Eurotubes - FAQ - Frequently Asked Questions Page for guitar and bass
Preface: Tubes are tubes, and it's not a matter of
if they will fail, but when they will
fail. They are magical little bottles of joyful tone that allow us to express
ourselves in a way that no other device on the planet can. We abuse them by
driving them into distortion until they are screaming their little heads off. We
plug them into amps that travel down bumpy roads in the back of vans and pickup
trucks to the gig from hell. Some of us put them inside of speaker cabinets
(combo amps) strategically placing them within an inch or two of the speakers
and then punish them relentlessly with back waves. Some of us use them until
they are a thousand dog years old and then express disbelief when the die.
In general tubes are taken for granted. They are
archaic little beasts by nature and the first time I witnessed the entire
process a tube goes thru when they are born I was in awe as they seemingly
battled to survive the almost medieval process! This page is here to answer some
common questions about tubes and to explain a few things that will give your
tubes a good start to their hard lives. Proper installation and handling is very
important. A large portion of the phone calls and emails that we receive come
from players who have purchased tubes from other sources and now that they have
experienced problems they are contacting us because their source cannot help
At Eurotubes we are all players who understand
amps and tubes, we are not refugees from the corner pizza joint, we're not suits
behind a desk. We research what we know. I have personally spent thousands of
hours researching every amp I can get my hands on, documenting what types of
tubes an amp can safely use, what works for different styles, bias info,
etcetera. Now that Eurotubes has grown I thankfully have help with this as we
continue the research daily, so we don't guess, we know, and if we don't know,
we will tell you we don't know and then put it on our "to learn" list. Even if you have
purchased tubes from somewhere else we will offer you assistance.
I received a call from a player that prompted the
writing of this preface. He called stating that he had purchased tubes for his
amp from a "groovy" supplier only to find that after installation his amp made
no sound, so he removed them and reinstalled his old tubes which brought the amp
back to life. He then threw away the "groovy" tubes and chalked it up to a
"bad batch" of tubes. He called me asking for "good tubes".
The first thing I told him was there really are no
"bad batches" of tubes. I ask him to retrieve the tubes in question and
explained how to diagnose the problem. It turned out that he had one preamp tube
that had fallen down so he was able to get some use out of the very expensive
tubes he had tossed away.
We hope the following information will help you to
understand a little more about your amp and your tubes. Knowledge is power!
How do I change my tubes?
Should tubes glow?
What is biasing?
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?
#8 Are my tubes microphonic?
What's that rattle noise coming from my combo amp?
HELP! My amp stopped working!!!
Damn! I broke the guide pin!!
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 tubes 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... Here is example of an email exchange we get all too often;
Sent: Saturday, April 25, 2009 6:44 PM
Subject: Help me with my tone!
hope you are having a good day. I read over your entire site and it is obvious
you know tubes and you care about your trade so I am hoping you can help me. I
hope I can do business with you in the near future.
situation. I have a 1989 Marshall JCM 800 2210. It was an awesome sounding amp
but the tubes were original and needed replacing. I bought a set of Svetlana
EL34s power tubes and took the amp in to have it biased. As you stated on your
web site the amp tech told me the tubes were bad and re tubed the amp with all
Groove tubes. I got the amp back and it was unplayable. The sound was harsh
and grating. I put my original pre amp tubes back in and the Svetlanas
(naturally he didn't give me back my original power tubes) and got the amp
playable but it is still a far cry from what it was. The amp gets that fuzz you
talked about on your site. I hate that. The lead notes are mushy and to
what I am looking for. I play fast and I need the notes to be tight, clear and
singing. I like my distortion to grind but I don't like fuzz. I like allot of
gain but I like everything to be clean. I am hoping you know exactly what I am
provide me a set of tubes that would fit the bill for what I need in my playing?
I thank you for any information you can provide me. It is really frustrating to
know what the amp used to sound like and what it is now. It's actually down
right sad. It's to the point that if I can't get it back to it's former sound I
will have to sell it.
you for your time and look forward to your response.
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". If you do decide to seek out
a tech that you have no history with, you may want to read our warranty info at
the bottom of the testing and info page here.
