In the original publication of the 90s a 556 consisting of a double 555 is suggested. The circuit drives a speaker with good power. The power transistor shall be fitted with a heat sink.
This PWM control circuit was found in an old documentation, but appears elsewhere on this site...
a We find this circuit which has a traditional configuration in a 1988 publication. The circuit is...
Indicated for applications with a PC, this circuit was obtained in an English publication in 1992....