Geotech

The values look reasonable to me. T3 might have the collector-emitter swapped, that's the only thing I spotted.

25mA sounds reasonable. What does "discharges completely" mean? Is that when it stops running? If so, 32 hrs also sounds pretty good, but I don't know what is normal.

It's a very basic PI detector, meant as a simple do-it-yourself construction project. It's on the level of the Surfmaster PI or Sandshark, and no where even close to a Minelab PI. It has no ground balance so would be a poor choice for prospecting.

The MX-series is still one of my favorite, I have an MXT, MX9, and MX-Sport. Except for salt water, they are still competitive detectors. I never liked the T2/F75 (again, same design) because of the single-button interface, which I found to be awful. The F70 is a much better experience.

Guys, the MXT is no more analog than the MX-Sport. They are the same basic design: analog demodulators, everything else is digital. The MXT used an 8-bit PIC micro and assembly language. The MX5 moved it to a 32-bit micro and "C" language, and cleaned up the analog portion a bit. Otherwise, same design. The MX-Sport is the same design as the MX5, with feature changes. The T2 is also the same design as the MXT, with feature changes. None of them are any more analog, or more digital, than the others. Tidbit: When the MX5 was released, there were also MX7 and MX9 models ready to go, with progressively more features. White's did not want to release them, because they didn't want them to impact the sales of the MXT. No, I don't understand that logic, either. Years later, a different MX7 was released. I still have an MX9 prototype, the only one in existence.

This would be a major violation of anti-competitive laws. If it was in writing, some lawyers may end up gainfully employed.

I know a lot of the history but it would take a long time to write it up. Good references are catalogs and the White's "Discovery" magazines; I have complete collections of both. Most of the catalogs are also available at https://treasurelinx.geotech1.com/Whites/Whites.html. There was a woman named "Patty" who worked at White's who knew every detector model and every date off the top of her head. She ran the literature dept; she had 6 filing cabinets full of historical info and photos, I'll bet every bit of that went to the landfill.

Jim, I guess you could say it was price, as the owners considered the company worth way more than it actually was. In the end, the owners (& dependents) didn't want to give up the cash cow. Joe, I'll not rehash old history, other than to say in all my 50 years of work experience, the 6 years at White's has been my favorite. I wish things had turned out differently. I have no idea why Garrett bought White's, but I suspect we've seen the last of White's tech from Garrett.

What is the battery for? Are you using this to measure TX waveform signals?

When I was there, an employee buy-out was proposed but the owners had no interest.

If it's an Equinox locked in single freq mode then those single frequencies are still square-wave drive and, as such, can be demodulated at 1x & 3x frequencies to do salt cancel. This is exactly how the Fishers CZ's worked.

The Garrett Axiom is way overpriced, should be around R$20,800.

LMAO

Sorry, no further comment.

I know I'm late to the party, but I watched Merrill's video and it's so bad that it's "not even wrong." The funny thing is, Mark Laurie gave Merrill the correct information and he didn't even know it. It's convinced me that I need to add a section to my book that covers transmit power mythologies.

Sorry, I have no idea.

It is mostly the market. Steve is right, there is an R&D aspect to it but the hardware costs are only marginally more than a VLF. The real problem is lack of competition. As the technology matures (read: patents expire) then prices could drop, assuming more companies jump in. But by then, Minelab may have another design that sells for $10k and the cheaper PIs just won't do. The TDI-SL was specifically designed to support an MSRP as low as $700 but what people wanted was ML performance, and they were willing to pay for it. So, yeah, it's mostly the market.

Circuits will last 50 yrs or more. With vintage models the biggest problems I've seen are bad coil cables and bad speakers. Capacitor problems are rare.

The ultimate deep silver detector would run at 1kHz. The lowest frequency detector I can name off-hand is the old White's Coinmaster V, it ran at 1.75kHz. I seem to recall something ran at 1.25kHz but can't say what it was. For more modern models, the V3 runs at 2.5kHz, the 1280x runs at 2.4kHz, and BBS/FBS/CTX runs at 3.125kHz (and 25kHz).

The optimum frequency for any target is when that target has a 45° eddy response. That is where the R-channel response is maximum, and that is the channel used for raw detection. Most likely 4kHz creates a stronger response for the gold coin because its response is closer to 45° and it's roughly the same physical size as the dollar coin. If you could set the frequency to 1kHz you would likely be at the peak of the dollar while the gold coin is lower.

Probably 2010 is when they started creating digital versions. Until recently I had every W&ET ever published, including the original Western Treasures and the Silver&Gold issues. I had intended to get them all scanned to searchable PDFs but never got the time, and I had to get rid of the magazines. ☹️

Archives are still there.

Nor me.

At White's I designed a transmitter and analog front end for a combined MXT+SMPI. I breadboarded it and it worked, but never built a prototype because I mostly did it on a bet. It was intended to be a switchable design, not simultaneous. But then I built a truncated half-sine system which was a true hybrid VLF+PI system. The prototype was working great, already beating the TDI. I was working on auto tracking and disc when I left White's. No one ever picked it up and continued and now Garrett owns the patent.

I can't imagine a scenario where any TDI will outperform a GPX5000. In a nutshell, the TDI-Pro/Oz are the high-power models, the SL is a lower power version but also quieter and lighter, and the SPP is a reduced-function SL. Search this forum for more details. Aureous is correct, the detector you need depends entirely on what you are looking for.