I’d also like to get anyone’s input on 12ax7 tube replacements. My budget would be $200-$250 per tube.
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The NOS tubes in my phono stage have been sounding great for nine years now, so if it is your Mullards that seems short lived or a defect. Are the Mullards supposed to be NOS? Is it coming from both channels? Both tubes, both channels, same time, does not sound right. If one channel then switch the tubes and see if your distortion has moved.
Todd, as Kenny pointed out a little judicious tube swapping can lead you to a bad tube if the distortion is channel-specific. You don't mention what "way up" might mean but 15 hrs/week for 1.5 years puts you in the 1,200 hour range. Unless you have a preamp that is know to run tubes exceptionally hard (Audible Illusions comes to mind), preamp tubes can usually be counted on for 5,000-10,000 hours of life. Dick
Shuguang Treasure12AX7 LS from Grant Fidelity.
Give then 20 hours to break in. They best my Telefunkens.
@kennythekey @djohnson54 thank you for the input. I should have qualified a little more...
”Way up”, they probably ran for about 4-6/day for the first year, due to the preamp being inband of the home theater signal. I’ll swap the L/R channels, but it sounded more as if it was coming from the L channel; which could be due to the pan/mix. I bypassed my preamp all together and am running it direct from my DEQX unit and it’s DAC. I use a McIntosh C2500, I don’t know if those run super hot or not, per your comment @djohnson54 . Running it through the DEQX, the harshness is removed. Faulty tube, very well could be. I probably have about 2.5k - 3.5k hours on them.
@kennythekey They are NOS. I bought them from Kevin at Upscale Audio. They’re the Mullard CV4004 12AX7 NOS.
If they're starting to get noisy they're probably about done. Kind of a rushing slurry sound. By the time they make static they're getting close to failure I think.
Upscale I think still has British surplus Mullards. I bought two sets of the 12AT7s years ago for a VTA ST70. I'm still on the first set.
I agree, if you're using it for a home theater pass through you stack up the hours fast. I've gone through sets of 6922s in ARC preamps in a couple of years that way.