Part 1 of 2

Guitar Amplifier Blueprinting


What are the differences between tubes? What is a phase inverter? What about a matched phase inverter? What is matching? Static versus dynamic matching? Aren't all tubes really the same? Is 100 watts twice as loud as 50 watts? How much power do I need? These questions and more are covered in this document


Version 3.30 9/23/04 part 1 of 2 BEFORE WE EVEN GET STARTED ... IF YOU JUST WANT A FEW BASICS AND HATE TO READ ....................................................... 4 BRIEF TUBE AND SOLID STATE DIFFERENCES ........................................................................................................................................ 4 DITTO ­ THE SWISS ARMY KNIFE OF THE RECORDING STUDIO AND FOR LIVE PERFORMANCE TO THE HOUSE SYSTEM......... 5 MY PERSONAL FAVORITE OR MOST IMPRESSIVE AMPLIFIERS............................................................................................................. 5 MATCHING IN BRIEF .................................................................................................................................................................................... 12 BIASING IN BRIEF ........................................................................................................................................................................................ 13 WHAT TUBES SHOULD I USE IN MY AMPLIFIER? - A MODERN DAY TUBE SELECTION PRIMER .................................................... 13 PREAMP TUBES ........................................................................................................................................................................................... 17 SAG ­ SPECIAL APPLICATIONS GROUP (SPECIFICALLY SELECTED TUBES FOR SPECIFIC NEEDS) ............................................ 17 THE BASICS OF PREAMP TUBE DIFFERENCES ...................................................................................................................................... 19 12AX7 (ECC83, 7025, 12AT7, 12AY7, 12AU7, AND MANY OTHERS) PIN CONNECTIONS..................................................................... 21 12AX7 RATINGS............................................................................................................................................................................................ 21 12AX7 SHORT DATA .................................................................................................................................................................................... 21 CHARACTERISTIC NOMENCLATURE USED BY TUBE ENGINEERS ...................................................................................................... 22 PREAMP TUBE OVERALL CHART OF SOME NOS AND MANY CURRENT TUBES ............................................................................... 32 ADDITIONAL SMALL SIGNAL TUBE TESTS AND REFERENCE .............................................................................................................. 35 RECENT TUBE TEST RESULTS .................................................................................................................................................................. 37 THE OUTPUT TUBES ­ THE PENTODES AND BEAM PENTODES .......................................................................................................... 46 BIASING ­ A NEEDED CONSIDERATION WHEN REPLACING OR CHANGING POWER TUBES .......................................................... 47


6V6 OUTPUT TUBES .................................................................................................................................................................................... 49 6L6 / 5881 / KT-66 TYPES............................................................................................................................................................................. 52 EL34 ­ E34LS ­ AND 6CA7 TYPES ............................................................................................................................................................. 59 MISCELLANEOUS AND OTHER OUTPUT TUBE TYPES........................................................................................................................... 64 6L6 / KT66 / 5881 / EL-34 TUBE OUTPUT CURRENT OUTPUT COMPARISONS..................................................................................... 66 POWER OUTPUT COMPARISON TEST RESULTS OF VARIOUS OUTPUT TUBES ................................................................................ 67 6550 / KT-88 TUBES...................................................................................................................................................................................... 70 POWER COMPARISON CHART OF CURRENT OUTPUT FOR THE KT-88 / 6550 FAMILIES .................................................................. 77 THE EL-84 TUBES......................................................................................................................................................................................... 78 TECHTIP ON EL-84 AMPS............................................................................................................................................................................ 78 OUTPUT POWER CHART FOR EL-84 FAMILY ........................................................................................................................................... 82 7027 AND 7591 TUBES................................................................................................................................................................................. 85 RECTIFIERS ­ VACUUM TUBE AND SOLID STATE .................................................................................................................................. 85 THE GT RATING SYSTEM ­ AN EXPLANATION OF "DISTORTION RATING" ALSO KNOWN AT TIMES AS "HARDNESS RATING" 92 CONVERSION INFORMATION ­ GT NUMBERING, FENDER COLOR CODES AND MESA COLOR CODES......................................... 92


Before we even get started ... if you just want a few basics and hate to read

There are three items that are the foundation of most of what is in this document. Tube and solid state differences, matching, and bias. I will cover these briefly.

Brief Tube and solid state differences

Much is available on this subject, but from a very high level there are a few points worth mentioning. Some folks feel that solid state and digital components have greater frequency response than tube devices. I suppose this may be true in some area out in areas that are so far out in the frequency spectrum that it's crazy, but for our purposes, this is not the case. Remember, there are tube devices operating in the gigahertz range, way beyond what we need in the world of audio. There are devices such as the DITTO, which have a bandwidth of 6 Hz ­ 200 kHz which are tube units, as an example, in the audio business. Solid state devices have sort of an "on or off" aspect to their operation. This is something akin to one being in a dark room, with their eyes closed, while another in the room flips the light switch on and off. You cannot see the light, but know that something is going on, as you hear the switch being flipped. This is true in the digital realm, and is sometimes called "hash" or has other terms, for this by-product if digital products. You think this is no big deal or does not matter? Thankfully today, there are very powerful tools available to mere mortal men, only available in the past to folks that worked at places like Bell Labs. Pro Tools, a popular recording suite, can illustrate this pretty easily. Look at any digitally recorded aspect of one of your recordings. Drum tracks are great for this. Zoom in on one short area of a sample of the sound. You will see a lot of information there. Now, borrow something like a DITTO box or Brick. "THE BRICK" is something of a DITTO but has onboard phantom power so you may use it for microphones also. THE BRICK shares some of the ViPRE technology. More can be found on THE BRICK at


DITTO ­ The Swiss Army Knife of the recording studio and for live performance to the house system

Take the original track, reroute it through the DITTO, and reproduce it to another unused track area. Now listen to the difference. Look at the difference. You will notice that the DITTO rerecorded track lost NONE of the original material, has more dynamic range, sounds much more open and alive, and yet has less on the display. Why is there less on the display? Zoom in on the "missing" part of the waveform. LISTEN to only that aspect of the sound. I think you found it was clicks or noise, or whatever you want to call it ... but in any case, stuff you did not want and stuff that did not help your sound. Try plugging a POD XT into one of these before you go to the board or the amp. You may be surprised Tubes do not have the "on-off" aspect. They are always conducting and flowing the electron flow. This is one of their differences. This is not better or worse, it is different. Before you think or buy the fact that sticking a tube in the front end of a digital or solid state amp is going to turn it into a tube amp, think again. It may give you everything you are looking for, and that may be just what you wanted, tube or no tube.

My Personal Favorite or Most Impressive Amplifiers

Being a big fan of Aspen Pittman's "The Tube Amp Book" for almost two decades, one of the first sections of the book that caught my interest was Aspen's Top Ten amps of all time section. Today, there is a wider selection of amps than ever before, and although many of the original amps are still considered the classics, some of todays amps are what I consider to be the classics of today, and probably tomorrow. I picked these amps for various reasons, but some of the aspects are unique features, design, and superior build quality. I will explain some of my thinking as I go along. I do not own all of these amps by the way, but have had access to them and they impressed me enough to stick in my mind. I know many will complain as there are not amps such as the Matchless DC30 and many other great amps here that they feel should be here. These are amps that a higher number of folks out there can afford, and amp that in their price range give up nothing in the way of tone and build quality compared in cases to amps with two or three times their retail cost. This book is primarily a tube document, but I could not keep myself from saying a little more about the amplifiers themselves.


HIGH POWER MODERN PCB CHANNEL SWITCHER AT A STEAL $$$$$ ­ THE RIVERA KNUCKLEHEAD REVERB 55 AND 100 WATT AMPS This amp is one of the few, if not the only, that has two differently voiced channels, one British and one American. Most other amps just alter the gain on the channels. The amps are built using aspects such as threaded inserts in the cabinets, and machine bolts, rather than just self tapping wood screws. I have NEVER had any client Rivera amp fail due to design or workmanship. VERY flexible front end with great EQ and tone controls. Sub level control if you use a sub system. With the Rivera Head Master controller, total control of the amp is just a tap away. The amps are really nicely priced compared to a lot of things out there that might do as much and are not built as well. To my way of thinking, Rivera amps are the best made production channel switching amplifiers today; heads or combos using PCB construction. For more info:


THE `MARSHALL" STYLE AMPS in the non-master volume style Dr Z Delta 88 There are a number of great "non-master" volume "Marshall" type amps out there. This is one I have found that gives the tone and feel of the EL34 and 6550 Marshall amps but is not just a copy or modification of the original design. Much more pedal friendly than the originals and with a very simple front end and over 100 watts on tap via a duet of KT88 output tubes these amps are worth a test drive. More things than I can really say here.

"VOX AC-30" AMP - THE VOX THING AND MORE WITH SIMPLICTY AND EVEN MORE VERSITILITY Dr. Z Mazerati and new Prescription Extra Strength Lots of clean headroom if you need it, lots of AC-30 tones it you need that, only one tone and one volume, and trust me, that is more than enough. It also seems to be enough for Brad Paisley who chose this amp to replace his own vintage AC-30. If you want more controls and a more "conventional amp", then look at the Dr. Z Maz 38 which is voiced more like a Fender Tweed Bassman / Marshall Plexi, but can do the Vox AC 30 stuff as well. Dr. Z can even optimize the Maz 38 in more or less of either direction. Read the Guitar Player Magazine March 2004 review at:


BLUES / SMALL CLUB AMPS ­ TWO STANDARDS OVER DECADES The Victoria 20112T (tweed deluxe) and Fender Deluxe Reverb The Fender Tweed Deluxe (on the right in the photo). There is little to be said about these Deluxes, and this Victoria is one of the very best. The phase inverter on the tweed amp is only one half of a 12AX7, and the tone control works directly on that triode. This lets one balance the ratio of preamp to output distortion just so, a feature that I miss on the Black Face Deluxe Reverb that came in later years. Then again, pick either of these amps, depending on taste! For a lot more info on this amp head to MY FAVORITE CLEAN AMP ­ FOR COUNTRY PICKERS, RHYTHM PLAYERS, BUT ALSO HUGE LEAD CRUNCH FOLKS ALA JOE WALSH / TED NUGENT The Dr. Z KT-45 for Fender Twin Reverb or Super Reverb fans This amp puts out close to 70 watts or more. Again, simple controls, but not limited tones. The EF86 in the front end has huge gain and is driven by the tone stack, so a very huge sound with massive sound stage image is possible with this amp, more so then with the old classic, the Fender Twin Reverb. These amp are currently with Brooks and Dunn, and many others. This is the amp Joe Walsh used on the Eagles "Hell freezes over tour".


HUGE ROCK AMP COMBO FOR THE CLASSIC 1950S AND EARLY 1960S TONES Victoria 80212T and 50212T Massive clean tones, more headroom and larger transformers than a 100 watt Hiwatt. The Tweed Twin is what you see being used by folks from Clapton to The Stones these days. This is one huge sounding amp, the sound of Rock and Roll. If this amp is too much for you, there is also a 50 watt version which frankly, is more than enough for most stages and outdoor venues. I know some folks are going to say, "what about the Victoria Bassman"? I don't think there is any reason to list that amp in here, doesn't everybody already have a tweed Bassman?

MONSTER GAIN IN A SMALL PACKAGE ­ STUDIO MASTERPIECE ­ SMALL CLUB MASTERPIECE Dr. Z Carmen Ghia ­ "if I could have only one amp for the rest of

my playing days, it would be a Ghia" ... msr

One tone, one volume, and can be pretty clean at less than 10 o'clock on the volume with a decent amount of clean headroom, a bit louder than my Deluxe Reverb. The amp is rated at 18 watts ... don't let that fool you, look at the power transformer! Hand wired turret board, the best parts, and turning the volume past 10 o'clock the fun starts and the surprised looks never stop. A necessity in any studio. Conjunctive tone filter and fixed bias phase inverter ... you won't see these in other amps


JUST GREAT ALL AROUND, SUPER AMP(S) IF YOU CAN ONLY HAVE ONE AMP Okay, I cannot pick one, as this is for the great all around amp. The Rivera Quiana is a departure from Paul Rivera, as it uses 6L6 output tubes rather than EL-34 tubes. This amp does Fender on channel 2 and high gain Brit (sort of the Bluesbreaker thing on Channel 1. A lot of versatility and features and the 2x12 configuration will fill any venue. The Dr. Z Maz 18 (MAZ Jr.) Hand built, PTP, best parts and construction, ultra versatile, compact, light, loud, reliable in the worst situations, and at a price that is generally less than ½ of what many amps hand built amps of this class sell for. A lot of output and great reverb too, in an easy to move package. This amp has a different sort of flair than the Rivera, quicker to distort as it is based on a duet of EL84 tubes. These amps are very loud, much louder than their power rating suggests. These are also one of the few EL-84 based amps that can do the Vox sound AND the Fender sounds. This amp should also be in one of the other sections above, as one of the best club and blues amps. This is perhaps one of the most versatile amps anywhere .... Rock, jazz, blues ... and pedal friendly to boot. This amp is also very portable. 1x12, 2x10, and head. The Dr. Z Z-28 (not shown here but can be seen from the below link) All the great Fender tones and more. This amp has replaced many of my Fender amps for those applications. The Z-28 puts out more level than one would expect though. Think of the amp as bigger than a Black Face Deluxe. It easily keeps up with a BF Super Reverb.


