Lawrence,

You probably have looked at this and rejected it for some reason... or
maybe you haven't.

You mentioned that you are essentially going from full wave to half wave
rectification for power control purposes. This can be done by using 2
diodes in the full wave bridge and 2 SCR's for the other two.  Gate 'em on,
full power. Remove gate drive, half power. No relay.

Tom M.

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