Please do not consider me pedantic, but I think that such thing as the "6h30 sound" does not exist.
I owned Audio Research REF2 mk2 , REF3 , conrad johnson ACT2 and ACT2 series 2 (all using the 6h30 exclusively in the amplifying stages) and could not find a common trait between these four preamplifiers. A friend of mine owns a BAT phono unit and it does not sound as a cj or an ARC!
Circuit topology, operating points, power supply and choice of passives have great importance in sound balance. I think that the main reason why many manufacturers are using the 6h30 is because it is reliable and lasts long - I recently measured the 6h30s of my REF3 that have 4093 and they still measure as new!