Frequently asked questions.
#5 How will changing from 6L6's to EL34's affect my tone?
#6 What is a phase inverter ( splitter ) and why should I use a balanced one?
#7 Basic amp questions including what is headroom? And what is breakup?
#9 What's that rattle noise coming from my combo amp?
I would like to open this section with a word about amp tech's. As you can well imagine having tens of thousands of customers, we hear about everything having to do with tubes, amps and our customers experiences. We also field hundreds of calls from non-customers seeking support because they cannot get it from their tube vendor, so you might say, we hear it all.
We get the occasional call from a player who has read on a forum somewhere that changing your tubes requires a degree in Nuclear Physics and you will surely die from electrocution if you attempt to change your own tubes... So heeding this false information given by the unknown "amp Guru" who is more than likely afraid to change a light bulb, the player will dial up the closest tech he can find to do this all but impossible job. So at this point let me state that there are a lot of very competent and talented tech's out there that are happy to install and bias your amp for new tubes if necessary, and charge a reasonable fee to do it right. So now the bad news... There are also a lot of tech's out there that will be extremely unhappy that you have purchased tubes online and want them to do the install. The reason for this is the price you paid for tubes online (especially if they came from us) will be right at the same wholesale price the tech pays for tubes, which is why you will find on average that music store and tech tube prices are very expensive! It's called making a living.
The worst case scenario is the unsuspecting player leaves his amp and tubes with a tech, only to receive a phone call telling him that the tubes he supplied were "all bad" and of course the tech can supply him with "good" tubes but good are more expensive. We have even received calls from players who asked the tech for the so called "bad tubes" back, only to be told that they simply threw them away because after all, they were no good...
The moral of the story? If you are afraid to change your tubes and have a trusted tech that has served you well, then simply ask him if he minds doing an install with supplied tubes. What we highly recommend is that you learn to do it yourself. You own the car, so learn to change the oil. There is no black magic voodoo involved and you don't need to swing a dead chicken over your head three times while reciting an incantation. Even if you have an adjustable bias amp it's very easy to do yourself which is why we put up the "how to bias video's".
Please read on, and prepare to change your own tubes!
I get asked all the time "How do I change my tubes?" Here is an in-depth overview of everything I can think of about changing tubes. First, read your manual! Check to see where your power tubes and pre-amp tubes are located. If you order a retube kit from us, or leave a note in the comments box on the checkout page with your order telling us what amp the tubes are for then we will automatically list on your invoice any of the tubes that are located in special positions.
Removal is easy. Simply pull the tubes out. If they are stubborn, pull while rocking them a little bit from side to side but go easy! If you tilt them too much you will break the guide pin. It's a good idea to cup one hand over the top of a power tube when pulling it out so that when it lets loose you don't smack the tube against the cabinet and break it, I'm not afraid to admit I'm talking from experience here!
When installing preamp tubes first check the pins to see if they are straight. Then carefully install them making sure not to bend any of the pins. Power tubes like 6L6’s and EL34’s are easy because they have large pins and a central guide pin. One word of caution! Do not tilt the tubes from side to side too much or you will break the guide pin off!
Any octal base tubes such as 6L6's, 6V6's, EL34's, KT77's, KT88's, 6550's, KT66's and GZ34's to name a few should be gripped by the base of the tube when being installed and removed. Pushing and pulling on the glass can easily cause small cracks in the glass where it is glued to the base and if a small crack is made in the glass then the tube will lose it's vacuum in the first few hours or less of use. When this happens the silver getter flash in the top of the tube will turn white bearing witness to the fact that the vacuum in the tube has leaked out and the tube is no good.