Great designs with something worth considering ­ MASTER BUILT, PTP TURRET BOARD, ATTENTION TO DETAIL AND GREAT TONES AND FEEL. The Mako amps Hand wired, PTP, turret board, channel switchers. Hand built PTP channel switching amps. An amp where there is no room for improvement. Even the transformers are done in house. There are not a lot of PTP wired channel switching amps out there, only one other crosses my mind. These have a waiting list, and are generally only sold direct unless things have changed, but they are worth the wait. The wood cabinet in the photo I stole here from the Mako Website was a custom cabinet. These folks also have some of the best speaker cabinets in the world, from my point of view. A BRITISH FLAVOR / USA HAND BUILT AMERICAN STANDOUT ­ 60 WATT MASTERPIECE ­ A GREAT ROCK OR CLEAN AMP The Victoria Sovereign is not really a master volume amp. With an EF86 in V1 (huge clean headroom or gain) an amazing reverb driven by a 6BM8 Pentode/Triode and 60 watts easily out of a set of even 25 watt EL-34 tubes such as Svetlanas, this is an amp that is a real masterpiece. There is too much to say here, but you can read a detailed PDF format review at There is also more at:


Matching in brief

There is a lot more on matching deeper in this document. Let me just briefly say here, that folks need matched output tubes and at times, matched triodes. If you have what is termed a Class A amp, such as a Vox AC-30, Matchless, Fender Blues Jr., and think you got lucky as there is no bias adjustment, you are wrong. These amps are what is termed cathode biased, but are not what are called single ended. They have two or four output tubes, and operate in push-pull, just as the class AB brothers. What gave the Vox AC-30 the reputation for being unreliable, was the heat that was generated, the lack of ventilation, and a few other aspects. Balanced output tubes are critical in these amps. They are idling at close to 100% idle dissipation, much higher than their AB counterparts. An unbalance in the output set is akin to two riders on a tandem bike. If one is tired or slow and does not contribute 50% to the effort ... no more, no less, the other rider will tire more quickly due to additional work effort required. This is the same with tubes, one tube or duet is working harder than the other, and this causes a few problems. The first aspect is the sound most would surmise. Yes, this is true, a lack of sustain, less power, less clarity. There is another important side effect. Heat. Lots of heat that is not nearly as high as when balanced tubes are used. The tubes of the past were not matched at times. Vox AC-30 amps were known at times to also catch on fire and have reliability issues. It was common for groups using these amps to have more than one, and "matter of factly" just wheel one in to replace the one that failed on stage. Don't believe it? Read a bit or ask around some of the folks from the sixties. Look in the Vox Book where this is mentioned in passing. Lower chassis temperatures also give longer life to the resistors and capacitors that also reside in the amp's chassis, extending their life. There are big differences in the ways tubes are matched, and this is covered later in this document. From an Internet post I answered in regard to "matching" preamp tubes, specifically the phase inverter::


Originally posted by proudmore Hey Myles, for a PI, what brand of tube would be the best? What should I look for, other than matched triodes? Should be a high gain tube, high output..? Does it matter? The brand of the tube or tube type is not really critical. Some runs have more balanced tubes than others. The PI is not part of the tone generation stage, so it is picked for specs and performance, tone is not an issue. You want proper gain, but proper output current is MUCH more important. This is why simple gain matching or transconductance matching is pretty good, but will not yield the same results as a tube that has proper current drive (most are about 1/2 of what is spec) for today's tubes on average, or at least 3% down for the most part. Even more important is the tubes curves and rise time. In some amp designs that balance (actually they average) the output or gain of the two sides ... they cannot average rise time. Sort of think of it in a way, that is you have a rise time of 20 "counts" on one side and 40 on the other, now you have a wobbly window of 20-40 counts overall, or a 20 count spread. This is a lot less articulate and defined than a count of 0-2 or so. This is where pretty sophisticated test rigs come into play, and cannot be done with conventional tube "matching" equipment. 12

Biasing in brief

Bias your amp properly every time output tubes are replaced, if not of the same distortion rating, type, and maker. The bias is something like the idle of your car in a simple way. Setting your bias so the amp runs really hot is something like using this faulty logic to set the idle on your car to 5000 rpm. You want your bias set for great tone at low, mid, and high levels ... not just at high levels. Bias effects tube life, tone, playability, dynamics, and other areas. You also need to bias the amp properly. This does NOT mean pulling the old tubes out, slapping in the new ones, and THEN trying to bias. This will only lead to problems, or at best, take a big chunk out of the life of your new tube set. A proper bias method is described later in this document.

What Tubes Should I Use In My Amplifier? - A Modern Day Tube Selection Primer

Today in 2003, there is a lot of misconception on where tubes come from, how they actually perform, and what their characteristics are. Information that was valid only a year or two ago, is not always valid today. "Chinese tubes are less powerful than the Russian tubes". "Chinese tubes do not hold up to high voltages". "Matching is matching", or "there is no need to match tubes". This information gets passed along, and becomes something of gospel, when most of it is just plain rubbish. In the case of the Chinese tube issue, a few years back, this generally was the case. Today, the typical Chinese power tube is 15% stronger in many cases than its Russian counterpart. The Chinese have great tooling, and money. They are putting a lot of resources into tube manufacture. The Chinese 12AX7 as one example, is the most consistent tube in quality and specifications when compared to a lab spec 12AX7. As you proceed with this paper, examples and characteristics of many tubes will be given. These are not bits of data collected from magazine clippings, Internet spatter, or hear say. This data comes from my personal time sitting with thousands of tubes, one at a time, with very high end test equipment ­ not simple tube testers. Amps come in all types, sizes, styles, etc. You cannot turn a Marshall into a Fender, or visa versa, no matter how hard you try. If you "need " both of these sounds, the bottom line is, you need one of each of these amps. Some folks like Paul Rivera, have two different voicings in the same amp. This is pretty unique, as most folks just change the gain structure on the various channels, with the same voicing.


A 60 watt Sovereign amp from Victoria Amplifier ­ very versatile with it's variable front end which uses an EF86 in the front end, a 6BM8 in the reverb circuit, a cross between a Plexi era Marshall and Tweed Bassman. This is not a master volume amp. You can turn the gain all the way down and it's pure Plexi era. Turn the gain up, and it moves through JCM 800, 900, 2000, and beyond Mesa Rectifier territory. This is one example of an amp that is very unique, and built, and very unique. I have a full write-up on this amp someplace on my personal website. If you would like a copy of the review sent to you via email, just drop me a note. You can also learn more at for Victoria in general. A review of the Sovereign is at

Some of the proven classic amps ......... Fender Black Face Deluxe Reverb and the Tweed Deluxe (in this case a Victoria 20112T) Perhaps to some folks thinking, the best small club and blues amps around. This Victoria Deluxe is simply, one of the most amazing and touch sensitive amps one will ever play. This is just one of Victoria's amps in an extensive lineup. To see more, head to


The Dr. Z Carmen Ghia. Sure, the good Doctor makes lots of amps, but this is one of the most amazing pieces of gear around. This is a studio amp masterpiece and also a super club amp, Dr. Z is one of the folks out there that copies nobody. His amps are all very unique and built to the very highest standards of construction. His Route 66 has won awards that were not political, they were from real players. The Z-28, MAZ 18 and 38, and other models each do their target aspects VERY WELL. For much more on Dr. Z amps, internal photos, comments, pricing and more, head to

If you are one of those folks that thinks that wattage = manhood ... this older amp may be your cup of tea. The top section is two 60 watt EL34 based amp sections, and the bottom slave is 8 GE 6550 tubes, for a total of about a ½ a kilowatt of tube power. This amps runs with four 2x12 cabs and four 4x12 cabs. For more on Rivera, and their amps (which are a lot more current that this particular example, head to There are amps for every taste and need out there! This is a very old Rivera model, no longer produced. For their new and great amps see Some of my other personal favorite folks out there can be seen in the amps / guitars area of my website at


This is a THD Univalve. This is a single ended class A amplifier that one can change the tubes in with no adjustment necessary. There are a lot of other features on this amp. This amp is a great tool in the studio or for smaller club live work. Some folks think of amps such as Vox AX-30 amps as class A amps. Although this is somewhat accurate, they are really cathode biased push-pull amps. The Univalve is a true class A amp with no feedback loop. The THD UV is a MUST for any studio. For more information go to

Two Doctor Z amps, perhaps on each end of his product line. The red one is a Carmen Ghia, one of the coolest amps around and a great studio and recording amp. The tan amp is a KT-45 with loads of clean headroom, but with it's tone controls pushing a pentode front end (an EF-86, this amp is capable of a lot of gain too. The pair of these amps will cover just about any music base. Dr. Z has a LOT more amps, all of original design, and all built hand wired to extremely high standards. For more see


Preamp Tubes

Please note that the tests on tubes were done on raw factory samples. Some tube vendors test and/or select or grade, and some do not. Many rely on the end user's reluctance to return a single tube such as a preamp tube for problems, so just send their tubes out with no testing or minimal testing. A preamp tube that is not microphonic when first installed, can become microphonic in short order after a few heat up and cool down cycles with expansion and contraction. This is one reason to know and trust your vendor. Some companies such as Groove Tubes have a very long warranty on tubes, in the case of preamp tubes, six months. Some reasons for the cost of GT premium tubes are due to the labor intensive testing process (each tube, one at a time, in place in high gain amps and tested for various attributes), and their cost for the tubes initially when buying from the major tube factories. In many cases, the GT reject rate is in excess of 60%. The data below, are for the raw factory samples, not GT tested examples. This is the way they come from the factory, and the sort of performance you can expect if your vendor does not test for gain, output, noise and microphonics. In the case of power tubes, gas leakage, grid leakage, and low vacuum are also test parameters that require expensive and complex test equipment which very few vendors have in house. The complete list of Groove Tubes preamp tubes can be seen at:

SAG ­ Special Applications Group (specifically selected tubes for specific needs)

As you will learn throughout this document, all tubes, new or NOS are subject to very wide variations in characteristics. As an example, a 12AX7 is supposed to have as spec, a gain of 100, a transconductance of 1600 and a current output of 1.2 milliamps at a reference test voltage and bias. Tubes will typically vary +/- 50% or more, even ones tested from most vendors. For GT preamp tubes, this spread is much narrower, as the testing acceptance margins are tighter. Still, you do not know what you are actually getting in any case. One problem that kept coming into play, was a player would decide to retube the preamp section of his or her amp. The amp sounded worse in some cases with the new tubes. It was noted that perhaps the old tube had a current output of 1.0 milliamps, while the new tube only had a current output of 0.7 milliamps. This was a 30% drop in actual power off the first gain stage. Searching through tubes until one was found that met or exceeded the specs of the original tube would solve the problem and bring the amp back to life. It was found that things could be made even better, actually moving up or down in various tube characteristic parameters, to dial in to a particular player's taste of needs. Tubes with more or less gain, more or less current, faster or slower rise time (more or less compression), and other factors were "tweeked" as the player went from one tube to another. This is one of the cornerstones of amplifier blueprinting. Matched phase inverters also came to pass in this process, there is more on this later.


One of the biggest benefits of SAG tubes, is that the end user KNOWS what is in the amp. They can replicate this later, or go "up or down" in various parameters. For very critical requirements, the rise time of the matched phase inverter is also optimized to the characteristics of the output tube set. Most GT offered tubes can be processed through the SAG (Special Applications Group). It costs about $10.00 per tube to have one found, and in some cases, some tubes may not be able to be accommodated in short order. Some tubes from some vendors, have such a high reject rate, or extremely bad characteristics, that one would need to go through over 100 of them to find one example. You may contact Myles Rose for specific requirements. Some of the more common SAG tubes are available off the GT website or may be special ordered through any Groove Tubes dealer. There is more on the SAG on the Groove Tubes website at where one can also add the SAG labor cost to any of the tubes in the GT product line. Some of the more common SAG tubes generally in stock are: SAG-AT7-MPI - matched phase inverter (on a tracer, not just statically matched) generally used in Fender Black Face, Silver Face, and early Tolex era amps. SAG-AX7-MPI - matched phase inverter (on a tracer, not just statically matched). Used on most amplifiers SAG-FHG ­ Fender High Gain Kit for Black Face and Silver Face era amps, many of the newer amps also. SAG-FST ­ Fender Soft Touch Kit ­ same as above, also used for any 12AX7 front end based amp where a slower rise time is desired, a quieter tube, more clean headroom, and a higher ratio of output tube distortion compared to stock V1 and V2 tubes in these amps. This was the old "SRV" trick, where he would use 5751 tubes in the first gain stage. Unfortunately, there are not a lot of great new 5751 tubes around today, so finding tubes with the same sort of characteristics was the goal here. SAG-MHG ­ Known as the "Marshall High Gain Kit", this should really be called the high output kit. This kit is very popular in not only Marshall amps, but in Mesa, Bogner, Fender amps that need a more aggressive nature, Diezel, Rivera, and many other high gain amps. Most of these amps have very complex front end design. Having a tube that is down 30% or more on current drive ability will zap the life out of the best of any of them. Many folks love these with the included AX7 phase inverter in Fender Blackface and Silverface amps for an aggressive update on these amps.


