New Tube Break-In

Advice from Upscale Audio:
"First time start-up and flashing lights - If your gear has filaments that are constant on, first install the tubes, plug it in according to manufacturers instructions, and let it sit for a few hours. I know you want to hear it right away but if there has been a small amount of gas that has developed since the tube was tested, it’s best to let it burn off before turning the tube all the way on."

Of course most gear does not have filaments that are constant-on (same as "standby"). Many new tubes will "flash" when first powered up, and still go on to have a long and useful life.

Almost all tubes break-in without an input signal just only idling for a few hours. It might be some changes audiable within first 60sec of listening after a few hours idling.

Just a note to clarify that running a tube without a signal present is not the same thing as a standby mode. The full bias amount is still applied to the tube, not just the heater warm up.

I have 2 Radiotechnique 12AU7's in my Rogue 99 phonostage.
I found them bright with annoying sibilents (sic?) for many hours.Maybe even up to 100 hours.They have since mellowed very well.I find them to be very revealing (in my system at least)