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Roc8995 11-26-2006 12:19 AM

Everything you ever wanted to know about TUBES! UPDATES!
Update for 2015!
Since I can't make a list of everything anyone would ever want to know, please ask if your question is not answered somewhere here.

You will notice that I constantly use phrases like "in general" and "usually..." in this guide. Amps and tubes cover a huge range and this is meant only as a basic introduction. There are exceptions everywhere, so in order to make this guide as straightforward as possible I have chosen to focus on what is most often true.

Sections of the thread -
Post 1:
1. What's a tube and what is it doing in my amp?

2. Why tubes?
3. Why not tubes?
4. Which tubes can I use in my amp?
5. Is my tube broken?

Post 2:
6. What the hell is biasing?
7. I heard these things about tubes...
8. What common tubes sound like

1. What's a tube and what is it doing in my amp?

Simply speaking, tubes are devices that control the flow of energy. They're alternatively called "valves," which is a more descriptive term, since a valve nicely illustrates what a tube does. A valve allows you to use a small motion (turn a faucet on, or a light switch, etc.) to create a larger change (water flows, lights turn on, etc.) So, a tube takes a small signal (the input) and turns it into a bigger one (the output), which of course is amplification.
Of course, the method of amplification matters. There is no device in the world that can amplify perfectly; there is no such thing as "just louder." There is always some modification of the signal. The good news is that, in general, electric guitarists do not want an accurate amplification. Electric guitars just do not sound very good on their own. So the amplifier's job in our situation is not just to make the guitar louder, it is to give it some flavor by purposefully amplifying in a non-linear fashion. Tubes, it turns out, are pretty good at this.

For our purposes, there are four categories of tube:
-Preamp tubes. These are the smaller tubes in your amp, and they take the signal from your guitar and bump it up to a place where it can be amplified by the larger power tubes. They also do a lot of the tone shaping and are the ones most likely to distort, especially if you have an overdrive pedal or high output pickups. Some amps use preamp tubes to drive reverb, tremolo, vibrato, and effects loop circuitry as well.
-Phase inverter. This single tube is not found in all amps, but when it is, it is almost always the one closest to the power tubes, and it will be the same type of tube as the preamp tubes. Some people lump the phase inverter in with the preamp, which is reasonable. The phase inverter splits your signal into two identical but inverted halves, so the power tubes can amplify more efficiently.
-Power tubes. These are the larger tubes, and come in "sets" of 1, 2, 4, or very rarely 8. They do most of the amplification work.
-Rectifier tubes. These are not present in every tube amp. They're used to help convert the AC power from your electrical socket into the DC power that the rest of the tubes use.

2. Why tubes?
Because they sound good! There is quite a lot of debate on the subject, but the short answer is that tubes were the only devices available for amplification when the electric guitar was becoming popular, and so they shaped the way that we "expect" to hear guitar sounds. On top of that, tubes exhibit some odd characteristics that make them good for our purposes. For example, when faced with a larger input signal than they can properly amplify, tubes will gently start to squish the top and bottom of the signal wave. This is overdrive, and it evolves into distortion and compression as the signal increases. Solid state devices tend to have a more instant transition, where they go from "clean" (no distortion) to "squarewave" (fuzzy/lots of distortion) fairly quickly.

3. Why not tubes?
The invention of the transistor led to the creation of the counterpart to the tube amp, the "solid state" or "SS" amp. These amps use a much smaller, more efficient device to amplify. Again, there is a lot of debate about preference and performance, but a lot of it is confounded by the fact that, in very general terms, SS amps tend to be cheaper and made to be economical rather than high quality. This is not to say that anything is inherently less desirable about SS amplification, but it makes it difficult to talk about SS/Tube amps in general without falling into stereotypes.
In general, though, SS amplification tends to have some common advantages and disadvantages compared to tube. SS components are smaller and more efficient, so they can be made lighter and louder than comparably sized tube amps. On the other hand, they tend to distort ("clip") more harshly and abruptly than tubes, which means that often they sound worse as the volume goes up, as opposed to tube amps which generally sound better the louder they get.

