Wow guys so interesting. Page 1893 has quite some things I've never heard pf over the years. Senn. HD-250 and 580. I've tried the 280, 380, 579 which was a standout, 598, 600, 650, 660 S which was a major disappointment, and a few higher. Mainly I'm using the 380 for good closed 'cans and the 600 with an upgraded silver cable for good linear / punchy openbacks.
UT mentioned a user swapped 'Hexfreds' on the GEL3N amp. Was he rolling an op-amp?
Also that's interesting that the sound of the EL3N's can be described as airy, sweet, clear, punchy, etc. on the GEL3N amp - no doubt due to the prowesss of the amp itself and proper implementation, because on the Elise & Eforia with adapters anyway, they sounded the opposite - lush, slow, fairly dark yet still a great tone as if they have a lot of potential... One thing they always did great though was soundstage.
I still think the EL3N will sound beast then maybe the EL11 , EL3 , 6M6 I haven't tried the later 3 yet.
But I think the Philips EL3N sounds better then other brands like Tungsram that I have tried.
I have 6 Philips EL3N spurred on by UT's proclaim of them on the F.A. threads back in 2016. Those were the most readily available and perhaps cheapest, as well. I do wonder however if a GEL3N with 6x slots for EL3N (or 6x EL34 etc.) would yield even better resolution? In every case without fail I've always gotten better sound from 8x tubes with my adapted Euforia than 4-6x. (improved transient response, instrument separation, soundstage, bass definition, etc. depending on synergy of course with both tubes and headphones). Maybe 6x. EL3N + 2x rectifier or driver tubes as well.