I had a faulty Royal Princess 300b tube and they replaced it promptly and were very polite, I was impressed. That tube had wonderful sound in my SET amplifier.
Sophia Electric tube quality
I wonder if others have experienced poor quality with the Royal Princess 300b tubes. Purchased a new pair and one shorted out in a couple of months in their amp. Sophia replaced it and the new pair were extremely microphonic -- rang like bells when tapped with just my thumbnail. Sophia's response to my complaint was, "Stop tapping the tubes.