Indeed. Hence my comment, whether it are the tubes or the listener who is 'broken in'. I vote for the latter ;-)
Human perception related to sound can easily vary in the course of a few hours, let alone days or weeks.
Jan
re: early burn-in...
Annoyingly so @ 2-5 hours of burn-in time, "over the top" is not overstated. This week tried a pair of NOS CV4003/M8136 Mullard input tubes in my mono block amps. The midrange got to be overly forward, loud, overly clear midrange with more "in your face" sound. At hour 4-5 and I had to pull myself away from it and not do any critical listening and just let it run.
After hour 6 it settled in some. The MullardTubes seller told me 150 hours and a buddy suggested 30 hours. We'll see, sounds nice and articulate now but not full sounding yet like my other NOS tubes.
Hoping they will smooth out some more after 30-50 hours.
No tube, especially consumer grade tubes, are perfect. The vacuum is less than perfect and there are impurities on the surfaces of the internal elements, and locked within their metal and coatings. New production tubes often are less "perfect" than the NOS counterparts, but NOS tubes have been "sleeping" in their boxes for 40 to 90 years. Also, it is likely that much of what is sold today as "NOS" has seen some life, often as test subjects in a repair shop.
DF96 covered most of this, but the heat seen in first power up can release impurities that were trapped during the long sleep. Ion contamination can increase during the first few hours of use, especially if the tube is subjected to operation near it's maximum temperature. This can increase grid current, and change the bias in an amp with less than stellar design......Haven't we all seen designs where that maximum grid circuit resistance spec is violated in the quest for more gain?
It is possible for some audible, measurable, and sometimes visible break in to occur in some tube / amp combinations, while none occurs in others.
Sometimes a tube will improve over the first part of it's useful life as the getter grabs the "garbage" then degrade slowly as it's ability to collect it is used up.
I have seen some extreme cases of this including the bulk packed sealed box of NOS Sylvania 6V6GTA's that I bought at a NASA surplus auction. Upon opening the sealed box of 100 tubes I discovered that about 1/3 of the tubes had white, faded, or missing getters. About 1/3 lost or severely degraded their getters within a few hours of use. Now 20 years later only a few tubes remain and virtually all of them work great now, but will go soft within a few weeks of use.
Yes, this is one of several cases of poor Sylvania quality in their final years of vacuum tube production, but I'm sure that there are many more less obvious examples out there.
Lots of different possibilities, and may partly explain why a colleague of mine is selling off all of his large NOS collection and focusing on specific new input and output tubes he's telling me are getting to be very close to matching or beating his NOS tubes lately.
Some of the new production tubes are very good but another batch of the same tube may not be so good. Some of the high priced tubes seem great but have short lives due to vacuum contamination.
Some of those golden oldies may Outlast two or three sets of the new stuff. There is good and bad among both.
Some of those golden oldies may Outlast two or three sets of the new stuff. There is good and bad among both.
Notable change at 30 hours with the NOS Mullard input tubes in my monoblock amps.
Changes:
The overly forward midrange situation tapered off at 6 hours and disappeared at 30 hours.
Sound stage is deeper and more open. Background darkened up a little.
Detail smoothed out some, glare is gone, and yet upper air is still there.
Changes:
The overly forward midrange situation tapered off at 6 hours and disappeared at 30 hours.
Sound stage is deeper and more open. Background darkened up a little.
Detail smoothed out some, glare is gone, and yet upper air is still there.
Absolutely. The last pair of Mundorf EVO Silver Gold coupling caps I installed in my former Cary V12R took well over 250 hours until they came to a consistent set point. I was pre-warned by my local 40 year tech to "prepare for a roller coaster ride". He wasn't kidding, patience required. The wait was worth it.
A capacitor is just two plates of metal separated by a dielectric.
What mechanism causes the sound to change so much ?
And if it is changing then surely the capacitor is faulty to start with or to end with ?
Valves are different as they age due to cathode deterioration.
While I'm not a pro tech, and I've heard differences in some of my better amps, and repeatedly on custom speakers over time using VCaps, ClarityCaps and others. Mundorf, Jensen, others on my tube amps. Several members of the audio engineering society in our local regional chapter share thoughts and changes about different brand/type caps over time. Learned things such as mention of physical change occurring inside caps as metal moves or flattens out (???), or oxidation on the cathode disappearing once voltage is applied for a long period of time. Some in the same group noted measurable difference over time, but not a lot of change.
HHH did some fun tests on a whole bunch of different caps, and notes about burn-in needed on many caps before sound improved, fwiw Humble Homemade Hifi - Cap Test
"We're uncomfortable steeped in ignorance"" Human perception system is rife with always getting it wrong...we are poor data taking devices, that's why we have such a thing as science...because we have machines...they'll get the data right." Neil DeGrasse Tyson.
----------------------------------------------------------------------Rick....
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