This next tip is the MOST important of all. Whether your amp is old or new you should always clean the tube sockets before installing new tubes and we HIGHLY recommend doing this! Failure to do this can and often will cause you to burn out tubes and here is why. The pins on tubes are all different just like a fingerprint so when you remove an old tube and replace it with another tube the pins will contact the socket collars in a slightly different location. Cleaning the sockets can easily be done by spraying electrical contact cleaner on the pins of one of your old tubes or preferably the new tubes, and working the tube in and out of each socket a few times. Do this for both preamp and power tubes. If you do not have any contact cleaner, then at the very least you should work each new tube in and out of it's socket a few times to help scrape in a decent connection.
In an amp that uses a quad of power tubes, 99.9% of the time even though the two inside tubes and the two outside tubes work together as pairs, the two right tubes most often get their B+ high voltage from one tap on the transformer, where the two left tubes get their B+ high voltage from the other tap on the transformer. So if one of the tubes on the left is not making a good connection especially to ground, then it can drastically overheat, red plating the tube and then this will also take out the tube next to it that gets it's B+ from the same transformer tap. Just before writing this I received a call from a player who bought a quad of =C= EL34's (not bad sounding tubes) for his TSL Marshall, he said that he set the bias just as I show in the "how to" bias video we made for these amps and then after playing the amp for five minutes he started loosing power and hearing distortion on the clean channel. He looked at the tubes and saw that the two tubes on the right were fried and the painted logo had turned brown so he called the vender who sold him the tubes but they had no clue about what might be wrong (typical) and told him to take the amp to a tech and that he must have screwed up the bias...
When he called me this morning and described the problem my first question was "did you cleanup the sockets?" The answer was of course no, followed by the statement "my amp is new so why would I need to do that?". I never turn anyone down as far as helping them with tube issues so an explanation ensued. I told him there was nothing wrong with his amp and to clean his sockets, put his old tubes back in, do an initial bias adjustment and then watch the tubes for the first few minuets the amp was on and in the play mode. Then after about ten minuets I told him to do a final bias adjustment if necessary after the tubes were hot. So about twenty minuets later my phone rang again and low and behold, his old tubes were running just fine! His next question was "so what do I do with these burned up tubes? Will they still work?" I proceeded to give him the bad news with an answer of no... Once a tube has red plated its done, it will red plate every time you try it and you can usually tell if a tube has overheated if the paint on the tube has turned gray, brown or black. The first part of the question was a bit tougher to answer because he had not bought the tubes from us. I proceeded to tell him that we send out an instruction sheet with every order about cleaning sockets but we still get the occasional call where a customer will neglect to do this and sure enough he has red plated two tubes. We will usually not warrantee two tubes when this happens.
Tubes do fail once in a while which is why we warrantee them and if a tube does fail of it's own accord then 99% of the time it will not take out the tube next to it. On rare occasions it will take out it's partner, which in an amp that uses a quad of power tubes would be the other outside tube if an outside tube fails or the other inside tube if an inside tube fails but 99% of the time if the two right tubes or the two left tubes red plate it IS due to a connection issue. I have witnessed this many times in amps where the sockets are a little loose and I've made the bad decision after cleaning them to not retension them (covered a couple paragraphs down) and had a tube start to red plate and then grab the top of the tube and push it from side to side and then see the tube calm down and start to function properly. The cause being a poor connection.
One of my customers pointed me to a thread over on the HC Zoo (that's the harmony central forum) where someone had posted about cleaning sockets and several people climbed on the thread stating that this was the most ridiculous thing they had ever heard of! One poster stated that he had four amps and changed the tubes numerous times and never had to clean them, therefore this was a load... Well when you deal with thousands of amps as we have done here over the years you get to know what is a load, and what the truth is, so if you enjoy playing the odds and don't mind a little excess noise or static, or putting your amp at risk by burning out the occasional tube, then by all means please take the novice advise given over at the zoo...
So back to reality, I can't tell you how many calls and emails we get from players who have installed new tubes of all different brands and from all different sources without cleaning up their sockets and and then call us complaining of odd noises like "pops" and "scratchy" sounds and want to know how to "fix it". We also get the occasional call stating "I installed my new tubes and now my amp doesn't work so I must have a bad batch of tubes". In reality there are no "bad batches" of tubes and 99.8% of the time in both these scenarios the player did not cleanup the sockets and after doing so the noises are gone or the amp mysteriously comes back to life.
