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What does a broken tube sound like?


thom

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Sure, when one of the tubes doesn't light up, it's broken. But Isn't there anything that can be wrong with an output tube that causes your amp to sound em...f*cked up?

 

The preamp tubes aren't visible, so I wouldn't know if one just isn't working.

 

My amp sounds extremely buzzy and weak, it's actually quite similar to playing through a fuzz pedal with a flat battery...

 

Anyone?

 

Cheers.

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Originally posted by thom

Sure, when one of the tubes doesn't light up, it's broken. But Isn't there anything that can be wrong with an output tube that causes your amp to sound em...f*cked up?


The preamp tubes aren't visible, so I wouldn't know if one just isn't working.


My amp sounds extremely buzzy and weak, it's actually quite similar to playing through a fuzz pedal with a flat battery...


Anyone?


Cheers.

 

 

You'll know when you blow a preamp tube when you hear a really loud screeching sound, even with your guitar not plugged in. You can find a blown preamp tube by just looking down the center of the retainer (the aluminum sleeve holding it in place). Just look for the one that's not glowing.

 

When a power tube completely craps out, your amp usually just cuts off, at which point you have to replace it and the fuse as well. If your amp sounds weak, it could be because one of the power tubes is on it's way out. Replace it ASAP if you want to avoid having to replace the fuse.

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Originally posted by thom

Sure, when one of the tubes doesn't light up, it's broken. But Isn't there anything that can be wrong with an output tube that causes your amp to sound em...f*cked up?


The preamp tubes aren't visible, so I wouldn't know if one just isn't working.


My amp sounds extremely buzzy and weak, it's actually quite similar to playing through a fuzz pedal with a flat battery...


Anyone?


Cheers.

 

 

sounds like a power amp tube.

 

broken preamp tubes = no sound at all

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Originally posted by Eye_Of_The_Liger



You'll know when you blow a preamp tube when you hear a really loud screeching sound, even with your guitar not plugged in. You can find a blown preamp tube by just looking down the center of the retainer (the aluminum sleeve holding it in place). Just look for the one that's not glowing.


When a power tube completely craps out, your amp usually just cuts off, at which point you have to replace it and the fuse as well. If your amp sounds weak, it could be because one of the power tubes is on it's way out. Replace it ASAP if you want to avoid having to replace the fuse.

 

Pretty much everything you said is not true. :thu:

 

-Joe

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Originally posted by OverDriven



Pretty much everything you said is not true.
:thu:

-Joe

 

Well, it's true for my amp (Ampeg Reverbrocket Reissue, not that you care), and I work on it all the time.

 

Preamp tube craps out = EEEEEEEEE!!!!

Power tube craps out = guitar tone fizzles out into nothing, and if I'm lucky to turn it off quickly enough I can avoid having to replace the fuse

 

My god, this is why I wonder why I even bother posting on here anyway! People on the amp forum are assholes who swear they're right about about everything all the time...

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Originally posted by Eye_Of_The_Liger



Well, it's true for my amp, and I work on it all the time.


My god, why do I even bother anyway??? People on the amp forum are assholes...

 

 

Not trying to be an asshole man, its just that misinformation irritates me, and I'm a little edgy today. *lights cigarette* Anyways, let me go through your post and explain:

 

 

You'll know when you blow a preamp tube when you hear a really loud screeching sound, even with your guitar not plugged in. You can find a blown preamp tube by just looking down the center of the retainer (the aluminum sleeve holding it in place). Just look for the one that's not glowing.

 

 

Ok...a bad preamp tube can do a number of things. It can go microphonic and can cause excessive feedback. It can make your amp much quieter than it should be. It can make your tone thin and lifeless. It can make you amp lack gain. It can also make the amp lack punch.

 

About looking for a tube thats not glowing...95% of the time a bad tube will still glow. The glow is just the heater filament. Many other things can go wrong with the tube that will have no effect on the tube's glow, though the tube is still bad.

