Tube Preamps Should Have This Feature

Passive mode is by far the worst  for an active gain stage ,you are using the power 

supplies and soundstage imaging and dynamics are better.

The $1k Schiit Freya + is very good for the money,

but not in the league  of  a Aesthetix , or Linear Tube Audio preamp  a truly good

preamp is much better built in every. Respect and is a fully  active gain stage preamp.  If you have to worry about the expense of  a quad of tubes then  just just save for a good solid state preamp and be done with it .Myselfonlyuse matched vintageNOS tubes  far better then todays Russian,and china tubes, and last much longer ,if bought from a reputable dealer.like Brent Jesse audio,who offers a 2 year 

warranty for little money, or vintage tube services.

Your speaker coils need the 20-30 minute warm up more than the tube amp or pre amp......According to Steve Deckert ( who knows something about sound)

My PrimaLuna amp won't allow me to switch between triode and ultra-linear until the tubes are sufficiently warmed, and my Vincent hybrid preamp has a flashing red LED in the volume knob that goes out when it's ready to play. If those time spans are good enough for the much more knowledgeable people who designed the equipment, I trust their judgement. 

Two issues come into play: 1. My preamp uses four 6H30 tubes (and two tubes which I assume are rectifiers). It’s very hard to acquire GOOD 6h30 tubes these days so, until Western Electric can clone 6H30-DR (Russian mil-spec and the best I’ve heard), I’ve got to conserve. 2. I worry about the thermal effects doing damage over time. I’m also retired and trying to live off only SS. I’m also Scottish who are known to be somewhat "thrifty" so that comes into play. It would just be nice to have the option to NOT burn tubes if I’m going to bed in 20 minutes but want to hear some tunes.

Life is too short. Flip on the tubes and enjoy your system.