Here are the transformations from this season:
Tv [B-V] = -0.011 +/- 0.005
Tbv = 1.005 +/- 0.015
Tub = 1.179 +/- 0.035
(U-B) is nonlinear, but these values should be ok for AZ Cas.
Arne
Links:
[1] http://www.aavso.org/forums/variable-star-observing/aavsonet