Bob,
With 71B-1122 yeast, I have been using 1/2 cup each time I start or do a secondary ferment. It seems to be working well...
Oskaar suggests chopping the raisins prior to adding. I just allow them to swell and then power stir the batch with my drill to aerate it, which also shreads the raisins.
Siobahn suggested to me that I use white raisins, in order not to inherit the "brownness" from the regular raisins in the final color of the meads. This also seems to be a good idea.
I started a batch of plain mead for my raspberry mead. It had water, honey, some citrus, the raisins, and the yeast. In tasting it before I racked it onto the fruit, I was really pleased with the taste and believe the raisins help. I am not an educated enough pallate to know whether it was tannins or something else that was making it good.
Welcome to Gotmead and good luck in your brewing.
Pewter