In order to hit 600watts you would be looking at about a half dozen 6L6 tubes.
Rick
If you're talking about RMS watts, it's more like 20 to 24. All the data I've ever seen on 6L6 types are that most of them are 25 watts, with a few types being 30 watts. My Mesa Bass 400+ is 300 watts RMS with 12 5881 or 6L6GC.
OTOH I really don't know more about it than what I've read.