Hello, Could someone confirm please if the L-7 PSU is an *exact* replacement for the L-4 PSU? I am particularly interested if the transformer is the same ? When running an L7 amp (with L-7 PSU) in the "SSB" position there's a *very* loud BUZZZZ from the transformer after about 20 minutes or so. Using an L-4 PSU it's fine. Thanks Steve