Glowing Blue Power Valve

Gulliver

Mesa started making a weird 'ticking' noise, had a look round the back and one of the power valves has a weird blue glow that I've not seen before.  The glow disappears when the amp is on standby, as does the noise (obviously) 

Is the glow something I ought to be concerned about?

Gulliver

Found the source of the weird noise - powerline adapter was making noise - hasn't done this with any amp ever before. Quick reset and the weird noise has gone!

Read an article that says the blue is fine.   As you were!!

ICBM

More concerning - but still probably OK - is that the other one *isn't* glowing blue...

It does vary a bit. When you switch from standby to on, does that valve glow blue momentarily, and/or do you see any blue glow inside the plate structure?

If not, the valve may not be working properly - but at low volume it may not be obvious. To check, take out the blue one and try the amp - if it works, even if the sound is quieter than normal and sounds oddly distorted above very low volume, then the other valve is at least working.

Gulliver

ICBM said:

More concerning - but still probably OK - is that the other one *isn't* glowing blue...

It does vary a bit. When you switch from standby to on, does that valve glow blue momentarily, and/or do you see any blue glow inside the plate structure?

If not, the valve may not be working properly - but at low volume it may not be obvious. To check, take out the blue one and try the amp - if it works, even if the sound is quieter than normal and sounds oddly distorted above very low volume, then the other valve is at least working.

They both glow blue in 50W mode, but in 5W mode only the one is blue.  It's in 50W 90% of the time anyway so it's probably fine.  Might just need to swap the power tubes round every so often to ensure they're being worn evenly

ICBM

Gulliver said:

They both glow blue in 50W mode, but in 5W mode only the one is blue.

Aha! that will explain it .

Gulliver said:

Might just need to swap the power tubes round every so often to ensure they're being worn evenly

Yes, but don't worry about it too much. Probably only once at about halfway through the valve life would be enough - maybe once a year or something like that.

DJH83004

You'd be surprised how many customers ask if I can set their amps up to produce the blue effect, particularly the HiFi guys where the valves are displayed prominently. Its a while since I researched it, but I think it is just stray electrons (they don't all make it to the anode), bouncing off the glass & structure  and exciting harmless impurities (I think the element cobalt?) I'm sure the physicists on the forum will advise accordingly.  

ICBM

DJH83004 said:

You'd be surprised how many customers ask if I can set their amps up to produce the blue effect, particularly the HiFi guys where the valves are displayed prominently. Its a while since I researched it, but I think it is just stray electrons (they don't all make it to the anode), bouncing off the glass & structure  and exciting harmless impurities (I think the element cobalt?) I'm sure the physicists on the forum will advise accordingly.  

Yes, that's it - it's mineral fluorescence in the glass due to bombardment by stray electrons. I'm not sure about the cobalt but that would make sense given the colour. It does not indicate 'gas in the valve' - although there is another type which does (inside the plate structure, quite hard to see usually), but again is not a sign of a fault, almost all valves contain a small amount of inert gas.

It's so frustrating that it's become mythologised as a sign of a faulty valve - I can only imagine the number of perfectly good valves that have been thrown away because of it. If anything, it's the sign of a high-quality valve (with a good vacuum and high quality glass) working properly - old US GE and Sylvania 6L6s are some of the most prone to it and they're among the best audio valves ever made.

The colour to really watch out for is an intense purple-pink, that very definitely *is* trouble - it usually means imminent valve death because air has got in in a big way - the pink is ionised Argon which is the third most common element in the atmosphere - basically the valve has turned itself into an Argon lamp.

ecc83

Ah yes! The Purple Death! 'We' had a big batch of KT88s that did that. In a 200 watter that takes out anode fuse, HT fuse, mains 3.15A AND the 13A in the plug sometimes!

Dave.

JayGee

Gulliver said:

ICBM said:

More concerning - but still probably OK - is that the other one *isn't* glowing blue...

It does vary a bit. When you switch from standby to on, does that valve glow blue momentarily, and/or do you see any blue glow inside the plate structure?

If not, the valve may not be working properly - but at low volume it may not be obvious. To check, take out the blue one and try the amp - if it works, even if the sound is quieter than normal and sounds oddly distorted above very low volume, then the other valve is at least working.

They both glow blue in 50W mode, but in 5W mode only the one is blue.  It's in 50W 90% of the time anyway so it's probably fine.  Might just need to swap the power tubes round every so often to ensure they're being worn evenly

If it’s the same as my 5:25 then 5 Watt mode runs a single valve in single-ended, may or may not be Class A depending on who you ask and how far the volume is turned up configuration. The other valve isn’t doing anything and, presumably has its HT supply turned off.

