@bimmerlover Do note:
Tubes in a Audio System are not a device one can Power On and forget about.
My Valve EE, has always encouraged the discipline for not leaving the Audio System unattended for long periods of time.
The Idea being one stays within the audio set up room for the bulk of the Power On time and even has a revisit not too long after Power Off.
Having said that I have a all Valve Power Amp's in the System for over 30 Years and today the system is inclusive of Valve Phon' and DAC.
I am vigilant when it comes to being present when the system is on. It is this same requirement that put my wife off using the audio system, even though she owns 50%+ of the Albums.