I finally put in a 6550C from ARC to compare it with the 6L6GC tube and the 6550WE tube. First I put about 50 hours of burn time on it.
All I can say is WOW!!! As in 'WOW, why would anybody want to degrade thier Ref 3 with this tube?"
With my present analog setup I usually listen with the volume between 55 and 65, depending on the record. When I really want to crank her up for some electric blues or rock and roll the volume goes up to 75 or even 80 if I want to be wall shaking loud.
With the 6550C in place I first put on Muddy Water's acoustic recording, "Folk Singer". I kept turning up the volume until I was at 90 and yet it sounded like I had furniture blankets over the speakers, talk about veiled. Then I put on Rob Wasserman's "Duet" and went right to the duet with Lou Reed. With the volume at 85 it had no impact, muddy, almost impossible to distinguish the two instruments playing.
I turned off the pre-amp, let the tubes cool down and dropped the original 6L6GC back in. Put the volume at 70, kept the mute on, dropped the needle back on to the Lou Reed track and sat down. Picked up the remote and unmuted the preamp. Back came the visceral bass, the furniture blankets were off the speakers and all the detail and seperation of instruments were back.
Maybe Oneobgyn is mistaken and the bypass caps are necessary in order to improve the sound using the 6550C tube. At this point I would have to hear it in someone elses system before I would chance putting the bypass caps in and trying the 6550C tube again.