Please let us know how you like the Sylvania 7308 JAN. I haven't tried that one myself.
I ended up going with E88CC TESLA Gold-Pins / NOS. Made in Czechoslovakia in the 1970s. The website says that these are "the closest E88CC to the legendary Telefunken frame-grid E88CC tube", but the price for a matched pair was around 80€.
I warmed up the WA3 and let the music run for a few hours, now have been listening for a couple of hours. Obviously one can't A/B with tubes, but playing some tracks I know very well I would say that there is an obvious sound difference. These sound smoother than the Telefunken branded E88CC’s made by JJ Audio I had on before. The sounds seem more blended together, maybe this is what people mean when they say something sounds more "tubey". I really like the emotion it creates but definitely this is moving away from transparency. The New Telefunken had some sparkle, these are much mellower.
But don't interpret much from what I say. I am too new to tubes.
Question: What are good practices with the WA3? Correct me on the below:
1) Turn the amp on, volume at 0, let it warm up 5 minutes minimum.
2) Start playing music not at a very loud volume for the first 10-15 minutes.
3) Don't leave it on without music/sounds playing. (Is this right? I read that the tubes suffer if they are warm and not under load)
4) If one wants to switch to other tubes, turn it off, wait 30 minutes for a full cooldown, then change tubes and go back to #1.