Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

Sine and square generator (CB21949E)
This circuit was found in a publication by Gernsback from 1960. The circuit generates signals from...
Wien Oscillator MOSFET Stabilized (CB12452E)
This oscillator has the output sine waveforms stabilized by a MOSFET. Equivalent types can be...
3-input Preamplifier and Monitor (CB16851E)
This circuit that uses components that are still very common on the market was obtained in a 1997...