Favorite 300B: Sophia vs KR

"The tubes don't hold bias well neither. Every other few days, I would need to re-bias the tubes.”

Bsimpson,
My experience couldn’t be more different. I installed the Royal Princesses and after three hours, set the bias at 1.09. By the next day, one channel drifted to 1.08. Having read your post, and it being about a month since my last check, I took new readings and measured one channel at 1.07 and the other at 1.08. While I only kept Sophia’s Carbon Plates for about a week, they seemed similarly stable. I guess I can only hope that your experience with short tube life will prove equally atypical. At least for me.

Do not want to repeat myself again, but I think for those who own mono's or not Adaptive auto bias amps this can be a very huge issue.
Thing is, many manufactures offering auto-bias right now, so, this keeps you away of the fact what ever your tubes are stable or not, cos you just don't see that, so, why bother? The guys from PrimaLuna developed Adaptive Auto Bias http://www.primaluna-usa.com/product-main/prologue/prologue-two , which offering you the best possible solution and the reason, I believe, is basically the mass production of really bad tubes, which are used all over the world. You should see the stock KT88 I got when I bought Prologue Two, very poor quality and cheap material. They even dare to say that they produce a decent sound. Well, I don’t think so…
So, to me, tubes should be at very high quality, especially when their price range starts around USD 350-400 for a pair, not even want to start about USD 1000 a pair, which Royal's are, but that's not what we were talking about, cos not many users are around who bought a pair , I guess, and I do hope their quality check is better now. But than again, if you have to get the quality at that price range only, man, I am out, even they sound great.

Maxmad & Charles1dad: Yes, the Thoress F2A11 integrated.

It's too early to judge the stereo amp, and my system is still being completed, dialed in, but so far the sound is very musical and satisfying. I finally tracked down a NOS 1945 Tung-Sol Black Round Plate/Bottle 12SN7GT and awaiting it's arrival. I'm eager to hear the result. It should provide some positive sonic improvements. The 6SN7 of the same is my one of my top two favorite (Ken-Rad being the other). I was also trying to find some earlier NOS F2A11 (black plates, non-perforated metal base...) but it's proving to be difficult. Otherwise, I think this amp will be a joy to listen to. It already is. Not the Tron Cantata of course, but nonetheless a highly pleasurable listening experience, one that'll only get better once the system is finished. No more 300B for me. I'm kind of glad. hard to choose and expensive. Btw, I also have the Thoress FR20CD mkIII speakers.

Thanks for sharing Sakahara.

You probably knew, but you may want contact to Michael about Tung Sol http://www.vacuumtubes.com/

Most what I can see are Siemens made with metal base and they are not cheap at all:-)

Sakahara,
I was an admirer of your Tron/Horning system. I`m happy to hear you`re pleased with your Thoress components(they seem to be very well made) and wish you many years of musical enjoyment with them. As for me, I absolutely love my 300b SET amplifiers and will keep them for a long time.A good 300b tube in the right amp makes beautiful music.
Best of Luck,