I own a Peavy Classic 50 212 amp (prior 2000 model) and after 19 years of use, I had to replace all tubes, since the reverb became unusable (too noisy) and the sound had become muddy, with constant "ups and downs". After searching in various sites, blogs and forums, I ended up to buy the Tung-Sol for position V1 (clean).
The overall response of my amp has returned to its prior condition with an improvement in the bass (feels tighter and I can crank it up to near 11), smoother highs (treble) in general and you get way far improved sound than before when you use the presence control (the sound is sweeter).
Combined with the other two 12AX7 (TAD, Sovtek), my amp has transformed back to the rocking blues machine it meant to be (and no bias moderation needed). I definitely recommend it!