Just got my 6 x 6BL7 adapter for my Elise amp. First experiment is 2 EL3N as drivers + 4 x 6BL7 and 2 x 6N7. Previously I got very good results with 6BL7 + 6N7. The 6N7 is an all metal tube from the 6N7G/6N7GT family.
First impression: More of everything, more authority and that old cliche - ruthlessly revealing:
Cannot think of any power tubes that give you bigger bang for the dollar..... Been listening for an hour now - gets better and better.
As time goes on I will try different combinations. Some tubes work in synergy; others in allergy of whatever it is called lol...... Don't know of any way to figure it out - just trial and error. (Strangely enough the related 6N7G (too much hum) and 6N7GT(didn't sound good) with the 6BL7 did not sound as good as the neglected top hat 6N7 - seems that nobody wants tubes without glass&glow, so these tubes are easily found in the bargain bins).
Looked up the opposite of synergy - there is no accepted word: dysergy, antergy. I think allergy is good enough lol. Negative synergy is maybe the closest.
PS: If anybody is interested in how to power this or similar adapters externally without breaking the bank, I could write it up.