This circuit is from Motorola's Linear Databook from 1990. The integrated circuit and transistors are uncommon, but the circuit can be assembled with equivalents.
This circuit, from the 70's, can be assembled with a more modern FET like the BF245. The circuit is...
We found this telephone amplifier in a European publication from the 1980s. The transistor can be...
This is the factory setting (National Semiconductor) of the TDA2006 as an audio amplifier. The...