Found in an 1868 Mullard documentation this circuit has a dynamic range of 10 Hz to 25,000 Hz. Modern equivalent transistors can be used.
This TTL decoder circuit for PC ports was found in a document from 1992. The power supply can be...
This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even...
The basis of this circuit is a CA3130 operational amplifier. The transistor can be BC548, and the...