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.
Found in documentation from Analog Devices from the 90s, this amplifier uses a component from the...
This charger was found in an 80's Electronic Design. The circuit uses components from that time....
This double tone generator uses a specific integrated circuit, having been found in a 1977 CMOS...