It can be frustrating. Even with the best testing NOS tubes can go zingo. But I have about 1 in 10 Mullard CV4003 that we select that seem to be hanging together. Just for clarity....we have stock now and a process that works. While we have about every 12AU7 under the sun, and have always had them, there were two problems with that preamp. As I recall it has no feedback, which is why they do sound quite good. They also have a bit of gain. So when a tube starts to "burp" you will know it. Also some preamps that suffer from the tubes starting to ring need the tube sockets OR the transformer rubber mounted. I have suggested this to some folks that have doine it with good results. Transformers ring and over a period of hundreds or thousands of hours the micro-vibrations are picked up through the tube pins and the elements loosen up. It seems to be more evident in a few products using 12AU7's. As to eagerness...it depends on what I hear from a customer. Sometimes I will get a call like "I can't get tubes to last and they go goofy every couple months. I've gone through six pair this year...what's your warranty?" You can see how that may not be an attractive sale. The PV-10, 11, and 12 are fine preamps.
Conrad Johnson PV11 tube noise
After about 2 hours of being on, my preamp will occasionally give a sustained "chirp" or sometimes a longer high pitched ringing sound, pretty basic tube noise. I typically listen at low to moderate levels, and it is therefore often audible during listening. What can I do? CJ says to use the tubes they supply, because it was designed around them, Upscale Audio says that the PV 11 is a pain with regard to retubng, and He wasnt in a hurry to sell me ANYTHING because of this. It simply cant be that this type of noise is just what you have to deal with when you want to use a tubed pre. What do you think I should do?? Has anyone used a PV 11 successfully with NOS or other non-CJ supplied tubes?? Thanks.