This circuit is from a factory manual from the 80s. The circuit can be implemented with modern operationals. The supply must be symmetrical, and the diode is general-purpose.
This 4-transistor amplifier can work from 4.5 or 6 V power supplies. We found it in a Mullard...
We found this conventional astable circuit in Ferranti's 1974 transistor manual. Transistors are...
We found this circuit in an old documentation for radio amateurs. The circuit uses an analog...