Actually the blue glass Sophia in my amp is their 274B. it seems to provide more tone and texture than others and doesn't get crazy with soundstage tricks.The input tube on the amp can make a good difference with grunt as well. I found the Sylvania vt-229 to provide the most slam of several other 6SL7's. Of course all this glass rolling can be substantially further enhanced if you want to get into power cords and outlet experimentation. Put an Acrolink 4030 with Oyaide 004 ends on the amp and it will sound like you added a good subwoofer. Put a Oyaide Black Mamba cord on the preamp, all plugged into an Oyaide SWO-GX outlet and you will raise the performance of the rig quite a few notches up.
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