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How does the sound of a power tube change, over time?

I have a pair of Rogue M-180 monoblocks that each use a quad of KT-120 power tubes.  I'm considering a new set of power tubes (same brand, Tung-Sol)  

I realize this question will depend on the specific tube type and amp, but I'm curious about the common experiences.  For those of you experienced owning the same tube amp over years and replacing the power tubes with the same brand of power tube, what did you gain, sonically?  E.g. as power tubes age does the amp suffer in terms of frequency extension, dynamics, volume, etc? 
c_s
10 responses Add your response
c_s OP
15 posts
 
I installed a fresh set of KT-120's in the Rogues a few days ago.  The improvement was greater than I'd anticipated - I guess the old tubes were older than I'd realized.  Similar to other impressions on this thread, out of the box they new tubes were notably more dynamic, articulate, with better frequency extension (and with a reappearance of midrange) As well, they've improved over a few days in terms of depth of stage and bass extension.  I.e. the M-180's are back in top form and sounding fantastic
billstevenson
352 posts
 
I have a cj ARTsa amp that uses eight KT120 Tung Sols. I replaced all the tubes annually, not just the power tubes.  The sound improves noticeably as follows:  Quieter - big difference probably not due the the power tubes.  Sweeter highs, cleaner overall, better delineation of lows - rosen on the strings kind of thing.  My system gets used a lot, 20 or more hours a week.  YRMV.
wolf_garcia
6,695 posts
 
lloydc…That's actually a great comment. You know when the tube's time is up when your other tubes sound better. Ears are certainly the best tube tester as long as they're not wooly…if so clean 'em.
c_s OP
15 posts
 
Thanks for the responses.  I'll be trying a new set in the Rogues soon and will report back. 
lloydc's avatar
lloydc
751 posts
 
For the reason Wolf gave, you tend to accumulate backup tubes.  You can't tell you needed to, until you replace them, and then things sound a little better.  I have at least 5 sets of 12 power tubes, and many preamp tubes, in reserve...not worth the bother and expense of a decent tube tester. 






wolf_garcia
6,695 posts
 
Wooly. It's wooly. Anybody that is a "serious" tube freak frequently changes out their tubes for absolutely no reason at all (for example, I put a pair of Sovtek KT88s in my SEP amp to replace a perfectly fine set of Gold Lions because I like the Blue Glow the Sovteks produce), thus never knows when they're dead (the tubes, not the freak) or at least loses track of them. Until they get wooly.

ebm
9,311 posts
 
Over time they get dull lose definition get wholly that why i use tube preamp and ss amp.Enjoy though!!
atmasphere's avatar
atmasphere
11,794 posts
 
Does this happen with amps which employ auto-biasing?
Yes.

I find that triode power tubes tend to go downhill a bit slower than tetrodes and pentodes.
rockadanny
1,224 posts
 
Does this happen with amps which employ auto-biasing?
lowrider57's avatar
lowrider57
5,417 posts
 
as power tubes age does the amp suffer in terms of frequency extension, dynamics, volume, etc?
Yes, what I notice is a loss of top-end extension and a dullness to the sound, as in a loss of dynamics.
But this change due to aging tubes happens gradually, so it’s not something you notice immediately.

That's why I've been looking for an affordable tube tester.
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