Yep, seen all these. I'm just a little wary nowadays as I like the idea of getting optimal usage out of each valve, the 5691 escapade has made me slightly paranoid.
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I guess with the 5691 having twice the filament current, it would need an appropriate power supply to ensure correct operation.
Did the sonic signature revert to original when you switched the 5691s back out?
Nope. The modification truly brought out the 5691's capability. So it wasn't a backwards step. It was initially quite difficult to assess what had changed and then within about 30 minutes I'd realised that the timbral quality was just on another level. Notes on things like the double bass had so much more resonance, soundstage was a little deeper with better coherence. Subtle but a big leap forward!
Ahhh, I get ya. That’s good then.
I am impressed with the 5691s, very musically satisfying.