One man's experience: The 2A3's sound much more musical than the 300's, more natural mid's that are absolutely lifelike, and airy highs. The bass is suprisingly good, at first blush not as deep and full as a 300, but after listening, actually as deep and full, just tighter and more defined. The 2A3 sounds more articulate than the 300, to me, like a thin veil or film has been lifted from the sound. Clean. Different tubes sound different, I like the RCA NOS 2A3's, but the KR Enterprise 2A3's are just phenomenal, especially bass. These tubes put out less power than the 300's, and are obviously therefore more speaker dependent, but with the right speaker, the 3-5 watts from a 2A3 will suprise even the harshest critic. Another thing to consider, the tubes aren't alone in the amp circuit, and different 2A3 based amps sound VERY different. I have a pair very simply designed Don Garber Fi 2A3 monoblocks, and when I swapped out the stock OPT's for Tamura OPT's, the sonics went through the roof. Cliff notes version: to me the 2A3 is just more musical, delicate and detailed. Thanx to the above posters, I always learn something from this site. Mark