Experimenting is an understatement..
I have now created a philosophy and theory..Hahaha.
First of all.. Any modern Tung Sol is not allowed within 150-ft of my amp. I have a restraining order against them. They are evil beasts that tried to kill my tone.
Over the past month, I've been able to successfully save 3 local Mesa users, (and 1 online TR owner) from their tone hell.
All of them had one thing in common.. They all thought the problem was their power tubes. When in fact it was their preamp tubes (more specifically, what brands they were using).
I have yet to run across a power tube that creates sparkle. It's not their job to. A poor power tube might restrict certain frequencies from coming through. Better power tubes might enhance certain highs or lows. But they're mainly responsible for the boldness, tightness, sponginess, saturation level, ect..They don't create tone. The sparkle would have to come from your preamp.
I'm not familiar with Bass amps, but if yours has preamp tubes, there's hope to find that sparkle you're looking for. If not, try the Svetlanas and hold your breath. That is what I have in my DR right now, they sound great, but I didn't find them to be any different than my Mesas. Nothing significant anyway.
So I guess my first question would be, what's in your preamp?