TDI Pulsescan modifications AND BIG coils

[AVXVA]

Hello all,

I just registered on the forum for a single reason: I am seeking advice from the best medal detectorists on the planet--the Australians. (I'm in the States and I detect in Wyoming, Colorado, Kansas and New Mexico for about everything.)

Several months ago, my wife bought me the last Whites TDI Pulsescan available from any dealer in the entire United States as a gift. Since then I've been working with it and trying to learn it's secrets. (My primary machine is an ETrac.)

I've called several (former) Whites dealers who have experience with the TDI, and bottom line, the answer to the hard questions was the same, "contact the TDI experts in Australia, they know A LOT more than we do about them--and detecting in general."

So here I am.

The TDI Pulsescan has a GEB circuit (and conductivity discrimination) which is handy, but when it is turned on it robs the machine of considerable depth.

When the GEB circuit is turned off the machine becomes a pure PI detector and I'm interested in connecting a BIG coil to the TDI and seeing how deep it will go. (Running hot and set to the correct GB channel, I can get 6-feet of depth on big iron with the Etrac.) What after-market coils are available for the TDI?

I am also interested in performance modifications, of which not much is known in the States.

Thank you for your help!

Rob

 

[Ridge Runner]

I located the Cast Iron Train Subway Tunnel with mine holding the Coil about 5 or 6 feet in the Air using the same coil yours came fitted with.

Thing is Depth on large Items is easy but depth on tiny things is the hard part, Also PI Machines don't work well on freshly buried targets either so if you bury some targets in the ground be sure to soak the soil/ground afterwards so the small bits of soil with fill all the Air Gaps, This also makes the ground more conductive so you want to soak the ground one day and leave it for a day or two before you try doing any coil depth test's

Hope that helps. :Y:

 

[Jaros]

Welcome Rob to P.A.

 

[XLOOX]

Howdy Rob,
a search of this subforum and Steve Hersbachs Detector-Prospector will find that question answered a number of times but summary is any coil described as suitable for Minelab GP or GPX series detectors will work on any Whites TDI series detectors even coils upto 20" but coils over 12" will probably require you to increase Delay from 10us to +12us.

If you only after targets bigger than an inch dia then no loss in depth by doing this adjustment. Just keep turning it up until detector behaves.

nuggetfinder,coiltek,detech,x-coils,jimmy sierra and of course whites and minelab all make suitable coils

 

[user 4485]

I'm surprised former Whites dealers said that all the TDI experts are here in Australia? They were far more popular in the USA than here & there was really only a small, but dedicated, following here in Australia.
Detector Prospector forum might be a better place for your questions? https://www.detectorprospector.com/forums/forum/45-whites-metal-detectors/
Also re: modifications search up Reg Sniff (unfortunately Reg has passed away) as he did a fair few posts on mods etc. on various forums. Reg did assist an Australian (Luke Lindsay) with some mods. I believe some of them became standard in later TDI's i.e. used by Whites. Last I remember he was working on better sensitivity mods & had some success but it's been a long while since I've seen anything on them.
Karelian tested a lot of coils on the TDI here: https://www.prospectingaustralia.com/forum/viewtopic.php?id=21209
There were specific TDI coils made by places like Miner John & Coiltek but I'd assume they may have stopped when the TDI ceased? Any mono coils made for Minelab SD/GP/GPX series will work but some may need trialling or investigating what other TDI users have found to be ok.

 

[AVXVA]

Most of the American desert (Arizona, New Mexico, California) gold hunters are actively mining YouTube for Australian metal detecting content--it's the best way to learn the best techniques. And the big dream for everyone is to go to western Australia and find it. (I have to admit, I'm one of them.) Going the other way, there are enormous opportunities for finding gold in the desert West of the US. The vast majority of land +/- 95% is public land and very few people are seriously detecting out there. And Mexico (if you are willing to risk death) is almost completely 99.999% unexplored with a metal detector. The placer gold that could be found in Mexico is beyond comprehension.

