Hello Friend. I would tell you not to make that change because the d1555 has a damper and the bul312fp has no damper if you want to replace the d1555 you can put the d1556, the d2499, d1877, d1878 ,. d1650, d1651, tt2024, and if you want to replace the bul312fp you can put the 2sc6090ls, 2sd2689ls, tt2222, md1802fh, 2sc6092ls, bu1508ax, but12ax, but11apx-1200, buh515xl, bu4508az, but11ax. I hope this data served you. Cheers