My really dumb tube mistake(s)

8 years ago, I bought a sweet sounding Line Magnetic amp for my office system which a few years ago died and had to go to the repair shop. $500 later it was back working, but then recently I noticed the sound was getting thin, I couldn’t bias the tubes and thought something else was wrong with it, arghh.

Then I noticed one newer tube was able to be biased and decided to replace all 4 KT-88 power tubes.
Presto, the amp sounded great again!

Like the boiled frog, the sound degradation had been so gradual my brain had gradually adjusted. But the new tubes brought it back to life.

So, then I thought, wow, maybe I should try the same thing in my primary system with my Primaluna monoblocks, switch out the Primaluna tubes for some new Gold Lions. Again - wow! What a difference. Like I bought new amps, much richer and fuller sounding.

Tubes wear out, even if they don’t blow out.
Yes, duh, it’s a good idea to replace them every 4 years or so and not wait eight.