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Tube newbee question

After 30+ years of solid state I now have a bran new Octave V70se currently running sed winged KT88's. I noticed 1 tube glowed a much a brighter blue than the other 3. 2 nights ago (day 5) I also noticed the blue would flicker with the bass. I turned the volume from a 9 o'clock position to about 10:30 when 1 cornor of the tube seemed to get super bright - then a bright blue flash occured with the Octave going into protection mode. Also heard a thud/pop from my right speaker. Recycled power and verified that the bias was set corectly - which it was. I left it in for a couple more hours and it still works but has a much brighter blue glow to it. Octave included a spare KT88 and the next moring I replaced that 1. Well that spare tube also has a brighter blue side. Note I will not put that original back in. Today I swapped that tube position to another and it still has a brighter blue side in the different spot. Today is day 7. So for now I have to assume I had 1 bad tube. My question is seeing a KT88 or even 6550 that glows a brighter blue than the rest a problem to worry about? The last thing I noticed is that both tubes that glow blue brighter needs to have the bias turned lower. The tubes are supposed to be a match quad set.

I also have a matched quad set of EL34's and a matched quad set of 6550's on order. All are factory sed winged c's. I want to eventually pick a favorite tube which is why I got the other sets.

Last my Octave dealer forwarded my concern to Octave and we are waiting for a response. I would like to get any opinions if this is something to worry about.

THANKS
xti16
newbee
4,757 posts
 
A gaseous blue glow in KT88s and 6550s in itself is not a bad thing. It is normal to some degree or another and its absence is also normal. The amount of gaseous blue glow varies from tube to tube. What would concern me is that it is fluctuating when you crank up the volume. Sounds like a tube with a short and I would replace it (as you are doing).

For an understanding of the blue glow look up FAQ's on the AudioAsylum site.
xti16 OP
1,525 posts
 
Newbee
Thanks for the response. I'm interested if 1 glows more than the others it a possible problem? Octave offers an option called the black box that increases the capacitance 4 fold and a super black box that increases it by 10 fold. Do you think that may be part of the fluctuating? I'm driving Dynaudio C1's (which love current).

Thanks
griffithds
852 posts
 
The Tube Depot (tubedepot.com), has factory 2nd SED's on sale for 1/2 price. Bought a quad set of 6L6, 6V6, EL84's, and the KT88's. Some had scratchs on the base, some were just dirty. All measured new+ and work perfectly. Just a heads up if you need to replace a tube or want to buy a backup set
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