This power control from a 1968 Motorola manual shows how to use a contemporary diac as a zero-crossing detector. The SCR is of the type depending on the power of the load.
This is a combined circuit of tone generator and preamplifier. We found it in a 1975...
We found this simple alarm circuit in a 1986 documentation. The circuit uses sensors of the NA...
We found this circuit in the Linear Applications Handbook by National Semiconductor. The base is...