Post by myles on Oct 13, 2005 8:26:37 GMT -7
This is another area of my site on preamp tubes and how they are the fastest, cheapest, and easiest way to give your amp a wider range of tones.
Please excuse the formatting as I just copied, cut, and pasted this here from my site. This may have been missed by many as my website is not exactly all that user friendly.
Preamp Tubes - The most critical, least expensive, most overlooked tubes in your amp.
The tonal signature of "your sound" and interchangeable without adjustment or the need of an amp tech.
Unlike power/output tubes, which are routinely matched when they are sold (in different ways, some much better
than others), preamp tubes are tested at best to: (a) make sure they work ? (b) they are not microphonic. In
testing, we have found that some suppliers don?t seem to test their preamp tubes at all, as we have found one side
of the triode that is dead at times. Since most warranty preamp tubes for up to 6 months and longer, they possibly
figure that is cheaper to just send them out as they get them in, and if there is a problem, it is cheaper to just give
the customer another tube. This is of little comfort to somebody that either has to make another trip to their music
store, or worse, box up the bad tube and ship it back to the supplier, and then wait for its replacement. This is one
reason to consider a proven supplier when you buy preamp tubes.
Today?s amplifiers, whether modern high gain types or boutique amplifiers, have one thing in common; the preamp
tube in the first gain stage (usually V1 and / or V2) sets the tone and initial gain structure of the amplifier.
Amp design -
Today?s modern amps get just about all of their characteristics in the preamp section. How the gain stages are set
up, how the EQ is set up, gain structure, and tone stacks, all are the main aspect of the sound character of the
amplifier.
Amps such as Mesa Boogie, Fender, Marshall, Bogner, Peavey, and others, all use the same Sovtek, Svetlana,
JJ/Tesla, Electro Harmonix, and other power tubes from the same factories. In spite of the same output sections,
and in many cases the same range of B+ voltages on the plates of the output tubes, these amps sound different.
This is all because of different designs, primarily in the front end, or initial gain section of the amplifier.
Inconsistencies -
Today?s newly made preamp tubes are very inconsistent compared to the tubes of the 1940?s to 1960?s. There
is little need in the medical sector or the military sector for tubes. They are primarily used today in audio
applications. For the high end audiophiles, their needs are more easily met, as their tubes are not subjected to the
same stresses as those on a guitar amplifier, they use less of them, and they last much longer. There are high end
audio suppliers that will match tubes and hand select them, at much higher costs (check out a Western Electric
300B matched pair for example). They pop their tubes in, and ten years later, all is still just fine.
Tubes for the guitar and bass player for use in the preamp section, are a different story. The tubes today are very
inconsistent. You contact your local tube supplier, plunk down your money, and the roulette wheel is now set into
motion.
To show the inconsistency, we went through a batch of over 100 tubes that were from the Electro Harmonix
12AX7EH, ECC83, 7025, Sovtek 12AX7WA, LP, LPS, Chinese 12AX7C (old tooling and new tooling), and a few
others.
Basically, the standard 12AX7 spec that applies to 12AX7 / ECC83 / 7025 tubes, has a reference of 1.2 mA at 250
volts with a -2 volt bias.
Some people like to use those little references that say if you want less gain than a 12AX7, use a 12AT7, as it has
only 70% of the gain of a 12AX7 etc. These little tips are cute, but with the wide range of inconsistency out there,
they are not all that useful, as it is still a matter of chance. The 12AT7 has a different current capacity than a
12AX7, so if you are just looking for less gain, then you may, or may not get it with just a different 12AX7, even from
the same brand, same date code, and same batch ? just by swapping tubes around already in your amplifier. With
today?s inconsistent offerings, the old tables of gain cannot be used with much accuracy.
In the tubes we went through, keeping in mind our 1.2 mA / 1600 transconductance industry standard spec, we
found our samples ranged from 0.7 mA to 1.6 mA. When you take into account, that the amplification factor of a
12AX7 is 100, there is a dramatic difference in these tubes.
Looking at a 1.6 mA tube, we see a factor of increase over the standard of 33%. This is a LARGE number. A 1.0
tube versus a 1.2 tube will turn the gain you loved in your 5150 into something less than what you used to know
what you liked there. You sit dumbfounded ? how can this be? I just put in new tubes, the same as what I had
before?
