Need tube 101 info

Ok I'm new to this tube preamp world and I'd like to know a few things. I've acquired a BAT Vk-3ix that needs new tubes but I'm not sure I understand what tubes do what and how to properly "roll" them. I don't want "bright" tubes but I'm completely at a loss as to which brands I should be looking at.

Also what do the two tall inboard tubes do, and what do the small pairs to the left and right do?

When you get a matched pair of the small tubes does one go on the left and one go on the right?

Can you mix brands on the left and right. For example can you have brand x and y on the left and x and y on the right? Will that hurt anything? Or should all be the same brand?

I know these may be simple questions but I gotta start somewhere I suppose.
Hi Last Lemming.

I would also recommend familiarizing your self with which tubes do what. In a tube amp, certain parts of the tube layout will alter the sound of the amp more than others.

That is one of my questions in my original post. I would like to know what and why on my specific piece.
Last_lemming...with regards to your last question, I would recommend calling BAT's customer service/technical support folks to walk you through what the difeerent tubes do and if they have recommendations on which sets impact the sound more than others. Also ask them if they have recommendations for certain NOS tubes in each of the slots. You will likely get an explanation of the first question for sure (what the tubes in different slots do and which to tube roll first for bigger impact on sound) and less likely to get specific recommendations on what NOS tubes to try out (although you never know).

The other respected source you will find often talked about on Agon when it comes to tube rolling (although somewhat controversial) is Upscale Audio. They carry BAT and the owner will have strong opinions about what tubes to roll. He sells NOS and current production tubes and he may be another good source to talk to. Good luck.
I have been following your story about this new BAT preamp in your other threads, as well, with interest. Here's what I know for sure. BAT preamps, tube or solid state, don't make noise. I have nothing to do with the company and don't currently own any BAT equipment but I know your problem is not normal. I know people that have used BAT amps and preamps with ultra efficient speakers, like horn designs, and they are dead quiet even under the most demanding applications.

In my opinion, this is the safest and easiest way to get to the bottom of what your problem is. 1. Call BAT. I'm pretty sure that you have some tube issues. Given your explanations in the other threads, I'm not 100% convinced, though. I would explain the problem to BAT and see what they say. You have nothing to lose and BAT is very concerned about quality issues. 2. If you do need tubes, try to go about it with 0 risk. I recommend The Cable Company. Yes, they are known for cables, but they sell a huge amount of tubes, as well. They are also known for their lending program. They lend me all kinds of stuff other than cables to try before I make a purchase. I am fairly certain that they will lend tubes as well, but you will need to ask them. 3. I know in the other thread, I said you made a good purchase. I stand by it. You probably just need a new set of tubes. Don't make a nightmare out of this for yourself. Get the preamp working, listen to some music and don't 2nd guess every little thing. You'll see what I mean once you get the preamp working.
Get a hold of Jim Mcshane and ask about the current New Sensor Gold Lion series of 6922, and 6V6 tubes, which I believe your preamp uses.