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.

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.
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).

The Tube Depot (, 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
Thanks Griffithds
I'll keep them in mind. Hoping Octave will replace it. I did just buy the V70se and 2 additional quad sets of tubes.
MOST manufacturers warranty the tubes for at LEAST 90days if not longer when an amp is purchased new from an authorized dealer. Not sure why your dealer would even have to wait for a response from Octave but ...

Yes I am getting a replacement.

I have tube rolled Octave MRE 130's for years, driving B&W N800's. Currently, I have a set eight of SED KT88's in primary use. I also have EH KT88's and Gold Lion KT88's that I swap in and out from time to time. Originally I have TAD tubes that were good but seemed to bite the dust after a few months. You have experienced a bad tube for sure. Good thing that Octave builds in bullet proof protection circuitry to save your components.

The advantage of getting a Black Box or Super Black Box is that you will have more AC capacitance in the transformers, an increase in available AC power to drive your speakers. The difference between an amplifier using a Super Black Box; V70, V80 and MRE 130 is night and day. The bass is more powerful and the system can play louder. Overall, the musical presentation is more defined and it is easier to drive your difficult load speakers.

The dynamic and tonal stability of an amplifier is strongly dependent upon the stability and capacity of the power supply, therefore the Black Box and Super Black Box were developed as external upgrades to the OCTAVE amplifiersÂ’ power supply storage capacitors by increasing their capacitance by a factor of 4 (Black Box) or 10
(Super Black Box), respectively. This is a tremendous benefit if the speaker is difficult to drive. Loudspeaker efficiency is made less critical, while the amplifier is enabled to handle speakers with minimum impedances as low as 2 Ohms.
The power supply capacitance increase realized via use of the Black Box or Super Black Box stabilizes current delivery and reduces the impedance interaction of the load. This improves dynamic range, separation, depth, soundstage size and articulation, rendering the
musical reproduction clearer throughout the entire frequency range.
The amplifier remains unaffected by mains variations and interferences due to the noise filtering characteristics of the capacitors.

I just upgraded to the Octave Jubilee preamp. What a difference that has been compared to the Octave HP500SE. I am seriously thinking about upgrading to the Octave Jubilee monoamps.

I have been a satisfied Octave customer for years.

Where are you located?


I live in a suburb of Chicago. My speakers are Dynaudio C1's. Funny you mention the black box. I've asked my Octave/dyn dealer to set me up with a black box demo. I read avsforum and Mick from Dynaudio recommends the black box for the C1's and super black box for the larger speakers.

I was able to audition the Jubilees with the Dynaudio Consequence UE at a private showing. All I can say is WOW.
The blue glow in tubes is not normal. If the blue glow suddenly appears it means the tube has developed a vacuum leak. If the blue glow has always been there it means the tube did not have a good strong vacuum to begin with. The strength of the vacuum does affect the performance of the tube.

The bright flash that shut down your amp was most likely a short in the tube. Without a protection circuit your amplifier could have suffered severe damage.

I had a tube short in my Audio Research M 300 which had no protection circuit. It blew resistor pieces all over the room and damaged the circuit board in the area of the resistor.

If Svetlana tubes are all showing signs of low vacuum or they are not holding vacuum I would look for another brand. I have had good luck with Chinese KT88 tubes when they are properly sorted.
Thanks for the Info Rrog. I got my replacement last night and it glows just like the other 3. Octave protection is great. Just got a demo Octave 'black box' which increases the capacitance 4 fold to about 60,000uf. Helps in all ways. Control - power - sound stage - imaging - depth. I think it's going to be a keeper.