TESORO GOLDEN SABRE

[maxbiri]

Thanks foe answer Max.

Bye Maxbiri

[Max]

Hi ! MAX

I intend experiment graphite shields on TGS(L) coils.
Exactly where and when can I use coils with graphite shields?
How to conect wire or terminal on graphite?
How the high resistance ohm. stuffs work in magnetic(eletromagnetic) fields?

Thanks in advance

DIRCEU

Hi,
the graphite I used expecially in CC coils, cause it's not easy shielding all with foil or mylar in that case. Also I've used in pinpointers as well.

You can use also in other situations. One advantage of graphite is that you just need to spray it inside the housing before apply and positioning the coil(s). You need uniform surface to shield with it... very flat or with little imperfections is ok, and many housing are so, many stuff you can find this way too to employ as homemade housings.

Usually putting graphite on e.g. insulant tape is not a good idea... so you could need using a paper tape around the rubber tape before apply graphite paint.

Terminal is like in Dave Emery's article , where he employed nickel varnish (super shield) to shield the example coil. You cut some strips of copper foil or other material suitable and place inside housing with e.g. instant glue. Then leave a free space (use masking tape) for later soldering of shielding wire... then spray over the graphite varnish. That's it: when it dry you have a very good contact and can solder on copper easy.

About resistance: with graphite is higher than with foil or mylar. No problem.
You need a path for static charges discharge... and that resistance is suitable for that purpose. It could vary much with various paint kind... and if brush applied or in cans... I suggest spray can, cause it's easy and give always good results. You need resitance in the range of 1-10Kohm per cm for best results.

The scope is not blocking magnetic field... but give faraday cage to stop capacitive interaction with soil.

You often don't need gap with graphite (when high resistance) but often a 1-2mm gap you made with a strip of paper tape... I do so... you remove after like in custom cars painting the tape and leave the narrow gap there.

Kind regards,
Max

[DIRCEU]

Hi,
I use always shields on both tx and rx coils. I use, depending on what I have available or usable for that, the following as shielding material (in the order described):

1. mylar
2. foil
3. graphite varnish

Kind regards,
Max

Hi ! MAX

I intend experiment graphite shields on TGS(L) coils.
Exactly where and when can I use coils with graphite shields?
How to conect wire or terminal on graphite?
How the high resistance ohm. stuffs work in magnetic(eletromagnetic) fields?

Thanks in advance

DIRCEU

[Max]

Max can you thell us,you use aluminium foil for shilding on booth coil or onlu rx coil?

Regards!

Hi,
I use always shields on both tx and rx coils. I use, depending on what I have available or usable for that, the following as shielding material (in the order described):

1. mylar
2. foil
3. graphite varnish

Kind regards,
Max

[miki73]

Max can you thell us,you use aluminium foil for shilding on booth coil or onlu rx coil?

Regards!

[Max]

Hi Max

Interesting yours big DD!
Is the 2 coil ovelapped 20 mm?
In yours opinion which is a good ovelapping meausure? Is a % of coil's diameter?

Thanks in advant

Bye Maxbiri

Hi,
it's something 23-24 mm inner separation from one coil to the other. Don't used a formula to get it... just tuned nulling voltage and phase for best results.

I noticed that small overlaps are good at widescan coils... I've made smaller with narrow overlap area and work very nice.

The problem is pinpointing: the coils made this way are good as widescan action but the pinpointing is difficault...often after dug soil you need external pinpointer to find the spot, and with a big coil like this it's sure you need one.

Kind regards,
Max

[maxbiri]

Hi Max

Interesting yours big DD!
Is the 2 coil ovelapped 20 mm?
In yours opinion which is a good ovelapping meausure? Is a % of coil's diameter?

Thanks in advant

Bye Maxbiri

[Max]

bigfoot coils... advantages ? Anyone knows ?

