Problems with my new TGSL

[Sebastos34]

Hello, i've some problems with my tgsl:
I've build a 27 cm coil, with 93 turns for TX, and 103 turns for RX. I'm not sure that values are correct.
I've replaced the LF 353 with a TL072, the LM308 with a TL071, and the BF245C with BF245A, cause I didn't find this components in my electronic shop. Datasheets seems to be similar...
When I connect my coil, I have lots of interferences, and have a 15 cm depth maxi in all metal mode.
In disc mode, I have no sound, it's not working.
Sensitivity and GB buttons seems to have no effect on depth, and stability.I also points out that when I move aside both discs, sound becomes less treble.
Could anyone helps me please?
P.S.: I have oscillosound, but I don't know if I can use it for measurments???
Many Thanks

[dfbowers]

Hello, i've some problems with my tgsl:
I've build a 27 cm coil, with 93 turns for TX, and 103 turns for RX. I'm not sure that values are correct.
I've replaced the LF 353 with a TL072, the LM308 with a TL071, and the BF245C with BF245A, cause I didn't find this components in my electronic shop. Datasheets seems to be similar...
When I connect my coil, I have lots of interferences, and have a 15 cm depth maxi in all metal mode.
In disc mode, I have no sound, it's not working.
Sensitivity and GB buttons seems to have no effect on depth, and stability.I also points out that when I move aside both discs, sound becomes less treble.
Could anyone helps me please?
P.S.: I have oscillosound, but I don't know if I can use it for measurments???
Many Thanks

Not sure about the TL072 as a replacement for the LF353. In reading some post, looks like both are JFETs and have the same pinout. If you can't find anything else wrong with your TGSL I can give one a try in mine. The TL071 for LM308 and BF245A for a BF245C are OK.

You should be getting at least 25cm on coin size objects and 30 to 34cm in quiet environments.

Try this method to determine if your coils are correct:

http://www.geotech1.com/forums/showt...357#post115357 (post 546)

Or, if you have a way to measure frequency, you should be running at 14.5kHz. Or, if you hook your Rx coil to where your Tx coil connects, you should be running at 13.9kHz.

Don

[Sebastos34]

Hello,
Thank you for your answer.
I Will test that as soon as possible ans I'll tell you, if it's better.

[Sebastos34]

Hi!
I finally ordre a lcr meter and a oscilloscope. I'll have it soon.
I've changed my tl072 with lf353, and bf245a with bf245c, as in the original placement parts draw.
It's really better, I've won in stability, but depth is really poor: about 18 cms for a sesterce with Ground balance at min. Disc switch on all metal, and sensitivity at the Max! Disc mode doesn't work for me, and When I turn GB to the Max, it's reject my coin.
Do you think that all of my problems comes from the coil, or maybe annoter problem from my pcb?
I prefer wait a little to have inductance meter to do another coil, and I'll tell you frequency as soon as I have my scope.
So, what do you think about Hameg 205-3
Many thanks

[Qiaozhi]

Hi!
I finally ordre a lcr meter and a oscilloscope. I'll have it soon.
I've changed my tl072 with lf353, and bf245a with bf245c, as in the original placement parts draw.
It's really better, I've won in stability, but depth is really poor: about 18 cms for a sesterce with Ground balance at min. Disc switch on all metal, and sensitivity at the Max! Disc mode doesn't work for me, and When I turn GB to the Max, it's reject my coin.
Do you think that all of my problems comes from the coil, or maybe annoter problem from my pcb?
I prefer wait a little to have inductance meter to do another coil, and I'll tell you frequency as soon as I have my scope.
So, what do you think about Hameg 205-3
Many thanks

Yes, it's most likely a coil problem.
Have you read all the information posted here? -> http://www.geotech1.com/forums/showthread.php?t=15710
Your GB pot should be somewhere near the middle when the coil is balanced correctly. It certainly should not be at maximum or minimum. Is it possible to reject a ferrite slug by adjusting the GB pot? If not, then the coil balance needs to be re-adjusted.

[dfbowers]

Hi!
I finally ordre a lcr meter and a oscilloscope. I'll have it soon.
I've changed my tl072 with lf353, and bf245a with bf245c, as in the original placement parts draw.
It's really better, I've won in stability, but depth is really poor: about 18 cms for a sesterce with Ground balance at min. Disc switch on all metal, and sensitivity at the Max! Disc mode doesn't work for me, and When I turn GB to the Max, it's reject my coin.
Do you think that all of my problems comes from the coil, or maybe annoter problem from my pcb?
I prefer wait a little to have inductance meter to do another coil, and I'll tell you frequency as soon as I have my scope.
So, what do you think about Hameg 205-3
Many thanks

When I had constructed my first TSGL, I had a similar sysmptom that turned out to be a cold solder joint. No disc and poor depth. You might have a dead channel. It's difficult to troubleshoot without a scope.

