Jamie

What you're referring to is a 12VCT transformer. Connecting either a
bridge and not using a center tap or just two diodes across the full
secondary with cathodes tied together using CT as common connected to
an output filter will yield 18VDC. A 24 V transformer under the same
circumstances will produce 36VDC. I've tried it and it does. Lenny.

That's not true, I'm afraid. Using the CT as common, and having a diode on
each 'hot' limb of the winding will produce half the voltage of hanging a
bridge across the same two limbs, and *not* using the centre tap. If you do
the same, but continue to use the CT as 'common', then you will get +18v at
the "+" terminal of the bridge, and -18v at the "-" terminal ...

Arfa