We found this circuit in a Radio Electronics from October 1963. The circuit uses an output transformer with a center tap. The trimpot is adjusted for higher gain and lower quiescent current.
This sophisticated repellent uses a double 555. We find it in an American documentation from the...
This circuit was found in a publication by Gernsback. It uses two batteries and in addition to the...
Found in Popular Electronics from the 1980s, this circuit uses two operational amplifiers from...