Tube Preamps Should Have This Feature

Having a hard time seeing the use case here. Tubes are designed to get up to optimal temperature very quickly - that’s what the "heater" is for. Transistors can be a very different (and frustrating) story on this front, plus they overheat easily and behave VERY poorly in those conditions. A couple minutes in, and your tubes are good to go.

If you’re entering a several-hours stretch where you want to do several short sessions, just leave it on for that stretch. Or turn it on/off a few times. The tubes will be fine.

If you tally a lot of hours a year and don’t want to pile that onto rare NOS tubes, then the Russian tubes these days are quite excellent.

The Rogue Apollos had a "standby" switch which cut down the high voltage rails while leaving heaters on, but that was specifically for the power tubes (not pre tubes) and even then I hardly ever felt a need to use it.

I start listening right away, and the amp and linestage sound very good within a few minutes; I don't fret over whether the sound is at any sort of absolute peak.  But, I do know someone who complained about the sound of his amps and how long they took to warm up.  The dealer/builder of these custom amps could not figure out why they were failing to please the customer until he heard the amps in the customer's home, under the owner's listening conditions.  It turned out that the owner only listened for short periods and would turn the amps on and immediately start to listen, while the dealer/builder kept the amps on all day.  The issue wasn't tube warmup, it was the capacitors used in the amps.  The amps had Blackgate capacitors, and when they were swapped out for other capacitors, the warm up became MUCH shorter.  It turned out that Blackgates take a very long time to warm up and stabilize.

I have the same sort of issue with my music server which is a solid state unit.  The manufacturer recommends leaving it on all of the time and claims it does not sound its best until about 24 hours after being turned off for a few hours.  This has to do with the capacitors in the power supply of the unit.  

Hmm I might strongly consider another tube preamp that allows me to bypass those sometimes PITA tubes. Good to know. 

mulveling, I thought tubes didn't like on/off cycles. 

I wait for 30-45 minutes after turn on. Do I hear a difference ? YES !  First ten minutes is no go, after that you can go but better wait a little longer. Tubes or capacitors or both, it's exactly as VAC recommends.

Yeah, reissue tubes if you must save.

mulveling, I thought tubes didn’t like on/off cycles.

@inna Maybe, if you turn gear on/off a dozen times every day. Who does that? Or if your component slams full voltage on plates immediately, before heaters have a chance to bring cathodes to temp - but again, who does that? Most hifi gear has some kind of soft-start consideration.

Most small tubes are pretty robust and will outlive our interest in them :) A few duds will emerge, that’s just the way of these things. We audiophiles generally over-worry about tube life & care, IMO. I’ve stopped worrying about it so much, and just turn a tube component on when I want to use it. I have not noticed significant changes in warmup with tube gear (unless it’s a hybrid with transistors in there), but don’t discount maybe some cap or resistor might prefer to be toasty. But I think generally you want to minimize heat on those components - especially electrolytic caps (like 10-years OOP BlackGates)!

For all the concern over tube life, the great thing is you can always replace them! A high end amp using OOP transistors might be SOL unless your manufacturer stocked up well (and is still around to service). Transistors are far from immortal, and in fact they can be a LOT more sensitive than tubes to over voltage and overheating conditions.