Tube Aging and Sound

It has lately come to my attention that tubes change in a pattern (Cary SLP 09 preamp). Any one notice this:

  • New tubes sound great, but with a slight edge
  • As the tubes age, the edge goes away
  • At some point (in my case just around New Year’s eve/day), the tubes hit a point of perfection – smooth, detailed, perfected soundstage
  • Shortly after that period of perfection (lasted about a month), the tubes are sounding noticeably dull – still sound very good (fatter midrange, softer highs), just no magic.

Unlike the PS Audio pre, I don’t know how many hours it took to get to perfection, but I’m thinking this set of tubes are about 1.5 - 2 years old.

I’m also thinking I haven’t swapped the rectifier tube since I’ve owned the preamp (bought it used). Any chance it’s that? I was under the impression the main tubes would last longer.

SLP09? Don’t know that one.

Do you have a tube tester to check them with? And how many different sets of tubes have you had this experience with. Not familiar with that preamp…which tubes are you using.

Oops! Meant the SLP-05.

I had Cary components for years. They’re beautifully made, sound wonderful and I never had a failure.
For tube questions, I’d call Kevin Deal at Upscale Audio.

If you speak to those who are familiar with tubes, they just gently fade off into the sunset as they age. They just stop doing their job effectively and stop sounding as well as they used to. Incineration is often the result of another component failure.

8 ea – 6SN7 octal tubes for the balanced, headphone and gain stages
1 ea – 5AR4 Rectifier Tube in Power Supply

1.5 - 2 years old-------How many hours on these tubes?

These? One or two of the 6SN7s could be bad.

Try switching out the tubes in question with fresh ones and listen to see if you hear any difference in sound quality…if not,the tubes are still good…I would use them until you hear a definite loss in sound quality.

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Since tubes die slowly generally, mark-d’s advice is quite sound. There’s not really a better way to keep tabs on things unless you have a tube timer built into the unit.

That is scary, to swap tubes that is. I found I always hear a difference… and this may be not due to age, but each tube from the same maker can sound a bit different. Don’t torture yourself.

Tubes stabilize after say 40 hours or so… then they remain great… until they fail. Or, you just get weird about it and replace them yearly or every two years. When you do, you hear a change… remember, new tubes don’t sound burnt in… so how are you to make a judgement?

I guess… what you should do… is buy two sets new… then burn in a set… then shelve them and run off of the second set. This gives you a burnt in control. While I think this is a “good” idea, I don’t do this nor ever will. This just takes the fun out of it all.

It is one of the charms of tube ownership. I don’t sweat this. I change out my tubes about every two years and have come to a simple truce with the minute changes that occur over time. Difference does not automatically mean better or worse. If this concerns you, you should not be into tubes… or must have very deep pockets.

Bruce in Philly

My experience with good NOS tubes is that they work easily 10 years or more. But it seems not many amps have soft start circuits to preserve tube life, this might be most important.

Agreed… I had some driver tubes in my VTLs that easily must have been 10 years old… I tried changing them just because and the old ones always sounded better. So I have real experience that old does not mean degraded.

Power tubes are another story… and that depends on the amp design… my VTLs ate 6550s.

Bruce in Philly

I pull them out and check my tubes when they sound “MUSHY” to me.

Thanks for all the suggestions. Turns out, it was the rectifier tube. Replaced that and Magic’s back!

I did decide to replace all the tubes — just so a full set can age together. Going to see if I can have magic for two years…

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I’ve thought of that for my headphone amp as it uses 6 tubes 2X300b, 2X6SN7 and 2x5U4G. A tube guru said it didn’t make sense as the tubes all age at different rates depending amp characteristics and usage. Some tubes are just under more stress.

I pretty much follow Bruce’s methods and philosophy.

I do have amps that have meters that show me tube strength for the output tubes which is a handy aid. When the meters show a certain level I swap in a newer pair and compare the sound. I buy the output tubes from the manufacturer who does extensive testing and selects only the best which have quite a consistent sound making comparison for age and characteristics easy enough.

For our vintage tube lovers, the manufacturer had been gone forever.

I heard a metal base GZ34 will last for many years.

Absolutely. I have a cabinet full of tubes I’ve collected over the years, realistically for signal and rectifier tubes I’m likely good for a decade or more, but I’ll buy my favorites when I see them reasonably priced; they’re still out there, but there’s no new production of the classic favorites, which are favored for a reason.

I should have been clearer above–I buy my power tubes from the manufacturer/designer of my equipment who puts NOS Russian power tubes through rigorous testing and his selections really ARE better than I can get elsewhere, or at least better than any I have gotten elsewhere in the last two decades.

How a tube Is biased in a circuit determines a lot but rectifier and regulation tubes can last many years. . . a good thing. I love tube rolling and the rectifiers and regulation tubes really anchor a tube complement.