Hello Nick, All 
Original Poster: NickandSim-at-aol-dot-com 
 To All,
           an scr cannot be turned off once it is turned on.  The only way to
 turn it of is to cut the current flow through it"

This is not quite correct. The current DOES NOT need to be turned off. It
simply must go below the "holding" threshold level of the SCR. If I remember
it correctly, you can even "up" this threshold level by applying a negative
pulse to the gate.

Coiler greets from germany,