Ok here goes....put the bar in and drop the bridge...look at the back of the block...notice the small allen set screw behind where the bar is....BINGO. Tighten that bad boy and you're off to a tighter bar! Rock.
This picture from an earlier thread should also help, you will need to tighten screw A
A= Trem Bar Tension Adjustment (spin control)
B= Bar Spring Mounting Screw.
C= Bar Spring (this is what the notch in your trem bar hits to keep it in the trem)