The basics of preamp tube differences

The primary and most common family of preamp tubes is the 12AX7 / 7025 / ECC83 family. These are directly interchangeable in most guitar or bass amplifiers. Contrary to popular opinion, these are not the same sounding tubes in many ways. They each have their own sonic signature and sound characteristics. Below one can see the difference between a commonly used Sovtek 12AX7WA (the green line) and a long smooth plate 7025 (the blue line). The 7025 is a brighter tube, with more treble and high mid response. The 7025 was used in the Black Face Fender era, and was one aspect of the bright clear sound of these amps. There are many factors in a tubes character. In the case of preamp tubes, aspects such as gain (Mu), output, transconductance, and other factors, are all part of a bigger picture. Many people use the terms gain and output interchangeably. This is NOT correct. A tube can have high gain, but be very low in output current capability. This is a very common mistake today. In a clean front end preamp circuit, such as a tweed or blackface era amplifier, low output is less of a factor than in a modern channel switching amp with a complex circuit topology design. These newer amps perform their best if a high current drive tube is utilized. Today's most common factory tube, the Sovtek 12AX7WA, is picked for many reasons. It is not expensive, it is sturdy (so the amp makers have less warranty return), and it is generally low on gain and output. The latter characteristic makes the amps more quiet with less background noise, and this helps cover up other manufacturing or design shortcuts.

Today's tubes are VERY inconsistent. You may re-tube your amp, just to find that is sounds worse than before the replacement. Why? As one example, a "spec" 12AX7 should have a gain of 100 for a "typical" tube based on specs set many decades ago. It should have a transconductance of 1600, and an output of 1.2 milliamps. If your V1 (first gain stage tube) had an output of say 1.0 milliamps before it was replaced, and the new tube had an output of 0.8 milliamps, right there you just lost 20% in your front end. Remember, this signal gets amplified now down the rest of the amplifier chain. 1.2 milliamps is the "spec" number we look for in a 12AX7 / ECC83 / 7025. Unfortunately today, the vast majority of the tubes we see made newly are on average, much less, and at times 0.7 milliamps on average. This is almost a loss of 50% of our expected output. Poor plate materials that are inconsistent, fast work, incomplete vacuum pump down procedures, cathode coatings with high percentages of impurities, and more. These all contribute to today's inconsistency. These are some of the areas where the Chinese are improving faster than in other geographic areas.


The most important tube(s) in the preamp section are in the first stages, the tone and gain stages. Changing V1 in many amps will yield the most results. Tubes used for current drivers as their primary function, such as reverb drivers or effects loop drivers, do little in most amps to change the tone. This is generally not part of the tone or gain stage. The exception to this is the phase inverter or driver, of the power tubes. There will be more on this subject later in this paper.

Moving on to the tubes

What we are looking for are specific factors in testing, and other factors in sonic aspects. Rather than list all the technical data for each tube, where I have this data, I will provide additional information for gain, output, and consistency. The consistency factor I will call QA for quality. For this "spec", the lower number, the better. A perfect tube factory run would have 0% inconsistency. A factory run where the tubes were +/- 20% off target factory expected specifications, would have a number of "20". The standard specs that are the target numbers for gain is 100, and output is 1.2 milliamps, in the case of the 12AX7/ECC83/7025 family. Output will be shown as a percentage of factory expected target. If a tube has 1.2 milliamps of output, it's Output would be 100%. The most important factor in all of the above, is know and trust your tube vendor. Tubes need to be tested for microphonics, low output, and noise. With today's material inconsistency, a tube that is quiet today may become microphonic after a few hours of use, so a vendor with a good warranty is one that one may wish to have in your corner.

NOTE: This test data is from bulk factory batches of large quantities of tubes, at times 1000 tubes of each type from each factory run. This illustrates how random these tubes are, and shows what a chance you may be taking with untested tubes in general. These tubes, after testing using good methods, will narrow this inconsistency considerably. In one Tube Company's case, Groove Tubes, their reject rate on factory tubes can exceed 50%. You can sometimes easily tell how well a tube has been tested easily ... price. When there is a lot of test time and labor, and half of your stock hits the trash bin, the end retail cost has to be higher. The data below was collected at one part of late 2002 and early 2003. For the most current data, see the updated information elsewhere in this document.


12AX7 (ECC83, 7025, 12AT7, 12AY7, 12AU7, and many others) pin connections

12AX7 (ECC83, 7025, 12AT7, 12AY7, 12AU7, and many others) pin connections.

12AX7 Ratings 12AX7 ratings

12AX7 Short Data 12AX7 short data

Note the Mu, or sometimes called gain, in a "spec" tube has a target of 100. Few tubes made today will reach this, most falling below 90.



Characteristic nomenclature used by tube engineers


Keep in mind, the specs on the tubes below was, at the time of testing. This is an average of many factory runs. These numbers are always changing from factory run to factory run. The most current data which is more detailed, can be found elsewhere in this document.


12AX7-C ­ Chinese 9th generation tooling Gain: 93 Output: 92% QA: 17% This is possibly the best of the current 12AX7 family. This is a warm and linear tube. It is suited to rock, blues, and jazz. It is perhaps the most versatile of the 12AX7/ ECC83/7025 family. There are many Chinese variants, and many tube vendors sell older tooling versions. This is perhaps the most linear and most warm of new 12AX7 / ECC83 / 7025 tube production. It is also the most close in specs and the QA from the Shuguang (not to be confused with Sino), is higher than any current production tube in this family. The Chinese are pouring money into new tooling that is of very close tolerances, and has the money to do so. This is not true in the case of other companies generally. This is a great all around tube for 60s rock, blues, and is a favorite of jazz players or players that wish to tone down a harsh amp.

12AX7-R ­ Sovtek 12AX7WA and Sovtek 12AX7WC Gain: 86 Output: 77% QA: 42% This tube comes from the Reflektor factory in Russia. It is perhaps the most commonly used tube by many amp makers. It is reliable, and quiet. The main reason it is quiet, is it's generally lower gain and output. This tube is the "old standby". It is the most commonly used preamp tube. It is lower in gain and current output than most of the others in this family. This is a long lasting tube, and amp makers like it (and have influenced it's production specs) to have lower gain and output, so their amps will pass their own QA easier, and the amps will be quiet. It is a good all around tube, but there are others that are sonic improvements with more detail and harmonic content. The newest (2004) Sovtek 12AX7WC looks the same to the eye but is a VERY different tube than the WA. The WC has all the "proper numbers". It's gain, current, and transconductance are right on original NOS 12AX7 spec. A job well done by Sovtek on this tube.


12AX7-R2 ­ Sovtek 12AX7LPS Gain: 83 Output: 83% QA: 42% This tube is made in the Reflektor factory and sold under the Sovtek name. It is also known as the Groove Tubes 12AX7R2. It is a long plate structure, that is brighter than a 12AX7WA, 12AX7R3 (EH), or ECC83. It is not as bright as a 7025. It's long plate structure can be more prone to microphonics is some combo amplifiers. A newer tube with a long plate structure, these can tend to be microphonic in combo amps more often than the shorter plate tubes. These are brighter in most amps than the 12AX7WA or 12AX7C. These need to be selected by a good vendor that really tests these tubes, as the factory out of spec range is very high in my own testing, they are somewhat more inconsistent than many other tubes, and can become microphonic in short order. Their curves are not as smooth or linear than the 12AX7C.

12AX7-R3 ­ Electro Harmonix 12AX7EH Gain: 87 Output: 83% QA: 17% This tube is made in the Reflektor factory on newer tooling and also sold as the Electro Harmonix 12AX7EH. It is a shorter plate structure, a linear tube. It is not quite as warm or linear as the 12AX7C, but is just about as versatile. It is a quiet tube, and works nicely in many amplifiers. It is a touch brighter than the 12AX7C, but not as bright as a 12AX7R2 (LPS) or 7025. One of the photos shows a factory tube on a Kaye Audio Labs tester, before it goes through any GT processing. This is one aspect of the factory testing I perform at Guitar Amplifier Blueprinting. From noise data here, these tubes move on to other test equipment such as curve tracers. I go though thousands of samples each month from all the tube factories collecting the raw data to see how close or consistent to specs they come.


The 12AX7R3 is the second most consistent tube made today in this family, just about a tie with the 12AX7C (9th generation). This tube is great in Rivera, Bogner, and Diezel amps of my clients.

This is typically how factory bulk tubes come to the tube vendors from the factory. This happens to be 200 Sovtek 12AX7LPS tubes (2 layers of 100 each). On average, the reject rate on most new tubes can run 50% and higher if the tube seller has tight specs. Many vendors just ship whatever they buy, and hope for the best from the end user as far as them not complaining. After looking at a LOT of tubes, my advice is; trust your vendor.


ECC83-S - from the JJ factory Gain: 85 Output: 112% QA: 58% This is the sound of Marshall and the British era amps. A stronger mid range response, with a bit of roll off on the high end compared to many other tubes (but not the 12AX7WA). The BLUE line shows the typical response curve of the ECC83 in an average tested sample compared to the reference 12AX7WA (as the WA is a common tube in so many amps today). This tube may be brighter or darker depending on amplifier. This is due to the higher output of this tube and it's ability to "push" signal with it's high current through complex front end circuits where other tubes show their limitations. ECC83's need to be purchased from a trusted tube vendor that tests tubes pretty extensively, as they can be very inconsistent. A good one is a find for sure. These are the masters of current drive in MOST, but not all factory batches. In modern amps such as a Bogner, Diezel, Rivera, or Mesa Recto series, these are the tubes that will push signal through those complex front ends. Also limited SAG in High Gain Kits:

The curves of an ECC83 in blue, compared to a Sovtek 12AX7WA in green. Notice the increased response across the range, with an even stronger mid range response.


7025-Y from the Ei factory Gain: 90 Output: 46% QA: 25% - 60% Long smooth plates, the most bright of the current tubes. The graph on this tube is at the start of this paper. These are the characteristic sound of the Fender Tolex years. These are very articulate. In V1 and V2 of a Fender Tolex era amp, these give the original sound signature. These tend to be too bright in Marshall Plexi era amps for some tastes when used with a Strat or Tele, but if you tend to load these amps down with pedals in the front end, they can help resolve the loss of treble from the pedals. Long plates can tend to be microphonic in combo amps. The Ei factory was the OEM for many "premium" tubes folks in the past, such as Siemens and Telefunken at times, so if the plate structure looks familiar, this may be a clue. These are VERY inconsistent from the Ei factory. Over at GT, their reject rate can exceed 60% and I saw one batch go through test where Groove Tubes tossed 90% of them. These are the tubes that many other vendors just pass on along that do not test, so beware. When you find a great one of these though, they are magic. They are very close to the original long smooth plate Telefunkens, so close in fact, that some folks screen these with Telefunken logos and counterfeit them. Look for a diamond molded into the base of real Telefunkens to be sure when buying NOS.

These are some NOS 5751 tubes. The famed GE 5 star is on the left, another NOS in the middle, and the RCA Command Series black box plate is on the right.


5751 New Manufacture Expected Gain 70 Expected Output 1.2 milliamps Used in V1 by some folks like SRV to change the ratio of preamp distortion to power tube distortion. Current manufacture from Russia is so far outside of NOS sample specs on curve traces that this tube is not at all like NOS 5751 versions. Perhaps down the road things will change, but in 2002-2003 this is the case. If you use these new 5751's and like them, that is great, but they are not a vintage 5751. When there is a good new 5751 available, it will be noted here in an update. 12AT7-Y Ei / 12AT7-C / 12AT7-A USA NOS JAN spec Expected gain 60-70 Expected Output 10.0 milliamps These are commonly used as phase inverters and reverb drivers. In the first gain stage of an amplifier, they will drop the gain a bit, make some amps a bit quieter in background noise, and yield more clean headroom. This is also one way to change the percentage of output distortion to preamp distortion in non master volume amps when used in the first gain stage. One of the differences between the later Fender amps and the Marshall JTM-45 / Fender tweed era amps, was the use of the 12AT7 in the Fender tolex era amps in the phase inverter position, rather than the original 12AX7. The 6201M is a selected low noise tube for use in some microphones. It is an NOS JAN selected tube. As of May 2003, GT will generally be offering the 12AT7A NOS as it's 12AT7 if marked as 12AT7 without the Y or C designator. 12AT7-A 12AT7-Y (currently not in stock ­ replaced by 12AT7A) 12AT7-C (currently not in stock ­ replaced by 12AT7A) 6201M ­ This is a low noise selected tube generally used in studio gear or microphones. 12AY7 ­ various makers / 6072M NOS JAN Spec selected low noise Expected Gain 44 Expected Output 3.0 milliamps This tube was the first gain stage of many Fender tweed era amps for many years. It has about ½ the gain of a 12AX7, but much greater current output. In modern Marshall type amps such as a DSL or TSL series, this tube in V2 will bring the touch, feel, and sonic qualities, closer to Plexi era Marshall amps if this is an objective. This tube is also known as a 6072 or 6072M, a selected low noise version used in studio equipment and some microphones. These are the common V1 in Fender Tweed era amps in many models. 12AY7 6072M


12AU7-Y ­ Ei Expected Gain 16-18 Expected Output 10-11 milliamps These are commonly used as phase inverters in McIntosh Hi-Fi amps, some Ampeg amps, and will yield the most clean headroom in many amps. In the latest Fender Pro Series amps such as the Pro Reverb, Concert, and Twin, this tube in V2 (or a 12AY7), will drop the gain of the gain channel where some feel the tone is of a less intense or "buzzy" character. This will then allow a much wider range in the sweep of the volume and gain controls of this channel.