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
calls all the time from Marshall DSL and TSL players as well as Peavey XXX and
JSX players saying that they only have three preamp tubes. We explain that the
forth tube is usually hiding under a metal RF
cover (these help block radio interference and
other noise). These covers simply pull off or turn slightly and pull off. We
state on every invoice we send out for DSL and TSL amps that the phase inverter
tube is located in V4 closest to the power tubes but we get several calls a week
asking "are you sure the phase inverter is closest to the power tubes, shouldn't
go in the spot where the tube has a cover on it?" NO!!! We are not lying! The
tube with the cover in a DSL or TSL is the V1 tube and not the phase inverter.
The V1 tube is the most sensitive tube position in the amp and this is the
reason for the cover. Other amps like Mesa Dual Rec's usually have covers on all
the preamp tubes.
preamp tubes or EL84's first check the pins to see if they are straight. We
straighten all our nine pin tubes when they are tested but you can slightly bend
the pins even removing them from the box if you're not careful. A slight bend as
in a few degrees is not a problem but if you bend a pin more than about 20
degrees which is right about the angle of
this backslash "/" then you should NOT just pull it back into position with your
finger! This can and most often will, cause a minute crack in the glass
Then when the
tube heats up and expands the crack grows and if it goes clear thru the glass
then air will leak in, the tube will fail and the silver getter flash will turn
white. If you bend a pin beyond about 20 degrees and do not have a pin
straightener then use a pair of needle nose pliers to grip the pin very close to
the glass and carefully bend it back into position without stressing the glass.
Here is an
example below where you can clearly see the pins are bent in different
directions and a crack has formed directly thru one of the bent pins. Click on
the picture to enlarge.
If the pins are straight then
carefully line them up with the receptacles in the socket noting the gap between
pin 1 and pin 9 and push them into place.
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
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 but if you do this then watch the
power tubes closely! Just running them in and out without using contact cleaner
will NOT insure good contacts!
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
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
Here is an email exchange that is
From: Trubador tv [mailto:email@example.com] Sent:
Sunday, April 12, 2009 11:56 AM To: firstname.lastname@example.org
Subject: RE: I bought your tubes
Yup, that was the problem. Although I put them in and out with no cleaner
before, when I finally got the cleaner and did it, all the gain and sustain came
back in full force. dude, ur the best. Now i have "my
baby" back and we're movign to nashville in 2 days to launch this band. peace
Subject: RE: I bought your tubes Date: Mon, 30 Mar 2009 17:57:37 -0700
There is no way we would have time to fix the amp before you need it and the
only Marshall amps we have are old vintage amps that we would not loan or rent.
I’m not convinced it is an amp issue. Did you
clean the sockets? Even if you did you should do it again.
From: Trubador tv [mailto:email@example.com]
Sent: Monday, March 30, 2009 2:05 PM To: firstname.lastname@example.org
Subject: RE: I bought your tubes
Hi, The amp is breaking again. I ordered the tubes in the first place because
when I would play it was way quiter and the sustain was kind of gone.
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 re-tension 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
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
cause a tube to not function or function intermittently. If this is the case you
should re-tension 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 re-tensioning 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
#2. If you find the sockets are loose then
re-tension them as
#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.
Here is a copy of the instructions we send out with
replacing tubes you must always clean the tube sockets and if you're replacing
power tubes that do not fit tightly in the sockets then re-tensioning is
necessary. Failure to do these things can cause tube failure and will void your
warranty! Check out
the FAQ page here; http://www.eurotubes.com/eurotubes-FAQ-Frequently-Asked-Questions-Tone-glow-microphonic-biasing.htm
It's easy to clean the tube
sockets which can be done by spraying the pins on every new tube with some
electrical contact cleaner ( you can even get this at a Radio Shack, they call
it TV tuner cleaner ) and then work each tube in and out of each socket a few
times to remove dirt and corrosion. If no contact cleaner is available then at
the VERY least work each tube in and out of the socket multiple times! Remember
this will NOT insure a perfect contact!
If you have been using chinese
or sovtek tubes both sometimes have excess solder on the pins which can spread
the sockets open and make them loose which can cause a tube to not function or
function intermittently. If this is the case you should retention the sockets.