Just because your amp is new does not mean that your sockets are clean! In fact new amps are just as problematic because sockets are often kept in open boxes gathering dust until they are soldered into place on the board or mounted in your amp where they sometimes will sit around again gathering dust before being loaded up with tubes.
Old tube sockets are often loose which can cause a tube to not function or function intermittently. If this is the case you should retension the sockets. I use a dental pick for doing this but you can use a woodworking Awl which comes to a point or a very small jewelers screwdriver to squeeze each of the pin holders in each socket together so the tube fits snugly. For nine pin sockets used with preamp tubes and EL84's retensioning the sockets is more difficult so if you find that a tube does not seat tightly in a nine pin socket then very lightly roll the pins between your thumb and index finger holding it by the pins to ever so slightly bend them in which will make them a tight fit in a loose socket. Do not bend them too far!
So to recap all of the info you just read, here are the steps to a successful tube change.
#1. After pulling the old tubes, spray a little contact cleaner on the pins of the new tubes one at a time, then work them in and out of the sockets a few times. If you have no contact cleaner than at a very minimum run the tubes in and out of the sockets several times to help scrape in a good connection.
#2. If you find the sockets are loose then retension them as described above.
#3. If your amp has an adjustable bias then do an initial adjustment right after you flip the amp into the play mode. Wait about 10 minutes and do a final bias adjustment.
#4. If the amp is fixed bias then watch the tubes for a few minutes after they are in the play mode to make sure all is well.
A special note for you Peavey Classic 30 and Delta Blues owners and Mesa DC2 and DC3 owners. PLEASE be careful when removing and replacing those crummy wire tube retainers! If you push the wrong way upon removal or let them "snap" back into place too hard you will break the tips right off of your tubes!!!
We get calls and emails everyday from players who have purchased tubes from other "stores" and "depot's" and a couple east coast tube venders for support because they cannot get it from these venders. NEVER FEAR! We take the time to answer your questions and we have real world "hands on" knowledge and experience with thousands of amps. So when that guy on the east coast says "you can't run JJ's in a Mesa" or "you can't use 6V6's in your amp" just give us a call to get the real answers. You can also find about 700 customer reviews from real players on our site here, http://www.eurotubes.com/euro-t.htm
Yes! If they are not glowing they are not working! The plate structure should never glow orange or have any spots on it that are orange. The heater or filament which runs up the center of the tube is the only part of the tube that should glow orange.
A blue
glow that pulses under load is normal. A strong purple glow that shows
up when a tube is not under load at idle means the tube is "gassy" due to
cathode stripping and
is on it’s way out.
All 12AX7 type tubes are microphonic. Some are just more so than others. You can check your pre-amp tubes by turning the amp on, gaining it up and tapping lightly on each tube with the end of a pencil or a chop stick (my favorite). You will be able to hear the tapping through your speakers, which is normal. It is not normal for a tube to ring like a bell after it’s tapped. If it does ring then it’s what is called microphonic and should be replaced.
In the case of very high gain amps like the Peavey 5150 and Ultra or the Mesa’s and Marshall's you will find that by simply swapping the pre-amp tubes around you can find a combination which will yield the least amount of noise.
We also get lots of calls from players who think they have microphonic tubes because they get lots of feedback in the high gain channel of their amp. One way to check and see if it's your guitar feeding back or microphonic tubes is to simply roll the volume down on the guitar when it starts to feed back and if the feedback stops then it's your guitar, if it keeps going with the guitar off then it's your tubes.
Power tubes
on the other hand are rarely microphonic. EL84’s seem to be the most susceptible
to being microphonic and having filament rattle. The worst combination
of course is a combo amp using EL84’s especially some of the high powered
one’s. The speaker vibration can rattle those little tubes to death in
short order. All power tubes can be checked for being microphonic just
like pre-amp tubes.
