I recived my Chinook in march of this year .After two days of use It became defective and was a REAL problem . Manley handled the issue and replaced with a new unit . Now that I've run the Chinook for four months,Its Great . The stock tubes are very good ,I would not roll them for 2-3 months until unit is broken in. It does take time to break them in and you may find these stock tubes perfect. I just put in 4 NOS Amperex Gold pin 7308 that came from Upscale Audio . Maybe Its just me , it gets better ever day, these will be the only tubes I use !