in case you missed the technical descriptions of this AV-200, i will run them again...
there are 4 tubes on the chassis, 2 x 5Z4 rectifiers and 2 x 6N2 twin triodes..
the 2 5z4's are rectifiers that supply rail voltages for a rc4558 input buffer ic...
the output of these rectifiers are zener regulated at 6 volts...
the ic drives a tone control circuit with another rc4558 in active configuration,
this other ic however is fed rails off the power amp board via lm 7812/7912 regulators..
the 6n2 tubes are also fed off the regulated +-12 volt rails, configured as a cathode follower,
as we all know, cathode followers are 100% negative feedback circuit with voltage gains around 0.9
this and the use of tone control necessitates use of the rc4558 integrated chips..
cathode followers are not supposed to "color" the sound...
but the fact that very low voltages were used on a tube that needs significantly highish
voltages in order to be in the linear region, then this coloration happens...
the av200 represents a break with all tube design traditions that only the chinese can do...
incidentally, just about any type of b9 tubes ca be tried, i used the russian 6n23 in mine...
btw, Chino's sakura av-400 is much better than the av-200 in terms of power, owners of these units are advised to hold on to them...