To the left is a GT EF86 adapter. This was developed as new production EF86 tubes are very inconsistent, and can be noisy, or hard to find at times. For a group on tour using an older Vox amp, a Matchless, Victoria Sovereign, Bad Cat, or Dr. Z amp, these can be a life saver. These allow a 12AX7 to be used in the place of the EF86 / 6267 pentode tube. This adapter can be seen at

EF86 ­ 6267 Expected Gain 400-2000 and higher Expected Output 3.0 milliamps QA: 50% + A 9 pin pentode, used in the first gain stage of some newer amps such as the Matchless, Bad Cat, Dr. Z, and others. The current versions of this tube from the Russian factory, are very inconsistent. Their output is way above spec, sometimes as high as 50% over what is to be expected. They have transconductance that is not close to the original tubes 80% of the time in factory sample tests. These factors make finding a low noise version of this tube very difficult. These need to be closely screened and tested by a tube supplier that has very sophisticated test gear that is generally out of reach for most Internet tube vendors or smaller vendors.


The famed 7199 gold pin of the past.

The GT 12AX7M "Mullard" reissue was shown at the NAMM 2004 show and has been hard to keep in stock since. The M is not as bright as the ECC83S and many folks have chosen this tube as a replacement in Fender Blackface/Silverface amps in V1 and V2 and in Marshall amps. Dr. Z is using some of these as phase inverters for their strong current drive. More info at


Preamp Tube overall chart of some NOS and many current tubes

Tube Tolerance Ave output % of mA expected Ave TC (gm) TC % Average gp Average Gain

Guitar Amplifier Blueprinting

1600 Reference small signal tubes - in some cases, single tube tests. Items marked * were three to five tube test averages

GE 6072A 1970s Date Code * GE 6072A Black Plate 1963 * GE 12AX7WA (1980s) * GE 5751 (1950s) JAN/Philips 12AT7WC 1980s * RCA 12AX7 NOS 1950s-60s RCA 5751 Black Plate (1950s) * RCA 7025/12AX7 NOS 1960s * Telefunken ECC83/12AX7 - diamond base * RCA 12AU7 NOS Cleartop * 12AX7 Telefunken smooth plate new Dynaco 12AX7/ECC83 Telefunken Diamond Bottom Ribbed Plates * 12AX7 MINIWATT / SUPER RADIOTRON AUSTRALIA 1960s 12AX7 Amperex Bugle Boy Holland LONG PLATE 1950s * (10) 12AX7 AMPEREX BUGLE BOY HOLLAND 1967 * 7025 Amperex Holland orange Globe Logo 1971 CV4004 Brimar 1961 CV4035 / 12AX7 Brimar NOS flying leads 7025 GE ribbed plates 1950s * 7025 GE ribbed plates 1960s M8137/CV4004/12AX7 Mullard Box Plates * 12AX7 Raytheon black ribbed plates square getter halo 1950s * JRC-12AX7 RCA Black Plates 1954 * 12AX7A RCA gray ribbed plates 1960's-1970's * ECC83/12AX7 Siemens long plates early 1960s * 12AX7 Sylvania Gray Plate square getter halo 1958, 1959 *

2.6% 1.9% 8.7% 2.5% 11.6% 8.8% 3.7% 6.6% 11.6% 2.1% 12.6% 2.7% 0.8% 4.4% 6.1% 7.7% 4.5% 9.8% 2.2% 3.7% 11.2% 5.4% 4.9% 12.6% 9.9% 8.2%

96% 100% 92% 98% 105% 99% 96% 97% 102% 96% 102% 94% 100% 112% 109% 94% 92% 108% 100% 100% 92% 94% 101% 93% 95% 102%

1710 1750 1520 1190 5780 1620 1251 1580 1680 2180 1610 1680 1606 1640 1580 1690 1570 1740 1610 1590 1640 1520 1590 1660 1620 1710

1750 1750 1600 1200 5500 1600 1200 1600 1600 2200 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600

42/44 44/44 98/100 69/70 72/70 100/100 69/70 97/100 102/100 18/18 98/100 105/100 100/100 105/100 101/100 92/100 91/100 112/100 99/100 102/100 92/100 100/100 100/100 96/100 104/100 101/100

12AX7R3 Electro Harmonix (10/7/02)





#DIV/0! 32

12AX7R3 Electro Harmonix (10/29/02) 12AX7R3 Electro Harmonix (12/12/02) 12AX7C - Chinese (10/28/02) 12AX7C - Chinese (12/13/02) ECC83 JJ (10/07/02) ECC83 JJ (11/07/02) ECC83 JJ (12/13/02) 12AX7R - Sovtek 12AX7WA 10/7/02 12AX7R - Sovtek 12AX7WA - (10/28/02 batch) (note a) 12AX7R - Sovtek 12AX7WA - (12/13/02 batch) 12AX7R ­ Sovtek 12AX7WA (5/16/03) - This batch was stronger than the prior groups, but was more inconsistent. There was generally a very large spread between the A and B sides of most of these dual triodes so these are NOT recommended for phase inverter use. Average output ­ 1.1 mA (closer to spec of 1.2 and better than the past) 91% of expected output. Good by today's new tube production from all vendors, and better than their past production of this tube. Output ranged from 67% of what was expected as spec to 125% of what is expected. Very inconsistent current output. Average gain ­ 82.99 (spec 100) Good by today's production standards in new made tubes. Average TC ­ 1278 (1600 spec) ­ slow rise times, not all that great for high articulation players such as metal folks or folks that play harmonics. Lack of harmonic content and detail. Tolerance range ­ 58% Still not good at all. There is a lack of consistency from one tube to the next, near the bottom of the batch of vendors for the most part. More noisy than past production ­ due to more proper output and gain.

16.7% 16.7% 25.0% 16.7% 33.0% 66.7% 58.3% 41.7% 41.7% 41.7%

85% 83% 83% 92% 93% 113% 112% 78% 88% 78%

1382 1403 1461 1588 1467 1664 1604 1190 1293 1180

86.38% 87.69% 91.31% 99.25% 91.69% 104.00% 100.25% 74.38% 80.81% 73.75%

0.0162 0.0161 0.0160 0.0170

85.31 87.14 91.31 93.41 #DIV/0! 85.33 84.87 #DIV/0! 87.96 86.13

0.0195 0.0189

0.0147 0.0137


50.0% 12AX7R2 Sovtek LPS (10/7 batch) 12AX7R2 Sovtek LPS (10/23 batch) 12AX7R2 Sovtek LPS (10/31 batch) 12AX7R2 Sovtek LPS (12/12 batch) 7025 ­ Ei (10/31 batch) 7025 ­ Ei (12/12 batch) 7025 ­ Ei (4/03 batch) Output = 1.1 / TC = 1490 / Gain = 93.1 / QV = 33% - Nice gain this run, current way up too, great batch. Svetlana 12AX7 4/8/03 JJ 12AT7 / ECC81 4/7/03 - output = 8.9/ 10.0 gain = 58.8 / 60.5 67.0% 75.0% 42.0% 33.3% 25.0%

83% 70% 83% 97% 87.50% 46.67%

1469 1418 1505 1557 1419 1064

91.81% 88.63% 94.06% 97.31% 88.69% 66.50% 0.0182 0.0186 0.0155 0.0118

#DIV/0! #DIV/0! 82.69 83.71 91.55 90.17






TC = 4711 / 5500


Additional Small Signal Tube Tests and Reference

Tube Tolerance Ave output % of mA expected Ave TC (gm) TC % Average gp Average Gain

Guitar Amplifier Blueprinting

1600 Reference small signal tubes - in some cases, single tube tests. Items marked * were three to five tube test averages

GE 6072A 1970s Date Code * GE 6072A Black Plate 1963 * GE 12AX7WA (1980s) * GE 5751 (1950s) JAN/Philips 12AT7WC 1980s * RCA 12AX7 NOS 1950s-60s RCA 5751 Black Plate (1950s) * RCA 7025/12AX7 NOS 1960s * Telefunken ECC83/12AX7 - diamond base * RCA 12AU7 NOS Cleartop * 12AX7 Telefunken smooth plate new Dynaco 12AX7/ECC83 Telefunken Diamond Bottom Ribbed Plates * 12AX7 MINIWATT / SUPER RADIOTRON AUSTRALIA 1960s 12AX7 Amperex Bugle Boy Holland LONG PLATE 1950s * (10) 12AX7 AMPEREX BUGLE BOY HOLLAND 1967 * 7025 Amperex Holland orange Globe Logo 1971 CV4004 Brimar 1961 CV4035 / 12AX7 Brimar NOS flying leads 7025 GE ribbed plates 1950s * 7025 GE ribbed plates 1960s M8137/CV4004/12AX7 Mullard Box Plates * 12AX7 Raytheon black ribbed plates square getter halo 1950s * JRC-12AX7 RCA Black Plates 1954 * 12AX7A RCA gray ribbed plates 1960's-1970's * ECC83/12AX7 Siemens long plates early 1960s * 12AX7 Sylvania Gray Plate square getter halo 1958, 1959 * Tesla ECC802S Tesla ECC82

2.6% 1.9% 8.7% 2.5% 11.6% 8.8% 3.7% 6.6% 11.6% 2.1% 12.6% 2.7% 0.8% 4.4% 6.1% 7.7% 4.5% 9.8% 2.2% 3.7% 11.2% 5.4% 4.9% 12.6% 9.9% 8.2%

96% 100% 92% 98% 105% 99% 96% 97% 102% 96% 102% 94% 100% 112% 109% 94% 92% 108% 100% 100% 92% 94% 101% 93% 95% 102% 10.9 of 10.6 11.1 of 10.6

1710 1750 1520 1190 5780 1620 1251 1580 1680 2180 1610 1680 1606 1640 1580 1690 1570 1740 1610 1590 1640 1520 1590 1660 1620 1710 2153 2601

1750 1750 1600 1200 5500 1600 1200 1600 1600 2200 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 1600 2200 2200

42/44 44/44 98/100 69/70 72/70 100/100 69/70 97/100 102/100 18/18 98/100 105/100 100/100 105/100 101/100 92/100 91/100 112/100 99/100 102/100 92/100 100/100 100/100 96/100 104/100 101/100 16 / 17 18.8 / 17


12AX7WA General Electric JAN NOS Green Printing 12/85 batch. 50 samples tested 5/21/03: All very quiet. Some popping on turn on, but after the tube warms up this stops. More gain than current production 12AX7 tubes. A touch more output than industry spec, far above current production 12AX7s from any current factory. A very nice tube, in a high percentage of samples, very close matches on two sides.

Test Specs: Average Output/TC High mA % Low mA % Average gp Average gain Tolerance Range 1.2 1.4 1.1 0.0154 93.12 25.0% 1434 102.50% 116.67% 91.67% <- Output average compared to spec tube <- Range above of spec tube highest tube <- Range below spec tube lowest tube


<- Lower number is best

As of June 2003, this will be the new format that will be published in this document on tube tests from vendors. In future updates of this document, updated factory results will be published here, in the above area as tests are completed and as time permits.


Recent tube test results

DATE TUBE B+ BIAS volts volts mA actual 1.2 12AX7EH 250 -2 1.0 1.0 0.9 1.1 1.1 1.1 0.9 1.1 0.8 1.0 Current Averages 1.0 83.3% TC (gm) gp actual 1600 1450 1440 1380 1490 1510 1530 1400 1560 1330 1470 TC 1456 91.0% 0.017 0.017 0.016 0.017 0.018 0.017 0.017 0.018 0.015 0.016 Gain Comments

Expected 6/19/03

100 85.29 84.71 86.25 87.65 83.89 90.00 82.35 86.67 88.67 91.88 Gain 86.73 86.7% <- Output averages <- % of standard spec

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

1560 1330 14.4% 1.1 0.8 25.0% 91.88 82.35 9.5%

97.50% 83.13%

91.7% 66.67%

91.88% 82.35%


DATE Expected


B+ BIAS volts volts

mA actual 1.2

TC (gm) actual 1600


Gain 100



Sovtek 12AX7WA



1.2 1.3 1.3 1.2 1.0 1.2 1.1 1.3 0.9 1.3 Output 1.2 98.3%

1420 1440 1410 1360 1250 1360 1330 1450 1240 1520 TC 1378 86.1%

0.017 0.017 0.016 0.015 0.015 0.016 0.016 0.017 0.015 0.017

83.53 84.71 88.13 90.67 83.33 85.00 83.13 85.29 82.67 89.41 Gain 85.59 85.6%


<- Output averages <- % of standard spec

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

1520 1240 17.5% 1.3 0.9 33.3% 90.67 82.67 8.0%

95.00% 77.50%

108.3% 75.00%

90.67% 82.67%

Current is up from earlier batches. Improved in this respect. Current very close to NOS spec, perhaps the best in the 12AX7 family at the moment. TC a bit low, rise time a bit slow on the curves, but a nice tube that has improved with this batch.


