Seventy years ago this month, the February 1956 issue of Popular Electronics showed how to make this little audio amplifier. The problem of finding a chassis to mount the circuit was solved by using an aluminum battery holder. They were readily available in various sizes, including one for four AA cells. The circuit, using the venerable CK722, used only three volts. Therefore, half the holder was available for mounting the other components, and there were four spare solder lugs that could be pressed into service.

The magazine noted that the circuit would come in handy for things such as amplifying the output of a crystal set.

To avoid favoritism (or maybe that’s just what they happened to have handy), the circuit is shown with one Ray-O-Vac and one Eveready cell.