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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
wolf_garcia
6,696 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.

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. 






c_s OP
15 posts
 
Thanks for the responses.  I'll be trying a new set in the Rogues soon and will report back. 
wolf_garcia
6,696 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.
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.
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