 

 

When a power tube completely craps out, your amp usually just cuts off, at which point you have to replace it and the fuse as well. If your amp sounds weak, it could be because one of the power tubes is on it's way out. Replace it ASAP if you want to avoid having to replace the fuse.

 

 

A power tube crapping out is just like preamp tubes...there are many many effects. If you have a major failure in the tube, yes it can blow a fuse. You can also just lose some volume, punch, tone, etc.

 

My guess about this guy's amp is that one or more of the pre tubes are bad. Usually when the amp develops a bad gain structure, its coming from where the gain is generated...in the pre tubes. Check those first.

 

-Joe

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Thanks a lot.

 

So would it be safe to check the tubes by replacing them with the tubes in my twin reverb? They're all EL34's btw.

 

I understand there's more involved then just plugging the tubes in when you plan on permanently replacing 'em, but will it hurt if I just try it for a minute and then put the tubes back in my twin?

 

What about the fuses? If they're dead will I risk damaging the amp more by swapping the tubes?

 

Cheers.

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Originally posted by thom

Thanks a lot.


So would it be safe to check the tubes by replacing them with the tubes in my twin reverb? They're all EL34's btw.


Yep, you should be fine doing that to test


I understand there's more involved then just plugging the tubes in when you plan on permanently replacing 'em, but will it hurt if I just try it for a minute and then put the tubes back in my twin?


Yeah, you should rebias (or at least check the bias) when replacing tubes, but you're right; just for testing it's fine to swap and see if the amp works.


What about the fuses? If they're dead will I risk damaging the amp more by swapping the tubes?


If the fuses are dead, you're going to have to replace those as well, the amp won't run without them

 

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"Won't run"...Meaning a broken fuse would totally cut of the power, I wouldn't be able to turn the amp on.?

 

So in that case the fuse in mine should still be okay, right?

 

Thanks again, you've been of great help.

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Originally posted by thom

"Won't run"...Meaning a broken fuse would totally cut of the power, I wouldn't be able to turn the amp on.?


So in that case the fuse in mine should still be okay, right?


Thanks again, you've been of great help.

 

depends on which fuse blew; typically tube amps have at least 2; one for the high voltage, and one for the heaters. When a power tube goes and takes a fuse with it, it's generally the high voltage one, so the amp may still power on (the power light will light up, etc), but switching from standby to operate won't do anything.

 

if your amp is still making noise, your fuses are fine (as far as I know, someone please correct me if I'm wrong)

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Yup, my amp has two fuses. And I do get noise, so if you're right the fuses should be okay.

 

Thanks again dude. I'll be back in half an hour or so, gonna try swapping the tubes now.

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Originally posted by OverDriven



Not trying to be an asshole man, its just that misinformation irritates me, and I'm a little edgy today. *lights cigarette* Anyways, let me go through your post and explain:




Ok...a bad preamp tube can do a number of things. It can go microphonic and can cause excessive feedback. It can make your amp much quieter than it should be. It can make your tone thin and lifeless. It can make you amp lack gain. It can also make the amp lack punch.


About looking for a tube thats not glowing...95% of the time a bad tube will still glow. The glow is just the heater filament. Many other things can go wrong with the tube that will have no effect on the tube's glow, though the tube is still bad.




A power tube crapping out is just like preamp tubes...there are many many effects. If you have a major failure in the tube, yes it can blow a fuse. You can also just lose some volume, punch, tone, etc.


My guess about this guy's amp is that one or more of the pre tubes are bad. Usually when the amp develops a bad gain structure, its coming from where the gain is generated...in the pre tubes. Check those first.


-Joe

 

There. Now was that so hard? ;):D

 

Yeah, I know I don't know everything, but since I have 5 different pieces of tube gear, I figure it wouldn't be a bad idea to learn a thing or two.

 

Right now I'm at the point where I feel I have bits an pieces of the "right" info, but there's still plenty that I don't know yet.

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Oops, I was confusing my marshall JCM800 with my marshall Super Bass...Silly me.

 

The super bass doesn't have EL34s in it, I won't be able to swap em with my twin's tubes.

