Preamp tube problem?

[chedwerks]

Hey fellas, still check out the site and read all the time, just don't post very often. I plugged in today and I think my tubes are finally going, especially the preamp tube. The drive channel is really flabby and produces hardly any gain at all. The clean side is decent sounding but with a definite decrease in volume output. Also on clean I get a tiny bit of crackle when I roll the gain over a little bit. This is my first tube amp and I haven't changed the tubes since I got it over a year ago. I just wanted to see if y'all thought this would be the best place to start in getting my amp back up to speed? It's an Egnater Tweaker btw which comes with pretty unimpressive stock tubes in the first place which might explain their failure. I hope this is the problem so I can try new tubes as well and see how they change my tone
Thanks
Mike

[meowmix]

The pre-amp tubes should be replaced first. Those are the 12A_7 ones. Don't replace the power tubes yet, they better with age.

It is not uncommon to replace the pre-amp tubes every year or less.

[chedwerks]

Thanks meowmix I was thinking the same thing because the power tubes don't seem to be showing problems and they rarely get pushed too hard due to complaining neighbors. I was kinda surprised the preamp lasted as long as it did but when it happened it was kinda sudden so I was worried it could be something else. I know this was a newbie question but I think some of you might know how it is when your stuff isn't working right. Immediate panic

[KenC]

My Fender Bassman Ten is in the shop right now having a defective pre-amp tube replaced. I used it thirty years on the original tubes and caps, and finally had to replace them two months ago. I was getting a flabby sound and loss of volume in both channels. After the retube/recap, the tone was wonderful but I got some crackling for the first week or so. Over the past 2-3 weeks the crackling came back, and finally the volume started dropping on the bass channel. It should be ready with another new pre-amp tube tomorrow.

Good luck!

Ken

[blargfromouterspace]

The pre-amp tubes should be replaced first. Those are the 12A_7 ones. Don't replace the power tubes yet, they better with age.

It is not uncommon to replace the pre-amp tubes every year or less.

IME its the power tubes that go before the pre-amp tubes. I've changed power tubes twice in the last year, and have had no problems ever with pre-amp tubes.

If you have some tubes handy you can do it yourself, its as easy as changing a lightbulb and you don't need to get the ladder out . According to the Egnater website the Tweaker is a fixed bias amp, so you don't need to re-bias if you change the power tubes.

[louis cyfer]

The pre-amp tubes should be replaced first. Those are the 12A_7 ones. Don't replace the power tubes yet, they better with age.

It is not uncommon to replace the pre-amp tubes every year or less.

IME its the power tubes that go before the pre-amp tubes. I've changed power tubes twice in the last year, and have had no problems ever with pre-amp tubes.

If you have some tubes handy you can do it yourself, its as easy as changing a lightbulb and you don't need to get the ladder out . According to the Egnater website the Tweaker is a fixed bias amp, so you don't need to re-bias if you change the power tubes.

the other way around. all the egnater amps other than the tweaker are fixed bias, so they need bias adjustments, the tweaker is cathode bias, so no biasing is necessary. fixed bias (adjustable) needs biasing, chatode biased does not.

"Are the Egnater amps cathode or fix biased?
All of the models, with the exception of the Tweaker, are fixed/adjustable bias with easy to use test points. Consult the owner’s manuals or contact support@egnateramps.com for information on how to properly adjust the bias. The Tweaker is cathode biased so there is no adjustment required when replacing tubes."

[meowmix]

KenC: What tubes were those? Tubes built 30 years ago had higher standards no doubt. It is hard to tell what one might get today.

Blarg: Your power tubes go out before the pre-amp! Never heard that before. I need to do some researching on that one.
The 12A_7 should be the easiest and cheapest to test. Every tube owner should have a least 1 good 12A_7 laying around. Pop one out, replace, test. If no sound difference, then it wasn't that tube. Put the old one back in and go to the next tube in the signal chain and test.

[blargfromouterspace]

Meow - Happens to me and everyone I know. I've personally never seen a pre-amp tube go, but have seen several occasions where a faulty power tube has ended the night early.

Louis - I've always assumed that amps that don't require adjustment were called fixed bias, because thats what the name implies. To me the term "fixed/adjustable bias" is directly contradictory. I'm sure that the fellow at Egnater knows more about the nomenclature of valve amplifier biasing arrangements than I do, but that is confusing.

