What would you change?

If you haven't already done it try putting your gear on a dedicated AC circuit - 20 amp breaker, dedicated wiring to a hospital grade outlet and proper grounding. Removing all non-audio loads from the line cleans up the incoming AC and you will be amazed at what that simple upgrade does to improve sound quality. If you're in a condo or can't run the circuit you may want to try one of PS Audio's Power Stations. I highly recommend the P-500.

As mentioned, a dedicated line and some power conditioning should help. A balanced power piece or a sine wave generator, like from Exact Power. Also, I would consider changing all of the wires and power cables, before replacing any equipment. Might be just the tune up you need.
Sonny

Clean all connections.

As stated earlier, check your tubes.
I've a LS-15 and put in some Ediswan tubes. Real smooth.

Try cleaning all connections. The difference it can make is like investing in the multi-buck wires that most of us object to. Also the wires can develop an electrical field that may degrade your sound. Try wiping with some cleaning product like Pledge lemon or other appropriate electrical wire cleaning agent available at the electronic supply house.

Thanks for the suggestions. I'll try a good cleaning of all connections, and the tube sockets. Time for the ProGold treatment!and the Nordost.
I've got a dedicated 20 circuit, actually two of them ,but power conditioning might help. I'm in an rural area and have no interferance from condo-type problems, or neighboring buildings, but other than that I may still have power probs and not know it.First a good cleaning. Thanks for all the helpful advice.
Carl