Do I have tired tubes?

System has been up and running since the first week in August. The Line 1 is in standby when not in use and the tubes have some plate voltage across them to keep them warm. Everything else in the system is solid state and not likely the culprit. I have Virtual Dynamics Audition cable package throughout with biwired Paradigm Studio 100v2. Nothing in the room has been moved furniture wise. I am considering having the preamp modded by parts conneXion next year or the one after as budget allows. Have a few more pressing needs at the moment like a stand and a power conditioner. Any tube recommendations for this preamp? I don't want any rolled off highs and want firm bass with excellent mids. Thanks.

Alex, I pulled and reseated cable ends - didn't have any cleaner or Pro-Gold although that is coming. The VD cables are coated at the factory with some kind of protectant so that may not be the problem.

Jwaugh, yes the sound does seem symmetrical. One thing I haven't considered is tube creep. It could be that the tubes creeped out of their sockets a hair when they were powered off. This sort of thing is common in socketed ICs in computers - chip creep. Caused by thermal expansion/ contraction. Phase and connections are all good. I can invert phase from my remote on the Line 1, very handy on some CD's.

Power in my area is generally very good possibly the best on the continent. I don't even remember the last time I had a power outage. I am going to use a hospital grade outlet soon - that should help somewhat. I live in an apartment and the sound is always better in the late evening but that isn't a hard and fast rule. The block was built in 1960 just like me. I am considering getting one of the Monster power conditioners for the meantime - somewhere between a HTS2000 and HTS3500. Just out of curiosity does anyone know the difference between Monster's HTS and PB line of power conditioners?

Are gold pinned tubes necessarily better than non plated ones all else being equal?