TGSL Experiments

[simonbaker]

Hello,
I have made more coils and a lot of tests.
Not much time so will try to write brief.Have made 4 DD27 and 3 DD19.
Still dont now why but all 27 have poor sens when nulled./around 27cm and usualy last few sm-s are with cracked sound/I had some doubts even about the PCB.But not anymore.
The interesting part is that one of my 19DD have greater sensitivity than all DD27 I made so far.Around 30cm for 1E coin.Disc is ok but cant GBalance device with this exact sensible coil.While all 27 have reduced sens and can be GBalaced very well.What could be the reason?This exact DD19 have great audio.Much more louder and in all area of detection!
The thing that I notice is that when my windings are on former and still not constrinkted are around 4,8 mH and when finished they show 5,98.And Ivconic say that he measur around 5,7mH when not constrikted,so later have 6,0mH.
So I am winding too woosed maybe?

This is very interesting and useful information.

It would be good to see photos of all your coils, along with:

1. TX, RX Dimensions
2. TX, RX Inductance
3. TX, RX Resistance
4. TX, RX Wire gauge/thickness
5. TX, RX Shield arrangements.

------------------------------

Ok -- 27 cm is not bad of course, but 30 cm is nice, especially if audio is "fat".

Why one 19 cm coil good??? But not GB??? This is important mystery! You have some useful experience now. Maybe we can get some insight.

Q: what do you mean "cannot ground balance"? How do you test ground balance?

Q: only one 19 cm coil good? What about other two?

I notice with my TGSL that target signal in GB channel is very small compared to Disc channel. Perhaps with some coils GB channel signal is bigger, more like Disc channel, and audio is better, because both signals needed to make audio.

Possible explanation: If target phase becomes shifted so it overlaps both the disc and GB sync pulse phase more evenly, then maybe makes more sensitive detector -- but destroys GB control.

This could happen if the RX coil resonant frequency is not normal distance from oscillator freq, or the the RX coil resistance is changed causing the phase to shift.

But I don't know. I have tried to vary those parameters, but no good conclusions yet.

-SB

[simonbaker]

Humidity in combination with other (salt, acid etc) molecules. Never use water soluble or hygroscopic glue or lacquer on oscillator or VF stage.

What glue is convenient/best for:

1. Binding coil
2. Gluing coil to form

????

-SB

[ivconic]

For example you can replace 1N4148 with 1N4448.
For transistor pair you can try BC327&BC237 or BC557&BC547 or BC107&BC177. I noticed some differences when transistors are changed.
Also try to balance coils now with 4mV residual voltage.
Regards!

[Ultimate_Haze]

Thanks!
So negavive voltage is - 6,26.
That is good idea.I never try change tr's in chopper stage because things seems to be ok there.What pair you sugest to suit best there?Used 2n2907-2n2222.Have sowhere 2n3906-2n3904 will try those.I used silicone 1n4148-will try other kind.
Have notice that when target is i detection with DD27 negative voltage drop fast and under some values that is too low and there is no sound from speaker/while there is still target that have to be indicated/!But with this 19DD this wasn't that way.Everything were 6+ except that coil just cant be GBalanced!

[ivconic]

Depends. Relation should be 0.4 - 0.5 mH on such former.
You noticed very well some things there!
Some coils "producing" better audio and some don't, same as i noticed.
Also is possbile smaller diammeter to be more sensitive than larger, i noticed that too.
About audio; negative voltage supply must be perfect. -6.xx volts not -5.xx volts. Check that. Try to change those 2 transistors in chopper stage, use different kind. Also in chopper stage try to put faster diodes.
Scope TX amplitude.
Regards!

[Ultimate_Haze]

Hello,
I have made more coils and a lot of tests.
Not much time so will try to write brief.Have made 4 DD27 and 3 DD19.
Still dont now why but all 27 have poor sens when nulled./around 27cm and usualy last few sm-s are with cracked sound/I had some doubts even about the PCB.But not anymore.
The interesting part is that one of my 19DD have greater sensitivity than all DD27 I made so far.Around 30cm for 1E coin.Disc is ok but cant GBalance device with this exact sensible coil.While all 27 have reduced sens and can be GBalaced very well.What could be the reason?This exact DD19 have great audio.Much more louder and in all area of detection!
The thing that I notice is that when my windings are on former and still not constrinkted are around 4,8 mH and when finished they show 5,98.And Ivconic say that he measur around 5,7mH when not constrikted,so later have 6,0mH.
So I am winding too woosed maybe?

[WM6]

This is splendid.

Yes, indeed, simple but splendid solution.

[Darko]

I saw other posts about checking grounding carefully and that seems like best advice -- sure sounds like cable shield not grounded or something.

Last thing you can try for general tuning is changing the oscillator frequency by varying the oscillator capacitor (.022) and seeing if it works a little better at some frequency.

I use a capacitor bank like in photo, adding values together to get any I want.

Maybe improve a little, maybe not.

-SB

This is splendid. Fast and clean way for to determine right value of capacitance without soldering and desoldering again and again. Thank you Simon.

Kind regards

[simonbaker]

I was tray with other cable and noting. Winding two more coils with spatial attention to Al shielding and nothing. Nulling, nulling and nothing. All is right but when touch coil enclosure sensitivity fall. Why!! When GB trimmer not adjusted to reject ferrite rod, all is right and sensitivity stay normal even I touch enclosure, but when adjust GB, story come to beginning. I'll crazy about that. Please guys...
Dear Ivconic max qiaozhe simon…

I saw other posts about checking grounding carefully and that seems like best advice -- sure sounds like cable shield not grounded or something.