4. Which tubes can I use in my amp?
It depends on the amp. Consult the manual or ask here if you're not sure. Most amps will take only one kind of power tube, so if for example your amp uses EL84s, you will only be able to use EL84s in the power section. You can usually use any brand of tube you like as long as the type of tube (EL34, 6L6GC, etc) is the same.
Power tubes should be bought in "sets," which are tubes with matched characteristics so they work efficiently together in your amp. "Pairs" and "Quads" are sold at any tube retailer. Power tubes should all be replaced as a group; preamp tubes can be replaced one at a time.
Preamp tubes are more flexible, and most of the time you can use any of the common preamp tubes interchangeably since nearly all amps use the 12AX7 family of tubes. The differences are in output, so a lower gain tube will get you a cleaner sound. Your amp probably has several preamp tubes. What each of them does varies by amp, but usually the ones farthest from the power tubes do the early amplification, and the ones closer to the power tubes handle the later amplification stages ("gain stages"), the phase inversion, and the reverb/tremolo/etc if they are present.
Common and interchangeable preamp tube types, from most to least gain, include:
Tubes on the same line are all the same tube, and will often have some extra letters afterward, e.g. 12AX7A, 12AX7B etc.

Please ask here or contact your amp's manufacturer or a decent tube dealer if you are not sure about what tubes your amp can use safely. Many tubes use the same sockets but have very different operating characteristics, and you can smoke a set of tubes, or even your entire amp, if you just stick tubes in and assume they're ok because they physically fit in your amp.

5. Is my tube broken?
Tubes will eventually die, break, or wear out. The easiest way to test if a tube is dead is simply to replace it (or, in the case of power tubes, the whole set) to see if the amp goes back to working properly. Keeping spare tubes around is a good idea.
Tubes are not lightbulbs; whether or not a tube is glowing is not a good indicator of it working properly. Some tubes glow more than others, and some tubes will exhibit a blueish glow, or a bright flash on startup. These are normal.
The one visual cue to look for is redplating. This is where the grey sides (plates) of the tubes start to overheat severely. While glow from the top, bottom, and interior elements are normal, plate glow is a bad sign, and you should turn off the amp immediately and replace the tubes. If the new tubes start to redplate, the amp needs to be serviced.
Tubes, most usually preamp tubes, can go "microphonic" which causes them to start amplifying ambient vibrations and not just the electrical signal from your guitar. They'll get loud and "splatty" sounding and generally the amp will sound terrible. An easy test for this is to turn your amp on and tap each tube with a pencil. The preamp tubes will make a bit of a tapping and ringing sound through the speaker normally, but a microphonic tube will give you a loud thump when you tap it.

Roc8995 11-26-2006 12:23 AM

6. What the hell is biasing?

6. What the hell is biasing?
Biasing is a way to adjust the amp so that it uses the power tubes efficiently. A "hotter" bias will cause the tubes to run harder and not last as long, but they will distort earlier and may sound better. A "colder" bias will cause the tubes to last longer and distort less quickly (more headroom). Biasing is often done only when installing new power tubes, to dial the amp in to the particular tube set. Tube characteristics vary a fair amount, and biasing lets you keep the amp's sound consistent despite those variations.
There are plenty of bias guides available around the internet, I won't repeat them here. The process depends largely on the particular amp, so searching for bias instructions for your model or brand specifically will often prove helpful.
Not all amps need to be biased, and there is some confusion about what the different terms mean. Particularly confusing is the term "fixed bias" because it is often assumed to mean that the bias of the amp cannot be adjusted. This is not true.
-Fixed bias refers to the type of circuit where the tube's bias does not change during normal operation - its bias point is set, "fixed," by the user or manufacturer. Within the fixed bias genre, there are two subtypes: adjustable and non-adjustable. This simply refers to whether or not there is a mechanism within the amp that lets the user adjust the bias. Some modern amps run the power tubes very cold, so the manufacturer does not provide a way to adjust the bias because they assume that any tube used in the amp will not be in danger of being biased too hot. It also saves the manufacturer the time and cost of installing and setting a bias adjustment circuit. These types of amp are therefore called "fixed, non-adjustable."
-Cathode bias is the counterpart to fixed bias. In this circuit a tube's bias actually changes dynamically while it's being played, based on a feedback loop within the circuit (at the cathode, naturally enough). These amps are generally not manually biased, since the circuit should keep them within reasonable range.
In general, the only type of amp that should be biased every time the power tubes are changed are fixed, adjustable bias amps.
Preamp tubes are almost always cathode biased, so they do not need to be manually rebiased after a tube change.

7. I heard these things about tubes...
Under construction. **** what ya heard.

8. What common tubes sound like
*Keep in mind that these are my opinions and should only serve as a very general guide. Tubes are an art, not a science, and a tube I hate may be something you love. Your results may vary.*

Current Production Tubes:

Preamp Tubes:

12AX7/12AX7A/7025/ECC83/CV4004 (Different names, same tube):

A good preamp tube, a bit dark. They're well made. They are higher gain than most 12AX7s.

