sounds like a "B" w/ the detachable cord, which is the newer version with he "gainier" R2 channel.
btw, I used to have a 5150 2x12 60 watter, seemed it liked any power tubes, it didn't care much, it was gonna just produce gobs and gobs of gain no matter what!! I actually ran it in tandem with my Mark IV for awhile, but then I went to the Nomad 45 which I love even more now. My God what a cool little amp that EL84 Nomad is, now I see what all the gushing is over these lil EL84 monsters!! Well, that's another post though isn't it :?:
anyway, i have run the JJ's tubes in the Mark with success, and I have also had the Electro Harmonics 6L6 & EL34's in combination and they did a fine job. At that time, I also used the 12AX7EH preamp tubes and they were very "gainy" you might like them, you might find them a tad noisy though, all depends whether hat is an issue, and unless your recording it may not be a big deal.
I also used the Tungsol tubes, which i think i mentioned already, but they are a good choice if you are going for gain.
In terms of gain, either Bob at Eurotubes, or one of the dudes at Groove Tubes SAG group (I have dealt with Myles in the past) can hook you up with specifically matched preamp tubes and can hand select whatever you need, say for your driver tube, etc.
Well, i am only one person, there are tons of opinions on tubes, I have only tried a handful, so ask around as there is a lot to learn i admit. I have heard some Mesa guys like the recommendation they get from "Dougs Tubes" as well. He sells a combination of different tubes he recommends to use together. just go to www.dougstubes.com and check it out or give them a call. I have not tried his combination, but I plan to next go round.
Ultimately, you will find what sounds good to your ears, and if you are happy with your sound and enjoying it, then others will too....
May the tone be with you!
peace,
Force