Hi Zicos
you need to pick-up all transistors with same current gain h21e and balance gain to be same at input and output. This is sensitive symmetrical circuit. And you should shield the input and output particulary with metal boxes.
hyper big resisitor 100M-100G could be made easy with peace of ferrite core from small radio transformers and rf-chokes. simply find one core 1-2mm in diameter lenght 10-20mm and wound bare wire 0.2-0.3 several turns and solder all tightly. this would be one terminal of your resistor. same did at other side of core. Now you would have hyper big resistor for static detector. DCH85 box should be grounded and also earthed via your hand and body while searching for gold. Arm handle should made from metal not plastic also like a box. Other box variant is a very dry wood, Earthing derector via arm handle still worth for wooden box. Arm handle connect at virtual ground between batterirs - small triangle at sch. For 741 failures put 8 DIP socket and change 741 till find correct one. Good luck!
second variant
you need to pick-up all transistors with same current gain h21e and balance gain to be same at input and output. This is sensitive symmetrical circuit. And you should shield the input and output particulary with metal boxes.

hyper big resisitor 100M-100G could be made easy with peace of ferrite core from small radio transformers and rf-chokes. simply find one core 1-2mm in diameter lenght 10-20mm and wound bare wire 0.2-0.3 several turns and solder all tightly. this would be one terminal of your resistor. same did at other side of core. Now you would have hyper big resistor for static detector. DCH85 box should be grounded and also earthed via your hand and body while searching for gold. Arm handle should made from metal not plastic also like a box. Other box variant is a very dry wood, Earthing derector via arm handle still worth for wooden box. Arm handle connect at virtual ground between batterirs - small triangle at sch. For 741 failures put 8 DIP socket and change 741 till find correct one. Good luck!

second variant

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