Tung-Sol 12AX7:
These are excellent tubes. They sound very balanced and open. They are especially good in the microphonics department. DO NOT use them in a cathode follower stage! They will die. If you don't know if your amp has a cathode follower stage, ask before you put a tung-sol in.

E-H 12AX7:
These are decent tubes that seem to last a while. They're a little smoother than the Tung-sol but at the cost of often sounding dull or muddy.

Sovtek 12AX7-LPS:
These tubes sound "just ok." They're cheap and durable and are perfect for reverb drivers and phase inverters in high-gain amps. Like the Tung-sols, they should not be used in cathode followers.

Sino 12AX7A: Decently balanced tube, these are great for using throughout the amp since they're so cheap.

Sovtek: Finally, Sovtek makes a good tube. It's a bit bright, but not harsh. A good choice for taming Fender amps that are too aggressive higher up on the volume control.


A solid tube, good if you want to get rid of some hiss from your amp or lower the gain by replacing a 12AX7. Very quiet and even. I like these.

Suffers from the JJ preamp disease: It's too dark. Construction's ok, but nothing to write home about. Just an all right tube.

Production Power Tubes:


JJ: Far and away the best EL-34 you can get without paying an arm and a leg. Higher gain than most, and a tad dark, but very articulate. Sweet.

Not a bad tube. They sound weaker than a JJ, and bright. Not a good choice for Marshalls.

Very close to the JJ in durability and microphonics, and a good balanced tube as far as tone. Great if a JJ is too dark for you.

Groove Tubes (GT rebrands its preamp tubes but makes its own power tubes):
"very nice tube, long lasting but have a alightly harsh tone to them. great headroom, and add an overdrive..incredible crunch. compared to jj's el34L, they had a tab less headroom, and i prefer the jj's distorted tone better, its more agressive and tones down better." Thanks to godofshred for that review.


Tung-Sol: Bright, round and smooth, they get the thumbs-up for bassman style amps.

JJ: Darker than the Tung-sol, these are also very nice tubes with a warmer OD. Twin Reverb and Hot Rod deluxe people like these.

There are two versions, can't remember which one I tested. They're dead quiet, but the tone suffers badly from it. They sound pretty lifeless.

Not as quiet as a Sovtek but the tone is much better. Sounded a tad dark, which is good as they mostly are used in over-bright Fender amps.

An excellent tube. Very smooth and buttery. Sounds great in Deluxe reverb-type amps. No problems with microphonics.

Both this and the Tung-Sol are great choices for a 6v6. A bit darker and more aggressive than the Tung-Sol. Again, no worries with noise.

Not a bad tube, but painfully mediocre in comparison to the JJ and Tung-Sol.


Sparkly, aggessive, chimy, and awesome. Everything an EL-84 should be. Seems to be better than others as far as hiss goes, but almost all EL-84 amps have some small white noise going on. Very well constructed. Treat your AC30 to four of these!

They sound decent, but don't have the harmonic content or definition of the JJs. Generally good as far as durability.

Uninspiring and generally noisy. This is probably what came with your amp. Throw them away.

NOS Tubes:

I have not tried enough NOS Power tubes to give a good comparison. These NOS Preamp tubes range a lot in price, but none of them are cheap. However, expect them to last much, much longer than any current-production preamp tube. They should be good for at least 10 years. They all sound amazing as well.

Telefunken: These tubes will last you 30 years. For real. They sound very hi-fi and are perfect for your clean channel. Great in Voxy amps. They aren't for everyone though. I would not put these in a Fender twin. They will make any amp incredibly articulate, so all you high-gainers take note!

Dark and smooth. Perfect for Marshalls that are a touch too trebly. Not a good choice for darker-voiced amps, as they will get muddy.

Mullard: "Agressive but quiet, really livens up the amp. Adds sizzle and 'oomph.'" - Thanks to godofshred for that one.

Balanced and warm. No microphonics. All-around good tube. Worth the price.

RCA: Same as their 12AX7, with a bit less gain.

Mullard: Very cool, a 3-D sounding tube that's not real expensive and will last forever. Very warm, tight bass.

Here are some more reviews courtesy of darkarbiter:
Sovtek KT66:
Bright and chimey when clean, but has a weak low end and overdrives harshly.

Philips 5751:
Smooth highs, and solid lows. Good for smoothing out an amp with a harsher top end, and to get less gain from the preamp section.

RCA 12AU7:
Smooth and warm with low noise and microphonics.