Fairly wide current spread, so beware as one tube will work differently in the same amp as another. Gain is consistent, but consistently low. This will be a quiet tube but will not have a lot of gain.


DATE Expected


B+ BIAS volts volts

mA actual 10.0

TC (gm) actual 5500


Gain 60.6






12.3 7.6 9.3 8.6 10.5 6.3 9.6 10.9 5.3 9.0 Output 8.9 89.4%

6140 4590 5550 5710 5470 4000 4890 5640 3250 5140 TC 5038 91.6%

0.096 0.068 0.078 0.075 0.084 0.065 0.085 0.092 0.056 0.08

63.96 67.50 71.15 76.13 65.12 61.54 57.53 61.30 58.04 64.25 Gain 64.65 64.7%


<- Output averages <- % of standard spec

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

6140 3250 52.5% 12.3 5.3 70.0% 76.13 57.53 30.7%

111.64% 59.09%

123.0% 53.00%

125.83% 95.09%

1988 JAN Philips NOS tubes. Some of the worst tubes I have ever seen - new or NOS. This must be the bottom of the barrel. VERY mismatched, and very inconsistent. These were from 4/88 and 5/88. It may be that the last decent batch of these JAN Philips tunes was in 1987 or earlier. Be sure to test these before using.


DATE Expected


B+ BIAS volts volts

mA actual 1.2

TC (gm) actual 1600


Gain 100



12AX7C Chinese



1.2 1.0 1.2 1.0 1.2 1.0 1.1 1.1 1.2 1.2 Output 1.1 93.3%

1630 1460 1620 1510 1670 1550 1610 1580 1690 1670 TC 1599 99.9%

0.018 0.016 0.018 0.016 0.018 0.017 0.018 0.017 0.018 0.018

90.56 91.25 90.00 94.38 92.78 91.18 89.44 92.94 93.89 92.78 Gain 91.92 91.9%


<- Output averages <- % of standard spec

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

1690 1460 14.4% 1.2 1.0 16.7% 94.38 89.44 4.9%

105.63% 91.25%

100.0% 83.33%

94.38% 89.44% Higher gain than the Sovtek or just about anybody else. Still the best curve traces, still the best gain and TC of any of the new made 12AX7 types. By a wide margin, the most consistent tubes.


DATE Expected


B+ volts

BIAS volts

mA actual 1.2

TC (gm) actual 1600


Gain 100



12AX7B Chinese



0.8 0.9 1.2 0.9 0.8 1.0 0.7 1.0 0.8 0.9 Output 0.9 75.0%

1150 1300 1670 1510 1270 1530 1210 1460 1360 1440 TC 1390 86.9%

0.013 0.014 0.019 0.016 0.014 0.017 0.013 0.016 0.015 0.016

88.46 92.86 87.89 94.38 90.71 90.00 93.08 91.25 90.67 90.00 Gain 90.93 90.9%

Construction visually looks the same as older 1.5dB greater noise on average than 12AX7WA/G Wider current QA spread than new 12AX7WA/G Wide plate resistance specs. Quality declined Wide TC specs - quality declined Lower percentages of matched triodes A/B side Quality overall has dropped over all previous runs Current output down 10%-15% over previous runs Still better gain than 12AX7R/G 12AX7R2 12AX7R3


<- Output averages <- % of standard spec

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

1670 1150 32.5% 1.2 0.8 33.3% 94.38 88.46 5.9%

104.38% 71.88%

100.0% 66.67%

94.38% 88.46%


TUBE Expected

B+ volts

BIAS volts

mA actual 1.2

TC (gm) actual 1600


Gain 100


Plate construction changes - low T/C, higher gain than older WA. Excellent QA - Best of all tubes to date. (Last WA's had 59% QA range at best. High percentage of close A/B side matches. Much better current drive - well suited to Fender's complex front end Hot Rod Series amps. Very quiet.


12AX7R - Sovtek 12AX7WA/G Fender STR



1.0 1.0 1.0 1.2 1.1 1.0 1.2 1.2 1.2 1.0 Output 1.1 90.8%

1230 1190 1200 1340 1300 1210 1340 1350 1370 1200 TC 1273 79.6%

0.014 0.014 0.013 0.015 0.015 0.014 0.016 0.0155 0.015 0.014

87.86 85.00 92.31 89.33 86.67 86.43 83.75 87.10 91.33 85.71 Gain 87.55 87.5%


<- Output averages <- % of standard spec

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

1370 1190 11.3% 1.2 1.0 16.7% 92.31 83.75 8.6%

85.63% 74.38%

100.0% 83.33%

92.31% 83.75%


DATE Expected 8/10/2004


B+ volts

BIAS volts

mA actual 1.2 1.1 1.2 1.2 1.1 1.3 1.1 1.2 1.3 1.3 1.2 Output 1.2 100.0%

TC (gm) actual 1600 1500 1650 1610 1500 1590 1400 1530 1620 1430 1460 TC 1529 95.6%


Gain 85 81.08 82.50 80.50 83.33 83.68 82.35 82.70 85.26 81.71 81.11 Gain 82.42 97.0%

Comments Gain in this circuit. Most consistant batch yet. Good quality run Gain up over last batches Plate resistance vs TC on target Mica assembly best yet Current great - better than R2, R3

8th Mullard run



0.0185 0.02 0.02 0.018 0.019 0.017 0.0185 0.019 0.0175 0.018


<- Output averages in circuit <- % of standard spec

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

1650 1400 15.6% 1.3 1.1 16.7% 85.26 81.08 4.9%

103.13% 87.50%

% of spec % of spec

108.3% 91.67%

% of spec % of spec

100.31% 95.39%

% of spec % of spec


DATE Expected


B+ volts

BIAS volts

mA actual 1.2

TC (gm) actual 1600


Gain 100



Sovtek 12AX7WC 0311 datecode



Tubes tested AFTER accepted by GT tests

1.1 1.1 1.2 1.4 1.1 1.2 1.4 1.2 1.1 1.2 Output 1.2 100.0%

1350 1330 1470 1560 1340 1430 1550 1430 1350 1430 TC 1424 89.0%

0.015 0.015 0.016 0.017 0.015 0.015 0.017 0.015 0.015 0.015

90.00 88.67 91.88 91.76 89.33 95.33 91.18 95.33 90.00 95.33 Gain 91.88 108.1%

#1 - I did not find a problem #2 #3 #4 #5


<- Output averages <- % of standard spec No tubes showed low output

High TC Low TC QA tolerance TC High mA % Low mA % QA tolerance mA High gain Low gain QA tolerance gain

1560 1330 14.4% 1.4 1.1 25.0% 95.33 88.67 7.8%

97.50% 83.13%

Gain after GT testing was very consistent Very consistent overall results

116.7% 91.67%

112.15% 104.32%


The Output Tubes ­ The Pentodes and Beam Pentodes

A typical pentode trace. Many people believe that a 6L6 is a 6L6, an EL-34 is an EL-34, etc. This is far from the case. Each of these tubes have different sonic features. Many folks ask the difference between an EL-34 and 6L6. In a nutshell, I guess one can say that the EL-34 has more of an articulate mid-high and high end articulate response. If you like a lot of high end harmonic articulation and distortion with a high degree of articulation, than perhaps this would be the preferred tube. In the case of the 6L6, there are stronger lows and mid-lows, and for mass overall output, this may be the taste for you. Some folks love the 6550 and KT-88 tubes in amps if they get most of their tone and distortion from pedals or effects. These tubes yield a lot of clean headroom. Many ask me which is "more powerful" between the EL-34 and 6L6. Some feel the EL-34 is stronger, due to the 100 watt Marshall or Hiwatt type amps of the past. This is not the case in reality. These amps at times had higher plate voltages, so at times produced more wattage for a given tube type or tube set. A decade or so ago, Fender had an amp called the "75" that produced about 75 watts out of a duet of 6L6's, as one example. There will be charts as we progress, that show the same types of tubes used in the same circuits using the same plate voltages and bias voltages. The output is in milliamps. A tube with a higher reading, is more powerful than a tube with a lower reading. It is as simple as that. This does not mean a higher number is "better" ... there are many other aspects regarding tone. This is just a simple power measurement for the folks asking me which tube is stronger. This does not indicate or mean that a higher current tube is better in any way.


This is simply a basic power output scale. There are many other qualities that are the aspects of the tone and sonic signature of an output tube. The complete list of Groove Tubes output tubes can be seen at The links below on each tube when shown, will be for a duet, a matched pair of two tubes. The link just above has the complete list, where one can find duets, quads, and single tubes for use in single ended class A amplifiers as one example. Before we get into the details of output or power tubes, a few words on biasing may be in order.

Biasing ­ a needed consideration when replacing or changing power tubes

Biasing output tubes is critical to great tone and long tube life. Some folks feel that setting the bias so the tubes run very hot, will make the amp sound better or be more powerful. This is not the case. Think of the bias much like setting the idle on your car. You can set the idle to 4000 rpm, and the car might run fine at high speeds, but mid and low speed drive ability will suffer. You want an amp to sound great at all levels, don't you? Bias may be set by a few methods. One is the crossover notch method. This requires a signal generator, load, and scope. This method is not repeatable, as it is the technician's "take" on the waveform that is being judged. The second and most popular method used today, and by most amp makers, is the current draw method. Here, an adapter is placed between the output tube and it's socket, converting the current to an output voltage in a 1 to 1 ratio. You set a conventional DVM meter to the 200 millivolt scale, and read your current directly ­ one milliamp = one millivolt. In a typical Fender type amp using 6L6 output tubes, this will be around 30 milliamps or so, depending on plate voltage. These tools are sold under many names such as bias tool, bias probe, bias rite, bias king, etc. Some have meters attached, some do not. I personally prefer the tool with no meter attached as it is less complex, less costly, and takes less space in my toolbox. After all, I already have a DVM that I carry anyway, and need one to check other voltages. Adjusting bias on most amps is fast and easy, and these tools quickly pay for themselves the first two or three times used. An example of the Groove Tubes tools can be found, with or without a separate meter on the website page at Many folks do not know what the maximum output of a given tube may be. In fact, some tubes of the same family are very different. An example of this is the EL-34. Most EL-34 tubes have a stated maximum plate dissipation of 25 watts. In the case of the Groove Tubes E34LS tube, this is different. This is a 30 watt tube, quite a bit stronger. This is a proprietary tube design made in the JJ factory on GT tooling. Looking at the JJ version and the GT version side by side, you will see heat sink wings on the GT version ­ more plate mass. Tossing a set of these E34LS tubes into an amp that is no PROPERLY biased, is asking for trouble, and almost guaranteed. When I say PROPERLY biased, I am not only speaking of the current draw, but the method used to set up the amp initially for a tube change. Just plugging the E34LS in and "chasing" bias is a mistake. In the time it takes to get the bias in the proper range, you may blow fuses, ruin the tubes, or take many hours off their life.


The proper way to do this, is first install your bias probe on one of the old tubes, and set it's level to the lowest possible milliamp draw. You may also just take your meter on the DC scale (another reason for a separate meter), and set this to the HIGHEST negative voltage. This means that ­52 volts is the more preferred value than ­49 volts as an example. Now, you can remove the old tubes with the amp off, install the new ones, and work up to the proper idle dissipation target. 6L6 and 5881 tubes come in ranges from 19 watts to 30 watts. A KT-66 may have the same rating and be interchangeable with a 6L6, but in the same circuit, it may draw 10 more milliamps at load, so it's bias may be very different than a 6L6. Different 6550 tubes and KT88 tubes may also vary. If you have something like Groove Tubes, you will not have to rebias if you use the SAME TUBE OF THE SAME RATING after properly setting the bias the first time. If the tube type changes though, a rebias is advised. "Same tube" here means just that. If you had a 6L6 Svetlana, and you changed to a 6L6 JJ tube, these are NOT the same, even though both 6L6 tubes. Same tube means the same family, type, and manufacturer. Cathode biased amps (Class A) are thought of as self biasing, and this is accurate to a certain degree. The amp maker is expecting a tube within the original spec range to be used. Today, this varies more widely than ever before, and if a tube outside the "normal range" is used, the amp may run very hot, with tube life short at best, bad and harsh tone, and at worst, tube and output transformer failure. Using a tube with a mid range rating number, such as GT's 4-7 ratings, will be the best choice in most cases. You can also use a bias tool (there are 9 pin adapters for EL-84 tubes) and check your dissipation too. Remember, in Class A amps, the tubes run close to or at 100% idle dissipation. If a tube has a maximum plate dissipation of 12 watts, such as an EL-84, a bit of math will be needed to be done to see what milliamp value should be as the maximum. If this is too high, just go to a lower range tube. It is that easy. As an example, if you have a #7 tube in an amp and it is running too hot (high millamps value), drop to a 5 or 6 and the value will drop into a more proper range. This is also a cool trick on fixed bias class A/B amps such as Hiwatt and Mesa Boogie amps. Mesa amps like mid range tubes in the 4-7 range. Elsewhere in this document is a conversion scale to covert the Mesa and Fender color codes to rating numbers. Mesa amps typically are OVERBIASED, meaning they run cold. This is part of the reason that many feel they sound a bit grainy. On my own Mark 1, the stock idle with Mesa mid color (range) tubes is only 38%. What we are looking for generally is 50-70%. Using a GT #7 tube in the amp brings this into proper range. Cold running (overbiased) amps sound grainy, lack power, and definition. Underbiased amps (hot running) amps sound harsh, do not perform as well at low and medium levels, and have shorter tube life.


