We found this circuit in a 1968 General Electric publication. The circuit uses an SCR of the time, but any modern equivalent can be used. The relay must have contacts that support the horn current.
In this circuit of a 1968 publication the unijunction may be 2N2646 and the transistor BC548. The...
The purpose of this circuit is to improve a trigger circuit using a zener diode. The circuit was...
This interesting circuit of the American publication Electronics Handbook Volume XIII 1993 shows a...