Ideas for this detector?

[SoCalDesertFox]

So I'm picking up a Search Master DX 3500 metal detector tomorrow for $10. Assuming it is in working condition, are there any useful/recommended modifications that have been done, or perhaps custom coils? Any idea on the frequency this detector utilizes? (I can probably look at the in-line capacitors and know the intended frequency after seeing the values of what are typically two capacitors used to make a tuned circuit but I'd rather not open it up until necessary.)

 

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[Loco-Digger]

Good luck with that 34 year old detector, I think you'd be better off buying a used newer bounty hunter off of craigslist

 

[DeepseekerADS]

It's tough to find any info on this detector....

The closest I could find is this DX8500

http://www.detectingequipment.com/index.php?id=1236

 

[SoCalDesertFox]

Good luck with that 34 year old detector, I think you'd be better off buying a used newer bounty hunter off of craigslist

I am not sure I see a point to that when the technology has literally not changed in about thirty years, judging by the patents these companies have on file.

I could probably replace the transistors and go to higher voltage (but same capacitance value) capacitors and compete directly with newer models of metal detector, or out right beat them. Considering they almost all use NPN transistors with a nominal AC hfe gain of 200-250, that's the biggest issue with their depth range - there's not enough gain for any appreciable EM flux beyond several inches. I've got NPNs from micro radar systems that have a nominal gain ten times greater. Granted, the inverse square law will come right in to bite my butt, but I'm pretty sure I could get 3-4 feet of air depth with higher gain transistors, better caps, a slightly higher operating voltage, and coils with diamagnetic parabolic reflectors attached. That could translate into 15+ inches of ground penetration by cranking the gain up an order of magnitude, and even deeper assuming the ground is non-mineralized and wet.

I do loads of mechanical and electrical engineering. These are the kinds of things I enjoy doing and thinking about on a near-constant basis.

 

[foiler]

sounds great. should you build that be sure to bring a backhoe.

 

[SoCalDesertFox]

sounds great. should you build that be sure to bring a backhoe.

Nah, just a Bobcat with scoop and jackhammer attachments would be enough, no need for massive excavators!

 

[BigWaveDave]

Too bad you don't have a budget for more than $10, you could buy a nice detector, and not overthink it at the same time.

 

[SoCalDesertFox]

Too bad you don't have a budget for more than $10, you could buy a nice detector, and not overthink it at the same time.

Why spend more than I have to when I can DIY/mod at a lower cost even once labor and parts and time is factored in?

Those who can, do. Those who can't, buy!

 

[SoCalDesertFox]

Got the detector. It constantly buzzes once the sensitivity is turned past 10:00, so there might be a cap or two that needs to be replaced. The ground balance potentiometer is broken, but an easy fix. The rest of it works. Picks up Tungsten ring in-air at about 5 inches - what I expected. Picks up my glass container with about 1g of gold at roughly the same distance.

Tried to take it apart only to find out that is easier said than done. Well, if I break the power/sensitivity potentiometer while trying to disassemble it, I have others I can use to replace, again an easy fix.

For now, let's go play with this thing across the street at the new park!

 

[BigWaveDave]

Hope it works out for you... sorry if I came off sounding like a Richard.

 

[SoCalDesertFox]

Hope it works out for you... sorry if I came off sounding like a Richard.

It worked out VERY WELL. Don't worry about coming off strong. Water + duck back = me.

Backs of shotgun shell casings about 7 inches deep. .22 shell about 5 inches deep. A HUGE chunk of angled iron that given the shape might have been part of a mining brace or mining cart of some sort cast/forged iron, roughly 15 inches deep. A square nail, and a regular nail, couple inches down. And a top to a stove pipe, about ten inches down. This is around the base of Mt. Rubidoux. I do believe a mining camp existed here at one point and time. I do know of claims filed on this mountain long ago, plus rumors of Rubidoux's lost gold mine.

 

[Loco-Digger]

Now don't be messing with the flux capacitor, or we all might be in trouble.

 

[DeepseekerADS]

I am not sure I see a point to that when the technology has literally not changed in about thirty years.

Well, really it has. The same plagues we face using them, they continue. Depth of detecting have barely changed. But we're seeing multi-frequency detectors now. The major change I see was coil development. In the early 80's we used concentric coils, and now we have the DD's = and we actually cover a whole lot more territory each swing. Hunted out spots using concentric coils are now giving up deeper targets. We're sending broader signals into the ground today.

You look at it, a whole lot of detecting technology has changed over the last 30+ years.

Of course, my 32 year old 1260X still plays effectively with my CTX. In that sense nothing has changed. But then it really has, new ball game today.

 

[SoCalDesertFox]

Now don't be messing with the flux capacitor, or we all might be in trouble.

So that little .22 shell? from the 1880s. The shotgun shell backings range from 1900-1920, after double-checking the markings.

I think I need to adjust that capacitor to before the gold rush.

 

[SoCalDesertFox]

I finally got this thing apart. Definitely easier said than done, there was a bunch of corrosion underneath the potentiometer nuts and washers holding the thing in place. It took more force than I was comfortable using on such an old board but I got it off with a *POP* and squeak.

After a tiny bit of brushing and clean-up, here's what we have!





A First Texas 3000 board. ICs had their casings dremeled to hide the markings though I bet a deeper patent examination would reveal what sort of ICs were used. Matched 4401 NPNs for the coils. 2907 PNP for I think driving the MPS-A13 going to the meter and speaker (I haven't looked too closely at the board yet to make a block diagram.) Caps look fine. The pots, a couple of resistors, and the MPS-A13 NPN need to be replaced, that should bring this back to original 'factory' condition and likely eliminate most of my major buzzing issues. Not comfortable with the potentiometers being used as the primary board mount, I might make an insulated internal mounting bracket for it instead.

Once I get this back in proper condition and give it some better test runs, I'll begin modifications.

 

[Charlie P. (NY)]

I'm guessing that's an old BFO detector, isn't it? Receive frequency may be 200 to 400KHz. As I recall they were right up there. Transmit was even wider; like 100 to 500KHZ and you tuned it until you got the stable beat note.

Probably some of the buzzing is corrosion on the whiper of those potentiometers.

 

[SoCalDesertFox]

I'm guessing that's an old BFO detector, isn't it? Receive frequency may be 200 to 400KHz. As I recall they were right up there. Transmit was even wider; like 100 to 500KHZ and you tuned it until you got the stable beat note.

Probably some of the buzzing is corrosion on the whiper of those potentiometers.

Actually, it's an old IB VLF (6KHz) using T/R, according to the patent listed on the casing. (4300097)

One of the pots is broke - wiper post moves freely up and down and rotates freely. That's for the ground balance/discrimination. The switch pot for power/sensitivity is corroded a bit. I'll see if I can find some contact cleaner. I can't turn it past 10:30 but it's still pretty sensitive even at that level.

Definitely need to get a coil plug made. I want to be able to swap out coils on this thing.