Found in Electronics Now from the 1980s, this amplifier can also be seen in commercial amplifiers of the time. The integrated used is uncommon nowadays. The power is 33 W.
This filter that rejects determines frequency (notch) was found in a Popular Electronics of 1993....
Found in an Elektor from the 90's, this double door-bell drive circuit switches a relay by...
Using a 555 this circuit was found in old documentation, but it is still valid. | Clique na imagem...