How expensive are best NOS tubes ? And how difficult to find ?

I just want to add a vote for NOS or lightly used tubes, but I can see that the benefits might not be worth the trouble and expense for many people. 

The plates are the black or gray (usually gray) rectangular or square objects that take up most of the space in the tube. Long plates are usually found in older tubes, early (1950s) versions of tubes like the 12AU7. They may sound different from the later short plate or box plate or square plate (three different names for the same type of plate) versions of the tube but any 12AU7 socket that can use a long plate should also be able to use a short plate.

Tell us what brand of preamp you have and we may be able to help you get the right tubes in it.

Welcome to the world of tubes.  The Rogue should be a nice sounding integrated.  I know we have some Rogue fans here.

Tube rolling is just trying different tube brands in your amp to tune the sound to your liking.  There are also variations on the 12AU7 like the 5814 and many others that work where a 12AU7 is called for.   So there are a lot of tubes that you can roll into your amp, but it's not a cheap form of entertainment.  The Rogue has 2 12AU7s from what I can tell and any 12AU7 should be able to work in your amp.  What brand of tubes did it come with? 

Why don't you start a new thread asking Rogue owners what tube brands they found to work well  in their amps.  They can probably give you a better educated opinion than I can.

gillatgh, Unless you plan to become a tube fanatic, when you do start to roll tubes buy them from a reputable dealer rather than off ebay.  There are good tubes available there and they are probably cheaper but you need to know what you're looking for and have a tube tester to make sure they are as advertised.

Good tube dealers will talk to you about what sort of sound you would like to get with your new tubes and offer educated opinions on what  might work for you.  Some good dealers are:

Brent Jessee - he has a lot of information about tubes on his web site if you would like to study up a little.

Andy Bouwman at Vintage Tube Services - He can be a little slow getting your tubes to you but many people feel he's the best.

Kevin Deal at Upscale Audio - very knowledgeable and very straightforward with his advice.  He knows what he likes.  Some people don't like that but I enjoy talking with him.

There are others that other people will recommend.  That's just 3 to get you started.