You want even MORE GAIN from your Triple Rectifier or Bogner? Look at those first gain stage preamp tubes, and
get some tube vendor to measure them for you. If you have a 1.1 in there, and put in a 1.3, you will hear the
difference in gain IMMEDIATELY. This is not a subtle change that only the "experts" can hear. Leave the settings
on the guitar and amp the same, swap the tube, and listen again.
When we see a transconductance of 900=1200 versus the 1600, the way the tube reacts is different too, in this
case, its rise time is about 25% slower. This might be just the ticket for a blues player, looking for some nice initial
compression on the pick attack, but it may not be the sound for a metal or speed player.
Transconductance in the testing, ranged from 1060 to 1790. 1600 is the industry standard.
There is one other aspect of preamp tubes. Unlike power tubes, where one tube is one tube ? a preamp tube is
two tubes in one bottle. There is an A side and a B side. The are independent units sharing only the heater. In a
Marshall amp as an example, the NORMAL channel input 1 uses one side of the tube, and input 2 (lower gain input)
the other side. The BRIGHT channel uses the other side of the preamp tube. BUT, anytime we use that tube in the
phase inverter position or driver position of the amp (which is the driver for the power tubes), then having the two
sides matched is important. This matching subject has been covered before, so I won?t elaborate on this again
here.
New versus Vintage amp needs -
NOS tubes are sought after by folks that have original amps like Fender Tweeds and the like. If you want the
original sound, feel, and character of these amps, then NOS is about the only way to go. Getting NOS tubes for
your amp to be correct is much easier in some ways than getting decent new tubes for an amp. There are folks
that deal with NOS tubes. Some of them are on my website, but I will say here, that I can recommend KCA and
Tube World very highly. Please DO NOT confuse Tube World with TheTubeStore ? they are NOT even close.
Either of these folks have the tubes and the equipment that will let you know that when you purchase a Mullard or
RCA 12AX7 or whatever, it?s characteristics will be noted for your information. If you are in Europe, check with
Watford Valves, as they also have NOS offerings. Eurotubes in the USA, a JJ importer, also may have some NOS
offerings.
When it comes to new tubes for you modern or class amp, or new boutique amp, there is the problem. Preamp
tube suppliers guarantee the tubes to work, and not be microphonic. That is about all they can do. Going though
tubes that retail for less than $20 in most cases, one at a time to measure them, is beyond reason economically.
Watford Valves will do this for folks. Other folks offer these services, and in most cases, they are an additional
cost. In my mind, the money is well spent. When you want a nice high gain tube for your Rivera or Demeter,
putting in a tube that is 30% down from spec., is not the ticket! At that point, what can you do with that tube? Take
it back? Why? It works. The store or vendor never stated it would do anything more than "work". Perhaps they
will exchange it, and now you start the process over? And over. And over.
Recently I was working with a fellow named Tom Dunn. He plays a 5150 II. We performed a blueprinting session of
his amp, and it was found after going through maybe 2 dozen of his own tube stock, that he had picked out his
tubes by ear, and placed them in the most advantageous position in his amp. You can do this by ear, if you have
the ears of this guy, and also the time (he did this over many months), and the tube stock.
Conclusion -
Your first gain stage in your amp is its soul, sound, and character. We talked here about gain, and a little about
rise time, which is a subject in itself. We did not get much into "sound", such as the articulation and definition that
comes from NOS tubes like the Mullards and Telefunkens. If you have an older amp with a more moderate gain
structure, and want it to sound closer to magic, than this is the way to go. In a modern amp, a lot of the articulation
from the output section is not the target of these designs. Today?s designs look for two or three or more stages of
gain, channel switching which we did not have on the older amps of yesterday, and flexibility. The only flexibility we
had when I was the age of most of you, was a high gain input and low gain input ? or tuning the reverb on or off J
All I can suggest, is try to find a tube vendor that can supply you with the tubes you need with some degree of
classification. This way, if you have a 1.3/1670 tube in there now, and you want to tone it down a bit, then maybe
go for a 1.1 ? it will make a difference. If you want tonal changes in color, rather than gain and compression, then
you want to go with a little stash of tubes, depending on your use for the day or evening. Most of my clients keep
the following:
JAN 12AX7A - Most often general use.
12AX7C - Chinese 12AX7 - take off some amp edge or brightness
12AX7EH - Electro Harmonix - general use
ECC83 - for the Marshall sort of sound
7025 - for the Fender 60?s and 70?s sound
5751 - for blues and less aggressive attack (and perhaps less gain as compared to an in spec 12AX7)
(this was written in May 02 or earlier. Since that time, there have been many new developments, so be sure to look
around in other areas here for ongoing test reports on all the latest 12AX7 / ECC83 / 7025 family.
