PS Audio BHK lacking..

I bought a used PS Audio BHK preamp to replace my Rotel.  It sounds thin with no depth & bass compared to my Rotel so I let it run for over an hour with no change. I'm new to tubes so I'm looking for ideas. New tubes or what?
My BHK suddenly sounded horrible.  I reseated the tubes and all was right in the world.

I wonder if the tubes might be on the way out so ordered a variety of tubes yo tey out. Each really changed the sound but did settle on a pair that sounded much nicer than the original factory tubes.

My advice is to roll the existing tubes left to right , etc and then repower.