Found in documentation from the 1980s, this circuit uses an operational amplifier from that time. Transistors are also from the era, and general-purpose equivalents can now be used.
This circuit was obtained in a Hobbyst Handbook from 1990. The circuit can be easily assembled...
This circuit is intended to recover a very weak signal at a receiver, for example, a CW signal or a...
We found this circuit in Sperimentare magazine number 4 of 1977. The magazine no longer exists, but...