Questions from a Tube Preamp newbie

@stereo5  Good to hear that the NOS Mullards are working for you.  I sourced NOS Mullards from Upscale several years ago, and they sounded good but they just didn't last very long in my circuit.  No catastrophic  failures, just the tubes got very noisy.

1) Some pre-amps are 'hard on tubes' - usually the manufacturers will acknowledge this and will recommend using only very rugged tubes (Audible Illusions and Audio Research come to mind. ) Under normal conditions with most tubed pre-amps you should be able to get at least 3000 hours. (You can do a search on line to find out Rogue's reputation on this unit, or call Rogue for the real skinny.) Some a lot more! 10,000 hours is not unheard of.

2) For small tubes 24 hours will reveal their sonic signature. Change thereafter will be nominal until old age sets in.

3) Small tubes in both pre-amps and power amps are influential on the output, the pre-amp perhaps more so because it output is dependent on one tube type, but with a power amp its sound is based on a matching between the power tubes and the small tubes which gives a lot more flexibility in the sound of its output, i.e. you can fine tune it more easily. 

4) JJ tubes can be fine if you like their sound and they are low noise. I have used them often without problems. I usually change them out only to change tone. Good life expectancy and they are cheap(!) so you can have a few spares around should you need them. Since you already have them just enjoy and wait for the time you want to explore sound changes using different tubes.

JJ tubes are a fine budget tube (~$15/tube).

I once had a preamp that used 12AU7 tubes that came with JJ’s. I found the sound to be pretty uninspiring so I changed them to Psvane 12AU7-TII.

At US$50 each, they were a significant step up sonically from the JJ’s.

Here's a review of them on AudioAsylum.

What are the sound signatures of the Gold Lions vs the stock JJ's? The NOS Mullards are pricey plus, I hear they do not last as long