[Sebastos34]

Hi everybody,
good news! I've replaced R48 from 200K to 220k, and have make a better nulling of my coil, and I can now get a Sesterce to 26-28 Cms depth... But without disc.
After that I've replace C6 from 15n to 22n and now disc. works very well, but with a poor depth. I think I must find the good value for C6, on RX output.
I've just buy an oscilloscope, and I have done tests you told to KRISMEA about this post:
http://www.geotech1.com/forums/showt...roubleshooting
Look at photos,it seems that my TGSL haves a problem...
All pictures Were taken with 5V/Div. apart the tx-rx signal which was measured with 0.5V/Div.
If I understand well my TGSL works around 16.1 Khz.









If somebody have any ideas about my problem, I would wonder!!!

[porkluvr]

Let's see, there are five different photos, and not a one has a description. But you do refer to another link, so what you posted is not a TOTAL secret.

[Sebastos34]

Sorry, I've just see that...
Pic1 is point TX and RX signals at the output. (0.5 V/Div)
Pic 2 are points 1 and 2 (5V/Div)
pic 3 are points 1 and 3 (5V/Div)
pic 4 are points 1 and 4 (5V/Div)
pic 5 are points 1 and 14 (5V/Div)
Thanks

[dfbowers]

Hi everybody,
good news! I've replaced R48 from 200K to 220k, and have make a better nulling of my coil, and I can now get a Sesterce to 26-28 Cms depth... But without disc.
After that I've replace C6 from 15n to 22n and now disc. works very well, but with a poor depth. I think I must find the good value for C6, on RX output.
I've just buy an oscilloscope, and I have done tests you told to KRISMEA about this post:
http://www.geotech1.com/forums/showt...roubleshooting
Look at photos,it seems that my TGSL haves a problem...
All pictures Were taken with 5V/Div. apart the tx-rx signal which was measured with 0.5V/Div.
If I understand well my TGSL works around 16.1 Khz.
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If somebody have any ideas about my problem, I would wonder!!!

16KHz is too high. That would suggest that your Tx coil is at 4.8 mH!! Should be 6.0 mH!! I would expect you to have some phasing problems and DISC not working right. Your Oscillator should be around 14.5 kHz and your Rx coil should be tuned to 16.12 kHz. Now just for checking the inductance of your Rx coil, connect it where you would normally connect the Tx coil. It should then oscillate at 13.9kHz.

[Sebastos34]

Hi,
Thanks for your answer.
I don't understand how I Can mesure inductance with the oscilloscope.
What is the method to do that?

[dfbowers]

Hi,
Thanks for your answer.
I don't understand how I Can mesure inductance with the oscilloscope.
What is the method to do that?

Super easy!

You know that the equivalent C for the oscillator is (20nF.. if TSGL if built correctly)
And.. you know the oscillation frequency from looking at your scope.
Just calculate using the online calulator!!

http://www.whatcircuits.com/lc-reson...cy-calculator/

[Sebastos34]

Many thanks!
It's very easy. The C of my oscillator is: 20.1 nF and the frequency is 16.12 Khz.
Too bad... Tomorrow I'll try to do a coil with too much roll-ups, and remove some until I achieve 5.8 mH before tight and glue.

[porkluvr]

You know, there are a number of "coil calculator" programs available (?). My favorite selection is part of the MiscEl program (see Google) but that may not be the best for you because I also use a comprehensive wire-data table that allows me to indirectly compensate for various insulation thicknesses.

Coil calculator programs will usually assume that you want a circular coil. What do you do if you have a D shaped coil?

Even if your coil is DD instead of circular you can estimate its circular equivalent by measuring the distance around one of the Ds. Wrap a string around it and measure its length.

Set that length equal to circumference, "C".

C = pi*D
D = C/pi
(D = diameter)

Then plug value "D" into the coil calculator. Not 100% accurate, but something to start with.

Qiaozhi has often posted a coil calculator program that is used by a lot of folks, but I am not well organized enough to be able to tell you exactly where to find it. (for shame)

[Sebastos34]

I've mesured inductance of my rx coil,
It's 6.36 mH. Can I hope use it with a new coil (tx or rx), or I need to rebuild all two?
Otherwise I ever have download coilcalc, but I didn't know how to use it with a D coil.