TDI, TDI Pro, TDI SL

[Reg]

Hi guys,

Since it appeared part of the Infinium post was being taken over by questions about the TDI, I felt it best to move some info about the three different TDI models to this thread. Hope you don't mind.

First of all, there is basically no difference in the design of the sensitivity of the three detectors mentioned. The TDI and the TDI pro differ basically in a few basic features which are; The pro has a vernier ground balance added, it also has a volume control, and last, there is a slight filter change that makes small gold a little more obvious in signal. Keep the sweep speed slow on the regular TDI and small gold sensitivity is basically the same as the Pro. Unfortunately, most people sweep too fast.

The SL design is basically the same as the the other two but has one more added feature that minimizes noise. This feature wasn't available when the TDI came out but was thought of later. That is why it isn't on the TDI or the Pro.

If you look in the latest White's catalog, you will notice the regular TDI is no longer listed. Instead, the SL sales have been sufficient that the TDI will be or now is no longer made.

The SL loses a little depth when compared head to head with the TDI or the Pro, but as many have mentioned is much quieter and more stable and this is much more comfortable to the ears. This depth loss is the result of a lower voltage used. The TDI and the Pro use 14.8v Li Ion batteries while the SL uses 12V Alkaline or about 9.6V Ni Mh types. A third party 12V Li Ion pack is available which boosts the voltage a little over the factory rechargeable battery systems and provides a longer run time.

In theory, the SL could run on the same voltage is the TDI, but a different battery pack would be needed. I suspect the third party pack could be modified and hold 4 batteries, but the cost would be significant and most likely will not happen.

Along similar lines, a lighter battery pack could be used on the regular TDI and Pro, by cutting the battery presently in half and only using 4 batteries (equipped with the protection device). Obviously, the run time would be considerably less, thus requiring a more frequent change of batteries, but it would be lighter. I have done this so I know it works.

Reg

 

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[Hard Prospector]

Thanks again for these pearls of knowledge Reg, you should be on the Whites payroll.

 

[nuggetshooter323]

Thanks Reg, I'm trying to decide which one I want. The weight difference between the two is not a problem for me, I'm just trying to decide if the lighter design of the SL, smoother threshold, and being $500 cheaper is worth the potential loss of depth and the other features you mentioned for the Pro.

 

[Reg]

When it comes to depth loss between the TDI and the SL, this isn't much of a big deal when it comes to nugget hunting because most nuggets found are small and there is very little depth loss on the small ones.

Now, as I said, you can use a lighter battery on the TDI which sort of cuts down on the weight, so this helps for those still interested in the TDI but don't like the weight.

As for the difference in the threshold instability, I have been trying some mods to my SL to simplify the design. What I need to do now is to implement some of these changes into a regular TDI and make it switchable, so a person can have the TDI the way it is or change it to a reduce noise design similar to the SL. This will take some time to find the easiest way to do, but I feel it is possible. Fortunately, my work on modifying the SL partly relies on several changes which include the noise reduction circuitry.

Now, as for me ever working for White's, well, it isn't ever going to happen as a hired employee. I am retired and prefer it that way, and as such, I prefer to work on my ideas at my own pace and my own style now.

I am playing with a couple of ideas in coil design and that is fun. They allow for better noise reduction of the original design which also helps.

So, even though I don't work for White's, I do my own design work on their detectors and I have been doing this even before Whites purchased the rights to the PI used as the initial TDI design. The reason I prefer working on White's is because I am familiar with the design of the detector and that makes things a lot easier. Besides, the design is a good solid design that works.

Reg

 

[goldchaser3]

Hi Reg,
Thanks for the info. How hard is it to create your own coil shape? I ask because I have one of the original RB 10x14 mono coils and it is a different shape from the newer ones. The sides on mine have some flat sections and the top isn't as pointed as the newer ones, and i really like its depth shape/performance. I was thinking that the "oval" shaped coils may work better/deeper if the coil shape was closer to a rectangle in shape. i have heard that the Jimmy Sierra "T Foot" coil (5.5x18) gets great depth, and it is basically a rectangle with rounded corners. Just a thought...

 

[Reg]

Eric Foster did some calculations on rectangular coils and found that a coil with a ratio of 3:1 to 4:1 gave the best depth when compared to a coil having the narrow side size as a diameter or square. So, one could build a coil with the ideal ratio's and see some improvement, but not as much as one would hope for.

I suspect there are other factors as to why one coil you have does better than another having similar coil but not the same coil dimensions. Factors such as wire size, number of turns, and shielding are the primary items that one has to take into account. Inductance and resistance values will help determine the wire size. Sometimes looking at the decay curve can help in determining shielding, but not absolutely.