[meowmix]

Meow - Happens to me and everyone I know. I've personally never seen a pre-amp tube go, but have seen several occasions where a faulty power tube has ended the night early.

My Fender amps 12A_7s were the first to stop working correctly. They don't blow up. They just stop giving off good tone or sometimes you here static in the amp. Same thing with my G.T. Trio. What amp do you have where the power tubes break all the time?

[chedwerks]

Agreed Blarg, the wording on that one is completely confusing. Would the consensus be that I can just take the old one out and put a new one in? Any general things I need to watch out for to avoid killing myself or my amp?
That's also interesting about the power tubes going before the preamp tube(s). Just seems logical -to me- that the preamp would take more stress while using the amp.

[meowmix]

Agreed Blarg, the wording on that one is completely confusing. Would the consensus be that I can just take the old one out and put a new one in? Any general things I need to watch out for to avoid killing myself or my amp?
That's also interesting about the power tubes going before the preamp tube(s). Just seems logical -to me- that the preamp would take more stress while using the amp.

Blag is from down under. Everything is the opposite over there. Keep that in mind when communicating with him.

[louis cyfer]

Meow - Happens to me and everyone I know. I've personally never seen a pre-amp tube go, but have seen several occasions where a faulty power tube has ended the night early.

Louis - I've always assumed that amps that don't require adjustment were called fixed bias, because thats what the name implies. To me the term "fixed/adjustable bias" is directly contradictory. I'm sure that the fellow at Egnater knows more about the nomenclature of valve amplifier biasing arrangements than I do, but that is confusing.

"There are two main types of biasing: fixed biasing and cathode biasing. Fixed biasing does not mean the bias is not adjustable, in fact, it usually means the opposite. Cathode biasing is usually fixed, and not adjustable, and fixed biasing is usually adjustable with a small trimmer potentiometer, or "trimpot". It is no wonder the subject is confusing to people!"

Fixed biasing means the tube is biased by means of a DC voltage, which is usually a negative voltage applied to the grid of the tube with respect to the cathode. As the negative grid voltage is adjusted, the bias current will increase or decrease, depending upon the direction the bias voltage is going. In general, as the bias voltage becomes more negative, the bias current becomes smaller, and the tube is biased "colder". As the bias voltage is adjusted less negative, towards zero volts DC, the bias current becomes larger, and the tube is biased "hotter". This is because a tube is a "normally on" device; that is, it allows current to flow from the cathode to the plate when the grid is at zero volts with respect to the cathode. The tube can be turned off, and the current flow stopped, by making the grid voltage negative with respect to the cathode. The tube can also be biased by referencing the grid to ground, or zero volts DC, and applying a positive DC voltage to the cathode. This is the same as keeping the cathode at ground and applying a negative DC voltage to the grid, because it is the grid voltage with respect to the cathode that determines the amount of bias current in the tube.

Since vacuum tubes are "normally on" devices, a trick can be used to bias them without having to supply a negative DC voltage source to the grid. If a resistor is placed between the cathode and ground, and the grid of the tube is referenced to ground (usually by connecting a large value resistor, such as a 1Meg, from grid to ground), the tube will try to conduct a large current from cathode to plate, since the grid and cathode are initially at ground potential. However, this cathode current flow will cause a voltage drop across the cathode resistor, making the cathode voltage positive with respect to the grid. Since the cathode voltage is now positive with respect to the grid, the current flow will decrease, and the tube will head back towards cutoff. A point of equilibrium will quickly be reached where the increase in current is offset exactly by the increase in cathode voltage,

[louis cyfer]

Agreed Blarg, the wording on that one is completely confusing. Would the consensus be that I can just take the old one out and put a new one in? Any general things I need to watch out for to avoid killing myself or my amp?
That's also interesting about the power tubes going before the preamp tube(s). Just seems logical -to me- that the preamp would take more stress while using the amp.

with the tweaker you can just swap the tubes, no need for measuring and adjusting. if you really want to be safe, unplug the amp and let it sit for a while so the large capacitors drain so there is no risk of shock.

[blargfromouterspace]

Blag is from down under. Everything is the opposite over there. Keep that in mind when communicating with him.

The power tubes don't break "all the time", they just wear out after 6-12 months of use, no big deal. I run the power section of my amp at maximum and the pre-amp around a quarter of the way up, so the power tubes do wear quicker. Simple as that. If your pre-amp tubes go then thats fine too.

