Found in an Electronic Design from the 90's, this circuit uses an SCR according to the controlled power. The circuit is for 12V heating elements.
The frequency of this astable depends on the capacitor that can be changed over a wide range of...
This circuit is from a documentation from the 90s. The transistor can be any general-purpose FET...
In the figure we have one of the many options found in this section for an intercom using ordinary...