Maximum plate dissipation on tubes will be found in tube data sheets or in manuals such as the RCA tube manuals. As a quick point of reference on a few common tubes: EL-84 6V6GT 5881 EL-34 / KT77 6L6 E34LS KT-88 6550 12 watts 14 watts 19-30 watts depending on type 25 watts 25-30 watts depending on type 30 watts 35-42 watts depending on type 35-44 watts depending on type

6V6 output tubes


6V6 Types

Some of the classic RCA 6V6 tubes to the left.

6V6R - a newer Russian 6V6 that is from the same tooling as the Electro Harmonix 6V6. This tube holds up well to plate voltages of 450+ volts, and will do very well in amps such as the Fender Deluxe Reverb.


6V6C - a new 6V6 off new tooling that is holding up to higher plate voltages nicely and has a sound more folks are starting to prefer over the 6V6R as time passes during 2002-2003.

A GE black plate on the left and a GE gray plate on the right. Some folks think that the black plates sound better or perform better than the gray plates. I will leave this to your own judgment.

Comparison of new and NOS tube tubes in a mid rating (bear in mind, the "NOS spec" number we are looking for here is 45.0 milliamps below for a 6V6


6V6 ( #6 rating) 6V6A USA NOS RCA Blackplate 6V6GT Tung Sol 6V6 Chinese 6V6R Russian EH

Output in Milliamps

43.7 45.4 47.2 51.9


6L6 / 5881 / KT-66 Types

The shorter bottle (but very strong) 5881

6L6-CB - Chinese, softer vacuum, coke bottle shape. Quicker to distort, with a warm soft tone. A great blues tube for smaller venues when you want to tone it down a bit. In a 50 watt Fender type amp, in a Groove Tubes 1-3 rating, the typical Super Reverb will start to break nicely at "3", with a humbucker guitar at "10". Sometimes these are not easily available and being phased out by the factories in China. If you purchase these, be sure they are tested. If you want the sound and character of these, but cannot find the coke bottle tubes, some of the straight bottle Chinese in a 1-3 rating will a close result. There are also though, straight bottle Chinese tubes, that have higher output than many of the current (2003) Russian offerings, so be sure you know what you are getting.


This is the 6L6C or straight bottle Chinese tube. There are MANY variants of this tube. There are versions from Shuguang (the major tube factory in China with the highest quality), and Sino ( a co-op in a manner of speaking, of many smaller factories. In the past, Chinese output tubes developed about 20% less output than their Russian counterparts from Sovtek and Svetlana. In 2003, this is no longer the case, and their power for some of their tubes are 15% or so ABOVE that of the average Russian 6L6 offering in many cases. In mid 2002, tubes from Shuguang, also put to rest the issue of Chinese tubes not handing higher plate voltages. The Chinese have new tooling, and are pouring a lot of money into tube production. This tube in a 1-3 rating is a blues masterpiece. In a 4-7 rating, it is a upgrade from the stock Sovtek 6L6 tubes offered as standard issue in many new amps. In the summer of 2003, there will be a new version of this 6L6 offered by Groove Tubes that will be built off their proprietary tooling to their specifications. This tube will be offered by no other tube supplier.

6L6-B (also known as the R) - Russia, Reflector, the Sovtek 5881WXT, Fender 6L6GC. Sturdy tube, one of the physically most robust. Great for touring stuff that gets thrashed by heavy handed road crews. This is the stock tube in currently manufactured Fender mid and lower priced amps. A very nice general purpose tube. This is the most common supplied 6L6 in most production amps today. This is stock in all of Fender's 6L6 based amps with the exceptions being their Custom Shop amps such as the 2003 made Vibro King and Vibroverb amps. Vibro King amps prior to 2003 were shipped with this tube, New amps are shipped with the 6L6GE


6L6-S - from the JJ factory but re-based and re-pinned by Groove Tubes if or when they come in with stamped pins with dipped pins that tear up some vintage sockets. The rolled polished pins are also tapered. A bit of an extended midrange that a lot of heavy rockers love. Something of a cross between an EL-34 and a 6L6 in the mids. This tube is favored by some Fender folks looking for a bit of an edge over the stock tubes, or in a Blackface Twin Reverb, Bassman, Bandmaster, or Showman, will give a bit more aggressive nature. With ECC83s in V1 and V2 of these amps, they will come a bit closer to a British sort of edge or character. These tubes are very inconsistent at times from the factory so good testing is very important. They also are one of the few tubes that need an extended burn in period before testing, or the testing will be rendered useless as they change dramatically in many cases after the first 5-10 hours. If you buy these from a generic vendor, be sure to have your bias rechecked, and probably readjusted, after the first 50 hours or so of use. The GT supplied tubes go through an extensive burn in process, as well as testing process, and thus may cost a bit more than bargain brands of these tubes.


6L6-R2 - The Svetlana 6L6. Prior to 2002, this was a great tube, something of a Sylvania STR-387 copy. Due to the manufacturing changes, possible lower vacuum and material inconsistencies, these are not the same as the tubes in the past. You need to get these from a vendor that will test for low vacuum, gas leakage, and grid leakage. This is costly and time consuming, so expect vendors that have the equipment to test for these things to charge a premium. These tubes were patterned off the Sylvania STR-387 that was a popular Fender 60s era tube. These are one of the finest 6L6 tubes sonically and also from a reliability standpoint. Just make sure yours are checked for low vacuum and gas issues during your vendor's testing cycle.

5881-A - NOS, Tung-Sol, JAN Philips 6L6WGB, or other NOS tubes at times, great in Fender Black Face amps for a lot of my Blueprinting clients. The tube used a lot in Black Face Fender amps as original. These amps also used the Sylvania STR-387 and GE. These may not be carried in the future as the new 6L6GE is preferred. As of maybe April of 2002, these are generally no longer stocked by Groove Tubes. The NOS tubes left are not in sufficient good supply to offer reliable matching using the GT system. These were replaced in the GT lineup with the short bottle NVM (new vintage manufacture GT-6L6GE USA tube.


A GE version of the Tung Sol 5881 ­ probably made by Tung Sol perhaps as this has the same plate structure, the same mica spacers.

KT-66-C - China, the KT-66 that folks like Valve Art and others sell as the KT-66 at times. Many times the Valve Art folks and others sell the Sino co-op tube which is not as high of quality as the other Chinese tube from the main factory in China. Good to about 450 volts B+ maximum. Don't try to run this tube at higher plate voltages, you are only asking for trouble. The KT-66 is a full bodied tube, with stronger and more linear mids than most 6L6 tubes. The GEC (UK) KT-66 was used in the Marshall JTM-45, and the first 100 watt Marshall amps. It's tone can be heard by Eric Clapton on the John Mayall Blues Breakers recordings. This is the tube that is standard issue in the Carr Amplifiers Mercury model The "C" version of this tube is not as close of a reproduction of the original GEC tube. It is also limited to about 450 plate volts to function in a reliable way. Some prefer it's tone over the HP version though, such as Steve Carr in his Mercury amp.


KT-66-HP - Russia, built under contract for GT to GT specs on Groove Tubes tooling. A copy of the GEC tube. Handles higher plate voltages than the KT-66C. Great to 525 volts, and the tube the Dr. Z Route 66 was designed around. The tube to be used in Marshall JTM-45. Also a great tube in Fender Black Face and Silver Face amps. The "KT" meant "Kinkless Tetrode, and this tube was developed to get rid of the 6L6 kink in the response curve. This was accomplished, and this is why the mids of this tube are smoother and more linear than a 6L6 or 5881. This tube is standard issue in the Dr. Z Route 66 amplifier. This is the tube that I use in my own JTM-45 amp.

These are new KT-66HP tubes before going through the GT (Groove Tubes) process. These are only available from GT, as this is proprietary tooling of theirs over in Russia. As you can see, the Russians are not all that consistent. These two tubes are from the same factory run. Their size is quite different visually, as were their specs. This is yet one more reason to trust your vendor.


6L6-GE - made in the USA by the Groove Tubes factory with USA parts and labor. This was the tube used in the four Fender Showman heads at the 1968 Hollywood Bowl concert by Jimi Hendrix. (not always a Marshall guy). This tube has received a lot of praise in various reviews. One original set of these from February 2002, I have had running at 105% output, 24 hours a day, seven days a week. They currently have over 6700 hours on them, and they have only dropped 34 milliamps during this period. This is due to a very high vacuum, and USA parts, cathode coatings, etc. These are more expensive than most non USA 6L6's due to materials and labor costs being much higher. Their cost is offset with a very long life, and sonic qualities. They typically have at least a 15 degree wider sound stage image in any amplifier that uses 6L6 tubes. The traces on this tube are duplicates of the traces of the original General Electric tubes. This is not surprising, as these are made on the original tooling from the last plant that made these in the USA, and they use the same formula for plate materials and coatings. The mica spacers come from the original source. I coined these tubes "NVM", for New Vintage Manufacture", before I came to Groove Tubes while I was doing the original run testing. This tube is the standard offering in Fender's Custom Shop amps such as the Vibro King and new (2003) Vibroverb.

6L6WGB China ­ Groove Tubes tooling A new tube (July 2003). Output is strong, over 80 mA where 72 would be the expected standard. The output puts these tubes at the top of the 6L6 list as shown in the below snapshot of the 6L6 / EL34 test results. Nice curves, handles high voltage to 475 plate volts with no problems. Static match is well within industry standards, meaning testing and matching by any vendor would be necessary as usual. Dynamic traces are about average on these unmatched samples, again, GT matching will turn these into a nice finished product.

6L6GCR Shuguang 5/03 JJ 7027 6L6GCM STR Ruby April 03 KT-66 Genelex GEC 6L6S JJ 6L6WGB GT tooling China KT-66 Genelex GEC 76.6 78.3 79.4 80.4 81.7 82.6 83.7 58

EL34 ­ E34LS ­ and 6CA7 types


To the left are the RCA 6CA7 tubes. Even though a replacement for the EL-34 and marked as such, they are different tubes than the EL-34. They have a much stronger vacuum, an active beam forming element, a bigger bottle, and handle in generally, higher voltages. The GE version is preferred by myself over the other USA versions from a sonic point of view and testing. There are more "6CA7" tubes showing up all the time these days. They are currently nothing more than big bottle, low vacuum, EL-34 tubes. They generally have even less output than the same maker's EL-34 offerings.

GE6CA7 ­ A strong beam pentode with an active beam forming element. Some folks think of this as an EL-34, but this is a stronger tube in all aspects. This is a drop in replacement for an EL-34, but a rebias is advised. This tube has a much higher vacuum than an EL-34, and much stronger construction. It is currently being developed for re-release as the Groove Tubes 6L6GE had been released. Look for a possible late summer 2003 release. The initial tests on this tube show very strong results. These will run at over 800 plate volts. There are current numerous "6CA7" tubes being made today, which are little more than the same plates and materials of a makers EL-34 in a larger bottle. In most cases, these do not even have the performance of the same companies EL-34 offerings. These do not trace or perform in any way as the original USA GE 6CA7 of the past. This tube is now in development by Groove Tubes for possible release in the summer of 2003. The original GE tooling from GE in Kentucky was purchased by Aspen Pittman of GT, and is up and running. The 6L6GE was Aspen's first GE tube reissue. There are more to follow, this 6CA7 next in the list.


EL34C - Chinese EL-34 (25 watt tube). This latest ChineseEL-34 has closer response curves and performance of the Siemens EL-34's used in the late 60's and early to mid 70's Marshall amps. This is a great tube in Marshall model 1987 and model 1959 amps.

EL-34-R - Reflector (Russian) EL-34 (25 watt tube) sometimes sold as the EH tube. Pretty linear and Mullard like in some aspects of its character. Not as close to the Siemens tube in Marshall amps or in the curve traces. The current Chinese offerings are more close to the original Siemens tubes in a Marshall amp.


EL34R2 - Svetlana (Russian) 25 watt tube, used a lot as standard in Rivera amps. This is a stronger tube than the R or older C in the pre 2002 factory runs. The 2002 factory runs were down about 15% on power. Most current EL-34 types show better curves and more linear response than the 20022003 versions of this tube due to changes at the factory. If you have a vendor that can test for low vacuum and gas leakage, then this is a super tube.

