blown rectifier bridge question

Help! I am assembling my control box and have installed and wired the
fans and the toroid primary. I gently secured the rectifier bridge
(from mouser, 25 amp 600v) I wired the 55vac to the a/c side of the
rectifier and was going to read the d/c voltage at the d/c terminals
before hooking anything up (capacitor, etc..) instand loud hum and
shorted rectifier bridge! measured resistance across a/c terminals of
rectifier after this and it is shorted (0.2 ohms). Figured bad bridge,
installed 2nd bridge (this time testing resistance prior to hooking
up, and instant short again. It isn't the secondary of the trans as
that tests fine and there is no short if I plug in the primary from
the trans and leave the secondary not connected to anything- good a/c
output and no short. I am wondering if the capacitor MUST be installed
before hooking up power?

Help!

Bill H