What Unusual SET tubes you've tried & liked?

I'm hungry to try something new and different and want to build a SET headphone amp. Does anyone have any weird and wonderful tubes they have tried successfully used for this type of project that sound decent and are still available
Not unusual but the 45 followed closely by the 50 and 2A3, in that order, are my favs.

The higher output tubes, including 300B and 845, simply don't have the "sweetness" and linearity of the flea power single ended triodes. IMO of course; to each his own.

The 50 will be the most difficult to source.
Cheers Audiofeil. My amp builder has similar tastes. You hit the nail on the head and here's the method behind my madness. I can run my AKG K 702 headphones with out the problem of limited headroom that speakers present for these musical tubes. Do you run 2a3 single plates?