Reg Modded TDI Pulse Scan

[CaliGold]

17 hours ago, Steve Herschbach said:

The coil has nothing to do with it. It's a limitation of the machine imposed by the pulse delay.

• How Metal Detectors Work by Mark Rowan & William Lahr - Originally published by White's Electronics as a booklet P/N 621-0395. Basic technical information on how induction balance and pulse induction metal detectors work.
• Understanding the PI Metal Detector by Reg Sniff. An excellent, understandable primer on pulse induction metal detectors.

Thanks for the reply, Steve. I've gotten a pretty good idea of how metals detectors work, not near to the extent you gentlemen on this forum have, but well enough to go out and find objects of interest (and trash) with them proficiently. The TDI Pro also has pulse delay 10us lowest setting. So what is it about the TDI SL that makes it so underwhelming to everyone? (even with increased voltage)   I'm installing a sadie 8x6 coil this afternoon to get better small target response or any signal reading at all for that matter on sub .6 gram targets in the ground. When I run GB at 7 as I have to in the soil here in all of the Sierras, Angeles forrest, and deserts from Mojave to Death Valley the sub gram response is poor or non existent with MJ 8x12 coil. It misses 1/4 and 1/2 gram gold on bedrock crevices 1-2" deep even. Are all the folks saying the NF coils blow the MJ coils away placebo or is that just on Minelab units?  If it doesn't have anything to do with the coil why all the coil talk on here? I'll check out the links because the info is very valuable so thank you for that. Anyone got a old minelab for sale so I can learn the difference? Should I bee looking at an old Minelab 3500 to get my feet "wet"? The weather is starting to cool a bit here in California so hopefull the next month I'll have some scenery and gold to share with the forum. 

 

Thank You!

-Patrick

[Steve Herschbach]

Changing coils is like changing tires on a car. It affects performance in a small way. But you still have the same engine under the hood and the TDI engine is basically a six cylinder compared to the Minelab eight cylinder engines. With any detector people look for the best coil for the situation, in general small gold means small coils and large gold means large coils. So if you have a TDI there is lots of talk about what is the best coil to use on it. But you can't make a TDI into a Minelab with coils. That requires an engine swap.

[Geotech]

As it turns out, the factory TDI coils are a major performance limitation. I've adapted an Impulse AQ coil to run on the TDI and can then reduce the minimum delay to 6us. It's still not gonna run like a Minelab, but it is a little more respectable.

 

[CaliGold]

On 8/24/2023 at 11:42 AM, Geotech said:

As it turns out, the factory TDI coils are a major performance limitation. I've adapted an Impulse AQ coil to run on the TDI and can then reduce the minimum delay to 6us. It's still not gonna run like a Minelab, but it is a little more respectable.

 

How did that sorcery come to be? lots of solder??? ha.

I installed the sadie coil with the 16.4v battery modded 2018 TDI SL of mine that I recently got back to life again. It blew the 680ohm resistor (R14) and the mosfet I suspect went south because the coil went warbly and started acting similar to when the coiltek 14" tdi series blew the resistors.... I replaced R14 with a spare 680 ohm 2 watt resistor I had on hand. I also replaced Q4 mosfet with a spare version that would had a little different specs. I put another heat sink  Below are specs.  The current mosfet installed has the specs with the lower input capacitance (1030pF @25V) and the other spec sheet shown is previous installed that matched the OEM you guys spec'd on it. Is that mosfet "better" "more durable" or have I just screwed up? Gate charge and VGS max are different on current one.  The coil runs good now. Took it to the UBER  mineralized river bed near my house and dug some nickels and lead "nugget" targets I made. Worked pretty good.  Got new headphones coming so I can run the threshold hot like I like it with volume down to get some real world depth tests done with proper threshold breaks. Old headphones volume adjustment is broken and have to run the buds hanging behind my ears near my neck so I don't go deaf... I like that little sadie coil though. Super maneuverable whens she's not blowing my machine up...

 

thanks again @Geotech 

[CaliGold]

@Jim in Idaho Made a couple test targets (.45 and .15 gram) from some gold had laying around. I rather enjoyed working with the gold after I was able to get my fire brick makeshift crucible glazed properly. The Sadie coil 8x6 on the TDI SL that I have been tinkering with picks up the .15 gram flake I produced at about 2" inches. The .45 gram sample is breaking threshold nicely at 4.5". Not bad considering I butchered this machine with my amateur solder work...

 

NOTE. I was messing around with the .45 gram gold sample to flatten it a bit and inadvertently turned it into a .33 gram gold sample nugget and it breaks threshold nicely at 100mm (4"inches) All this is with about 15.8 volts running through from mod battery. FYI I'll be using this a bedrock crevice detector mostly and waterproofing the coil with silicone and using by the river cracks and occasional up on the benches in feeder creeks and hillsides. I'll be panning any targets gold or other wise in gold producting bedrock or riverbed stretches...

[Jim in Idaho]

Id say that's not bad, at all. I think you'll be finding gold before long.

Jim

[CaliGold]

On 8/24/2023 at 11:42 AM, Geotech said:

As it turns out, the factory TDI coils are a major performance limitation. I've adapted an Impulse AQ coil to run on the TDI and can then reduce the minimum delay to 6us. It's still not gonna run like a Minelab, but it is a little more respectable.

 

Was this the TDI SL or TDI Pro? Obviously I'd love to lower the pulse delay to 8us on my SL. Is that even possible? 

[Jim in Idaho]

As far as I understand, the delay on the SL can't be lowered below 10 microseconds. The timing circuit is fixed.

Jim

[Geotech]

The AQ coil is currently on my TDI Pro, but the same can be done to the SL. For either you would need to reprogram the micro because that's what sets the timing. Only the original 200 TDIs had a timing circuit you could easily modify.