[Transformer adventures]

Your description sounds like a 3-phase auto-transformer.
Try 110v across two of the primary inputs (smaller wire
in the windings).  Use a ballast bulb like you have been.
IF that works out OK, the try 110v across one input and
the center-tap.  This should give the correct voltage on
the secondaries, assuming a 230v 3-phase winding on
the input.
It seems doubtful that it would be a welder transformer,
since there would be no isolation on the output.
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