Leaving tube amps on.

@pindac , well, the amp had been in service for many years and caps do occasionally fail, and I think that this failure was due to a mistake I made when I was doing something with the amp.

But, my point was: that if the amp was fully powered on and idling and that cap would have failed and no one was anywhere around, the bias would have climbed and continued to climb until I do not know what then happens. I did have an output tube fail catastrophically a long long time ago (I assume it was an internal short in the tube) and it blew the tube fuse on that side, but I still wouldn’t (on purpose) leave my amp on & unattended for an extended period of time.

Does turning the amps on / off throughout the day / night do more harm than leaving them on ?

in my view, no

You will pi$$ thru tubes leaving it on all the time. Tubes, especially NOS are not cheap. Shut it down when not in use.

Where do most of the world’s KT-150 tubes come from? And where did all the semi-reasonably priced (if compared to alternative) KT-150 tubes come from?

One large altercation later and those tubes aren’t being imported anymore. 
With Russia doing its thing and China redirecting much of its attention to newer tech development / fabrication, the world supply of current production power tubes is quite a bit lower than it was a few years ago.

KT-150 now = NOS unless perhaps you’re buying the costly version produced outside Russia.

I’ve zero interest in anyone making this political - please do not.

But so many of the power tubes that are unhealthy to manufacture come from two nations that are not up to makin’ em like they used to; that probably shouldn’t be something out-of-sight/out-of-mind for the audiophile who likes using tubes. Turn power tubes off when not in use. 

I have a Raven Audio Osprey with NOS tubes and have asked myself this same question many times. The simple solution that I've come to is: if I'm running the amp, I leave it on for at least 1 hour. This is easy to accomplish because most albums are around 45 mins and the amp really needs 15-20 mins of warm up before it's sounding its best. So, 15 mins before I'm ready to put on a record, I turn everything on and let the circuits settle-in. Then, whether I'm there for 1 record or 10, I haven't short cycled the amp. 

Good Luck!