I’ve spent some time with the GL gold pins now. Why when something is new it is exciting to listen to only to discover with time and comparing back to back to well regarded vintage tubes it is lacking. The GL is not a bad tube but compared to Tele, RCA, Mullard, Mazda, Tungsgram instruments just doesn’t have the natural tone or soundstage of vintage tubes. Fooled me.
Welcome to the most consistent quality of tubes: the here today, gone tomorrow sense of bliss (or merely contentment).
There's definitely a durable difference in sound quality between vintages & makes, but it will at times seem exaggerated (often on first listen to a new make), and at other times subdued.
Good vintage tubes are consistently better at rendering spatial information than new stock. But new has its advantages - they offer a good palette of tonal balances to choose from, and (crucially) it's easy to select for low noise at reasonable prices. Some of the new small tubes (12AX7, 12AU7, 6SN7) measure extremely strong for transconductance, more than any vintage tubes you'll find. This can be an advantage in certain slots. Russian Tung-Sol 6SN7GTB sound a lot more dynamic than any vintage 6SN7 in the V2 (driver) slots of my VAC KT88 amps. In V1, old 6SN7 rube, but in V2 the new ones can't be beat.
I only buy old stock now. Tried GL’s and Tung Sol’s but just didn’t sound nearly as good in my amps. I prefer a fuller warmer sound so I prefer RCA blackplates, Mullard long plates, Sylvania blackplates and Amperex. They provide warmth and detail without being bright. Not a Tele fan but they sound great in my phono preamp. Synergy match is at play here. Good luck with it all.
After spending a couple days with the Gold Lion started noticing soundstage was more focused in the center. Put RCA’s in and soundstage went beyond speaker boundaries and that’s no warm up, maybe I posted to soon. I still like them but better than RCA’s maybe not. Will compare to other tubes. I might have been wrong on this one.
The new tubes are very good and unless you have a large tube collection from which to conduct endless trials, it’s usually more about proper sonic pairing than raw sound quality IMO. Telefunken ribbed plates can be bright, but the smooth plate variant is warmer - check which you have. The Russian "re-issues" are good to mix & match in 3 variants:
Tung-Sol - little extra energy up top
Reissue Gold Lions are really quite nice as you’ve found, and their well tempered musical balance makes them a good "first guess" fit for most systems.
The best NOS tubes are more articulate with more 3D image, but if you don’t get the right sonic match then it doesn’t matter, as you’ve found out.
If you like re-issue Gold Lions you might like Amperex Holland, or black plate RCA (which you already mentioned), or even Tele smooth plates. The reissue Mullards and Tung-Sols track (somewhat) with their namesake vintage 12AX7. British Mullards are very warm.
I usually prefer Tele ribbed over smooth plates, incidentally, but you do have to deal with the brightness. If you can, I find them to be more detailed and dynamic. Mazda silver plates take this even further. Mazda silver with a Koetsu cartridge can be divine 😍
One brand I regret not exploring more in the 12AX7 space - Siemens. Their E88CC ended up being my favorite in the 6922 type, of MANY variants. They combine air & energy up top, sweet natural mids (bordering on lush) with top grade bass & dynamics. All while remaining super clean with top clarity. Almost seems impossible to pull off.
The JJ E83CC/12AX7 frame grid is my favorite current production 12AX7 at about half the price of the Gold Lion. A number of other folks have said the same. The Gold Lion is okay but not great and overpriced for what you get IMHO.
I have four Gold Lion 12ax7 gold pins in storage, they were the first I switched to over the stock tubes in my phono pre. A nice upgrade, for the money, but as @noromance inferred, I then replaced those with four old Telefunken smooth plates, and albeit being similar in tone, the Tele's were much smoother and really superior in all ways. After that I tried two 60's Blackburn Mullard's in combination with two of the Telefunken smooth plates, and liked that combo even more, in my setup.
All that said, yes, for the money, the Gold Lions are very good, but can be easily beat my venerable older tubes. But they will cost significantly more....but in terms of 'return on investment', an easy justification for me.