We found this circuit in a 1971 documentation. The circuit can be assembled with more modern transistors such as BC548 for Q1, BC558 for Q2 and BD135 for Q3.
Indicated to be used at the sensor input of a PC, this circuit was found in an English...
This circuit monitors extra-low frequency (ELF) fields. We found it in an American documentation from the...
With this circuit we can use a high impedance source to excite a low impedance output. The input is...