Hi again guys, I wonder if I should be concerned about possible early burn out from my EL39's? I've noticed the top of the glass has developed a fairly dark 'sun-tan' after being my mainstay powers for a month. I initially burned them in with music overnight for about 3 12-hour sessions, without a fan which may have been the cause because these EL39's actually do get fairly hot - albeit still only around 1/2 as much as those fire-hot 6080's. Since then I've been using a small fan on the tubes to reduce heat buildup in hopes to prolong the life.
Photo 1: before use
Photo 2 & 3 are from today, with #3 showing the top up close revealing the change in color.
Must admit DL, colour change usually happens with the getter flashing...from silver to brown as residual gases are extinguished. I myself have never had a tube that's clear up top change colour. But as @mordy says, perhaps it's just some of the anode coating burning off. I doubt it's use overload, as @Johnnysound has been cooking his own 39s at levels way beyond Euforia's demand lol! And I myself have put far more hours on mine than you have on yours! Mind you, twelve hour sessions are not normally recommended for tubes, although I myself have done so in the past...the usual - as recommended by F-A - is 5 to 8 hrs, with at least an hour cool off in between.
I'm also curious as to why you're using ferrite chokes on the anode wire...I myself have never had any issue whatsoever, even with the teflon tubing actually touching the transformer!...???...