We use a dental pick for doing this but you can use ice pick or a very small
screwdriver to squeeze each of the pin holders in each socket together so the
tube fits snugly. ****IMPORTANT**** All octal
power tubes should be gripped by the base when removing and installing them!
Pushing and pulling on the glass can cause small cracks in the glass which can
cause the tube to loose vacuum. When this happens the silver getter flash in the
top of the tube will turn white.
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!!!
You will not be able to re-tension your tube sockets easily so we use another
method for 9 pin EL84's which is what we call "rolling the pins".
We straighten all the
pins ( preamp and EL84 ) before the tubes ship and if you find that a tube does
not seat tightly in a socket then very lightly roll the pins between your thumb
and index finger to ever so slightly bend them in which will make them a tight
fit in a loose socket. be VERY careful NOT to bend the pins too far or you can
crack the glass!
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
well over 1000 customer reviews from real players on our site here, http://www.eurotubes.com/eurotubes-customer-reviews.htm
Should tubes glow?
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.
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" usually due to
cathode stripping and
is on it’s way out.
We get calls on a regular basis
from players saying they need new preamp tubes because they don't glow. The
first question we ask is "is the amp working?" 99.9% of the time the answer is
yes. So we explain that if the tubes were really not glowing then the amp would
not be working. The
heater or filament is mostly covered by the plate structure with a little bit of
it visible, and the amount of the heater that can be seen will vary so LOTS of
players who look at their tubes very closely will think one tube is glowing
brighter than another if they see a little bit more or less of the heater or
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
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.
We get calls and emails from customers and
non-customers all the time stating that all their new tubes are bad so they must
have received a "bad batch" of tubes because they are noisy. There really is no
such thing as a "bad batch" of tubes but occasionally a tube will fail or become
noisy right out of the box even if your tube vender tests them. The most common
mistake players make is not cleaning up the sockets when changing tubes. (Refer
to "How do I change my tubes" above for info). If you experience noises such as
hissing, popping or scratching then 99% of the time it's a contact issue with
one of the pins on a tube not making a good contact in a socket.
The second mistake players make in diagnosing a
noise problem is to pull all the tubes. Here's the scenario, a player calls
stating he bought new brand "X" tubes, installed them only to hear noise so he
pulled them all, reinstalled his old tubes and the noises went away so he knows
the tubes were bad. This really tells you nothing because you don't know what
tube may have been causing the problem or if it was a tube issue or connection
issue. The pins on all tubes are just like the fingerprints on your fingers,
they are all different and just like your fingerprints the pins on tubes will
contact the sockets in a slightly different place.
If you encounter noises and have not cleaned the
sockets then clean them and reseat the tubes. We have had amps thru here where
the sockets were so corroded and dirty that it took several attempts to get the
tubes to quiet down. You can install tubes and have no noise only to find that
when everything gets good and hot the noise will come back. This can happen
because when parts get hot they expand and move so a marginal connection can
become no connection. So if you have some noise then clean the sockets and
reseat the tubes, if the noise persists then you can diagnose the problem by
replacing the tubes one at a time with an old tube. If you have a tube issue
this is the only way to isolate it.
What is biasing?
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:
What is it?
Do I need to worry about it?
Will it affect my tone?
How can I adjust it?
Let’s Get To
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.
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.
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.
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/eurotubes-how-to-bias-video-probe-Pro-One.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
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. However this does not mean you have to
calculate them at 30 watts to get out of crossover distortion. You can use 70%
of 25 watts and they will get a great warm clean tone well out of crossover
Line voltage is also a
consideration especially if your electrical service is old and you run a lot of
appliances or have electric heat. During heavy usage hours in the evening you
can actually be down by 3 to 4 volts compared to lighter usage daylight hours
when your AC can swing the other way and be up by several volts. You may be
asking "what the heck does this mean to me?" Here is an example. You bias your
amp during the evening when and your voltage happens to be down at 116 volts.
You want to push those tubes so you wind up your bias to 80% of dissipation and
it sounds great. You fire up the amp during the day over the weekend and your AC
voltage happens to be at 122 volts. The amp screams for fifteen minuets and pops
a fuse. The difference between 116 volts and 120 volts can mean that your DC
plate voltage in your amp can vary by 30 volts! So it's a good idea to know what
your line voltage is.
