I'm trying a pair of 5881 power tubes in my Mission 32-20 harp amp, in place of 6L6 tubes. It seems punchier, more "forward," slightly more grunt. I'll try 'em for our show at The Toad Tavern Spring Blues Fest this Saturday, see how they sound in a big room. I predict major blues honk. Should be fun.
The 5881 tubes have slightly more grit and sparkle than the warmer 6L6 tubes. Punchy and loud.
UPDATE: At first I was dubious about these tubes. Now I'm thinkin' they are badass. I'll roll with them in the amp for a while...