Please excuse the formatting as I just copied, cut, and pasted this here from my site. This may have been missed by many as my website is not exactly all that user friendly.
Preamp Tubes - The most critical, least expensive, most overlooked tubes in your amp.
The tonal signature of "your sound" and interchangeable without adjustment or the need of an amp tech.
Unlike power/output tubes, which are routinely matched when they are sold (in different ways, some much better
than others), preamp tubes are tested at best to: (a) make sure they work ? (b) they are not microphonic. In
testing, we have found that some suppliers don?t seem to test their preamp tubes at all, as we have found one side
of the triode that is dead at times. Since most warranty preamp tubes for up to 6 months and longer, they possibly
figure that is cheaper to just send them out as they get them in, and if there is a problem, it is cheaper to just give
the customer another tube. This is of little comfort to somebody that either has to make another trip to their music
store, or worse, box up the bad tube and ship it back to the supplier, and then wait for its replacement. This is one
reason to consider a proven supplier when you buy preamp tubes.
Today?s amplifiers, whether modern high gain types or boutique amplifiers, have one thing in common; the preamp
tube in the first gain stage (usually V1 and / or V2) sets the tone and initial gain structure of the amplifier.
Amp design -
Today?s modern amps get just about all of their characteristics in the preamp section. How the gain stages are set
up, how the EQ is set up, gain structure, and tone stacks, all are the main aspect of the sound character of the
amplifier.
Amps such as Mesa Boogie, Fender, Marshall, Bogner, Peavey, and others, all use the same Sovtek, Svetlana,
JJ/Tesla, Electro Harmonix, and other power tubes from the same factories. In spite of the same output sections,
and in many cases the same range of B+ voltages on the plates of the output tubes, these amps sound different.
This is all because of different designs, primarily in the front end, or initial gain section of the amplifier.
Inconsistencies -
Today?s newly made preamp tubes are very inconsistent compared to the tubes of the 1940?s to 1960?s. There
is little need in the medical sector or the military sector for tubes. They are primarily used today in audio
applications. For the high end audiophiles, their needs are more easily met, as their tubes are not subjected to the
same stresses as those on a guitar amplifier, they use less of them, and they last much longer. There are high end
audio suppliers that will match tubes and hand select them, at much higher costs (check out a Western Electric
300B matched pair for example). They pop their tubes in, and ten years later, all is still just fine.
Tubes for the guitar and bass player for use in the preamp section, are a different story. The tubes today are very
inconsistent. You contact your local tube supplier, plunk down your money, and the roulette wheel is now set into
motion.
To show the inconsistency, we went through a batch of over 100 tubes that were from the Electro Harmonix
12AX7EH, ECC83, 7025, Sovtek 12AX7WA, LP, LPS, Chinese 12AX7C (old tooling and new tooling), and a few
others.
Basically, the standard 12AX7 spec that applies to 12AX7 / ECC83 / 7025 tubes, has a reference of 1.2 mA at 250
volts with a -2 volt bias.
Some people like to use those little references that say if you want less gain than a 12AX7, use a 12AT7, as it has
only 70% of the gain of a 12AX7 etc. These little tips are cute, but with the wide range of inconsistency out there,
they are not all that useful, as it is still a matter of chance. The 12AT7 has a different current capacity than a
12AX7, so if you are just looking for less gain, then you may, or may not get it with just a different 12AX7, even from
the same brand, same date code, and same batch ? just by swapping tubes around already in your amplifier. With
today?s inconsistent offerings, the old tables of gain cannot be used with much accuracy.
In the tubes we went through, keeping in mind our 1.2 mA / 1600 transconductance industry standard spec, we
found our samples ranged from 0.7 mA to 1.6 mA. When you take into account, that the amplification factor of a
12AX7 is 100, there is a dramatic difference in these tubes.
Looking at a 1.6 mA tube, we see a factor of increase over the standard of 33%. This is a LARGE number. A 1.0
tube versus a 1.2 tube will turn the gain you loved in your 5150 into something less than what you used to know
what you liked there. You sit dumbfounded ? how can this be? I just put in new tubes, the same as what I had
before?
You want even MORE GAIN from your Triple Rectifier or Bogner? Look at those first gain stage preamp tubes, and
get some tube vendor to measure them for you. If you have a 1.1 in there, and put in a 1.3, you will hear the
difference in gain IMMEDIATELY. This is not a subtle change that only the "experts" can hear. Leave the settings
on the guitar and amp the same, swap the tube, and listen again.