Since I like to run my gear pretty
hot I will routinely bias them at 44mA 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
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 as well as many
other amps which will accommodate different power tubes 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 if your amp allows. 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 KT66's which have about the same low end as a good 6L6 but have more complex
harmonics. Then of course if the mission is huge and your amp allows then the JJ
KT88's simply sound BIG all over with a massive low end.
#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
We get questioned quite a bit on the subject of balanced PI tubes
so I’ll elaborate a little. I use to be a real skeptic on this one because most
PI circuits are not designed to be perfectly balanced. Ah ha!!! Say what? So
it’s snake oil then?
No, I’ll explain. Most all
circuits using long tail phase inverters are designed with a slight amount of
asymmetry. The reason for this is because when both sides are dead on, the amp
will sound a bit sterile and be missing that bit of 3D swirl that makes a tube
amp sound alive. This is also the case with a way out of balance circuit, it
will sound sterile and certain frequencies will suffer from phase cancellation.
Logic says (I’m a big fan of
logic and common sense) then why balance the current on an imperfect circuit?
The short answer is, to get the result the designer wanted, but I’ll go further
into this. When I acquired the test equipment to check for balanced triodes I
started stuffing balanced tubes in everything I have to see if there was a real
difference or if it was snake oil. The results? In some amps it was nothing
short of amazing and in others it was noticeable but not jaw dropping.
A good friend of mine who
has a Marshall 6100 30th anniversary, (one of those amps I just love
to hate, I call it the little Blue bastard), had fought getting a good tone with
it for years so he brought it back in a few months after we started using
balanced PI tubes and when we changed the PI tube for a balanced tube we both
were astounded at the change. The amp simply went from so-so at best to, holy
crap, is that the same amp!!
So, morale of the story?
It’s just like the old argument that a rectifier tube does not change the tone
of an amp because it’s not directly in the tone circuit. This of course is
completely false and anyone who has ever done an A/B and compared a chinese, a
sovtek, a JJ and different NOS rectifier tubes will tell you there is an amazing
difference in dynamics and tone. A good balanced PI tube does make a difference
and it’s not snake oil. All you need is a pair of ears to hear the difference.
You will still find a lot of
skepticism and bad press from the "nay Sayers" on the benefits of
using balanced PI tubes. The only question I would ask them is "have you
personally had experience in listening to the difference between balanced and
unbalanced PI tubes in different amps?" Oh, and request an honest answer
when posing the question.
Basic amp questions including what is headroom? And what is
We 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!
We’re 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.
Are my tubes microphonic?
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.
We 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 we 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. We 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
We 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…
with tube dampers in torture chambers (combo amps) for quite a while we finally
decided to build them right. We had our own mold made for these and our
“EuroDampers” are made from a softer than standard durometer, special high temp
silicone. These are BIG dampers and measure 1.45 in diameter by .375 tall and
are usable on all 9 pin preamp tubes and EL84’s. You can see high res pictures
of these on our tube damper page here; http://www.eurotubes.com/eurotubes-EuroDamper-Tube-Damper-Rings.htm
#10. Help!! My amp
We get panic calls and emails all the time from
players who have amps that have simply stopped working. So here is a guide to
help you try an trouble shoot some common problems. I'll divide this into two
sections starting with power tube issues first and then preamp tube issues.
Power tube issues.
#1. If your amp blows a fuse and you have not
changed your power tubes in over a year then stop. Do not pass go. Do not
replace the fuse and play the amp again unless you had a power surge caused by a
power outage, a blown breaker, or you just decided to play your guitar while
bathing and survived, or you own a 5150 (more later). If you did have a power
surge or a blown breaker and popped a fuse then replace it and try the amp
again. If you blow a second fuse STOP! You probably have a power tube going
short and if you keep replacing fuses or "God forbid" use a 10 amp fuse
to cure the problem you risk causing serious damage to the amp. If your 5150
blows one of the conveniently located internal fuses on the PC board then pull
the chassis out of the box and replace the fuse, usually all will be well. These
amps like to blow these fuses just to screw with you...
#2. If you have just installed new tubes and you
have blown a fuse then carefully remove the power tubes to make sure you have
not miss-indexed one.
