This circuit is from a publication from the 60s. The circuit, with minor changes, can be assembled with current general-purpose transistors such as the BC548. The circuit has two inputs depending on the type of signal source used.

This circuit is from a publication from the 60s. The circuit, with minor changes, can be assembled with current general-purpose transistors such as the BC548. The circuit has two inputs depending on the type of signal source used.