Whites TDI Mod Help

[Dirty Nickels]

Thank you Reg! Email sent. Very cool!

[Reg]

Steve  pointed out how to attach a file and I wasn't smart enough to look at the bottom of the screen and use the attach files option.  Well, got it figured out so here is the pic of the GS 5 board and the control to adjust to reduce the delay.  The TDI board is basically the same so figuring out which pot to adjust should be easy. 

Reg

[Rick Watkins]

Glad to have someone with this TDI knowledge explaining this mod. I have wondered if this timing is closer to the 2300 now after this tweek. I seen first hand a 2300 pull out a very very nice pourus nugget that my TDI at every setting would not see at all. I wonder if this timing could hold the charge long enough to recognize this sponge gold. Got any comments Reg? Thanks Rick.

[Steve Herschbach]

Well Rick, the shorter the pulse delay, the hotter the PI, but it can also introduce ground issues so it is not quite so easy as just cranking it up. Some coils may not work properly. Reg can elaborate if he wishes but that is the gist of it.

Reg, what we are talking about is a spongy little specimen I found with my SDC and called Rick over to see it dug. It was several inches, loud signal. We could not get a peep out of his TDI no matter what settings, with specimen on coil. Even I was surprised, thought the coil was bad. We tried the 5" x 10" Sierra coil. Still nothing. The gold is also low purity, so just a perfect "invisible specimen."

[Rick Watkins]

I guess if im going to keep this tdi it wouldnt hurt to try this tweek and mark it so i can turn it back if it doesnt respond well. I do have the very small coil i could try for this.

[Reg]

Rick,

You don't need to worry about going back.  Simply advance the delay a little to do the same thing. 

As for coils, I strongly recommend Miner John's coils.  The reason is, they are patterned after Eric Foster's coils designed to work the best on the TDI.  The MJ coils draw less current and thus will work at shorter delays than a coil made to work on a Minelab.  Some GS 5's had a constant current to limit the ramp time on a coil.  That was not added to the TDI because White's coils are much closer in design to the Eric Foster design, at least coil current wise. 

I don't recommend dual field coils to be used with shorter delays.  This type of design doesn't ground balance that well to begin with.Shorten the delay time and it only gets worse.  Instead, use MJ folded mono coils to enhance small gold signals. 

The folded mono was something I designed to do the same thing as the dual field and that is, enhance small gold signals.  My design is in public domain and can be built by anyone. 

Now, if small gold is the primary objective, then I also recommend shortening the pulse on time to maybe 50 usec.  This will help with ability to sample properly at 8 usec

Reg

[Rick Watkins]

Reg, thanks for the reply i may try this one day. Makes sense to me on being able to still run the timings back up if too noisy. I will have my 2300 also to test against,just would like to know TDI could possibly see some of the sponge gold 2300 can with ease. Thanks again Rick

[Reg]

Steve and Rick,

PI's are different animals that are very dependent upon the target decay curve as to whether the object is heard or not.

If the minimum delay is 10usec and the decay of a target is done by 9.5usec, then you won't hear a peep. 

What you experienced with the TDI is what ML owners experienced several years ago when I was using a low powered PI with a shorter delay.  My detector would give a nice strong signal on a couple of "invisible nuggets" and the ML owners couldn't get a peep on any PI model out at that time. 

Now, the TDI wasn't specifically made to find small gold like the 2300 is, and the fact the design is quite old now.  So, one shouldn't be surprised at the results.  Dankowski has complained about the lack of being able to find small gold for years. 

Now, if the old TDI is adjusted back to 8 usec or even close to that setting, then I would suspect you will get some signal from the small sponge gold.  Also, after looking at the video made by a guy in OZ, a modified TDI Pro comes awfully close to the sensitivity of a 2300, so I would think it would come close to the 2300 on the sponge gold.  Remember, the test in the video was done with a later model TDI Pro with a few mods, which included a quieter preamp, a special noise reduction board and an additional addition that further enhanced small gold signals.  The later TDI and the Pro only differ by a couple of changes and additions.  The mod package only costs about $140 max which makes this mod quite reasonable when you think it reduced the warble to almost nothing when in the LOW mode and dramatically less warble in the ALL mode, plus gets a better response on small gold. 

So, there is or can be more life in the old TDI.

Reg

[Hard Prospector]

Great thread