Bias is the negative voltage which is applied to the power tube’s control grid to set the level of idle current.
So that’s the technical definition. Most of the questions I get about bias are:
B. Do I need to worry about it?
Let’s Get To It!
A. You read the technical definition but unless you have some background in tube theory it probably read like an insurance policy so I’ll see if I can do better!
Your power tubes need to idle properly. If they are set too cold (overbiased) they are not producing their part of a full sine wave and are in what is called "crossover distortion. If they are set too hot (under biased) they will distort too soon and the tube life will be shortened. Setting the bias on your amp is like setting the idle on your car. If it’s too high or hot it’s running away with you and if it’s too low or cold it will choke when you step on it.
B. Yes and no. All tube hi-fi amps need to be biased properly. Some have trim pots for each tube and some are cathode biased. Always stick with what the amp maker recommends. Guitar amps are a different story. Amps using EL84/6BQ5 tubes are almost always fixed bias and because of the type of circuit used are usually O.K. On the other hand, any guitar amp that is not cathode biased and uses 6L6, EL34, 6550 or KT88 power tubes NEEDS to be properly biased to sound it’s best no matter what the manufacturer says! Some Mesa Boogie and Peavey amps that use 6L6, EL34 and 6550 power tubes are biased very cold and can benefit greatly form being properly biased and over the past few years we have also come up with different tube sets that will get these amps up to proper bias. You can find these in the Eurotubes online store.
C. In one word YES! Absolutely, Positively, BIG TIME! Well that’s more than one word but I can’t stress enough the difference in warmth of tone and dynamic response that come with proper biasing. Every time I convince a player who owns a fixed bias amp that uses 6L6, EL34 or 6550 tubes to have their amp biased right the outcome is always the same. They can’t believe how good it sounds. This is because tubes that are biased cold or "overbiased" are in what is called crossover distortion and can’t produce a clean, warm tone and are sluggish in response.
D. Saying that an amp is fixed biased only means that the manufacturer used a simple resistor in the final bias stage instead of a variable resistor which is commonly referred to as a trim pot. So, if your amp is "Fixed Biased" and you want the best performance you can and should have the simple resistor replaced with a trim pot in series with a lower value resistor. Any decent technician can do this for about $50.00, including the adjustment. Once this is done then you can be in control of your tone and bias the amp yourself using a bias probe. We have even gone so far as to produce "how to bias videos" for you here! http://www.eurotubes.com/euro-video.htm
Now let’s talk about the adjustment. There are several different ways to bias a tube amp. The two main methods of biasing an amp are what I’ll call the old school methods. The first is using an oscilloscope to monitor the sine wave output of the amp while the amp is being driven with a signal generator. A fair degree of technical know how and experience is necessary when using this method. The second is the transformer shunt method which involves working very closely with extremely high voltages and I do not recommend using this method.
The newest and by far the easiest method of adjusting bias is by using a bias probe. This is a device that looks like the base of a 6L6 type tube which is installed in one (or two if it’s a dual probe) of your sockets. Your tube then goes in the socket in the top of the probe. Some probes need to be used with a multimeter and some come with built-in milliamp meters.
Some old schoolers don’t think much of the bias probe method but I can tell you from experience that it not only works but it works very well. I’ve compared the two methods extensively and I very much prefer the probe over the scope method, especially for guitar amps. All you need to know to bias your amp using a probe is what the plate voltage is which is measured from pin#3 to ground. Once you know this then the formula is simple. Divide the plate dissipation of your type of power tube into the plate voltage. This will give you the maximum plate current which should never be exceeded.
