Hey-Hey!!!,
You can still saturate a core with AC. It is inversely propprtional to freq. Drop into the subsonic and start increasing the voltage, and you can damn well be sure, at some point you'll run out of core.AC flux is also proportional to turns count squared, and to core area. This is why you should be sure that the audio PS Iron is wound with enough turns on ots primary, other wise it will hum and buzz with no load. This is because the bloody core is satruating( it will get hot too soon enough ).
regards,
Douglas