When we see a transconductance of 900=1200 versus the 1600, the way the tube reacts is different too, in this
case, its rise time is about 25% slower. This might be just the ticket for a blues player, looking for some nice initial
compression on the pick attack, but it may not be the sound for a metal or speed player.
Transconductance in the testing, ranged from 1060 to 1790. 1600 is the industry standard.
There is one other aspect of preamp tubes. Unlike power tubes, where one tube is one tube ? a preamp tube is
two tubes in one bottle. There is an A side and a B side. The are independent units sharing only the heater. In a
Marshall amp as an example, the NORMAL channel input 1 uses one side of the tube, and input 2 (lower gain input)
the other side. The BRIGHT channel uses the other side of the preamp tube. BUT, anytime we use that tube in the
phase inverter position or driver position of the amp (which is the driver for the power tubes), then having the two
sides matched is important. This matching subject has been covered before, so I won?t elaborate on this again
here.
New versus Vintage amp needs -
NOS tubes are sought after by folks that have original amps like Fender Tweeds and the like. If you want the
original sound, feel, and character of these amps, then NOS is about the only way to go. Getting NOS tubes for
your amp to be correct is much easier in some ways than getting decent new tubes for an amp. There are folks
that deal with NOS tubes. Some of them are on my website, but I will say here, that I can recommend KCA and
Tube World very highly. Please DO NOT confuse Tube World with TheTubeStore ? they are NOT even close.
Either of these folks have the tubes and the equipment that will let you know that when you purchase a Mullard or
RCA 12AX7 or whatever, it?s characteristics will be noted for your information. If you are in Europe, check with
Watford Valves, as they also have NOS offerings. Eurotubes in the USA, a JJ importer, also may have some NOS
offerings.
When it comes to new tubes for you modern or class amp, or new boutique amp, there is the problem. Preamp
tube suppliers guarantee the tubes to work, and not be microphonic. That is about all they can do. Going though
tubes that retail for less than $20 in most cases, one at a time to measure them, is beyond reason economically.
Watford Valves will do this for folks. Other folks offer these services, and in most cases, they are an additional
cost. In my mind, the money is well spent. When you want a nice high gain tube for your Rivera or Demeter,
putting in a tube that is 30% down from spec., is not the ticket! At that point, what can you do with that tube? Take
it back? Why? It works. The store or vendor never stated it would do anything more than "work". Perhaps they
will exchange it, and now you start the process over? And over. And over.
Recently I was working with a fellow named Tom Dunn. He plays a 5150 II. We performed a blueprinting session of
his amp, and it was found after going through maybe 2 dozen of his own tube stock, that he had picked out his
tubes by ear, and placed them in the most advantageous position in his amp. You can do this by ear, if you have
the ears of this guy, and also the time (he did this over many months), and the tube stock.
Conclusion -
Your first gain stage in your amp is its soul, sound, and character. We talked here about gain, and a little about
rise time, which is a subject in itself. We did not get much into "sound", such as the articulation and definition that
comes from NOS tubes like the Mullards and Telefunkens. If you have an older amp with a more moderate gain
structure, and want it to sound closer to magic, than this is the way to go. In a modern amp, a lot of the articulation
from the output section is not the target of these designs. Today?s designs look for two or three or more stages of
gain, channel switching which we did not have on the older amps of yesterday, and flexibility. The only flexibility we
had when I was the age of most of you, was a high gain input and low gain input ? or tuning the reverb on or off J
All I can suggest, is try to find a tube vendor that can supply you with the tubes you need with some degree of
classification. This way, if you have a 1.3/1670 tube in there now, and you want to tone it down a bit, then maybe
go for a 1.1 ? it will make a difference. If you want tonal changes in color, rather than gain and compression, then
you want to go with a little stash of tubes, depending on your use for the day or evening. Most of my clients keep
the following:
JAN 12AX7A - Most often general use.
12AX7C - Chinese 12AX7 - take off some amp edge or brightness
12AX7EH - Electro Harmonix - general use
ECC83 - for the Marshall sort of sound
7025 - for the Fender 60?s and 70?s sound
5751 - for blues and less aggressive attack (and perhaps less gain as compared to an in spec 12AX7)
(this was written in May 02 or earlier. Since that time, there have been many new developments, so be sure to look
around in other areas here for ongoing test reports on all the latest 12AX7 / ECC83 / 7025 family.