NSgarch- I'm a little reluctant to contradict you, since your posts are always thoughtful and (to me, anyways) very informative, but... I have some Herbie's on the 300b power tubes in my Cary 300 SEI. Now I don't push that amp very hard but there is no evidence of any discoloration anywhere, and I just checked the portion of the damper that actually touches the tubes. Maybe on a KT-88/6550 push/pull amp, but so far they are OK on my 300b amp.
