Yes! The You Tube links are working now... Nice demos! Hearing the filter sweeps on both chords and on single note lines is useful. In chords, the balance between the low and high notes is easily heard, along with the effect on the trailing harmonics. In the single note lines, it's more about the harmonics on each note, and that seems to carry through when using the pedals. The filter switches don't seem to pop as you rotate them, either... Very nice! The FET is basically a clean boost, so adding some overdrive to the first stage adds a nice little bit of grit when you are plugged straight in. I can hear the presence working, and it sounds like a nice thing to have. So, a UL Dumble? What's not to like, eh? You're enjoying the result, which is great. Congratulations!
PS: Which PT do you have installed? HTS-7157... stand-up Twin Reverb/Showman unit? (I think yes, from another thread here). Plate voltage still around 480, loaded? That seems a little high for a Twin. What idle current are you running on the 6550's now?