You do not need to use all the same brand and there are certain positions that will affect the sound more than others. The 7308s and also CCas are generally, but not universally, considered to be the best of the the 6DJ8/6922/E88CC/ECC88 family of tubes. Google Joe's tube lore to get info on the sonic differences btwn diff brands and members of the family. And also be aware that BAT products are not GENERALLY considered to be as susceptible to dramatic changes due to tube rolling. Also be careful of counterfeit and dramatically over-rated (meaning sold as NOS but barely functional) tubes on (Fl)ebay!! You should consider a tube tester and get return rights on tubes. A legit seller will provide that. Also talk to members Kalidekol and Jsautter for tube sales and good advice.
Tube handling/designations
I recently purchased a BAT VK-30.It came with 6922 Teslas installed as well as the original Sovteks.I would like to try some different tubes to see how they affect the sound.My first question is do you need to wear gloves so as not to get oil off your hands on the tubes like halide lights?My next question is are 6922's the only tube that will work or are there others?I ask this because in some ads for tubes I see a slash followed by EE????.Also,what does NOS mean and why are they supposed to be better?