Agreed Blarg, the wording on that one is completely confusing. Would the consensus be that I can just take the old one out and put a new one in? Any general things I need to watch out for to avoid killing myself or my amp?
That's also interesting about the power tubes going before the preamp tube(s). Just seems logical -to me- that the preamp would take more stress while using the amp.

Yep, just pull them out and put new ones in. Wiggle them out little by little rather than one solid tug so that you don't end up with glass in your fingers. Good luck with it Mike

[yowhatsshakin]

louis, excellent explanation of how these almost antiquated devices actually work. Thanks! I think this will be very helpful for a lot of people. Only thing missing is to explain how they work as amplifiers of the small signals your guitar is sending into the amp. But 'll leave that to you or Wikipedia of course ...

- Jos

[meowmix]

The power tubes don't break "all the time", they just wear out after 6-12 months of use, no big deal. I run the power section of my amp at maximum and the pre-amp around a quarter of the way up, so the power tubes do wear quicker. Simple as that. If your pre-amp tubes go then thats fine too.

Ahhh, makes sense now. That was going to be my next question. I never had that option on the early Fenders. I do on the new Power Amp, but I never turn it up more than 2-3 clicks.

[Graeme]

I have a egnater renegade combo and you are able set/adjust the bias voltage on the two banks of power amps. This even allows you to "tune" the tubes or use different pairs of tube types. My limited understanding of bias is it is needed to ensure enough idle current is fed in to the tube to stop it choking but not so much as it wears out by making it run too hot; a bit like setting the idling speed on a car. There is no mention of manually adjusting the bias for the preamp tubes so I assume that when it comes to replacing them it is simply a case of old out new in. From the previous messages it sound like this is done automatically. I am not sure what the set up is for the tweaker but I'd want to know why they were going. If you have been giving the amp some sustained hammer over long periods then fair enough. Good quality tubes are not cheap in the UK and I guess it's same in the US so if you are going for a new set then it might be worth having the bias voltage checked by an someone qualified just to make sure they are not running too hot.

[louis cyfer]

I have a egnater renegade combo and you are able set/adjust the bias voltage on the two banks of power amps. This even allows you to "tune" the tubes or use different pairs of tube types. My limited understanding of bias is it is needed to ensure enough idle current is fed in to the tube to stop it choking but not so much as it wears out by making it run too hot; a bit like setting the idling speed on a car. There is no mention of manually adjusting the bias for the preamp tubes so I assume that when it comes to replacing them it is simply a case of old out new in. From the previous messages it sound like this is done automatically. I am not sure what the set up is for the tweaker but I'd want to know why they were going. If you have been giving the amp some sustained hammer over long periods then fair enough. Good quality tubes are not cheap in the UK and I guess it's same in the US so if you are going for a new set then it might be worth having the bias voltage checked by an someone qualified just to make sure they are not running too hot.

the tweaker is cathode biased, unlike the egnater, not adjustable, and not an issue.

[meowmix]

The power tubes don't break "all the time", they just wear out after 6-12 months of use, no big deal. I run the power section of my amp at maximum and the pre-amp around a quarter of the way up, so the power tubes do wear quicker. Simple as that. If your pre-amp tubes go then thats fine too.

After speaking to my source. The tubes you think are worn out is just the opposite. They are broken in. Good for another 30 years. Of course, you can disagree.

What tone difference do you hear from
A.) Power turned all the way up, pre-amp a quarter compared to
B.) Power up a quarter, pre-amp all the way up.
?

I tried cranking the power, and minimizing the pre. And I don't hear any significant difference.
But if you say, you can hear a difference. It is all good. Let your ears decide not some dude on the interweb.

Thanks

[louis cyfer]

The power tubes don't break "all the time", they just wear out after 6-12 months of use, no big deal. I run the power section of my amp at maximum and the pre-amp around a quarter of the way up, so the power tubes do wear quicker. Simple as that. If your pre-amp tubes go then thats fine too.

After speaking to my source. The tubes you think are worn out is just the opposite. They are broken in. Good for another 30 years. Of course, you can disagree.

What tone difference do you hear from
A.) Power turned all the way up, pre-amp a quarter compared to
B.) Power up a quarter, pre-amp all the way up.
?

I tried cranking the power, and minimizing the pre. And I don't hear any significant difference.
But if you say, you can hear a difference. It is all good. Let your ears decide not some dude on the interweb.

