Dual Rec power tubes glowing blue

[tomprs]

Hi guys,

Today at a rehearsal all four powertubes (Sovtek 5881) of my dual rec started glowing blue ... and it won't disappear until I hit the standby switch. Tone wise I cannot hear any problem, the amp sounds fine. Should I worry??? I mean, last week all tubes looked like always and now there's this kinda blue shade in the middle of each one. The tubes are a bit more than two years old and I play once a week in a post hardcore band. It just looks like this pic I found on the web.

Thanks!

 

[Authorized Boogie]

Blue glow is normal. Its due to electron bombardment of the glass. Many materials flouresce or "glow" when struck by electrons. Not all the electrons in a vacuum tube strike the plate. A few stray off and strike other things in the tube, such as the glass envelope. Many types of glass will give off a faint blue glow when bombarded by electrons of sufficient energy. This is the most common type of blue glow seen in power output tubes. Often you will see small patches of glow that correspond to the holes in the plate or other structures in the tube. Tubes will usually glow blue when the tube is in operation with voltage applied. When you cut the standby switch off, this interrupts the voltage applied to the output tubes, and they stop glowing.

 

[bandit2013]

Sometimes you do not see it. I get weary when 3 out of 4 tubes glow but that is also normal. However I had a set of JJ 6CA7 in my Mark V, very faint blue glow, one stopped glowing and the amp sounded a bit more compressed. turns out the tube shut off due to poor connection in the tube. Most EL34 type tubes will not glow blue (have to look into the holes in the plates to notice the blue glow. This is will only be noticed in power tubes, rectifier will remain looking dead as well as the preamp tubes (only thing glowing will be the heater).

 

[tomprs]

Blue glow is normal. Its due to electron bombardment of the glass. Many materials flouresce or "glow" when struck by electrons. Not all the electrons in a vacuum tube strike the plate. A few stray off and strike other things in the tube, such as the glass envelope. Many types of glass will give off a faint blue glow when bombarded by electrons of sufficient energy. This is the most common type of blue glow seen in power output tubes. Often you will see small patches of glow that correspond to the holes in the plate or other structures in the tube. Tubes will usually glow blue when the tube is in operation with voltage applied. When you cut the standby switch off, this interrupts the voltage applied to the output tubes, and they stop glowing.

Thanks for the super complete answer! It also feels really good to see you guys at Mesa interacting with us, the customers. I still have a doubt though: why has it suddenly started now? I mean the tubes started glowing blue yesterday, after more than two years of use. Doesn't it mean that something happened to the tubes?

Cheers!

Tom.

 

[Authorized Boogie]

Blue glow is normal. Its due to electron bombardment of the glass. Many materials flouresce or "glow" when struck by electrons. Not all the electrons in a vacuum tube strike the plate. A few stray off and strike other things in the tube, such as the glass envelope. Many types of glass will give off a faint blue glow when bombarded by electrons of sufficient energy. This is the most common type of blue glow seen in power output tubes. Often you will see small patches of glow that correspond to the holes in the plate or other structures in the tube. Tubes will usually glow blue when the tube is in operation with voltage applied. When you cut the standby switch off, this interrupts the voltage applied to the output tubes, and they stop glowing.

Thanks for the super complete answer! It also feels really good to see you guys at Mesa interacting with us, the customers. I still have a doubt though: why has it suddenly started now? I mean the tubes started glowing blue yesterday, after more than two years of use. Doesn't it mean that something happened to the tubes?

Cheers!

Tom.

Thanks for the kind words! Occasionally a tube will develop a small leak. When air gets into the tube, AND when the high plate voltage is applied, the air molecules can ionize. The glow of ionized air is quite different from the fluorescence glow above--ionized air is a strong purple color, almost pink. This color usually appears INSIDE the plate of the tube (though not always). It does not cling to surfaces, like fluorescence, but appears in the spaces BETWEEN elements. A tube showing this glow should be replaced right away, since the gas can cause the plate current to run away and (possibly) damage the amplifier.