I suspect Jason used my recommendations on his early coils but have no idea what he used on his later ones. Also, when Jason started out, he used coil forms built by Bill Hays. Later he made his own coil housings.

So, in answer to your question as to how hard it is to make your own housings, well, it is something anyone can do if they have the time, skill and patience. Building the housing forms will take the most skill, but then building a good vacuum former takes some doing also. Personally, I don't recommend it for the casual coil builder. Instead, a person would probably be better off using one of the housings already made by Bill Hays or any other person building coil housings. You can find information as to size and price of Bill's housings over on the Geotech1 forum under the buy and sell listings. I use his housings because they are reasonable and available.

BTW, the housing used on the Jimmy 5" by 18" housing is one of Bill Hays housings. Dan Geyer used to make the coils for Jimmy Sierra while he was an engineer at White's. The housing used is one I asked Bill to build quite some time back.

Reg

 

[goldchaser3]

OK, as if I have any spare time as is it, I'm going to jump in and make my own coil.
Now the studying begins.....

 

[63bkpkr]

Well goldchaser3,
Just Coil up with a good book and have at it! May your rewards be sensitive and deep. Oh, try not to forget to come up for fresh air every now and then. Also, I hope you efforts are rewarded with success as with you and Reg on the line I would consider purchasing some model of TDI with mods forthcoming.........................63bkpkr

 

[Reg]

Hi GC3,

Building a coil that works on the TDI isn't difficult. Don't make any soldering errors and any coil with an inductance of about 250 uh and greater will work. Coils with less inductance may work but oscillate so an adjustment in the delay will or may be necessary.

The right recommended inductance is 300 uh. (I am happy if the inductance is between 280 and 320 uh). Sometimes getting the 300 uh exact is impossible due to the housing size. Any wire between 18 awg and 26 awg will work. Teflon coated stranded wire is the best for coils that will work at the 10 usec. I don't recommend using magnet wire. It will work but most likely any coil of any size will not work correctly at the 10 usec setting.

Shielding is the big problem. Many use Scotch 24 shielding tape, but I often use a special silver plated polyester tape. The down side of the tape I use is I have to tape a ground wire to the conductive tape since soldering is out. I have never had any problem with my coils, so I guess it works fine.

Don't try to use solid copper foil or other solid foil for shielding. Some people and many manufacturers use a special conductive paint. This can be tricky because both too much and too little can have a very negative impact on the coil's performance.

If the coil is to be used for nugget hunting, keep the coil size smaller than the 12" for the best results. White's dual field coil gives good results on both small and large gold because of its design. This design is patented so one can't duplicate it and try to sell it.

If the coil is to be used at the 10 usec, then keep the size less than 12". It is about impossible to build a 12" or larger that will work at an honest 10 usec.

My fold back design works well on smaller coils and gives good depth as well as good response to small gold. Details can be found on the Geotech1 forum as to the basic design.

Coil housings can be purchased from Bill Hays so that shouldn't be a problem. He still has a decent collection of sizes available.

The easiest coil to build is the simple mono coil. The DD isn't difficult and does offer less ground noise and in some cases, less overall noise. A DD coil works very well on small gold also and is easier to get to work at the magical 10 usec range. In some cases, it works better than a mono coil in the fact that if you know how to set up the detector and the ground is mild, you can determine ferrous objects that are shallow. Also, the DD is less ground sensitive.

One can build a concentric coil if they so desire and details can be found over on the Geotech1 main site under projects. Dave Emery did a good job of describing what is required.

In the same area, there is a detailed article on building a fast coil also. So, lots of coil info over there including a coil winding jig. Here is the link. Just drop down to the misc heading for the coil winder and coil building info.

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My coil winding setup is crude and simple but works on the same principle as the project one. I use a different counter that is electronic in nature and is triggered by a magnet. I bought the counter off ebay for $10 or so.

So, getting started in coil building is not that difficult or expensive for that matter. If a person can count then getting the turns number right is easy. Just use one of the many inductance calculators found on the net, but you should verify the results with an inductance meter if possible. In most cases, even a $30 LCR meter will be accurate enough. I use a $300+ model much of the time, but I will also use my $30 model and feel comfortable on the accuracy.

I add the necessary number of turns on my coil jig, then lace the wiring with synthetic sinew to keep the windings snug. I then coat the windings and the sinew with a silicone sealant that is low odor and electronic friendly. I let that dry before removing the windings from the jig. After the removal I add a layer of spiral wrap to further keep the windings snug and then I add the shielding. The spiral wrap also adds a small space between the shielding and the windings.

Building a coil can be time consuming but can be fun.

Reg