Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the frequency of the emitted sound is determined by R1 / C1.
We found this circuit in a publication for radio amateurs in 1974. The bipolar transistors can be...
Found in a 1980s American documentation, this circuit has a current consumption of only 1 mA. The...
This adjustable power supply was found in Ferranti's transistor manual from 1974. Power...