Groove Tube 12AX7:
Kind of harsh and brittle, not very musical. Works good as a tremolo tube to get a choppier, more agressive tremolo effect, though. Roc edit: groove tube 12AX7s are usually rebranded Sovteks, so this review is consistent with my previous estimation of that tube.

Groove Tube 12AU7:
Same goes for the 12AX7, but sounds decent as a phase inverter when you want low gain.

jj1565 11-26-2006 12:31 AM

nice post. worth adding to the amp sticky. :cheers:

Gutch220 11-26-2006 12:35 AM

that must have taken a while to do, but its too cut and dry. I think a lot of people will take that information as "written in concrete" and assume anything else is blasphemous. Many things dealing with tubes are subjective

Roc8995 11-26-2006 12:37 AM

I'll add a disclaimer. Thanks for the input.

bluespunkmetal 11-26-2006 12:41 AM

Ruby ?? Svetlana ?? MEsa ??

Erock503 11-26-2006 12:47 AM

Cool post. I haven't had the same experience with JJ preamp tubes though. Microphonic to me is a bad tube. I actually thought the EH were a little noisier preamp tubes, at least the sets I've owned.

Roc8995 11-26-2006 12:47 AM

Originally Posted by bluespunkmetal
Ruby ?? Svetlana ?? MEsa ??

Ruby and Mesa are just rebranded tubes, so I didn't list them here because they don't make their own tubes and it would be reduntant.

I have not had much experience with Svets, other than their EF86, which is a great tube, but so few amps use it I didn't think it would be worth putting up. I have heard their 12AX7 is incredible but haven't got my hands on one yet.

Rock Savior 11-26-2006 12:48 AM


good work Roc!!

Roc8995 11-26-2006 12:50 AM

Originally Posted by Erock503
Cool post. I haven't had the same experience with JJ preamp tubes though. Microphonic to me is a bad tube. I actually thought the EH were a little noisier preamp tubes, at least the sets I've owned.

There are two kinds of noise that come from tubes, microphonics and 'mechanical' noise. I didn't do a good job of discerning between the two. The EHs have a bit more mechanical noise (noisier in general), while the JJs go microphonic- that is, they are pretty quiet until they go bad. What I should have said is that the JJs are quiet mechanically but fail every once in a while.

bluespunkmetal 11-26-2006 12:56 AM

Nice... Thanks for the response....

Erock503 11-26-2006 01:11 AM

Originally Posted by Roc8995
There are two kinds of noise that come from tubes, microphonics and 'mechanical' noise. I didn't do a good job of discerning between the two. The EHs have a bit more mechanical noise (noisier in general), while the JJs go microphonic- that is, they are pretty quiet until they go bad. What I should have said is that the JJs are quiet mechanically but fail every once in a while.

IC, I'll have to keep that in mind, I didn't realize they were known to have a higher failure rate than other preamp tubes. That's not good, because I actually like their tone lot in my amp. I've been lucky with mine so far I guess, the only ones I've had actually fail on me are Mesa's and GT, however both were already in amps when I got them so they weren't new. I've only been using JJ preamp tubes for about 8 months though.

aznrockerdude 11-26-2006 01:33 AM

This should definitely be stickied.

forsaknazrael 11-26-2006 01:35 AM

This is exactly the kind of information I've been looking for. You rule, Roc.

aznrockerdude 11-26-2006 01:48 AM

Wait, what about Groove tubes?

Roc8995 11-26-2006 02:31 AM

Originally Posted by aznrockerdude
Wait, what about Groove tubes?

Groove tubes are just rebranded tubes. The problem is, they rebrand every kind of tube (JJ, Sovtek, Chinese crap, etc) so there's no way of knowing what you're going to get.

bluespunkmetal 11-26-2006 03:49 AM

Wait......... how do they rebrand a tube ??

Just peel the paint off ??

Wiro 11-26-2006 10:39 AM

Very nice Thread, very usefull!

Dave_Mc 11-26-2006 11:25 AM

nice post. I have no idea on the accuracy of it, lol, but assuming everyone else thinks it's good, i'd definitely second it for a merging into the stickies.

jj1565 11-26-2006 11:29 AM

in addition, if any of the guys familiar with any of the specific tubes mentioned want to offer their opinion, (different point of view)
we could get as much info as possible, merge them into the post and ask to add the finished post into the amp sticky.

edit: the nice thing about having info like this in the sticky, is that it's there to quote, when someone askes. (most new guys dont check stickies before starting a thread.)

i still quote stuff from the EG sticky from time to time. it saves me the trouble of saving / finding things on my own computer, or having to rewrite the same thing over and over.

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