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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
rockadanny
1,224 posts
 
Does this happen with amps which employ auto-biasing?
atmasphere's avatar
atmasphere
11,784 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.
ebm
9,311 posts
 
Over time they get dull lose definition get wholly that why i use tube preamp and ss amp.Enjoy though!!
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.

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. 






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