This LM380-based circuit was found in documentation from the 1980s. The components are current, and the transistor may be a general-purpose equivalent. Note the use of a medium impedance speaker.
This circuit was found in Radio Electronics magazine from April 1961. The device has a slot for...
This 1967 Electronics World circuit is suitable for frequencies up to 1 MHz. The setting applies...
Found in a 1968 Motorola manual, this DC circuit uses components from the era. The circuit fires in...