I've had tube preamps for years and have left many of them on 24/7 & changing out the tubes every 2 years, however the CD9 did concern me with the 6550 tube so I will be checking on it daily. I chose 3 weeks as this is very close to 500 hours, 504 to be exact. I hope it gets the job done, did the 6 week time frame come from someone you know VT?