Where for a tube-newb to start?

If your question is what is the characteristic sound of particular brand/year tubes in each of these tube categories, there's lot's of anecotal info on the web if you simply run a search using the tube type. I have 'rolled' various tubes in different equipment over the years, and it is an enjoyable aspect of the hobby that can make a noticeable difference in sound.
Recognize that for any given tube, it may yield different results depending on how it is used in the circuit; thus, one person may 'like' a particular tube in a piece of gear that, to you, in your gear, may sound too euphonic.
Also worth noting that unless you are really knowledgeable, there is much confusing info about the old tubes- apparently, different companies shared manufacturing facilties, so a tube legitimately branded under a well-known name and place of origin may have actually been made for them by another company in another country. It is worth dealing with a legitimate supplier- there are several- if you are going to delve into 'new old stock' since the price of some old, highly sought after tubes is considerable and the potential for fakery is there.

Read the descriptions of stuff that "thetubestore.com" sells. It's laid out reasonably (unlike a lot of other dealers) and clearly. Good stuff, and a nice company to buy from.

Quick, give it away to Goodwill. Otherwise you will acquire an 'addiction', which of course will leave you broke and deeply depressed. Their is no known cure, other then to go 'cold turkey' and give it away, and do it now. Sadly, others have not followed my advice and now they are looking for 12 step programs, but beware, those programs often meet in bricks and mortar audio stores and you hear all kinds of 'sweet' sounds that never cure you.

Think he was wanting to read up on tube amps and tubes, and read reviews on tubes he could roll in.

Thanks for all the replies!

@Zd542: I am not looking for an amp review. I have inherited the amp from my brother-in-law (RIP). I do not know what tubes may be in the amp at this point. He and I had similar musical preferences, and a tendency to tinker, so I suspect that 1) the tubes that are in the amp are not stock, and 2) I will like what’s in it when it arrives. At the very least, I will have to replace tubes as they go bad and was looking for advice on high-quality replacements, reliable tube vendors, and good sources of background information and in-depth tube comparisons.

@Rodman99999: Thanks for the links!

@Whart: I tend not to seek out the anecdotal, “you really need to listen to ______” (fill in any particular component), reviews. I’d be more interested in thorough, systematic reviews of a variety of tubes with ratings in a variety of categories. I don’t have sufficient background to know what those categories might be. I’m on a relatively steep learning curve at the moment.

@Wolf_garcia: Great link! I wish they had my M520 in the “Shop by Amp” section.

@Buconero117: LOL… Hi, my name is Brian and I’m an audio-holic.

@Bajaed: You said it much more succinctly than I did above.

Cheers... Brian