The sensors in this circuit that triggers when the temperature goes out of a certain range are common diodes. The circuit is from the 1991 Reista Electronics Experimenter's Handbook.
This high impedance and low capacitance buffer employs a junction FET that can be BF245 or...
This circuit was found in an American documentation from 1966. The transistors are from that time...
This circuit for the 85 to 95 MHz band has a gain of 15 dB. We find it in a 1980s documentation. The...