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 electronic switch published in the July 1970 Radio Electronics magazine allows the...
This control of DC motors for currents up to about 200 mA was obtained in an American publication of...
This circuit is based on an operational amplifier that is uncommon today, but that can reach the...