Protek Gtx 711

[Xtrem]

Dubulumach
thanks for your advice. now I don't think to test the machine,
the receiver must be done first and then we'll see.

[Dubulumach]

Xtrem καλή τύχη!

[Xtrem]

This is the final design for the transmitter,
the previous one had some errors.
There is also a case where a transistor can be inserted in place of the MJ301.
It might work better, I don't know, but it would require modifying the circuit.
Let's leave it like that for now.

[Xtrem]

The receiver works much more stably, and with better sound,
at the input we have the option to put whatever antenna we want,
in the case of the schottky diode it receives all frequencies simultaneously,
we can try whip antennas and also tuned loops.

[Geo]

No stable detecting without the agc stage....

[Jeg]

Thank you Xtrem for the simplification of the Tx circuit.

The Pot that we see on your board is it the R24A?
The ring choke inductance on your board, is it the L2A?

As for MJ301 do you mean MJ3001??

[Jeg]

Guys R37 on the Tx board shows a 20 ohm trimmer! It is wrong.

[Geo]

Hello Jeg, how are u???
Yes R37 is wrong, try a 20K trimmer .
Regards

[Jeg]

Hi Geo! I am fine brother i hope the same with you! Winter is coming so a new project is needed! :-))

Thank you for the pot value, it will work. But i think a value close to 550-600 ohm will be more appropriate as it will help zener to work without any strain. Does it happen to know the voltage level across C23??

[Geo]

Hello Jeg. No i don't remember the voltage across c23 but u can set R37 so as the voltage at output of Q13 to be near to 9 ... 10V.

[Jeg]

You mean Q11. Thanks a lot George i will report back any progress. I am still waiting for bd645.

[Geo]

Yes ...Q11. I note that this is not the schematic of Protek 711. This schematic is about 90% same with original.
It is from Positron. As i remember.... Protek uses 555 for oscilator and smaler transistors as 2N2222.

[Jeg]

What is your experience on both devices? Can they sense a buried target?

By the way.. what do you suggest as for antennas length? I found two antennas 40 cm length each but they look like very short for that low MHz frequencies!!

[Jeg]

Ok i just tested the Tx board.

800Khz oscillator tuned to 1.6Mhz 40V pk=pk between antenna and ground. Not so bad.

10.14Volts the output of Q11

7.5V the max output of LM317 when input is a battery of 12V. But i think here the problem is that i used a 10K trimer instead of 5K.

2N4427 runs hot!!! It needs cooling

Tx board looks that is working normally without any modification. I used an air core coil at the output.

Regards

[Geo]

What is your experience on both devices? Can they sense a buried target?

By the way.. what do you suggest as for antennas length? I found two antennas 40 cm length each but they look like very short for that low MHz frequencies!!

With Protek i did n't find anything. With Positron i located big objcts from 10m and 20m distance.
Positron had helical antenna