Matching tubes

Unfortunately, I think it is best to have your power tubes matched within reason.  I'm sure the amp manufacturer or distributor would be happy to tell you for sure.  If you know what the 300B you have measures, maybe someone could sell you a match for it.

I would always buy a matched pair. Considering the future, most likely one going at a time, preferably a matched quad if money is easy (hah).. In either case, having your one good used one will give you the luxury of time in the future.

I assume you like the sound of your existing brand/version. Exact brand/version available so no surprises and spare is the same?

Want to try different brand/version? Buy from a source that will allow returns or exchanges. Different brands/versions do sound different. I am now exchanging some NOS Sylvania’s I bought and tried for some NOS GE’s I know I love the sound of. Brent Jesse lets you break them in, and exchange them if you want, others will also.

Break them in before you do critical listening. You can just turn/leave amp on, nothing playing. After 3 days, that is how they will sound.

Different brand? After breaking them in, as a test, I would put one new one in with your used good one. Balanced? Sound Great together? Have a method to listen to each side individually? Learning about the sound of each brand is good info.

I don't used matched power tubes.  My two power amps use 8 KT-88's each. When a tube goes, It's replaced.  I've been doing it that way for years. 

Thanks to all. I'm using electro harmonics gold 300b. 4 in each amp along with 2 6sn7's. I'll replace 1 300b for now get a matched quad of 6sn7's and an octet of matched 300b's for back up. I just wasn't sure if the preamp or amp was the most important to use matched tubes in. 

I think tube matching is most important relative to the age of the tubes...you don't want to stick new tubes next to ones possibly on their last legs, or maybe you just don't care like some sort of gonzo tube abuse maniac which, admittedly, I kinda support...thus concludes a self defeating post.