Quote:
Originally Posted by Rob N
I’ve been using 4x 6BX7GT’s as output with 2x 6SN7 as input on my SDS-XLR for a while now.I really like the sound.I have noticed that with 6BL7GT’s,6BX7GT’s or 5687’s as output the sound is noticeably warmer that with all 6sn7’s.Has anyone else noticed this? Does running the 6BX7GT’s at higher voltages/currents give a more neutral sound (ie less warm)?
|
When I ran the 6bl7gt's and 6bx7gt's at 300 volts with the 6sn7 bias setting, single ended, I noticed more soundstage size, slightly better overall dynamics and the tubes definitely drove low impedence headphones better. But the 6bx7gt, in particular, has never sounded warm to me at 300 or 400 volts .... while the 6bl7gt is a warmer sounding tube in general. The 6bl7gta sounded horrible at 300 volts with the 6sn7 bias setting .... dark, muddy, slow and with a weird non-linearity that distorted vocalists perspective in the soundstage; along with added harshness in the midrange and upper midrange.
Moving to 400 volts/ high bias the 6bx7gt became airier, faster, more extended and much more dynamic; but the general character, or lack of character/ neutrality remained. I found the same improvements for the 6bl7gt .... but the 6bl7gt actually became a little fuller or "chuncky" sounding. The 6bl7gta was transformed at 400 volts/ high bias. The 6bl7gta gained in every imaginable way .... clairity, lineraity, dynamics, extension, soundstage size and air, bass power, speed etc... I found the 6bl7gta at 300 volts to possibly be the worst tube I had ever heard and the change was the most dramatic I have ever encountered with a tube. In fact, I prefer the 6bl7gta to both of the gt tubes.
Now .... I have discovered when using just the bias switch on my SLAM SE that any of the higher bias settings will correct the problems at 300 volts with the 6bl7gta and make all the tubes perform at a higher level. I also noticed all the tubes do sound warmer at 300 volts with a higher bias setting alone. If your amp was biased higher than the older SPS amps I would mostly agree with you. But, in my experience, to get the very best from the tube you need higher voltage and a higher bias. The tubes are more neutral, more impactful and much more dynamic at 400 volts along with just a small increase in bias.
