On Sunday, July 19, 2020 at 3:39:04 PM UTC-4, wrote:
One of the EL34 tubes in my amp was making intermittent noise so I
bought a couple new matched EL 34 tubes and put them in the amp. They
sounded OK but not great. At first I thought it was the particular
recording that was sounding so bad because the recording was bad. It
was the Happy Trails album by Quicksilver Messaging Service. The
original recording just wasn't the best quality.
Then about a week later I was listening to some Herbie Hancock and
the sound was kinda muddy or muffled sounding. It did not have the
same clarity as it did with the first set of tubes. So I swapped in
the old pair and and there was a marked difference in the quality of
the sound. I was really surprised at the difference.
Now I gotta shop for some better tubes. What is done in the
manufacturing of tubes that can have such a big difference?
Eric

I can't answer your question, but would it have killed you to put the brand names of the original set of outputs and the replacement set you installed, or the amp you're using?

Also, did you bias the new tubes properly? If they're running too cold they'll sound like crap.

I never heard much difference between brands of EL34s, 6CA7s, and even 8417s I've used in my vintage Fisher integrated amp. They all sounded fine until they became flabby with age.