E34LS - JJ factory but with a GT developed heat sink assembly extruded onto the plate assembly. Hold up a JJ and a GT and you can see the difference without any sort of equipment (with the naked eye its easy). This is a 30 watt tube and bias should be checked and adjusted when one uses these. Very high output and strong mids. Used by Gibbons, Perry, and Walsh to name a few. This is the stock EL-34 amp tube for Bad Cat and Matchless. The JJ version of this tube is a 25 watt tube. This tube cannot be dropped in to an amp without a rebias. It is a much stronger tube. In a typical Marshall 50 watt amp, seeing 70-80 watts is not uncommon. This tube has much stronger mids and lows than the "normal" EL-34. If you are looking for that gut punch power, than this may be the tube for you. If you want your British amp to have it's original sound and character, then stay with one of the 25 watt EL-34 tubes.


The Groove Tubes GT-6CA7GE "The GT6CA7GE is the classic American-style EL34 tube made in the exact likeness of the famed General Electric 6CA7 tube of the 60's. This was the tube we sold to Eddie Van Halen for his Marshalls used on the first two Van Halen albums (often cited for his best tone on record)." The Groove Tubes 6CA7GE is a USA-style power pentode tube with similar specifications to the European style EL34 tube. However, the 6CA7 differs in design from the common EL34 types by the use of an active beam-forming electrode similar to that of the 6L6 and 6550. Groove Tubes purchased the actual GE production formulas, along with many of the original General Electric machines and vintage Plate materials via the closing of the GE tube factory several years ago. Using these original machines, the original components and their "secret processing recipe", GT was able to authentically reproduce the classic GE power tube. Pittman says, "The 6CA7GE will appeal to players using Marshall EL34-style amps (and the many Marshall impersonators), providing a whole new sonic signature option that will certainly please a wide range of musical playing styles. If I had to simplify the description, the GT6CA7GE is somewhere between a Mullard EL34 and a GE 6L6...more `chest' and certainly more power than any EL34 tube. Plus, they are directly interchangeable in all EL34 circuits (with proper rebiasing, as always). This tube has a bias point between an EL-34 and 6550 (a bit more than a 6L6 actually). It's power output falls between an EL-34 and 6550. This tube has a true active beam forming element which is not present on the EL-34 which is one of the major differences.


Miscellaneous and other output tube types

The 1980s JAN Philips 6L6WGB This is also known as a 5881 a lot of the time. This is a military grade heavy duty short bottle tube, that looks very similar to the GE, less similar when compared to the Tung Sol 5881. This is fantastic sounding tube, and the tube I use in some of my 6L6 based amps.

The Philips 6L6GC This is similar in many ways to the Sylvania STR387 that is a favorite of many Fender folks.


The RCA Gray Plate.


6L6 / KT66 / 5881 / EL-34 Tube output current output comparisons

The "numbers" we are looking for here, for an average NOS sample run on a 6L6, is 72.0 milliamps as an example. In the case of the GE's the factory originals ran from 72-78 milliamps for the average sample tube as per the original GE spec. If you want to know which tube is the most powerful in a given circuit, this chart below will answer that question.

6/30/03 ­ Chinese 6L6GCS PM tubes ­ stronger output than 6L6S on average. These are an older somewhat modified coke bottle shape with an old mica spacer design and a fanout wire to base design. A dual bottom getter design. The plates are not aligned to the bases with any sort of consistency, meaning the plate orientation to the key slot of the tube base is not consistent. There were three duets of this tube tested. The average set, marked with a #74 sticker from the distributor was the final test set. The static match was only fair, even though the tubes carried the same "matching" number. The dynamic match was not very good, and in fact, at plate voltages above 410 volts, started to be on the edge of possible problems with current fall off. These tubes prefer voltages under 400 plate volts. Testing for burn in and stability, initial measurements on one duet was recorded at 83.0 and 84.8 mA respectively. The upper voltage curves (410+) were not stable. After a one hour burn-in the measurements were respectively were 83.4 and 83.6 mA statically, with a bit nicer curve traces, thus indicating that burn in may improve performance and consistency. These tubes would benefit from a bias check after the first 20 hours of use in a guitar or bass amplifier.


Power output comparison test results of various output tubes

Many of today's amps can switch power tubes via a bias switch of some sort or other method. This chart compares some of the same broad families of tubes using the same voltages, circuit, and bias for a power comparison

COMMON FAMILY (#5 RATING) 6L6 / EL-34 / KT-66 / 5881 6550 / KT-88 For 6L6 types, the standard expected reference output at 1957 RCA test settings should be 72.0 milliamps. The EL-34 tubes tested here were tested at 6L6 voltages and bias settings to show their performance in the same circuit. In an circuit set up to test EL-34 tubes specifically, the expected output would be 100 mA, higher due to lower bias voltage, and higher plate voltages.


7591 Russian 6L6GCMSTR Ruby Tubes (older) 6L6C Chinese

58.4 68.1 69.0 67

6L6B Sovtek (5881 WXT) 6L6CB Chinese Coke Bottle 6L6R2 Svetlana October 2002 6L6GE GT - Original run 6L6R2 Svetlana pre 2002 5881 JAN Philips 5881 Chinese 4/03 5881 NOS Tung Sol 6L6GE GT November 02 6L6GCR Shuguang 5/03 JJ 7027 6L6GCM STR Ruby April 03 KT-66 Genelex GEC 6L6S JJ 6L6WGB GT tooling China KT-66 Genelex GEC 6L6GCS PM China 6/30/03 KT-66HP Russia EL34R2 Svetlana (pre 02 date) EL34 Svet/Sovtek 0211 datecode GT-6L6GE 1/04 prod - new plate smaller bottle / higher vacuum EL34R EH / Reflector EL-34 Siemens marked Mesa EL34C China KT-66 China EL-34 Mullard 1970's E34Ls JJ / GT tooling 30W GT 6CA7GE 5/19/04 run GE NOS Ref 6CA7

71.0 71.6 72.3 72.7 73.5 74.8 75.2 76.1 76.2 76.6 78.3 79.4 80.4 81.7 82.6 83.7 84.0 85.3 86.3 87.2 87.9 89.0 89.8 91.0 91.6 93.1 97.1 97.9 108.2


A big KT-90



6550 / KT-88 Tubes


The KT-88C A very strong KT88, with multiple getters on the sides and on the top. This is actually the strongest of the KT88 family, and not in character with the original GEC Gold Lion tubes which were not quite as strong, but more linear. For something like a Hi-Fi amp, the SV version may be preferred.


This is a duet of the KT88SV tubes made in the JJ factory, once again on Groove Tubes developed proprietary tooling. If you compare this with the JJ sold version, you will notice that the GT version has four massive heat sink wings on a more massive plate structure. These are smooth and linear, tracing as the original GEC Gold lion tubes. These are very strong, and preferred by high end audio folks, or guitar players going for massive levels of clean headroom ... allowing their tone to come from their effects and pedal boards. These are very long lasting tubes, even in severe service. Notice than unlike the Chinese KT88 version, this tune does not have side getter flashes.

These are the Svetlana 6550. These are popular in Sunn amps, many Marshall amps, and amps looking for clean headroom. These are a good solid offering, but in mid 2002 dropped a bit in power when compared to the newer 6550 offerings from China.


Sorry, but I just HAD to show a photo of an NOS 6146 tube. These were the original Ampeg SVT output tube, and to me, just magic. High voltage comes in the top to the plates, not from the base. VERY VERY strong tubes, to say the least.

6550A - USA NOS GE no longer in stock. The strongest of all the 6550's. This is the longest lasting of any of the 6550 family.


6550-C - Chinese and a fun tube, as you can get these to distort in amps where the 6550A would not. These are in two types, the coke bottle shape (distorts faster), and the straight bottle with more power. Typically used in amps where a lot of power or clean headroom is desired. These may be either the coke bottle or straight bottle, depending on stock. You may want to inquire, as the coke bottle has a softer vacuum. The straight bottle is a great tube, and has more output. If you want a 6550 that will distort nicely instead of staying clean right until the end, this may be your tube. Just order it in a 1-5 rating or so. In ratings of 5-8, they will (straight bottle) keep up or exceed the power output of the current Russian (2002-2003) tubes.


6550-R - Russian 6550, takes longer to distort than the Chinese, maybe somewhere between the A and the current straight bottle C. This is a very clean tube. This is also a great Ampeg SVT tube. These are generally selected Svetlana or Sovtek tubes. Svetlana tubes generally have a brown base material in the metal base, and Sovtek tubes generally have black base material. These are picked and tested for characteristics rather than by maker.

KT-88-C2 - Chinese KT-88 ­ Nice and strong This tube finds a home in amps such as the Park 75, Marshall Major, and 6550 type amplifiers. This tube does not follow the original GEC KT88 curves. It is far stronger than the original KT88 from GEC, so if you are looking for a tube to replace that particular tube, be sure to check your bias, as these are much stronger than the common new KT88 tubes from most makers. For a Marshall owner, or amp owner using 6550 tubes, that wants even more power from the amp, this is the tube. These tubes are VERY pure inside. The have multiple getters, both top and side flashed, so they are also a very long lasting tube.


KT-88-SV - JJ factory made off Groove Tubes tooling. Different plate assembly than the JJ version, with a large heat sinks welded to the plate. It may have a different base, pins, at times if necessary. There is also a KT-88 that is a JJ tube that is stronger by a wide margin than the original Gold Lion GEC KT-88. It biases differently. The KT-88SV (think of the "V" as "vintage"), where the output of this tube and design was redone to copy the GEC Gold Lion. The SV traces as the original GEC tube traced and is great in McIntosh amps, Park 75's, and Marshall Major amps. This tube is NOT the same as the JJ version, even though produced in the same factory. This is a GT designed tube off Groove Tubes tooling, and is not sold by any other vendor that does not sell GT items. This is the most musical of the KT-88 tubes for high end audio applications also.


Power comparison chart of current output for the KT-88 / 6550 families

KT88 / 6550 / KT90 family 6550/KT-88 bias raised to CURRENT reduce current. Much additional IN mA power and clean headroom over 6L6 / EL34 if power supply has the capacity. At 6L6/EL34 voltages, typically 120-140mA + #5 rating

KT88 Svetlana 4/8/03 KT88 Svetlana 4/8/03 6550R Svetlana KT-88SV JJ / GT KT-88C China 6550C China KT-90 Ei

85.0 87.0 92.5 97.3 103.6 107.3 114.8



Before I get to the EL-4 tubes, I would like to address a few points. Typically, EL-84 based amps are cathode biased. (There is at least one exception I can think of here off the top of my head, a Fender Tremolux from the Black Face era, that for one model used 6BQ5 (EL-84) tubes in a class A/B configuration). Cathode biased amps typically run hot from the start, as the output tubes are always running full bore, even when you are playing quietly, or not playing at all. Added to this factor, is that most of these amps also run their output tubes at voltages in excess, and at times FAR in excess, of the original design limitations of the tube. These amps are typically called Class A amps at times, but when there is more than one output tube, these amps run in push-pull configuration, just as typical class A/B amps. Adding to the hard life of these tubes, amps such as the Vox AC-30 series, are not well ventilated. The stories of these amps being less than reliable, or even stories of them starting on fire, are not all that unfounded. When tubes are not matched, they work against each other. This is explained elsewhere in this book, but to briefly illustrate, it is like two riders on one of those tandem bikes. One is me at 165 pounds, where my main form of exercise is speaking while standing, and the other is a 165 pound Olympic class rider with .02% body fat! I will do nothing but drag the other rider down. Mismatched tubes produce more heat too, a lot more. If you have access to one of the remote thermometers, check you output transformer temperature on your "class A" amp after running for 20 minutes. Then check it with a dynamically matched set of output tubes. You will see at least a 20 degree drop, and the side benefit of better tone, level, sustain etc., are icing on the cake. This temperature drop will lengthen the life of parts like your capacitors buried in the chassis too, and the other components. Look inside a well used AC-30 at the discoloration from heat on the components as another example. The reason I am pointing this out here, is these amps have a somewhat DIFFERENT requirement than their 6L6 and EL-34 brothers that run in Class A/B fixed bias. Some folks feel that "matching is matching". While this can be argued, these EL-84 based amps really do require, from my experience, DYNAMICALLY matched tubes, and will benefit strongly using these over STATICALLY matched tubes. The differences on these two matching methods is explained elsewhere in this book. In typical Vox AC-30 and other amps using EL-84 tubes three hours per night, four nights a week in tour, I have found that typical life where the amp sounds best can be as little as 100 hours with statically matched tubes. It increases to 300 hours with dynamically matched tubes, and the temperature drops considerably. If you have a EL-84 amp with more than 500 hours on the tubes, I can guarantee that they need to be changed right now, and you will hear the result.



A pair of the famed Telefunken NOS EL84 tubes. Bugle Boy / Amperex are also sought after. In my personal experience, there seems to be less difference in many makes of EL84 tubes, and many makers made them for each other. Remember, Philips owned Mullard, and the Brits also made tubes for USA folks and visa versa, so this got very complicated. In some amps, these NOS types jump up and grab you. In other amps, they don't show as much of a change. In Hi-Fi amps they work very differently than they do in guitar amps. Currently, the JJ EL84 is my most used new EL84 tube, and my personal favorite for my own amps and my clients amps. Make sure they are closely matched in "class A amps", which are generally really push-pull cathode biased amps, that do prefer matched output sets.


