TESORO GOLDEN SABRE

[Dennis the Mennis]

Dennis, what is so hard about finding good quality capacitors?

You should use polyester or Mylar film caps for most. Polycarbonate is also good or maybe better but hard to find.

Use Polystyrene or polypropylene for the transmit tank and also the receive tank. These are desirable because you want low loss and temperature stability. Polyseter is mediocre but much better than any ceramic cap you'll likely find that's big enough to work here.

Ceramic capacitors might be OK in some places but you had better understand the differences and select wisely between Z5U, Y5V, X5R, and COG/NPO if you want decent performance. You also need to understand voltage derating before you employ ceramic caps, even more so than for film types.

Ceramics can be used some places, but not a good idea unless know the cap's specs and choose wisely after some research.

Hi Porkluvr ,

Thanks for your reply ,
It was not the problem finding good quality capacitors but more which type should be used ...
Your answer gave me enough food for thought so guess which internet sites were visited these couple of weeks.

I've found some 'inspiration' of the condensator types used on one of the photos posted somewhere in this hugh thread .
I guess I picked the wrong photo ( perhabs from somebody with the some problems: Nelson ?...) , recently I saw other photos of the TGS pcb with the type caps you've suggested .
Hmmmmm makes me think if this is the answer to my problem .
I 've also made another set of coils as Max suggested ( 25DD as described and build in the PDF Ivconic made) : 6 - and 6.5 mH , aprox 22 ohm , shielded with airgap , used the correct type of cable and managed to get 14,5 khz on both sets of coils .
The problem remained : very low detection hight ... so I've ordered new caps of the type you've suggested and I'll cross my fingers when replacing them .

regards Danny

[GeorgeGW]

I dont leave it for a detector from a shop, i made two detectors ( delta-pulse and Garys PI detector ) and works good.... i will try it again from the scratch with new pcb with the same parts, I know TGSL is a good detector.

[ivconic]

Well...what to say? I made over 40 TGSL's so far. Each of those is workable until today. Many people on this forum also succeed to make it correctly. In my country here also i know at least 20 people that made it and still using it as main detector.
Maybe you should buy detector from a shop? It is not given to anyone to make detector just like that.

[GeorgeGW]

3 diodes are ok.... so.... i put it in the box.... and i will try in the future one time to print another pcb and i will start from the beginning
thanks for all!!
GeorgeGW....

( i'll try to construct another metal detector now..... )

[ivconic]

hi ivconic and Pompey, i checked voltages and they are all ok... 7.9 and -6.26, i also checked the opamp supply voltages and they are ok.... i replaced 2 chopper tranzs and the buffer tranz, the chopper with 546 , 556 and the buffer with 546 and the 4024.. but the problem with continues sound remains!!!!

Ok, than only one thing left; those 3 diodes from 4024. One of those (or 2 or all 3) are shorted. Replace them all.
If that not solve the problem...than i don't know what else!?

[GeorgeGW]

TGS PROB

hi ivconic and Pompey, i checked voltages and they are all ok... 7.9 and -6.26, i also checked the opamp supply voltages and they are ok.... i replaced 2 chopper tranzs and the buffer tranz, the chopper with 546 , 556 and the buffer with 546 and the 4024.. but the problem with continues sound remains!!!!

[peih]

Hello everyone, I made the scheme from the first page, and made a coil of 10 khz, 18 millimeters works perfectly coin in air 30sm but discrimination is a little low iron counts always a way to make a strong diskriminatsiyata.</span>How to reinforce discrimination.sorry for bad English</span>

[GeorgeGW]

i appreciate for your help
thanks a lot!! i will try to fix it...
( sorry but i'am a student and i'am electrician and i dont know very well electronics... just a few things only... the basics!! )

[ivconic]

Hello,George!I had the same problem first.It turned out IC 4024.I replaced it ,and everything is okay about sound.I have a quiestion to experts.When I null with scope at pin 7(Lf353) ,and then measure the same pin with multimeter I read about -180mV.There is some sensitivity -1euro about 10sm.When I null at pin 7 with multimeter -it shows 5-10mV -the scope shows that is not nulled at all.I tried with two different pcb-s -1265 and the last one for the schematic above.Can this be a coil problem,or something else?Pin 1 of LF353 has broken graphic too.I turn this broken graphic into a nice sinusoide by placing 100pf paralel with 100k rezistor (Lf353)The same effect may get by replacing 2,2k (emiter 2N2907) with 4,7k.But the main problem is coil nulling -the meter and scope show different place of nulling coils.