There is a guide pin on the bottom of all octal tubes including 6L6's, 6V6's,
EL34's, E34L's, KT77's and KT88's, these power tubes have a timing key on them
and this has to lineup with the notch in the socket. If you turn an amp on with
a tube miss-indexed you can damage the tube and the amp! You may think this is
impossible and get a good laugh about it but believe me, we get lots of calls
from players and customers who have done this! If the tubes were indexed
properly and you did not clean the sockets or the sockets are loose and do not
grip the pins on the tubes tightly then clean the sockets and re-tension the
sockets if necessary. (Go to the top of this page to read about this under the
heading of "How do I change my tubes?") I cannot emphasize enough that having
good connections between your tubes and sockets is of paramount importance!
#3. So lets now assume that you have the tubes installed properly
and there are no connection issues but the amp still blows a fuse. Remove the
power tubes, replace the fuse and power the amp up. If the amp blows a fuse with
no power tubes installed then it's not a tube issue and the amp needs to see a
good tech. If you can power the amp up with no tubes installed and the fuse does
not blow then power down and install one power tube and power up again. Repeat
this process adding the second tube to the equation. If the fuse blows then
remove the tube you just added and you will be holding the trouble maker in your
hand. You can use this trouble shooting procedure for amps with any number of
#4. If your amp uses a rectifier tube and you simply lose power
or blow a fuse then this tube can cause both of these things.
#5. If your tubes are more than 6 to 8 months old and have seen
regular use do not simply replace one tube, replace them as a set. If your tubes
are new then contact your supplier about the failure. If you bought them on
do not pass go...
Preamp tube issues.
#1. If you have a single channel amp and you
suddenly loose power or your signal drops down substantially and your power
tubes look fine then it's probably a preamp tube causing the problem. The first
thing to do is to clean the sockets and reseat the tubes. If a tube was making a
marginal connection to begin with then as the components heat up and parts move
a bit due to expansion a marginal connection can become no connection. I can't
even count how many times we have instructed players who have called with
problems to clean their sockets and reseat their tubes only to be amazed that
their amp came back to life. Connections people! You know what they say, if you
don't have connections you don't go anywhere!
#2. If you have cleaned the sockets, reseated the
tubes and still have nothing, then replace the preamp tubes one by one using an
old tube that was known to be functioning. This will allow you to find a
malfunctioning tube. If you simply replace all the preamp tubes then you will
never find out which one is causing the problem.
#3. If you have a multiple channel amp and all
channels go down then it's probably either the V1 preamp tube which in most amps
is the preamp tube closest to the input jack or the phase inverter tube which in
most amps is either the preamp tube that is farthest away from the input jack or
closest to the power tubes. So trouble shoot these tubes first and you will
likely find the source of the problem.
#4. If you have one or two channels go down on a multiple channel amp but your
clean channel still functions then look to the tubes located between your V1
tube and the phase inverter tube. In most modern multi channel amps the signal
is cascaded thru several tubes compounding the gain.
Damn! I broke the guide pin!!
OK, it happens to the best
of us. If you tip or lean a tube a little too far you will hear a faint "snap"
and then when you pull the tube out the central guide pin stays in the socket or
drops into the amp. #!$!! Another scenario which is what we call a "noob
incident" (we were all "noobs" at one time) when the "I GOT NEW TUBES!"
adrenalin is pumping and you stuff the tubes in the sockets before even noticing
that silly guide pin. Miss-indexing a power tube can cause some catastrophic
results when the power is applied but some are lucky enough to miss-index a tube
in the one or two positions that will cause no harm. Then when the amp does
nothing and the tubes are removed the jammed in guide breaks off.
If you do break a guide pin then the tube is still usable as long
as the glass is not physically broken. If this happens the silver getter flash
in the top of the tube will turn white and it's game over. If the vacuum is
still in tact then all you need to do is draw a line with a sharpie or white-out
or even nail polish that runs up the side of the base of the tube so you can
properly index or line up the tube with the timing notch in the socket. The
first picture below shows a couple of "abused" tubes and the second shows a
socket and the timing notch and the third with one of the abused tubes installed.
So carefully mark the tube to show where the timing key once
pointed and then mark the chassis on your amp indicating where the timing key in
the socket is pointing and carefully install the tube.