Hi,
I was thinking at bigfoot coils yesterday... cause I read some interesting reports on other forums... and will like to know if anyone here tested some original bigfoot coil on TGS or other Tesoro's uMax stuff.

I know that good OO coils can be made for these uMax... but OO are large when using full diameters...

The bigfoot I have in mind is the 3x18'' one... all white...

What about that bigfoots? Are really so performative on small stuff ?

It's worth try to replicate one for use with TGS ?

Kind regards,
Max

[Max]

I tried similar variations of TGS oscillator with LTSpice. Results:

 
JFet Vcutoff      Zener          Vcoil P-P
------------      -----          ---------
-.5 V              4v3             -3.5 to 3.5 
-.5 V              6v0             -5.2 to 5.2
 
-2.75 V            4v3            -6.4/-6.9 to 6.5/6.7 (instability)
 
-5.0 V             4v3            -7.7 to 7.4
-5.0 V             6v0            -7.7 to 7.4

Conclusion: coil voltage is sensitive to JFet cutoff voltage and Zener breakdown voltage. If JFet breakdown is small (-.5), can be corrected somewhat by increasing zener breakdown. If JFet breakdown is big, zener not affect - maybe lose gain control.

With JFet cutoff of -2.75, LTSpice showed significant instability, peak voltages changing. Other cases may have had smaller instability too.

The instability shown by LTSpice was very fast, every other cycle. But slower limit cycles very possible in real life.

Maybe instability not important because lock-in amp is synchronized.

JFet cutoff is important because it affects the voltage of your coil oscillation. Variations in J107 cutoff voltage would make production models of TGS have different depth. What did Tesoro do about that? Test each J107?

-SB

Hi,
original piece was TIS75, J107 is a replacement.

Kind regards,
Max

[simonbaker]

Hi,
I've downloaded LTspice and using some parts of files from porkluvr I'm doing some training on the simulator... just to see how to move around menus.

I'm happy of results cause I find it really intuitive and easy to use...but that's my impression... you could contestate!

Anyway, I've simulated the original (about) TGS osc with a 4.7 zener diode and 8V supply....

then I've changed the params... using a 15v zener diode (BXZ84C15L) to see the jump at output voltage.

As you can see with that +18v supply and 15v zener it gives about 30Vpp instead of original about 10Vpp: 3 times.

No other mods seem required e.g. for PN2222 that drives the 4024... but , of course, one have to put a stable +18v supply for osc section only (few mA current required)...even 2x9volts batteries could be good for tests.

So maybe people that want experiment with osc signal amplitude can do that way... well signal is not a perfect sinus on sim but I think could be ok for some raw tests.

I think that there's no need of that change on TGS... cause I found really good as is... but if someone would like to try... and inform us of results e.g. in air will be cool!

I can't do cause I have to dismantle the thing from housing and it's now hard work.

Best regards,
Max

I tried similar variations of TGS oscillator with LTSpice. Results:

 
JFet Vcutoff      Zener          Vcoil P-P
------------      -----          ---------
-.5 V              4v3             -3.5 to 3.5 
-.5 V              6v0             -5.2 to 5.2
 
-2.75 V            4v3            -6.4/-6.9 to 6.5/6.7 (instability)
 
-5.0 V             4v3            -7.7 to 7.4
-5.0 V             6v0            -7.7 to 7.4

Conclusion: coil voltage is sensitive to JFet cutoff voltage and Zener breakdown voltage. If JFet breakdown is small (-.5), can be corrected somewhat by increasing zener breakdown. If JFet breakdown is big, zener not affect - maybe lose gain control.

With JFet cutoff of -2.75, LTSpice showed significant instability, peak voltages changing. Other cases may have had smaller instability too.

The instability shown by LTSpice was very fast, every other cycle. But slower limit cycles very possible in real life.

Maybe instability not important because lock-in amp is synchronized.

JFet cutoff is important because it affects the voltage of your coil oscillation. Variations in J107 cutoff voltage would make production models of TGS have different depth. What did Tesoro do about that? Test each J107?

