This circuit is one of many of its kind that can be found on this site. This one is from a September 1987 Radio Electronics. The triac must be controlled according to the load.
In the figure we have the way to control the frequency of an oscillator with a NE602 using a...
We found this circuit in the April 2013 issue of Electronics Now. Any JFET can be used. Note the...
This circuit, which we find in a documentation from the 70s, filters out the Ru [occurring in...