 

[tomprs]

Blue glow is normal. Its due to electron bombardment of the glass. Many materials flouresce or "glow" when struck by electrons. Not all the electrons in a vacuum tube strike the plate. A few stray off and strike other things in the tube, such as the glass envelope. Many types of glass will give off a faint blue glow when bombarded by electrons of sufficient energy. This is the most common type of blue glow seen in power output tubes. Often you will see small patches of glow that correspond to the holes in the plate or other structures in the tube. Tubes will usually glow blue when the tube is in operation with voltage applied. When you cut the standby switch off, this interrupts the voltage applied to the output tubes, and they stop glowing.

Thanks for the super complete answer! It also feels really good to see you guys at Mesa interacting with us, the customers. I still have a doubt though: why has it suddenly started now? I mean the tubes started glowing blue yesterday, after more than two years of use. Doesn't it mean that something happened to the tubes?

Cheers!

Tom.

Thanks for the kind words! Occasionally a tube will develop a small leak. When air gets into the tube, AND when the high plate voltage is applied, the air molecules can ionize. The glow of ionized air is quite different from the fluorescence glow above--ionized air is a strong purple color, almost pink. This color usually appears INSIDE the plate of the tube (though not always). It does not cling to surfaces, like fluorescence, but appears in the spaces BETWEEN elements. A tube showing this glow should be replaced right away, since the gas can cause the plate current to run away and (possibly) damage the amplifier.

Like this?

Cheers

Tom

 

[bandit2013]

I have had that issue with my Mark V. Usually when driving the tubes hard and the hot spot appears at the seam similar to your picture. If it does that at idle or on stand by, sure signs the tube is on the way out or is not suitable for the bias of the amp. Eventually it will redplate completely. I had issues with Mesa STR440 since they all did this readily and did not matter on the age. Only tubes I could find that did not overload were SED =C= 6L6GC or the Mesa EL34. Therefore I believe my amp may be running on the hot side. Still have to check bias on the tubes with a meter just to verify all is kosher. Also depends on the amp and how it is biased. The Mark V runs a bit hotter than the other Mesa amps as I have learned. It really cooks them in 45W mode. I should probably have the amp checked out by a Mesa Authorized service, however since I have only been using SED =C= I have not had any problems. I know it voids warranty but I could not use the amp with the Ruby power tubes since they would only last 2 months before redplating. Some of the common Russian tubes like Tung Sol, Svetlana did okay but it would not take long for the same issue you pictured. I suspect after 2 years of use they are due for replacement.

Also another factor is the load. Are you running a 4 ohm 212 or 8 ohm 412. Tube life will be a bit shorter with 4 ohm loads than 8.

I am curious to read what the Authorized Boogie will respond about your issue. It may help me to understand better what I am experiencing.

 

[tomprs]

I have had that issue with my Mark V. Usually when driving the tubes hard and the hot spot appears at the seam similar to your picture. If it does that at idle or on stand by, sure signs the tube is on the way out or is not suitable for the bias of the amp. Eventually it will redplate completely. I had issues with Mesa STR440 since they all did this readily and did not matter on the age. Only tubes I could find that did not overload were SED =C= 6L6GC or the Mesa EL34. Therefore I believe my amp may be running on the hot side. Still have to check bias on the tubes with a meter just to verify all is kosher. Also depends on the amp and how it is biased. The Mark V runs a bit hotter than the other Mesa amps as I have learned. It really cooks them in 45W mode. I should probably have the amp checked out by a Mesa Authorized service, however since I have only been using SED =C= I have not had any problems. I know it voids warranty but I could not use the amp with the Ruby power tubes since they would only last 2 months before redplating. Some of the common Russian tubes like Tung Sol, Svetlana did okay but it would not take long for the same issue you pictured. I suspect after 2 years of use they are due for replacement.

Also another factor is the load. Are you running a 4 ohm 212 or 8 ohm 412. Tube life will be a bit shorter with 4 ohm loads than 8.

