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 two-door doorbell was found in a 1990s US publication. The circuit is still current as...
Suggested by Intersil in documentation from the 90's, this circuit is valid for modern operating...
We found this circuit in an old RF documentation. The circuit must employ RF transistors and the...