Your speaker coils need the 20-30 minute warm up more than the tube amp or pre amp......According to Steve Deckert
Very interesting. Never heard of that before. And I am not saying this with any sarcasm.
Tube Preamps Should Have This Feature
So it's late or you just want some casual listening for a short time. "Should I fire up my tube pre for 30 minutes?". My answer is "No". Why not let me flip a switch (or push in the volume control) to put my pre into "bypass" mode? Bypass would, effectively, convert your pre into a passive device, keeping the tubes dark.
This sounds useful to me.