date: April 09, 2011 10:40PM
After reading a bit from the folks down at DIV, it got me thinking about a TDI or a TDI pro. I am a very happy V3i user with a few thousand hours of use with it. I have been detecting a site with great success for more than 4 years and now the finds are beginning to thin out. I am convinced that there is more at the site and it is beyond the range of my "V" even in all metal mode. This is especially true in the sections of the site with a thick blanket of pine needles.

I am wondering how well the TDI is on deeply buried small targets such as buttons.

What is your opinion on this application for the TDI?

Re: I am one...
Posted by: parrott
Date: April 26, 2011 12:21AM
Just wondering... has anyone used the TDI pro with the standard coil in Georgia?

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