to retube or not

anyone tried replacing X-10D jan philips tubes with NOS? are improvements worth it? if yes, what brand of 6922/e88cc would you suggest? thanx a lot....
In what equipment are these tubes going into?
i replaced with siemens and liked the change. go with what tubes you prefer in other units. (in my case i liked the siemens in the pre i had at the time. its a tight squeeze replacing but can be accomplished with patience. kurt
thanx david_berry and rcreations. to david, the tubes to be replaced are the musical fidelity X-10d tubes, which they say are not that good being jan philips 6922s. i use the x10-d between by rotel 951 and receiver. i posted this thread to know if anyone had any experience replacing the tubes, and getting the sonic improvements. hope this clears up matters. thanks......
Are you using the supplied factory power adapter? If so, I'd suggest changing to a 12 vac @ 4.5 amp adapter (part # 56-821) from for $7.95! After removing the factory power supply and using the hosfelt power supply in its place, I was impressed with a much fuller sound, more dynamics, and a cleaner sound. Another tweak you might want to consider would be Herbie's tube dampeners for your tubes.
thanx bradz...actually, i'm using the x-10D with a MF x-psu power supply.