What happens to the sound of a 12AU7 tube when...

TJHUB · « **on:** 28 Feb 2013, 12:35 am »

Can anyone tell me what typically happens to the sound of 12AU7 tubes when they are on their way out? I have a tube preamp that uses (4) in an mu-follower design, and I know I have over 5000 hours on since I purchased it used.

Thanks.

underdawg · « **Reply #1 on:** 28 Feb 2013, 12:36 am »

sometimes microphonics appear

TJHUB · « **Reply #2 on:** 28 Feb 2013, 12:41 am »

That's it? My issue seems to be much more complex, and microphonic isn't one of them.

FullRangeMan · « **Reply #3 on:** 28 Feb 2013, 12:49 am »

In power tubes is it unsual soft bass or lack luster treble etc
In preamps tubes Iam not sure, but would be a change in the usual sound too.

TJHUB · « **Reply #4 on:** 28 Feb 2013, 01:00 am »

Maybe it would help if I just stated what I hear since you just came close.

It wasn't that long ago that I had what I'd consider the best sound I've ever heard. Over the last few weeks, I've noticed the bass lose definition, the treble is missing some life, and the overall sound is lackluster. The treble seems a bit rolled off, the imaging is smeared, and I am noticing parts of the music seem very attenuated if not just plain missing. And all of this is at a level that isn't slap you in the face, but more me just noticing things that just aren't right. I was able to listen every day and be wowed, and now I find myself not liking the sound and not wanting to listen.

Tubes?

FullRangeMan · « **Reply #5 on:** 28 Feb 2013, 01:08 am »

If the power amp is a SolidState it would the tubes in the preamp;

TJHUB · « **Reply #6 on:** 28 Feb 2013, 01:12 am »

My amps are solid state. I just emailed the manufacturer about the potential issue.

SteveFord · « **Reply #7 on:** 28 Feb 2013, 01:17 am »

It sounds like it's time to throw in some new tubes.

TJHUB · « **Reply #8 on:** 28 Feb 2013, 01:19 am »

I certainly hope that's the issue...

FullRangeMan · « **Reply #9 on:** 28 Feb 2013, 01:19 am »

5000 hours is the usual life span for a preamp tube.
Some tubes manufacturers adv more than it, but in the real life I see no custumer yell 10K hours.

TJHUB · « **Reply #10 on:** 6 Mar 2013, 08:41 pm »

Just to update this thread:

I just received my new tubes about 30 minutes ago. I installed them and I immediately hear tighter bass and the missing treble. So it appears I was hearing my original tubes starting to die. Of course I now have the sound of new tubes for the next 50-100 hours which I am all too familiar with. Hopefully the sound settles into what I used to love.

borism · « **Reply #11 on:** 6 Mar 2013, 11:06 pm »

Glad that things are looking up with the new tubes. Ralph Karsten warned me about worn out 12au7 tubes in the Atma-Sphere MP-3 preamplifier I bought from him. He described the sound becoming "sleepy" which I took to mean lifeless. However, I haven't had the preamp long enough to experience this first hand.

TJHUB · « **Reply #12 on:** 6 Mar 2013, 11:13 pm »

My system is already sounding nearly normal. These tubes are changing fast.

I wish I had a better idea of what I'd hear when the tubes were giving up before it actually happened. I was blaming a recent change for the issue I was having, and no it may just turn out to be a horrible coincidence that my tubes started to fail at the same time.

And the sound had degraded even more than I was realizing. Of course this is obvious now...

jimdgoulding · « **Reply #13 on:** 6 Mar 2013, 11:52 pm »

There ya go. Good listening

ted_b · « **Reply #14 on:** 7 Mar 2013, 12:59 am »

Terry, did you try any of my NOS suggestions? Tube rolling 12AU7's is fun. My Concert Fidelity SINGS with Sylvania Gold Label Gold brand Triple mica 5814's, about $80/pair. They are wayyy more dynamic, yet organic, than normal 12AU7's, even the better $$ ones IMHO. But other 5814 and 5963's are fun, too.

TJHUB · « **Reply #15 on:** 7 Mar 2013, 01:54 am »

By the time I emailed you about this, I had already ordered tubes from Rogue Audio. I wanted the sound I had back again, so OEM tubes seemed to make sense. Unlike you, I find tube rolling extremely frustrating. Maybe I'm just too picky, but very few tubes seem to get things right for me. I really struggled with the 12AU7 in my DAC, so I now run it with no tube and I have Burson discrete opamps with great success. I think I tried about 10 different tubes over as many months.

Rogue sent me (4) JJ ECC802S tubes pretty cheap, but as soon as I have the funds, I'll buy a pair of the tubes you suggested just to try them.

ted_b · « **Reply #16 on:** 7 Mar 2013, 02:00 am »

I'll send you some to try.

underdawg · « **Reply #17 on:** 7 Mar 2013, 02:01 am »

I too prefer the sylvania gold brand 5814, and I also like the RCA Command black plates also. I use both in my amps and preamps.

TJHUB · « **Reply #18 on:** 7 Mar 2013, 02:01 am »

Quote from: ted_b on 7 Mar 2013, 02:00 am

I'll send you some to try.

Thank you sir, you are one of the great ones!

SteveFord · « **Reply #19 on:** 8 Mar 2013, 10:20 pm »

I just checked the tubes in the deHavilland and have a duff 6AH4.
I thought that things were sounding kind of dead and lifeless and now I know why.