Also, quite literally, the posts from mbasko, XLOOX and Ridge Runner have given me more information in three (3) posts than I've been able to gather in multiple inquiries with the biggest dealers in the States. (Question: "Will a coil for a Minelab GP or GPX series detector work on a TDI? Answer: I'm sorry, I have no idea.") I'm serious, nobody knows. But they did say, "email a dealer in Australia, they will know."

Thank you for welcoming me, I very much appreciate it.

If you don't mind, I will take the TDI out this week and will return with questions.

All my Best,

Rob

 

[Nightjar]

Hello all,
I am seeking advice from the best medal detectorists on the planet--the Australians.
Rob

Welcome Rob, Good luck with your ventures.
Aussies are the best because we pin the medals on our chests. :lol:

 

[nesral]

https://www.detectorprospector.com/forums/topic/17731-reg-mods-update/

A couple of excellent coils for TDI Pro.

Left : Detech 18/8" Dual Concentric, wired like a DD coil.

Right: Razorback 19" Mono.

 

[Adrian ss]

My TDI Pro OZ is still fitted with the original 11 inch mono after having tried several ML GP And GPX coils. They all performed well but I can not say they produced better depth or sensitivity than the stock 11 inch mono.
So the stock coil is back on.

Some air test figures with my TDI: and a 0.15g flat ish bit of gold.
Controls set at:
Vol 50%.
CGB 8
GBF OFF
P Delay 10
Gain 7
Threshold just audible.

Cond ALL 6cm
Cond H Nil response.
Cond Low 6cm

 

[AVXVA]

"Medal" detectors... Yep, I did that.

I went out over the weekend and ran the TDI PulseScan over a long buried 8" iron pipe that is exactly five (5) feet under the ground.

First thing I noticed--noticed it right off: I don't know what I'm doing without the GEB (Ground Balancing Toggle) turned ON. When the ground balancing is turned on, (1) the Ground Balancing Knob becomes functional, and (2) the Target Conductivity Toggle becomes functional and the machine works like a charm. The manual suggests different settings for the ground balancing knob depending on the Pulse Delay and "All" for conductivity, and when it's set like that you can do anything you want with the Gain. The machine is so pure and stable you can hear it purr.

Problem: When the GEB toggle is ON the machine is not as deep. How much depth is lost I'm not sure yet. But the manual says it's so. (I keep stressing depth because this TDI (hopefully) will primarily be a meteorite detector in central and western Kansas where people find them at depths of 2 to 5 feet. In Wyoming, Colorado, New Mexico, etc., they are right on the surface or just under.)

With the GEB toggle OFF I'm totally lost--the machine sounds like an accordion "wee wee - woo woo" every time the coil moves or the elevation changes an inch or so. The only controls on the machine that are functional with GEB off are Gain, Pulse Delay, Threshold and Frequency. The manual says that the machine's circuitry will handle the balance, but I haven't seen that yet.

Question: How do I set the Gain and Pulse Delay with the GEB off? As in, do I set the Gain and Pulse Delay at '0' then turn the machine on, and then I set the what??

Help!

Rob

 

[Adrian ss]

Maybe have a read of this>
https://www.detectorprospector.com/...ws/whites-tdi-pulse-induction-metal-detector/

Using a Pi without a GB mode will drive you nuts from the responses to ground iron mineralisation.
If you will be searching for meteorites in neutral ground then the GB Off mode will perform well.
Where the ground is even slightly iron mineralized the GB ON mode is the only way to go. Forget about lost depth.
Find the ground balance point for the area you are working in and then if possible test an iron meteorite to check the response at the particular gb level that you set.
Maybe adjust the Pulse delay up to around 15 to 20 usec, Conductivity to best response and set the gain for the best stability.

I think meteorite hunting with a PI is a bit of a challenge in mineralised ground due to the strong responses to hot rocks and ground noise. When these are dialed down so are meteorite responses.