EL-84R - Reflector Russia (as the Sovtek). Reliable, but not as articulate as the others. Darker sounding in most amps. The stock tube in most Fender, Vox, and many other EL-84 based amps. Not as bright as the EL-84-S, and not as articulate. If you liked the sound of your amp with these tubes it, then you may want to experiment with some others too, for a different tone which some prefer.

EL84-Y - Ei ­ This is an older photo, and when I get some time I will update this. The current version of this tube in 2003, is easy to spot. It's plates are silver, not the darker material as is shown in this photo that was used in earlier versions. Brighter than the S or R versions of EL84, these can be a bit unreliable in some amps if they are not checked for low vacuum or gas issues. Low vacuum will cause short tube life, and flat out failure at times, usually at what may seem the worst time. Many vendors sell these ­ be sure your vendor tests for gas leakage, grid leakage, low vacuum, and has a good warranty. A good tested set of these sound great though, so it may be worth the attempt to experiment.


EL-84S - JJ - The best of the current EL-84's by most folks thinking for higher power, more articulate mids and highs than the EL-84R. These are reliable, powerful and articulate. They are not as long lived as the "R", and not as reliable, but that is usually due to their moderate inconsistency. Buy these from a vendor that does proper testing and they will be long lasting, articulate, and full of rich harmonic content. My personal favorite EL84 for most applications for the moment. There is a new Chinese offering under test that is showing some amazing results, and a new offering from Electro Harmonix is looking great and may give this tube a run for the money, and be even stronger.

Output power chart for EL-84 family

The "stock" NOS number here is 45-48 for reference. TUBE EL-84 Chinese EL84 6/27/03 EL-84 Sovtek EL-84S JJ Philips EL-84 General Electric 6BQ5 EL-84Y Ei Electro Harmonix 6/27/03 Current in Milliamps 39.0 44.6 45.3 46.5 48.0 53.0 56.7


Chinese EL-84 from June 2003. Performed nicely, the first Chinese offering I have seen of this tube. It was the lowest in output of any of the current EL-84 tubes. This may be a good thing, as many cathode biased amps can run very hot, and this tube may help tone them down. The curves on this tube were typical. They static match was average, thus indicating matching is a requirement. Dynamic matching will be a bit more difficult without high end equipment. This tube ran reliably at Vox AC-30 voltages.

Chinese EL-84 traces.


New Electro Harmonix EL-84 (June 2003) This tube may be a winner. EH has a great 12AX7 and a great 6V6. They are also offering an octal preamp tube once more ­ hats off to EH. Nice curves - average dynamic match out of the box, will need matching. Static match close out of the box. Stronger than JJ EL-84 and may be preferred over Sovtek EL84 as well. A very nice tube, and another choice for folks with EL-84 amps. Ran high voltages without failure way beyond specs. Handles voltage far in excess and was MUCH more reliable than the Ei EL-84. Highest power of all the current EL-84 tubes. Very consistent in output power. No duds in the batch. This tube may be the ticket for the biggest sounding EL-84, an honor that was held so long in regard to new made tubes, by the JJ EL-84. It is going to boil down to user tone preference. This tube is worth a try.

The EH EL-84 traces. A bit hard to tell in this photo, but the two tubes are slightly off as far as maximum output (which would show up in a static match perhaps), but their dynamic curves were very smooth and linear. If you could see the scope and have one EH tube and one of the Ei tubes or the Sovtek EL-84 tubes, running at the same time, the difference would be very apparent. Perhaps on future tests I will show tube curve comparisons. In any case, this tube had great triode curves (as shown here) and pentode curves. They passed the torture high voltage and high current tests with flying colors.


7027 and 7591 Tubes

7027 ­ JJ ­ Used in amps in the past such as Ampeg. 7591 - Reflector, Russia. ­ Used in amps in the past such as Ampeg.

Rectifiers ­ vacuum tube and solid state

NOS JAN Philips 5U4GB rectifiers. Rectifiers convert AC to DC, and many feel they do not contribute to the tone of the amp. They may not be in the tone path, but they do (to me at least) affect the feel and the output of the amp. Many of today's rectifiers put out the proper voltage, but do not supply the current of the older versions. Less pure materials, faster production, lower vacuum, are all factors. The new rectifiers will generally not have the life of the older rectifiers of the same family or type, and may have more of a voltage drop at their maximum capacity or ratings. This may be a good trait for some folks looking to tone down an amp that is a bit too strong for their tastes. The increased sag will also give a different feel and compression. They may not impact tone, but they surely will impact touch and feel.


These are some of the 1980s JAN Philips 5Y3 rectifiers.

Many people have many opinions on rectifiers in vacuum tube guitar amplifiers. Some people feel that solid state rectifiers are more reliable. This is true in one sense, but gives vacuum tube rectifiers an "implied" unreliability. I found vacuum tube rectifiers rarely fail, although the Chinese 5U4 from 2000-2002 did have a high failure rate when new. In some cases at one point, a 50% new failure rate was not all that uncommon. If they do fail, it is usually a case of physical damage, or the rectifier being bad in the first place, and failing in newly made amplifiers where the rectifier failed due to bad manufacturing. In the case of the Chinese rectifiers, when new, I have seen a 50% failure rate. A bad rectifier will usually show itself in one of two ways. (1) Power light comes on, but NO sound at all comes from the amp. (2) When you flip the amp off standby and into play when all seemed fine, your fuse will blow. There are rectifiers with 4 pins and 5 pins, of the same type. The four pin rectifier may be indirectly heated, and not work well in some amp designs, so if a 5 pin rectifier comes out of your amp, put a 5 pin rectifier back in your amp. The rectifier basically converts the AC line current coming into your amplifier to the DC voltages that are needed. A solid state rectifier is easier to fit into an amp design, can provide more power, does not run as hot, and is less expensive than its tube counterparts. The Marshall JTM-45 used a tube rectifier, but when Marshall came out with the 50 watt version of the amp, a solid state rectifier was a change in the design. Most Fender amps over 40 watts use a solid state rectifier. If you have an older amp with a tube rectifier and want to replace it with a solid state replacement, be sure to first check your amp and make sure all the other portions of the amp are in good condition. The solid state rectifier is capable of higher voltages.


As you will see in the charts, different rectifiers have different characteristics. In many amps, you can get a different sound and feel by replacing the rectifier with different types. Matchless is one example that lets the user choose various tube rectifiers as part of their features. A solid state rectifier will give very fast rise time and response as the voltages are produced very quickly. A vacuum tube rectifier will yield more to the player's touch dynamics, sound warmer and less harsh by some folk's feelings, and give the compression and sustain in a much different way than its solid state brother. When one initially hits a loud note or chord, with a tube rectifier, there is voltage sag, in some cases, a LOT of sag. As the note or chord starts to decay, the voltage then builds, and what you have in essence, is a built in compressor / sustain device. If you look at the charts, you will see how fast the voltage is developed with a solid state rectifier versus a tube rectifier. Using the same circuit, we replace the rectifier section. We used the same voltage input in all cases, but in the case of the 5Y3GT rectifier in the last test, our transformer output of 333v had to be reduced to 330v, as the 5Y3GT would have been pushed just a touch beyond its design limits. This change had negligible results on the final outcome. The tests were measured over a period of 500 milliseconds, or ½ a second. Using the commonly used configuration of 1N4007 diodes, its easy to see in comparison with the vacuum tube rectifiers, the difference in rise time to get the voltage we are after. It is a bit less apparent, but in this case with the solid state rectifier, we had 449.08 volts available for our B+ voltage, the highest voltage in the group. This is also something to keep in mind when you replace a tube rectifier with a solid state replacement, as your output tube bias will probably need to be checked. In the case of a class A amplifier such as a Vox AC-15, AC30, a Matchless amp, most Carr amps, or others, the bias is automatically taken care of, but in older class A amps, you may also want to be concerned about the output transformers and capacitors if they are older. The amp will be running at higher voltages, and in some cases, much higher voltages as you will see later. In .01 seconds, with the solid state rectifier, we basically had full power. Our voltage was 449.08 as previously stated. Moving along, we substituted a 5AR4 vacuum tube rectifier. This is one of the strongest vacuum tube units used today. It took about two times as long, .02 seconds, for out maximum voltage to be developed, 413.9 volts. This is a fairly large drop from the earlier solid state rectifier. Going to a 5U4-G, commonly used in some Mesa Rectifier products, we found that it took .40 seconds to develop full voltage. This is a long time compared to the solid state device, and twice as long as the 5AR4. This is almost a half a second, and most people can hear something that is ½ a second long in duration or delay. Our high voltage was 357.06 volts, or almost 100 volts less than the solid state device.


The 5R4-GYB, often used in place of the 5U4-G. About the same rise time as the 5U4-G above, but had a maximum voltage of 330.93 volts. This is a nice rectifier in some Fender Deluxe type amps that have been made with everything from the little 5Y3 to a GZ34 in the past. Its a great blues rectifier in these amps. Lastly we tried the 5Y3GT. Rise time was almost a full half a second at .44 seconds. Our maximum voltage was 303 volts. Now you have a little more information on rectifiers, and how the changing of types in a rectifier equipped amplifier can change the sound of the amp, the power of the amp, and the characteristics of touch, feel, and sustain. In most cases, the NOS rectifiers are better than those of today. The Chinese ones still have a long way to go to reach the specs of those of the past. The Russian ones are the best of the new ones, and the JJ factory is currently working on a re-release of the GZ34 which shows promise. Mesa Boogie products currently use mostly the Chinese variety. As a safety note - you can generally go "down" but not always "up". This means you can generally put a 5U4 or 5Y3 in an amp that had a 5AR4, but it is not recommended to put a 5AR4 or 5U4 in an amp that had a stock 5Y3. The increase in voltages may be too much for the other components in the amplifier.

Rectifier substations / cross reference: GZ34=5AR4 GZ32=5V4 GZ31=5U4


5Y3 -60 volts @ 125 mA 5U4GB -50 volts @ 275 mA 5U4 -44 volts @ 225 mA 5V4 -25 volts @ 175 mA 5AR4 -17 volts @ 225 mA

It is worth noting, that comparing today's rectifiers with some NOS offerings of the past, may show measurable differences. In the case of the GZ34 / 5AR4, in the same circuit, an NOS Mullard or USA unit, may have a lower voltage drop (meeting the ­17 volts to the left here, while a new GZ34 may have the current but perhaps not the voltage. Thus the NOS rectifier may allow your amp to produce more wattage at maximum levels.

Rectifier charts

below ­ These are newer charts than those on my website from a later series of tests. The voltages may not correspond with the data in the text above, as the power transformer was changed slightly. In any case, the rise times and maximum voltages reached can be compared between the various rectifier types just as easily.


5AR4 / GZ34 above ­ 416 volts max.

5U4G above ­ 364 volts max.


5U4GB above ­ 362 volts max.

5V4G above ­ 380 volts max ­ Great in Dr. Z, Matchless, Bad Cat


5Y3GT above ­ 322 volts max.

6AX4GTB above ­ 387 volts max


The GT Rating system ­ an explanation of "distortion rating" also known at times as "hardness rating"

Basically, a #1 will distort sooner, and a #10 later. If, for example, with a mid range tube, say a #5, makes your amp start to break in the output section at a volume setting on the amp of "4", then with a lower number tube, like a #2, your amp would have a same sort of break into output distortion at say a volume setting of "3". With a higher tube, such as an #8, then you amp would stay clean to about perhaps "6" on the volume. High rating numbers are not more or less powerful, they just distort later. These are preferred by heavy rocker that want maximum clean output, as they get their distortion and tone from effects or pedals. These are not as touch dynamic. Low number tubes are very touch dynamic, and more suited for a lot of folks, for smaller venues and recording. These ratings are especially great in amps used to play blues or other touch sensitive styles. Most folks prefer the 4-7 range tubes, as they are the closest in character and touch to what the amplifier designer had in mind. They are also the most versatile.

Conversion Information ­ GT numbering, Fender color codes and Mesa color codes

Mesa to GT numbering system:

Mesa vs Groove Tubes scale Red 4 Yellow 4 Green 5 Gray 5 Blue 6 White 6

Fender to GT numbering system: Fender Blue = GT 1-3 Fender White = GT 4-7 Fender Red = GT 8-10


Myles Saunders Rose has worked in various development, design, support roles, projects including development work for Roland, Yamaha, and was Apple Computer's music consultant for the Vivarium project in the late 1980's. He currently has his own company, Guitar Amplifier Blueprinting, and also is the head of the SAG (Special Applications Group) at Groove Tubes and Tech Support at Groove Tubes. He started playing guitar at the age of 8, on equipment that is called vintage today.... when it was NEW. He will not generally admit that he played the accordion from the age of five ... but then again, there were only five or so channels on the television, and one was dominated my Lawrence Welk back in those days!

Myles S. Rose - Guitar Amplifier Blueprinting - 2003




93 pages

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate