This amplifier with gain control was obtained in a documentation from Signetics of the 80's. Transistors are of power and operational amplifiers are not common nowadays.
The MC15555 of this circuit is the old version of the common 555. What this circuit does is...
We find this circuit in an American 1980s documentation. The circuit can still be assembled...
This circuit triggers an LM380 oscillator, producing an audio tone with light falling on the LDR....