Replaced stock McIntosh 12ax7a with gold lion ecc8

Thanks for your responses - It's starting to sound better, I did not get a matched set, I was not sure I wanted to switch permantly, now I am convinced to switch. Most of my music sounds more involving, which is amazing! The only trade off so far is some of my program gets "Busy" where the stock tubes perhaps has more micro detail with a very dry presentation. I am going through all my music collection and having a blast listening which is a very good sign. Thanks for the info on hidden plates.

Matching preamp tubes is NOT essential, only when it comes to power tubes. but guess what?? ALL tubes drift so its "never" really matched (except at the beginning) but its always a good starting point.

Don't worry about the glow--it's pretty much irrelevant. What you're hearing is the difference in sound character from stock Mac tubes, which tend to be bright and edgy, IME. The Golden Lions are richer in the mids and bass. They'll open up more in the treble and become more focused as they break in, but some people find them to be a bit rolled in the highs. Give them 100 hours or so, then you'll be able to tell if you like their sound.