How do you tell when powertubes go bad?

[grunge782]

Pretty much what the title says.

I know about redplating, but if you see some blue in the tubes is that ok?

What are things you should look out for?

Thanks

 

[hunter]

Blue is usually no good. I only get blue when I don't have proper load on my amps.
Are you using an attenuator or a mismatched cab?

 

[LedZep77]

I believe that bad/mismatched power tubes will hum, where bad preamp tubes will hiss, so if your amp is humming that may be a sign.

 

[Inearthed]

Last time I had a power tube go out the amp was making a bunch of low end popping and such... Scared the hell out of me... Turned it back on on a low volume and lightly tapped on the tubes, found the bad one in a moment...

 

[sswanson]

Blue is usually no good. I only get blue when I don't have proper load on my amps.
Are you using an attenuator or a mismatched cab?

It's normal for tubes to have a bit of a blue haze in them, at least to some extent.

 

[Capulin Overdrive]

some 5881's get lots of blue.


power tubes just seem to get gradually tired, so if you're getting tired of your sound could be time for tubes.


when i just had one amp, i figured about a year for SED's with lots of playing and about 6 months for Chinese.

 

[grunge782]

Last time I had a power tube go out the amp was making a bunch of low end popping and such... Scared the hell out of me... Turned it back on on a low volume and lightly tapped on the tubes, found the bad one in a moment...

How do you tell when you tap it? It starts cutting in and out?

 

[grunge782]

Blue is usually no good. I only get blue when I don't have proper load on my amps.
Are you using an attenuator or a mismatched cab?

I'm using an 8 ohm Mills cab. I have 4 kt77 tubes in my Dual Recto.

I know that there is a fixed bias in the dual rec, but a friend of mine said that it would work fine. I have barely played at all with them yet so I wouldn't damage anything.

 

[glpg80]

blue haze inside a tube means that the tube is considered "gassy" - under heavy loads either from sheer volume or mis-matched impedances (done properly here - not the kind that cook OT windings). tubes should not glow blue under normal load.

if they do glow blue it means the tubes are on their last stance, and prone to failure.

biasing too hot can cause tubes to prematurely become gassy - causing the blue haze.

the only orange/red you should see in a tube are the heater filaments inside the tube where the anode and cathode are located.

the outer-edge plates of the tube should never glow red, this is a sign of thermal run-away, bias runaway, or prone to premature tube failure. usually this is the case for attenuated amplifiers running wide open for a very long period of time without proper ventelation.

proper ventelation for tubes do help tremendously to extend their life-span.

 

[glpg80]

Last time I had a power tube go out the amp was making a bunch of low end popping and such... Scared the hell out of me... Turned it back on on a low volume and lightly tapped on the tubes, found the bad one in a moment...

How do you tell when you tap it? It starts cutting in and out?

a normal tube should thud. it should not ring like a bell, and it should not rattle when hit. if there is rattling, then the tube has failed - probably from thermal damage or mechanical deffects in production.

if the tube sounds like a bell then its microphonic which is what happens normally with tubes - and only gets worse when heat is included in this variable. i always tap tubes with a wooden pencil slightly to tell. you dont want to touch a power tube - it will burn the piss out of you if it is on. you also want to keep fingerprints off of tubes, as it can cause hot-spots on the glass in reaction to the gas when the tube is on.

 

[grunge782]

Last time I had a power tube go out the amp was making a bunch of low end popping and such... Scared the hell out of me... Turned it back on on a low volume and lightly tapped on the tubes, found the bad one in a moment...

How do you tell when you tap it? It starts cutting in and out?

a normal tube should thud. it should not ring like a bell, and it should not rattle when hit. if there is rattling, then the tube has failed - probably from thermal damage or mechanical deffects in production.

if the tube sounds like a bell then its microphonic which is what happens normally with tubes - and only gets worse when heat is included in this variable. i always tap tubes with a wooden pencil slightly to tell. you dont want to touch a power tube - it will burn the piss out of you if it is on. you also want to keep fingerprints off of tubes, as it can cause hot-spots on the glass in reaction to the gas when the tube is on.

I'll have to try this.

I know all 4 tubes are matched correctly to each other, and I wasn't playing at high volumes. Since the Dual Recto is a fixed bias is that what was causing the blue gassing?

 

[glpg80]

nope, not at all. the volume you play at will only speed up a tube's wear time. but as long as the amplifier is on - your tubes are counting down their days.

as far as matched goes - when it comes down to it - matching only helps to keep the lifespan close because the bias will be simillar to each tube.

since your amplifier is fixed bias, its probably biased cold. i have yet to find a company that fix-bias' their amplifiers hot - that wouldnt make any sense.

but a hot bias will cause tubes to wear quicker, as if you were playing at higher volumes on a cold-biased power tube. 6 one way, half a dozen of another. kinda like comparing front wheel drive to rear wheel drive - you see both at the drag strips and both will get you down the road pretty quick.

good luck on the tubes. i prefer http://www.thetubestore.com for my matched quads of power tubes. i will only order pre-amp tubes from http://www.dougstubes.com because he is the only person that does burn-ins on all of his preamp tubes to check for microphonic or deffective tubes out of the box. this means high gain 12ax7/ecc83 tubes have less of a chance breaking down in the future.

rock on bro.

