Dave.. Good luck..Yeah..Bias excursion (For guitar amps is) IMO rather small..But every bit helps right!..Running them a bit hotter still might shorten tube life as I have not had mine long enough to really give an honest answer and there is not much info on biasing class AB2..The spec sheets (on 6L's) show an increase in plate dissapation (50w per tube) but with a 100v screen drop (ultraliner operation)..It sure feels like it run @ 450..Someday I need to run power output on a quad of 6l's in AB2 to find out .. BUT.. I like the tone set hotter..David Root wrote:Thanx Tony! I will try that 70% of max Pd bias on the STRs. That will drag the idle cathode draw down a bit. I think I'm running about 34 mA/tube on it now which at 440Vp is only 50% of max Pd. If it sounds better I may have to change the PT out for a bit higher voltage.
I have Richard Kuehnel's books including that Power Amp book which goes into bias excursion in mind numbing detail! He sure is a GEB (Giant Earth Brain). I'll have to reread that chapter though, it's been a while.
If anyone else can contribute on the AB2 operation please jump in..Love to see some hard data!!
Keep us posted on your opinion huh!
T