 

But it's safe to run a 100watt amp on only two tubes right? So if there's only one or two broken tubes, can't I check which ones they are by pulling out the outer tubes and trying out every possible pair?

 

Cheers.

 

Edit: Tought I'd mension...I don't know anything about this, so for all I know the tubes in my Marshall are EL34's with different sockets...

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Bump!

 

I found out it should be okay to pull either the two inner or the two outer tubes as long as I set the impedance of the amp to 8ohm if I'm using it with a 16ohm cabinet.

 

That's the case with all tube types, right?

 

Cheers.

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Sorry for the inpatience, but...Bump!

 

 

So I tried a couple of tube combinations. The first one was no good. I noticed what I probably should have noticed before: One tube didn't even glow or anything.

I replaced it with one that did, but the thin fuzzy sound is still there.

 

Then I noticed that one of the three preamp tubes wasn't glowing...

Isn't a preamp tube easy to replace? No rebiasing required, right?

 

Thanks.

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Yes, you can replace a preamp tube without worrying about bias or anything.

 

FYI, you shouldn't run the power tubes until they completely fail. When they go they can often take other components with them which just makes it more expensive to repair. As has already been mentioned, when tubes start to wear out they can sound dull and lifeless. This is when they should be replaced. If you're not sure, about a year of regular playing at moderate volume is the rule of thumb, possibly longer if you play less or at lower volume. Might take a few sets to get a feel for how long they last with your playing habits and how they sound as they start to wear out. If you don't notice a change with the new tubes, hang on to the old ones as a backup.

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Hey recently my twin reverb starts to sound like the link. At first it sounded to me like a broken speaker but after look closely i noticed the speakers were ok and one od the tubes flashes a blue glow at the same time that the noise.

Any thoughs here? is just a broken power tube?

Thanks!

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The blue comes from the Getter inside the tube. It's is rarely a sign of a defect at all. In fact, many tubes have a blue glow, especially modern tubes.

 

If they were glowing cherry red then you definitely have a problem.

 

Sound quality can be a number of different issues. I'd start by replacing the preamp tubes first. Preamp tubes tend to sound distorted or microphonic at any volume. They wear out quicker in a combo due to vibrations from the speakers. I would suggest changing them all at the same time. If one's starting to go the others are sure to follow.

 

Power tubes tend to wear out and loose they're headroom. They break up earlier at higher volumes. Low volumes they tend to loose they're presence and frequency response but may still produce clean tones when turned down. The number of hours you put on the tubes and the brand of tubes can help determine when they need replacement. Again, a combo used several shows a week may only get 6~12 months out of the tubes. A player who only plays occasionally may get double or triple that life.

 

Other issues can be caused by caps aging. As an example I was getting static and fuzz from the bass channel of my Bassman amp. I first thought it might have been the preamp tubes since they had been in there a good 10 years with minimal use. The preamp tubes made a huge sound quality difference but I still had a weak signal and noise on the bass channel. I traced it down to being a coupling cap in the preamp. After replacing it the amp worked like new again. The amp is 50 years old now so its not the kind of failure you'd expect with newer amps but the quality of newer caps aren't as good as they used to be. Any amp over 10 years old can still have these less kinds of failures just less frequently.

 

I'd start with the preamp tubes, then the power tubes. Power tubes need to be rebased if you replace them.

I tried out 9 different brands of preamp tubes and 4 different sets of power tubes. I found the Electro Harmonix to give me the strongest and brightest tones with the lowest noise. A Twin tends to be a very bright amp. You may want to try JJ's. The tubes have a slightly lower output and duller sound compared to the EH. Groove tubes are excellent in Fenders too. I got 15 years out of my last set of Groove power tubes. They come in 3 different power levels, low medium and high. Again, a Tins is a very loud amp, I doubt you need the high gain output.

 

You have to buy power tubes as quad sets too or you'll never get them biased properly. If you find your old tubes a mixed bag set it may explain why your amps gone south. A matched set is likely to fatigue more evenly like wear on car tires. If you have mixed brands or vintage tubes they can weaken or fail at different times.

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