Thanks

pretty simple to know when a tube is no good. put it on a tube tester. the tubes made back in the 50's 60's indeed lasted much longer. the current production tubes do not.

[GGL Stop]

Louis,
That reminds me of the days when you could go to the seven eleven and test a tube. I was in a vocational high school for electronics back then and the teacher would let us out to test tubes. Ahhh, the memories. Come to think of it, I was in an electronics class and we didn't have a tube tester, strange. I don't know of anyplace readily available that let's you tests tubes for free anymore.


Jeff

[blargfromouterspace]

The power tubes don't break "all the time", they just wear out after 6-12 months of use, no big deal. I run the power section of my amp at maximum and the pre-amp around a quarter of the way up, so the power tubes do wear quicker. Simple as that. If your pre-amp tubes go then thats fine too.

After speaking to my source. The tubes you think are worn out is just the opposite. They are broken in. Good for another 30 years. Of course, you can disagree.

What tone difference do you hear from
A.) Power turned all the way up, pre-amp a quarter compared to
B.) Power up a quarter, pre-amp all the way up.
?

I tried cranking the power, and minimizing the pre. And I don't hear any significant difference.
But if you say, you can hear a difference. It is all good. Let your ears decide not some dude on the interweb.

Thanks

You misunderstand - when I say they wear out after 6-12 months, I mean they wear out to the point of failure. It's dead easy to know when that happens because no sound comes out. I will happily sell your source all of my 'broken in' tubes for $10 each

With the master volume cranked on my amp there is a huge difference in the low end, it gets 'bigger'. With the pre all the way up my amp sounds trebly, scratchy and horrible, but that's not a sound it was designed for. Seeing as were not even talking about the same amp it's highly likely that your amp doesn't sound or behave anything like mine does.

[GGL Stop]

Blarg,
I am starting to think that he is wanting that fresh crisp snappy tone with new tubes and not broken in. I know some people just like that tone and when the tubes are broke in then don't feel it anymore.


My personal suggestion would be to take the amp to a tech, maybe there is something else going on in the amp and he is not getting that groovy tube sound he is seeking. You can always go in and get an estimate if it's a good tech that won't tell you you, you need all new tubes. Just my one and a half cents worth here. I am a big fan of matched tubes since my amp is fixed. The person who said to have a spare 12A_7s is on the right track here. But when you do a full throttle on the preamp then who knows right? Could be bad tubes all around or just pushing to hard. In that event they are going to wear down much faster. Go see a good tech my man and see what he/she has to say.

Also check out this site for debugging tube amps: http://www.geofex.com/ampdbug/ampdebug.htm




Stop

[meowmix]

You misunderstand - when I say they wear out after 6-12 months, I mean they wear out to the point of failure. It's dead easy to know when that happens because no sound comes out.

What amp is this? This sounds so odd to me. I wonder if this is by design, or there is some faulty equipment inside.

With the master volume cranked on my amp there is a huge difference in the low end, it gets 'bigger'. With the pre all the way up my amp sounds trebly, scratchy and horrible, but that's not a sound it was designed for. Seeing as were not even talking about the same amp it's highly likely that your amp doesn't sound or behave anything like mine does.

Mine do not operate like this, that is why I am so curious.
I was raised on the black face fenders. No master volume. The amp I use now is a DIY.

[louis cyfer]

You misunderstand - when I say they wear out after 6-12 months, I mean they wear out to the point of failure. It's dead easy to know when that happens because no sound comes out.

What amp is this? This sounds so odd to me. I wonder if this is by design, or there is some faulty equipment inside.

With the master volume cranked on my amp there is a huge difference in the low end, it gets 'bigger'. With the pre all the way up my amp sounds trebly, scratchy and horrible, but that's not a sound it was designed for. Seeing as were not even talking about the same amp it's highly likely that your amp doesn't sound or behave anything like mine does.

Mine do not operate like this, that is why I am so curious.
I was raised on the black face fenders. No master volume. The amp I use now is a DIY.

meow, if you run the power tube wide open, you get a cleaner, fuller, more touch sensitive sound. you adjust desired volume with the preamp level. with the preamp tubes wide open, you overload the input sage of the power section and get a lot more distortion, but kind of squished and harsh. running the power tubes wide open will cause them to fail much quicker.

[blargfromouterspace]

meow, if you run the power tube wide open, you get a cleaner, fuller, more touch sensitive sound. you adjust desired volume with the preamp level. with the preamp tubes wide open, you overload the input sage of the power section and get a lot more distortion, but kind of squished and harsh. running the power tubes wide open will cause them to fail much quicker.

