This step of two transistors has a high input impedance due to the use of FET. We can use BF245 for this function and the bipolar can be BC548. The circuit is from an 1975 American documentation.
This circuit was found in the September 1974 issue of Radio Electronics magazine. The circuit uses...
This circuit was found in the December 1983 issue of Radio Electronics magazine. The sensor is an...
We found this circuit in a 1975 publication. The circuit can be made with more modern equivalent...