I did look at Rodger's (RAM) tube offerings. While expensive he does offer some rare NOS tubes that he tests the hell out of to select truly quiet ones. It might be worth the investment. I had thought that Upscale was doing good work but have only bought 1 pair of Mullard 12AX7s a decade ago and used them as an output stage of a CD player. They worked great in that capacity but that is hardly a true test.
I have a lot tubes as rolling turned into collecting. There is a big difference between noise generated by the tube's normal function and microphonics. Testing for microphonics is sort of useless in my book, because the sound very very rarely feedsback into the tube to cause a problem. So, unless you are tapping the tubes with a pencil while playing for some strange reason, microphonic tubes have little impact on the sound.
Noisy tubes are different. They make a noisy base signal that gets picked up and amplified. In a phono stage or other very high gain situation, this is obviously a big problem. Sometime the tube has both a noisy output and a distorted output but I don't want to write a novel here. The most common noise is from a near dead tube or one in the process of dying and it makes that tell tale hiss, which makes this case frustrating. Upscale should and I expect would have tested the tube enough to find hiss. Could they have missed it ?? I don't know. But substituting any other compatible tubes should have fixed the problem...
I have a lot tubes as rolling turned into collecting. There is a big difference between noise generated by the tube's normal function and microphonics. Testing for microphonics is sort of useless in my book, because the sound very very rarely feedsback into the tube to cause a problem. So, unless you are tapping the tubes with a pencil while playing for some strange reason, microphonic tubes have little impact on the sound.
Noisy tubes are different. They make a noisy base signal that gets picked up and amplified. In a phono stage or other very high gain situation, this is obviously a big problem. Sometime the tube has both a noisy output and a distorted output but I don't want to write a novel here. The most common noise is from a near dead tube or one in the process of dying and it makes that tell tale hiss, which makes this case frustrating. Upscale should and I expect would have tested the tube enough to find hiss. Could they have missed it ?? I don't know. But substituting any other compatible tubes should have fixed the problem...