Ehh...
You should use my method of nulling - direct connection of millivoltmeter to RX coil. That way you would null coil properly and void any further doubts about it.
Else.... C9 and C10 capacitors must be PERFECT. Use high quality ceramic.
If still you can't get pefrect sinus on opamp output....than replace values 100pf with 56-68pf. Experiment....you'll manage to make it to work properly.

[ivconic]

You have +8v and gnd from 7808. Minus voltage is generated in stage after 4024. It should be approx. -6.20V +/- 0.15V.
Situation is already explained. But let me repeat:
TX transistor 2N2907 with LC tank forms oscilator and run at approx. 14kHz (if TX coil is 6mH). Signal is fed to buffer transistor 2N2222 base through 100K resistor. Than from it's collector, through 1K resistor to pin 1. of 4024. 4024 is divider and divides main 14kHz. On pin 12. there is 1/2 of main frequency, 14kHz/2= 7kHz. So 7kHz signal is further fed through 2 x 4K7 resistors to chopper transistors bases. Those 2 chopper transistors in conjuction with 2 x 4148 diodes and 2 x 220uF capacitors are forming "negative voltage generation stage" with approx. -6.xx volts at output.
...
So...if you get continous audio it means (in 99% of cases) that you don't have proper negative voltage. Reason could be buffer transistor 2N2222 or 4024 or those 2 chopper transistors. In most of the cases all the mentioned components are supposed to be alright. Problem lays in signal level in mentioned paths. Signal is not strong enough to "open" transistors bases. Somewhere from collector of TX 2N2907 to chopper bases signal is somehow attenuated. To void to much of phylosophy simply you can replace those 2 chopper transistors and put two of different kind (BC107&BC177, BC557&BC547....). Or to replace 4024 from one manufacturer and put one from other manufacturer. At the end you can try to replace buffer 2N2222 with BC547 or simillar. It will start to work properly for sure. Signal is a bit attenuated - not much. It will need a minor amplification to reach level enough to "open" bases at chopper transistors.
Pretty common source of that attenuation can be 4024. It acts like divider there. Logicaly in process of dividing it attenuates origin signal at some percentage.
....

[GeorgeGW]

7,9V in schematic at TX J1 pin and -6.xx J1 pin 2, right?

[Pompey]

thanks ivconic.. i will check the negative voltage ( 0V you mean)
thanks Pompey after checking voltage i will replace 4024!!

Voltages are 7,9V and -6,13V to me. You must get -6.xx for negative voltage when you atach Tx coil.

[GeorgeGW]

thanks ivconic.. i will check the negative voltage ( 0V you mean)
thanks Pompey after checking voltage i will replace 4024!!

[Pompey]

Hello,George!I had the same problem first.It turned out IC 4024.I replaced it ,and everything is okay about sound.I have a quiestion to experts.When I null with scope at pin 7(Lf353) ,and then measure the same pin with multimeter I read about -180mV.There is some sensitivity -1euro about 10sm.When I null at pin 7 with multimeter -it shows 5-10mV -the scope shows that is not nulled at all.I tried with two different pcb-s -1265 and the last one for the schematic above.Can this be a coil problem,or something else?Pin 1 of LF353 has broken graphic too.I turn this broken graphic into a nice sinusoide by placing 100pf paralel with 100k rezistor (Lf353)The same effect may get by replacing 2,2k (emiter 2N2907) with 4,7k.But the main problem is coil nulling -the meter and scope show different place of nulling coils.

[ivconic]

George don't worry, schematic and pcb are ok. You don't have negative voltage on your detector - that's why you get continous audio.
You should read this thread from a beginning and find answers to your problem. It is easy problem, 5 minutes to fix!
Regards!