H-C, that's funny - I knew the Blue Glow was nothing to worry about for half my life when it came to my guitar amps and their 6L6's. Then recently I changed my stereo rig's amp from one using EL-34's, which never Glowed Blue in that amp, to a pair of mono's using 6550's, which 3/4 of year later are starting to exhibit it. Despite what I always "knew", I had to come and check it out again. That's the difference between guitar players, who'll abuse an amp until it cries uncle and not give a damn before it stops working, and audiophiles, who worry and obssess over every little thing despite everythings' working fine - Even if that guitar player and that audiophile happen to be the same guy! :-)