-SB

[simonbaker]

Hi all,
I've made a new one...for teh collection... this is a 12''DD for TGS, as well as other uMax models, can use too.

Here's actual recipe:

wire 0.25mm bare (30AWG)
TX turns = 88
RX turns = 92

TX resistance is about 24ohm
RX resistance is around 25ohm

TX L = (about) 5.7mH
RX L = (about) 6.15mH

For those who need MUCH depth...

Can get a coin at 50cm (half-crown)!

1eur at 42-43cm , in disc mode.

Bigger stuff at incredible depth....like a small round copper thing (6cm diameter) at 65cm !

Do you think this will win the cache test challenge now hands down?

I don't care much... personally I don't like large coils over 27-28cm diameter but made this to check how much TGS can be pushed with 30cm... and it can be pushed to work in the 50cm range on big coins. (at least on air)

I've tested with a small container and 5 silver coins of about 2 cm inside... and it detects the container (plastic stuff) easy at 60cm on the air.

Disc seems works right way, iron about ignored if soft... steel detected sometimes (like other coils , also originals).

Ferrite is nulled well and works good on normal soil, not tested yet on hard soil... mineralized stuff.

All measures made on air.
Anyway... here it is... who like big stuff can try it.
Inner diameter of DD is exactly 30cm, so 12''.

DISCLAIMER:
Tuning is critical cause of sharp phase shift requirement to get good depth on silver and mantaining iron disc, but can be done with lot of efforts and patience...for this is similar to other homemades that require also similar trial and error process... using test targets to check at each small movement. Just this is more sensitive... and require enormous care on that.

So before attempting making one... ask yourself if you're brave enough! You can have lot of troubles trying to replicate it... I've told you.

MADE AT YOUR OWN RISK...and please no questions...I've already gave its recipe.

BWT, I think it will bust any original 10x12'' or widescan from Tesoro... but I haven't so cannot compare. Just my experience with originals say me that...

Enjoy!

Kind regards,
Max

Pure artwork!

[Max]

This is phase diference about 200° ?

Max you are the best man!Make me happy!

Hi,
yes it is... are 200° for RX... cause the positive edge is delayed 200° from reference (TX).

Kind regards,
Max

[miki73]

This is phase diference about 200° ?

Max you are the best man!Make me happy!

[Max]

just to have an idea... (only for this time)

blue is like tx
yellow is like rx

you should see something similar...on the scope.

[Max]

Max plese can you explain me bit more ``with phase required (around 200°) between tx and rx signals``

How measure and adjust phase?And if i dond ask too much some picture of that tunning..

And please what is center tapering? Coil wouded with alu foil and conect to ground or?

Regards too all!

Hi,
the phase is relative to Tx signal: you do this way...
connect channel one of scope to TX oscillator, ground to ground and probe to collector of transistor.

Then you connect channel two: ground to ground... probe to pin7 of preamp (LF353).

Then you trigger the scope using channel one.

OK... then you'll see that phase shift on the screen... adjust amplitude/timebase of both channels if required.

You'll look for rx phase it must be in the 200° range in tesoro coils... at least... both the two I have tested have that similar phase.

If it isn't you'll play with nulling... trying to get a good null but that phase shift too. Sometimes, I say you, it's impossible... you scrap the coil and made another... no easy solution to that till now.

It's easy... I think Qiaozhi posted a picture with both TX and RX signals from a CC coil from tesoro... but you don't need it... just that measuring phase of RX you'll get around 200°. Sometimes I saw it not critic... even with 185° works too (not as best... but works)... other times, like in these larger coils you need be more accurate...

When you have a good nulling and correct phase shift... your coil is ready to go.

I don't use center tap in these coils at now; maybe in future homemade I do that way too.

You can use foil...why not ? it's cheap and easy stuff... just avoid putting too much, overlap as few as possible.

Kind regards,
Max