Whats the deal with Preamp tubes?

[bmwm3cs]

I usually end up getting my my power tubes changed every 6 months. I have not ever changed my preamp tubes. How often should I be changing them? Are they like power tubes in the sense that over time they will cause your tone to diminish? Or will they last indefinatley? Also, what types of preamp tubes come factroy with the VH4?

Thanks Guys,
Jason

 

[Ampaddict]

If you like the tone leave 'em in.They should last a L O N G time. You might notice a prob sometime which than you could replace it or them.