I am curious to read what the Authorized Boogie will respond about your issue. It may help me to understand better what I am experiencing.

I'm running an 8 ohm 4x12 cab or a 16 ohm 4x12 cab. And my tubes ARE NOT glowing red like in the second picture...(please go back to my first post). I showed this one afterwards just to know how the glow of ionized air looked like. If it's what the picture shows then my tubes are perfectly fine as they glow blue

Cheers,

Tom.

 

[Don]

This is beautiful!

 

[deeman]

agreed. I don't think i've ever noticed my tubes glowing blue

 

[Authorized Boogie]

Like this?

Cheers

Tom

THAT is a red-plating tube, and in need of replacement. Thanks!

 

[Don]

Yes. That red plating is bad!

Here are the tubes in my (former) 5:50. Normal and beautiful!

 

[tomprs]

Alright! I know now that I can keep on rocking my dual rec without having to worry about my tubes "getting the blues" Thanks guys AND Mesa for the help!

Cheers,

Tom.

 

[bandit2013]

That red plate tube, that is what my Mark V does with every tube except SED =C= 6L6GC or Gold Lion KT77 (in EL34 mode).

Original Mesa STR440 were far worst than in the picture, Both V8 and V9 had the plates completely cherry red. That only took 2 weeks of ownership, amp was new. I was using the 45W mode in variac power setting. Only other Mesa tubes I had were borrowed from my Mark IV STR420 coke bottle 6L6GC (those were awesome tubes). Only took 10 minutes before they melted down. I did try the two survivors (ones in the outer positions) in the inner positions and they also began to red plate. They work fine in my Mark IV. Took a while with other tubes, Tung Sol 7581 which lasted much longer but also started to red plate but only with high volume settings. However, after trying the SED =C= for the first time, never had an issue. I could not get them to red plate and they lasted one year of continual use 3-4 hours per day, every day. The only other tubes that did not exhibit the issue are TAD 6L6GC-STR. I would not doubt I had a weak set of tubes from the start. Always used an 8 ohm load, standard Rectifier cabinet with V30's. I replaced them with EVM12L speakers and also removed the stereo jacks on the cabinet so it can only be used as an 8 ohm load. About the same time I made the change to the cabinet is when I started using SED tubes. Due to the age of the cabinet and possible issue with the contacts in the speaker jack, changing to a fixed 8 ohm load is probably the cure for all of my issues. I bought the cabinet new 14 years ago with my Mark IV. Speakers are still good since I did not use the cabinet all that much (3 times per year). I have nothing against the Ruby power tubes or the JJ preamp tubes. Without a doubt, I believe my Mark V is running a bit too hot on the bias since the obvious characteristic is blistering ice pick high end. I should have the bias checked with a tube probe, at leas I could be assured it is not running too hot. If any one has a clue as to which component in the Mark V that sets the bias for 90W setting and in 6L6 mode you can PM me. I would like to check its resistance value (I am sure it is not quite that easy). I have no desire to make it adjustable but it would not be bad if it had a means to adjust so I could prevent the issue I have had with my V. I would rather keep it fixed bias amp.

 

[domct203]

Also another factor is the load. Are you running a 4 ohm 212 or 8 ohm 412. Tube life will be a bit shorter with 4 ohm loads than 8.

That is incorrect.

As long as you are matching impedance (using the proper Output Transformer tap) it does not matter what the speaker load is. That's the OT's job. A 4 ohm speaker into the 4 ohm OT tap, 8 ohm speaker into the 8 ohm OT tap, or 16 ohm speaker into the 16 ohm OT tap provides the same load to the tubes on the OT's primary winding, the tubes could care less.

Dom

 

[bandit2013]

4 ohms into an 8 ohm output jack will shorten tube life, but should not cause immediate tube failure. Even a short circuit on the secondary of the OT will not cause immediate damage. However, a momentary open circuit will which was what I found with my Rec cab on the 8 ohm jack, could result in issues. The series contact on the jack was not in good shape. Had no further tube issue after removal of the stereo connections and fixed it to 8 ohm only.