 

[grunge782]

nope, not at all. the volume you play at will only speed up a tube's wear time. but as long as the amplifier is on - your tubes are counting down their days.

as far as matched goes - when it comes down to it - matching only helps to keep the lifespan close because the bias will be simillar to each tube.

since your amplifier is fixed bias, its probably biased cold. i have yet to find a company that fix-bias' their amplifiers hot - that wouldnt make any sense.

but a hot bias will cause tubes to wear quicker, as if you were playing at higher volumes on a cold-biased power tube. 6 one way, half a dozen of another. kinda like comparing front wheel drive to rear wheel drive - you see both at the drag strips and both will get you down the road pretty quick.

good luck on the tubes. i prefer http://www.thetubestore.com for my matched quads of power tubes. i will only order pre-amp tubes from http://www.dougstubes.com because he is the only person that does burn-ins on all of his preamp tubes to check for microphonic or deffective tubes out of the box. this means high gain 12ax7/ecc83 tubes have less of a chance breaking down in the future.

rock on bro.

Oh ok. I meant more that because the Mesa has a fixed bias, maybe the kt77's I ordered aren't correct bias for it? I ordered them at 37ma.

 

[glpg80]

did you give them your plate voltage when you ordered it, or have a technician look at it to order them? or did you order them at 37mA draw without any measurements?

if thats the case, then yes, they probably are cooking hot and/or deffective. 55-60% plate dissapation is what tubes should be biased at for high gain amplifiers. you would need to know exact numbers of your amplifier to get the correct tubes to do this and still stay outside of crossover distortion which happens when tubes are biased too cold.

 

[grunge782]

did you give them your plate voltage when you ordered it, or have a technician look at it to order them? or did you order them at 37mA draw without any measurements?

if thats the case, then yes, they probably are cooking hot and/or deffective. 55-60% plate dissapation is what tubes should be biased at for high gain amplifiers. you would need to know exact numbers of your amplifier to get the correct tubes to do this and still stay outside of crossover distortion which happens when tubes are biased too cold.

I had a pair at 37ma and ordered another pair from the same place at 37ma. I did not tell them the plate voltage.

 

[glassjaw7]

Hey grunge, I also run 77's in my recto. Been running the same pair for about a year and a half with no problems. I ordered JJ's from Eurotubes. Since then I've heard many complaints of their QC, but the tubes that I have still sound great to this day.

I'm not sure what "grade" my tubes are, I just know that they told me they were 29's on the phone. I told them I didn't want the high gain option because the recto has so much gain that its not all usable anyway. You could give them a call. They are VERY helpful and know a lot about running different tubes in all kinds of amps. 503-659-7401

BTW, heard great things about SED EL34's in the rectos.

 

[grunge782]

Hey grunge, I also run 77's in my recto. Been running the same pair for about a year and a half with no problems. I ordered JJ's from Eurotubes. Since then I've heard many complaints of their QC, but the tubes that I have still sound great to this day.

I'm not sure what "grade" my tubes are, I just know that they told me they were 29's on the phone. I told them I didn't want the high gain option because the recto has so much gain that its not all usable anyway. You could give them a call. They are VERY helpful and know a lot about running different tubes in all kinds of amps. 503-659-7401

BTW, heard great things about SED EL34's in the rectos.

Nice. I figured kt77 would give the el34 recto love with some more range to it. I like the sound, but I wanted to make sure things were running properly you know?

I got my tubes from a different vendor so I think that reading would be different based on what they ran their voltage at.

 

[sswanson]

blue haze inside a tube means that the tube is considered "gassy" - under heavy loads either from sheer volume or mis-matched impedances (done properly here - not the kind that cook OT windings). tubes should not glow blue under normal load.

if they do glow blue it means the tubes are on their last stance, and prone to failure.

biasing too hot can cause tubes to prematurely become gassy - causing the blue haze.

Once again, a little bit of blue haze is normal. If you replace every set of tubes you run across with some blue haze in them you are going to throw away a lot of money. And honestly, I'm not sure I've ever seen a set of tubes without at least a small amount of blue in them, on any amp.

 

[grunge782]

blue haze inside a tube means that the tube is considered "gassy" - under heavy loads either from sheer volume or mis-matched impedances (done properly here - not the kind that cook OT windings). tubes should not glow blue under normal load.

if they do glow blue it means the tubes are on their last stance, and prone to failure.

biasing too hot can cause tubes to prematurely become gassy - causing the blue haze.

Once again, a little bit of blue haze is normal. If you replace every set of tubes you run across with some blue haze in them you are going to throw away a lot of money. And honestly, I'm not sure I've ever seen a set of tubes without at least a small amount of blue in them, on any amp.

Hmm...

Seems like this topic is a bit disputed haha.

Well besides blue, what do bad power tubes usually sound like? Or what should you look out for?

 

[ke2]

Blue is usually no good. I only get blue when I don't have proper load on my amps.
Are you using an attenuator or a mismatched cab?

It's normal for tubes to have a bit of a blue haze in them, at least to some extent.

Yeah, I got stressed by the blue glow in my TADs, but after a quick search on the web, it seemed that it was quite normal.