ICBM

JayGee said:

If it’s the same as my 5:25 then 5 Watt mode runs a single valve in single-ended, may or may not be Class A depending on who you ask and how far the volume is turned up configuration. The other valve isn’t doing anything and, presumably has its HT supply turned off.

Technically not Class A because the class definitions strictly only apply to push-pull - it's just single-ended. If I remember right, the other valve is set to conduct a small constant current to eliminate hum via cancellation in the PT - one of the big advantages of push-pull - by having the input signal muted rather than the HT turned off, but I could be wrong.

ecc83

ICBM said:

JayGee said:

If it’s the same as my 5:25 then 5 Watt mode runs a single valve in single-ended, may or may not be Class A depending on who you ask and how far the volume is turned up configuration. The other valve isn’t doing anything and, presumably has its HT supply turned off.

Technically not Class A because the class definitions strictly only apply to push-pull - it's just single-ended. If I remember right, the other valve is set to conduct a small constant current to eliminate hum via cancellation in the PT - one of the big advantages of push-pull - by having the input signal muted rather than the HT turned off, but I could be wrong.

Several ways to stop one of a ppull pair. The early Artisans disconnected the grid drive to one EL84 but left the current running (so you get the hum cancellation and don't bugger the traff!)  but some geezer in the states said he held a patent on the circuit. No dosh to fight that so the valves were switched to triode operation.

Of course, both methods change the valve loading away from optimum.

Dave.

ICBM

ecc83 said:

The early Artisans disconnected the grid drive to one EL84 but left the current running (so you get the hum cancellation and don't bugger the traff!)  but some geezer in the states said he held a patent on the circuit.

He would have patented electricity if he thought he could hoodwink the US Patent Office into giving one...

martinw

ICBM said:

The colour to really watch out for is an intense purple-pink, that very definitely *is* trouble - it usually means imminent valve death because air has got in in a big way - the pink is ionised Argon which is the third most common element in the atmosphere - basically the valve has turned itself into an Argon lamp.

Sorry, I have to correct this, having spent a good bit of time working with vacuum chambers observing different types of plasma, and some of those had air leaks which needed to be fixed. If we had an air leak in the plasma gun, it was immediately apparent. You can strike a plasma with nitrogen, oxygen or even just air, as easily as any gas.

When you get an air leak, the dominant colour tends to be a reddish (or it could be called purple-pink) plasma, which represents nitrogen. There's a white-blue element (giving pink) which is oxygen. Argon (reddish purple)is present, but you'll  struggle to see it as it is masked by the other colours.

None of the colours are clear cut and have nuances to them, and the proximity of the red glow of the filaments will have an effect on the observed colour.

So you're right about the colour, but the reason for it is in proportion to the gases in air.

ICBM

Fair enough!

RiftAmps

ICBM said:

ecc83 said:

The early Artisans disconnected the grid drive to one EL84 but left the current running (so you get the hum cancellation and don't bugger the traff!)  but some geezer in the states said he held a patent on the circuit.

He would have patented electricity if he thought he could hoodwink the US Patent Office into giving one...

How on earth did he find out the (presumably confidential) technical details of the BS circuit? Is he going around reverse engineering every modern amp out there just in case there’s a similarity to his design?

Actually, this raises an important point. I’ve designed a circuit and since sold the IP to a third party. We had a nightmare trying to define the IP because how many other amplifiers use a standard RC gain stage or grid stoppers on the power valves? *all of them*

The only way that we could could correctly define was to say that the individual components are not themselves unique, but the exact combination and architecture is. Think of a Chef trying to protect his recipe, he can’t hold the rights to using a tomato, but he can protect unique combination and process.

jpfamps

ICBM said:

ecc83 said:

The early Artisans disconnected the grid drive to one EL84 but left the current running (so you get the hum cancellation and don't bugger the traff!)  but some geezer in the states said he held a patent on the circuit.

He would have patented electricity if he thought he could hoodwink the US Patent Office into giving one...

Might have been Peavey rather than MESA with their "texture" control, although MESA also hold a patent on this circuit.

Regardless, the circuit was in the public domain before the patents were issued, so both are spurious.

And of course Blackstar haven't ever published any spurious patents that wouldn't hold up in court.......

ecc83

You have to remember, this was in the very early days of Blackstar, maybe in the first year of the Artisans which was only their second product after the HT pedals.  The company was very small (my payroll number is 7 from then!) and would not have had any resources to fight an action.

How did they find out? Presumably someone read an advert that mentioned the low power mode and decided to investigate? If so that would point to Peavey or another big concern that could just splash $1000+ 'just to see'?

Dave.