Exactly, very well put.

What amp is this? This sounds so odd to me. I wonder if this is by design, or there is some faulty equipment inside.

With the master volume cranked on my amp there is a huge difference in the low end, it gets 'bigger'. With the pre all the way up my amp sounds trebly, scratchy and horrible, but that's not a sound it was designed for. Seeing as were not even talking about the same amp it's highly likely that your amp doesn't sound or behave anything like mine does.

Mine do not operate like this, that is why I am so curious.
I was raised on the black face fenders. No master volume. The amp I use now is a DIY.

Its one of THESE. Switchable 15/30W EL-84 powered 212 combo with Eminence Wizard speakers in it.

Its not faulty - there's no oscillation or squeal and it certainly doesn't lack volume. You can get a good driven sound out of it BUT the master has to be cranked, and by the time the pre-amp starts adding distortion it's incredibly loud.

What is your DIY thing based around? Some pics would be cool I have a tweed bandmaster clone project thats about 80% complete, looking forward to finishing it off.

[meowmix]

Its one of THESE. Switchable 15/30W EL-84 powered 212 combo with Eminence Wizard speakers in it.

Its not faulty - there's no oscillation or squeal and it certainly doesn't lack volume. You can get a good driven sound out of it BUT the master has to be cranked, and by the time the pre-amp starts adding distortion it's incredibly loud.

What is your DIY thing based around? Some pics would be cool I have a tweed bandmaster clone project thats about 80% complete, looking forward to finishing it off.

Thanks Jamie,
I don't think we will ever be on the same page here. If you like this amp, that's great. No need to listen to me. Personally, I think there is a design flaw in this amp. Power tubes break after 6-12 months of use tells me there is some unconventional thing going on. That can very well be the reason why you get that tone, but there are more than 1 way to skin a cat.


I have LR duty next month, I am saving the DIY amp for then.

[louis cyfer]

Its one of THESE. Switchable 15/30W EL-84 powered 212 combo with Eminence Wizard speakers in it.

Its not faulty - there's no oscillation or squeal and it certainly doesn't lack volume. You can get a good driven sound out of it BUT the master has to be cranked, and by the time the pre-amp starts adding distortion it's incredibly loud.

What is your DIY thing based around? Some pics would be cool I have a tweed bandmaster clone project thats about 80% complete, looking forward to finishing it off.

Thanks Jamie,
I don't think we will ever be on the same page here. If you like this amp, that's great. No need to listen to me. Personally, I think there is a design flaw in this amp. Power tubes break after 6-12 months of use tells me there is some unconventional thing going on. That can very well be the reason why you get that tone, but there are more than 1 way to skin a cat.


I have LR duty next month, I am saving the DIY amp for then.

meow, how often do you play with your amp wide open? when pushed that much, they break.


blarg, this is what meow using

http://www.londonpower.com/

[meowmix]

meow, how often do you play with your amp wide open? when pushed that much, they break.

How much do I want to go deaf? Answer: Never.
Louis, the manufacture states on their website that replacing tubes every six months or maybe 1-2 years is normal. Really?
I must be not normal. Far too often I seen guitar players wanting that "tone" and the only way to get it is by cranking the power tubes. Call me tone deaf, I don't hear a quality difference only a volume difference.
[youtube]nu0R96OZy6w[/youtube]

[suave eddie]

Far too often I seen guitar players wanting that "tone" and the only way to get it is by cranking the power tubes. Call me tone deaf, I don't hear a quality difference only a volume difference.

I don't know what kind of amps you have experience with but I have played enough low to moderate powered (non-master volume) tube amps to know that the tone changes drastically as you increase the volume.

On my 22 watt Mesa Boogie Subway Blues, I don't believe the volume increases once the knob is turned past about "7"......it only gets more compressed and thick sounding.

Here's an interesting excerpt from the Owners Manual that came with the amp:
"VOLUME: (GAIN)
This is by far the most powerful control in the amp. It not only determines the amplifier's overall Gain amount, shape and sensitivity...but it is also a powerful Tone control. Generally speaking, whatever is dialed here ultimately determines the amps personality. Set low, it allows cleaner, brighter sounds with enhanced dynamic response, especially in the higher frequencies. Set high, the whole personality of the channel becomes darker, fatter and more overdriven.