The blue SN7s are good tubes. I bought C grade tubes, which are fine for my application. At $99/tube, these are still pricey tubes. I had one go bad at about 6 months. It went microphonic an had 60 Hz hum issues. I would not leave these tubes on 24/7. Most of the ModWright stuff I have owned does not require a very long warm up time compared to other pieces in my system. When possible, I turn everything on about an hour before I plan to listen and that seems to do the trick.