Last thing you can try for general tuning is changing the oscillator frequency by varying the oscillator capacitor (.022) and seeing if it works a little better at some frequency.

I use a capacitor bank like in photo, adding values together to get any I want.

Maybe improve a little, maybe not.

-SB

[simonbaker]

Humidity in combination with other (salt, acid etc) molecules. Never use water soluble or hygroscopic glue or lacquer on oscillator or VF stage.

I will try other glue and see how different. Thanks.

-SB

[WM6]

Just another mystery to investigate...

-SB

Humidity in combination with other (salt, acid etc) molecules. Never use water soluble or hygroscopic glue or lacquer on oscillator or VF stage.

[simonbaker]

Glued Coil Changes Oscillator

Just an observation I don't understand...

I recently glued a TX coil to a plywood form. I used Elmer's glue (water based) and let it dry for a couple of days.

The oscillator in my TGSL Final now works a bit differently -- the voltage is reduced, and the "bump" is much less noticeable.

The inductance and resistance of the coil seems about the same as before.

I thought maybe water molecules trapped in the glue somehow changed the behavior of the coil.... but before gluing to the form, the coil had been previously soaked with a light mixture of Elmer's glue and water, to stiffen all the windings, and it acted normal then.

I don't see why gluing to the plywood form would make any difference to the amplitude.

I tried another unglued coil to check the oscillator, and the "bump" came back, so something happened to the glued coil.

Just another mystery to investigate...

-SB

[simonbaker]

I was tray with other cable and noting. Winding two more coils with spatial attention to Al shielding and nothing. Nulling, nulling and nothing. All is right but when touch coil enclosure sensitivity fall. Why!! When GB trimmer not adjusted to reject ferrite rod, all is right and sensitivity stay normal even I touch enclosure, but when adjust GB, story come to beginning. I'll crazy about that. Please guys...
Dear Ivconic max qiaozhe simon…

I don't know answer. Maybe will learn from my coils.

Trying different coils and different cable/shield arrangements is best idea for now.

Have you tried this outside away from all electrical wires, noise, etc?

-SB

[Darko]

If you have better depth with voltage on C15, C12 only a little negative (0 to -.5V), I think that may be better arrangement, especially if it allows you to ground shields. Important thing is actual performance.

I agree touching cable should not make such a big difference. If all else fails, can you switch to different cable just in case something crazy with the cable?

Best to check with Max, Ivconic on exactly where cable shield should be connected (did I hear "read the thread....").

- Do you have cable shield connected to PCB ground directly? That is how one picture shows it -- shield is used as one wire of TX signal to TX coil.

Regards,

-SB

I was tray with other cable and noting. Winding two more coils with spatial attention to Al shielding and nothing. Nulling, nulling and nothing. All is right but when touch coil enclosure sensitivity fall. Why!! When GB trimmer not adjusted to reject ferrite rod, all is right and sensitivity stay normal even I touch enclosure, but when adjust GB, story come to beginning. I'll crazy about that. Please guys...
Dear Ivconic max qiaozhe simon…

[simonbaker]

-A picture of your coil housing would be helpful.

It’s Bulgarian plastic housing like ivconic uses for his coils. I will attach here jpg when will make some shots.


- Does sensitivity fall as your hand comes near, or suddenly when touch coil housing?

Only when I touch housing , or cable.

- Are you sure you are connecting ground wire of TX to shield, not hot wire?

Yes, I’m sure.

- Exactly what type of cable are you using?

DIN cable, 5 wires. Tried with two similar cables.

- It is not too surprising that touching coil would reduce sensitivity, but before simple answer, I hope someone with good working TGSL will try it with theirs and see how touching housing affects sensitivity.

I know that this is normal if sensitivity falls just a little when touch coil but I’m loose 10-15 cm of sensitivity of machine!!

- It is possible touching coil housing affects null through capacitance, etc. -- maybe even deforms coil positions -- can you see any change in null on scope?

-I don’t have scope. I uses sound card scope until I noticed chatters when my PC is turned on. Now I null coils with multimeter.

- What problem are you trying to solve by experimenting with shield connections? Less noise/chatter?

I try (and success) to achieve good phase like you says that voltages on c12 and c15 must be a positive. With normal (both TX end and RX end on GND in search head) wiring I don’t have success.
Well, in both cases of coil setup I notice fall of sensitivity when touch search head housing or cable.

If you have better depth with voltage on C15, C12 only a little negative (0 to -.5V), I think that may be better arrangement, especially if it allows you to ground shields. Important thing is actual performance.

I agree touching cable should not make such a big difference. If all else fails, can you switch to different cable just in case something crazy with the cable?

Best to check with Max, Ivconic on exactly where cable shield should be connected (did I hear "read the thread....").

- Do you have cable shield connected to PCB ground directly? That is how one picture shows it -- shield is used as one wire of TX signal to TX coil.

Regards,

-SB

(thread 70 TGS)
Has or not contact to the negative battery pole clamp in RX coil?
According the schematics, in TGS Light - Not?, but in TGS - Yes?
What is true?
I readed contradictory opinions
-rdec3
------------------------------------
Hi,
yes one lead of RX is connected to gnd: in standard tesoro's coils that happens inside the coil housing, then the wire from tx side at gnd potential is connected to shield and lead of rx inside housing. No matter of e.g. pcb tracks at rx about that: coils are this way.

So, you have to made it as in original coil.

Then some users reported also that detector works cool (or even better) without connecting RX lead to gnd: it's your choice doing thatway, but remember you need shield connected to gnd in any case to avoid capacitive problems, otherwise coil will be totally useless on soil.

Best regards,
Max
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