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New power tubes lacking low end and slam

Quick question: I installed new KT120 power tubes (same as the prior original tubes) in my Cronus Magnum II for the heck of it. Previous tubes are roughly 3-4 years old. I had not been having any problems with the original tubes but figured fresh new tubes couldn’t hurt. After installing and biasing the new tubes they sound weak to me. Not as much low end and not as punchy. Is this normal? Will the low end improve after burning in? Or should I throw the older tubes back in? 
Thanks and happy 4th!
Paul
paulgardner

Showing 3 responses by daveyf

daveyf's avatar
daveyf
3,016 posts
 
You may want to check your driver tubes. I replaced these recently and the difference in low end slam was considerable. 
daveyf's avatar
daveyf
3,016 posts
 
I think you have an integrated? If so, you probably have driver tubes for the amp section and signal tubes for the preamp. This should be addressed in the manual.
daveyf's avatar
daveyf
3,016 posts
 
OP, how old are your small signal tubes...signal and driver? As lewm adroitly points out above ( better than i could) these could be the issue you are experiencing, along with break-in ( although this I doubt if the bottom end response is severely depleted, as you describe)
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