Stanley Meyer Shows  in 8xa 9xb versions a Scr here is a board with opto trigger to switch in variac or alternator voltage dc

Stanley Meyer SCR Gerber
https://oshpark.com/shared_projects/qZQfIT9V



Most will want to  Use Transistor Daughter board also in development on forum

Dan

 
scr part list
KBU808G bridged rectifier
100 ohm resistor (20 watt or so)
S4025L (or simular use a heat sink and make sure the pin out matches)
1N4007 diode
6 Amp 1000 volt diode
H11D2 and 220 resistor( not needed if using the 9xa or the 9xb)

A Better Bom made to help speed it up for ya