Found in the February 1983 Radio Electronics magazine, this circuit uses a FET and has good gain at the frequencies determined by the components. The FET is any general-purpose FET.
This circuit is from old European documentation. R1 depends on the output voltage of the...
This SCR circuit activates a buzzer when triggered. The circuit is from a Popular Electronics from...
This 130 V drive uses an integrated circuit not very easy to find, which is the LM143. The circuit is...