We will use the plate dissipation for a standard 6L6 for this example which is 22 watts. Example: 22 watts divided by 500 plate volts equals .044 or 44 milliamps of plate current draw at idle. The 44mA should never be exceeded! Then multiply the .044 by .7 or 70% which equals .030 or 30mA. This is where your power tubes will be out of crossover distortion and will perform very well. There is an acceptable window of correct bias and if you want a warmer tone or what some players refer to as a "brown sound" you can use up to 90% of the maximum current formula which would be 40mA rounded off. Your tube life will be a little shorter at this setting but only by about 20%. However, I would NOT recommend this for Chinese tubes or tubes that are sold by the Big guys that have been remarked unless you know for sure what tubes they really are. The JJ Electronic 6L6 is a very stout tube and JJ claims that it will dissipate 30 watts. Since I like to run my gear pretty hot I will routinely bias them at 50mA in an amp that has 485 plate volts. The tone is very warm and the tubes stand up very well. I tortured a quad in my Fender twin for a year, set at 50mA at 480 plate volts and they were still going strong until I swapped them out for a quad of KT88’s but that’s another story....
#5. How will changing from 6L6's to EL34's affect my tone?
This is a very frequent question and although there is no perfect answer that fits all amps I can give you a pretty good idea what to expect. I've swapped EL34's and 6L6's around in Marshall's, Fender's, Mesa's and Peavey's to name a few and the results are basically the same. EL34's in general don't have a low end that is as deep as a 6L6 so EL34's tend to sound hotter in the mids. EL34's breakup a little earlier then 6L6's and the harmonic content of the mids and highs are more prominent. These differences become more noticeable as volumes increase. You have probably heard the term "Marshall crunch" used before. This term is used to describe the sound of EL34 type tubes when they are being driven into distortion. So if you're looking for a great Classic rock tone with lots of complex mids you might want to try some EL34's. The JJ E34L's will crunch up real nice but they do have a deeper tighter low end than a standard EL34. If you like a big low end thump then I would either go with the JJ KT77 which has even a bigger low end than the E34L but still has the harmonic complexity of an EL34, or stick with a good 6L6 unless you have room for the JJ KT88's which have a BIG low end but sound more like EL34's in the mids and highs.
#6. What is a phase inverter ( splitter ) and why should I use a balanced one?
A phase inverter or splitter is the tube that keeps your power tubes ( in a push pull A/B type of amp ) running 180 degrees out of phase. This is necessary because in a push pull amp one tube creates the upper half of the sine wave while the other tube creates the lower half. One of the symptoms of an unbalanced phase inverter is that some notes will sustain very well where others will fall off or sound dead. In 99% of all guitar amps the PI tube is the closest preamp tube to the power tubes and 99% of all A/B style guitar amps use a circuit that splits the phase inverter duties utilizing both triodes in this tube.
#7. Basic amp questions including what is headroom? And what is breakup?
I get the question all the time, “what is headroom?” Headroom is often referred to as the volume your amp will achieve before distortion sets in. A more accurate description should include the explanation of dynamics and that most all music by it's nature is very dynamic with peaks and valleys. A couple of exceptions would be hard core screamer rock and punk that simply comes on full tilt, smashes you up against the wall and then finally drops you at the end of the song. Another would be rap which consists of a 60 to 100Hz pounding synthetic kick drum that never varies in volume and some guy trying to rhyme because he can't sing....
Now a good example of punk with great dynamics is the new Green Day "American Idiot" CD. While I don't really agree with their politics I think this is one of the best recordings I've ever heard and the song writing is top notch. It has a permanent home in my CD changer. I would give a good example of rap but there isn't one....
I digress, so back to dynamics and head room. A great example of this is evident on any Robben Ford or Ronnie Earl CD. These guys are Blues and Jazz based and you can hear passages that go from very subtle to really digging in.
A typical 50 watt guitar amp when cranked up to about half way on in the clean channel will be right at the point of breaking up when you dig in on a note or a chord. So imagine that you are recording a passage that is very dynamic and starts out softly and then builds in volume and that you want the tone to stay clean. Even with the amp half way up you are only using about 10 watts of power to play a light passage but when you dig into a note and the amp is called on to reproduce it then it will be using most all of it’s power to do so and this is referred to as headroom. If your amp did not have the power to reproduce the clean tone you wanted at the peak of the passage you would be out of headroom!
