This quad got noisy
I purchased a matched quad of these preferred 12ax7 for the phono stage in my Copland preamp in Dec 2014. While they weren't the quietest tubes, I liked the tone and so there they have stayed for the past 10 months. In recent weeks I have noticed the my phono input has gotten noisy. Unlistenably noisy. I'll be trying something else this time around. I think they should be good for more than a few hundred hours.