I have an 128g Wolf Creek Crater iron meteorite that I can not isolate (with the TDI) from the surrounding ground noise without loosing the response to the meteorite.

Just some thoughts, not Gospel .

 

[XLOOX]

As Adrian says - you can only use a PI with the ground balance off when the ground lets you.

Turn the GB on, start at GB=1 & adjust it up until detector is just silent when bobbed up & down from a foot to an inch over the ground ( do not touch ground with coil). Note the GB reading then start at GB=10 & bob coil & turn GB down until just silent & note that reading too.

If the 2 numbers are close together then you have no chance of turning GB off. In really hot ground the window can be 0.1. In really mild ground it doesnt matter where you set the GB it will still be stable.

Before you get carried away with concern of with the loss in depth with GB on, first get her working with GB on and see what depth you get.

5ft is more than I ever got with my TDI SL on anything - except maybe a car body. How big a meteorite are you looking for ?

 

[XLOOX]

regardless of GB on or off, set pulse delay to 10us for small gold and for small coils 8" or less.
for coils above 12" set pulse delay 12 or higher as needed to settle her down.

always turn gain up as far as you can whilst maintaining stable response. youshould be able to run 6 gain anywhere and upto 8 in medium ground. above 8 prob need mild ground.

start up with GB on, All mode, 6 gain ,15 delay and threshold gentle hum.
adjust GB to give silent bob.
adjust gain up until unstable then back off a little.
redo GB
swing and see how you go.
only adjust delay up further if have +12" coip and still not stable.

 

[Adrian ss]

I would be inclined to use a lightweight All metal ground balancing VLF for iron meteorites. If you use discrimination you are likely to miss some because most iron meteorites have a wide varying range of minerals in them . Best to use an All metal ground balancing detector and dig all targets.
detectors like the Gold bug Pro ( have a wide GB range ) with an 11 inch coil or larger will perform well plus they are light weight so you will be able to go all day.

Most of the Ground balancing PIs are heavy and will go deep but the majority of meteorites are small and on the surface or are at shallow depths.

Detectors like the Sea Hunter, CSI 4 PI were used for metal detecting in salt water and the Pulse Delay was fixed to not respond to salt. These detectors are fine in neutral ground but are noisy in iron mineralisation.

The Vallon VMH 3CS is a ground balancing PI mine detector that is sensitive and deep searching and performs well in moderate iron mineralisation..Cheap as chips on Ebay. I have not used mine for meteorite hunting but have a suspicion that it may be well suited to this purpose..Be interesting to hear what others have to say about that tecta.

 

[Adrian ss]

It is interesting to note that of the iron meteorites that I have none give a strong response from any of my current 19 metal detectors. Even a 2kg one hardly produces a murmur from my Infinium, Sea Hunter, SDC 2300 and Vallon VMH3CS. My Gold Bug Pro when ground balanced blanks on the 2kg bit, the other smaller pieces produce a few clicks and burps but nothing positive like what you get from a positive hot rock.

 

[AVXVA]

Thank you, Adrian ss for the link to this article! That really helped. Stupid me, in the area where I've been testing the TDI, the soil actual contains quite a bit of clay, and clay means iron mineralization. This is why my TDI is basically useless with the ground balance turned off--as you said. I will remember XLOOX's thoughts on this, "As Adrian says - you can only use a PI with the ground balance off when the ground lets you." Sooo... The GEB circuit has to be on.

Question: How do I get maximum depth with the GEB toggle turned on?

On my next trip out, I'm working on this: "Turn the GB on, start at GB=1 & adjust it up until detector is just silent when bobbed up & down from a foot to an inch over the ground ( do not touch ground with coil). Note the GB reading then start at GB=10 & bob coil & turn GB down until just silent & note that reading too.

If the 2 numbers are close together then you have no chance of turning GB off. In really hot ground the window can be 0.1. In really mild ground it doesn't matter where you set the GB it will still be stable.

Before you get carried away with concern of with the loss in depth with GB on, first get her working with GB on and see what depth you get."