I’m often asked “what is breakup?” Breakup is simply distortion. When the typical 50 watt guitar amp is about half way up you will start to get preamp tube, power tube and speaker distortion ( which is what I call the sweet spot ). One of the most asked questions is “how do I get more power tube breakup?” The answer? TURN IT UP! The other alternative is an attenuator between your amps output and speakers which allows you to crank the amp up higher and then choke down the output before it gets to the speakers causing a lower overall volume.
When you tap on a tube with the amp turned up you will hear the mechanical signal thru the speakers or the tube is dead. The definition of microphonic is that a tube when given a signal at a specific frequency will oscillate and carry on that tone by it's self like a ringing bell.
One way to check and see if it's your guitar feeding back or microphonic tubes is to simply roll the volume down on the guitar when it starts to feed back and if the feedback stops then it's your guitar, if it keeps going with the guitar off then it's your tubes.
#9. What's that rattle
noise coming from my combo amp?
Great question! Combo amps like Peavey Classic 30's, Fender Blues Juniors and Fender Hotrod Deluxes (these are the worst models) are nothing more than torture chambers for tubes because every time you play a note the back wave from the speaker pounds on the tubes. This vibration and continual pounding will shake the guts loose in just about any tube in short order. This is a universal problem with all brands of tubes, and the JJ's are no exception. I have LOTS of NOS tubes including RCA's, Mullards and Telefunkens which are among my favorites that rattle when they get anywhere close to a combo amp.
I get calls all the time from players who have just purchased brand new amps right off the showroom floor asking for new tubes because their tubes are bad. When I ask what the problem is they say have microphonic tubes and that is sounds like broken glass or a jar full of BB's when they play lower notes. I then have the unfortunate task of explaining that this is not microphonic tubes, it is mechanical noise and you have just purchased a torture chamber for tubes...
These noises are heard easily in a quiet environment or trying to record with it rather than playing at a gig where these noises are rarely heard. This is why combo amps are rarely used to record with or extension cabs are used for recording. In most cases just about the time your power tubes are starting to loosing their high end (about six months) they will also start to rattle and if you play at high volumes the rattle can start much earlier.
We test for tube rattle but a tube can be fine one minute and develop a rattle the next and this is something that we nor any other tube vender will warranty. Tubes were never designed to be placed inside of a speaker cabinet...
I get questions about tube rattle all the time from players who hold tubes up to their ears and knock on them to check for rattles and I always tell them one thing, STOP IT! Stop beating on your tubes or we will have to turn you into the ACVT! (Association for the Cruelty to Vacuum Tubes) It's not good for them! You cannot tell if a tube will rattle by holding up to your ear and knocking on it and this is why.
When a power tube is cold the insides of the tube are cold and contracted and in a very different position than when the tube is up to operation temperature. When a tube heats up the internal plate structure including the cathode, anode, filament and other internal components all expand at a greater rate than the glass that houses them. This is why the only thing touching the glass are the mica spacers which have a very small contact area because they literally move against the glass as the internal components expand into position.
So as you knock on a tube when it is cold it will not tell you anything about what it will do when it’s hot. A cold tube can sound perfectly tight and when it gets up to temp it can rattle horribly in a combo amp, and of course the inverse is also true where a tube that appears to rattle cold will be perfectly tight when it’s expanded into position and up to operating temp.
Tube rattle in combo amps, or torture chambers as I call them, is the biggest problem having to do with tubes that there is…
I have been experimenting with some dampening rings to use on the tubes to prevent this but so far I've had only limited success. Until then here are a couple alternatives because you will be battling this problem as long as you own a combo amp.
http://herbiesaudiolab.home.att.net/
http://www.jmrblue.com/servlet/Detail?no=3