NOS EL34 becoming extinct

One of my amps is a low power SEP from Dennis Had. I purchased a pair of the new production GL KT-77’s from one of the reputable sellers long before there were supply issues. At about the 50 hour mark one failed with a huge pop through my speaker and damaged my amp. I was able to ship it back to Dennis for repair. I included the tubes for him to examine as the bad tube showed no change externally. Out of the approximately 20 Winged C’s I’ve had , one failed. It was a 6550 in my 50 watt mono block not an EL34. I heard a mild pop and turned off the amp. The envelope had cracked turning the inside of the glass frost white. There was no damage to my push pull amp. Last month I had Rogue Audio upgrade a pair of M-180’s to their Dark edition and inquired about new power tubes in addition to the small signal tubes supplied in the upgrade. They currently use only Psvane KT-88’s in their amps as they do not trust the quality of new production GL or Tung Sol tubes. The octet of GL KT -77’s that I had were about done. I really want some Tung Sol KT 120’s and am not thrilled about paying Uncle Chester $1100 for an octet. Another interesting fact with the upgrade is they no longer supply nos small signal tubes ( same issue )  and supply new Tung Sol 5751’s and JJ gold pin 12AU7’s. The JJ’s still suck , but the Tung Sol’s sounded really nice. I think I’m turning into one of those snippy old farts that I dislike. 😆 I guess death , taxes , and new production tubes are inevitable. Cheers , Mike B. 
 

How did you like the sound of the winged Cs?  I hear they are a bit on the brighter side?

Most (but not all) EL34 amps can use variants like KT77. Sounds different and whether you prefer it to the EL34 is up to you. I prefer KT77 in my EL34 amps because it's a little bit punchier but YMMV.

I tried new Tung Sol EL34B and found them very musical if not a bit midband forward. I think they needed more time to burn in but went back to my 7581A which are pretty much perfect. GT tubes are not great in audio gear. Gold Lion KT77 do have a solid rep but I've not heard them. 

With respect to your 7581A are they NOS or new production?

And what brand?