We found this circuit in an old Mullard (Philips) documentation on the 555 and 556 integrated circuit (double 555). The relay must be 12 V with contacts that support the horn current.
This circuit uses an optical coupler called Raystor created by Raytheon in the 1960s. The circuit...
This filter, found in an old manual, has characteristics of reduced overvoltage given by the graph...
The purpose of this circuit is to provide a few watts of power to a heavy speaker with good sound...