Thyristor as a traic
I have seen those &amp;&amp;&amp;$ diagrams in texts too, many years ago. You cannot make a triac by connecting two SCRs like that- think about it- how is the "top" one triggered? It's not an equivalent to the triac structure at all, unless the gates are ignored. See the gate structure below: 



In your circuit, the gates will break down with reverse voltage (maybe -10V) then the opposite SCR turns on. 

You can connect an opto-triac between the two gates (and diodes across each gate to cathode to conduct when reverse gate voltage is applied) and turn them on like that, or use a triple coil pulse transformer (two secondaries) to trigger both gates at once. 







simulate this circuit &ndash; Schematic created using CircuitLab