The Ground Balance knob on my TDI is really sloppy. Would 1:6 ratio Vernier controls for GB & Threshold be a good modification? (I can't post a link to it yet.)

The meteorites in central and western Kansas are from three (3) massive shotgun blast falls--each literally tons of space rocks scattered over 50 square miles. (I will post links when allowed.)

The one I'm working on isn't named yet. I will post photos.

Thanks!!

Rob

 

[AVXVA]

Here are photos of the 1:6 ratio Vernier controls for GB & Threshold modification that is available on US ebay.

Description

"If, like me, you've had trouble getting the Ground Balance and Threshold controls right on that ragged edge for nugget-hunting, this is your mod. These controls have a 1:6 ratio, so you can easily fine-tune your control settings, and they stay put. No more tree branches, shirt sleeves, or jacket cuffs changing your settings. I've done both recommended mods to my SL, and this 3rd mod is the best! I can set the Threshold to that "just barely" level, easily. As the battery discharges, and the Threshold creeps up, it's easy to re-adjust to that ragged edge. They aren't cheap, but the controls are brass and stainless, and I make the other parts, mainly the bases out of solid aluminum. Installation is easy. The kit includes an Allen wrench for the set screws. The only other tools need are a pair of square-nose pliers or 10mm socket for the pot screws, and a really small Phillips and plain screwdriver. That's it. No physical, or electronic changes to your detector required. This kit may also fit other detectors, like the MXT. Check with me before purchasing. These are built on a custom basis and may take up to two weeks to be shipped.

Price is $150.

Is this worth the price?

Rob

 

[AVXVA]

Top View...

 

[XLOOX]

OldHand came up with the idea of using a 6:1 vernier mech on the GB pot. I tried it & liked it & told Karelian who told the guy in the USA who now does the conversions.

https://www.prospectingaustralia.com/forum/viewtopic.php?pid=553435#p553435

Nesral then suggested a multi turn pot for both the GB and the threshold and I tried it & can attest that they makes a huge difference to usability.

https://www.prospectingaustralia.com/forum/viewtopic.php?pid=573713#p573713

The multi turn pot for GB doesnt deliver any benefit over the vernier mech but is 1/10th of the price.

If you can solder you can do both mods yourself for about USD 20.

 

[Adrian ss]

That mod sounds really helpful.
My TDI Pro Oz is stock with course and Fine GB controls.

Best depth is achieved with the correct combination of Ground balance, Gain, Conductivity and threshold. and Pulse Delay.
Set volume high, Gain at around 3, Conductivity in "All", Pulse Delay at around 10 to 15, Set threshold to just audible,
With the coils not moving adjust for any EMI as best you can, then do a Ground balance. turn up the gain until threshold is a bit ratty and then do another GB then reset threshold to steady and just audible.
Re do the ground balance whenever you alter the gain, pulse delay or conductivity.

Check the ground minerals with the GB OFF just in case you are able to use the GB OFF Mode. This mode will provide great depth if it can be used.

I find the best depth in is obtained in GB OFF with Conductivity in All. In iron mineralised ground the GB will have to be on or you will find sweet bugger all. Dig all targets. Some depth is lost in either High Or Low although the detector will be more stable in either one of those modes alone but check the response to the type of target you are hunting for..and run in the mode that gives the best signal but for best depth operate in ALL. Don't be afraid to turn the gain down a bit to get stable operation, you won't loose a lot of depth until below gain 3. Remember, most of your meteorite targets will be near the surface.
Experiment with the Pulse delay to find out the timing that works best for your meteorites.
I hunt with a slightly chatty threshold as I feel that it provides a bit of extra sensitivity over a dead smooth threshold...But that is just me , others my think differently.

It will be interesting to hear what sort of response that you get from a nickle iron meteorite. As I said earlier; none of my detectors respond very well to the meteorites that I have.

Hope this makes sense to you coz I think I have just confused myself.