This circuit from General Electric was found in a 1967 documentation. The SCR is of the time, as are the transistors, but equivalents can be used.
This amplifier has a few Watt output, using old transistors. The speaker is 45 ohms, but with...
This circuit is from an old American documentation, from 1977, but it can be implemented with more...
This circuit was obtained from the CA3140 datasheet. This component consists of an operational amplifier...