The replacement set of tubes for the original set of Apos Ray tubes arrived yesterday. I let them come up to room temperature so I waited till today to install them. This set came directly from Ray Tubes of China. The original set were very good when they were installed in my BHK Preamp. These are far more impressive. I am hearing things within the soundstage that I have not noticed before. This is out of the box. I am sure they are going to settle in given some break in time. I hope that they outlive the first set. These are so far beyond the Gold Lions, the 6 volt Tungsram or any other tube I have used in my preamp so far. I hope that they will produce an equivalent 7DJ 8 that could be used in the BHK 250.
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Last night I heard a hissing noise from the right speaker. It was a faint one, but I could hear it when playing music. I switched sources and the noise was still there. Could it be the tube noise? These Apos Ray 12au7 tubes have been used close to 5k hrs. (Promised 10k hrs. life). Hmm, I need to investigate later.
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Could well be the tubes. Advertised lifespan has little relevance to real world lifespan in my experience. The number of times I’ve had “10,000 hour” tubes crap out and become noisy and unusable in a short time span is very depressing. 
Quality control and materials quality ain’t what they used to be.
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You are quite right. Between individual variability and how hard the component drives the tube, the published lifespan should be taken with a grain (or more) of salt.
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It is confirmed that the right tube was going bad. Both had 5k hours, which is quite good. My other tubes usually last one half of that.
I am putting back the stock Psavne tubes to see how do they do. I still have a pair Apos Ray and a pair of GL if I do not like the sound.
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I went from stock to Gold Lion, then to Brimar 12au7. I like the Brimar’s the best.