6L6 vs. EL-34 ~ FEEL the power ~ of your amp’s power section

by Boogie on August 9, 2010

in Mesa Tones & Tips

A rack of tubes glowing nicely at the burn-in stage of amp testing.

On the subject of tube amplification, you’ll often find discussions of one tube type being better than another. Guitar players are quick to defend the how-and-why of their preferences and the type of tube used is a common jumping-off point for what makes an amp great.

While there is certainly some truth to the idea that different tubes offer different flavors of tone, in Mesa’s humble opinion, the power tubes are largely ‘in service’ to the preamp circuit design; the circuit is essentially the cake and the output tubes are the icing. Like most things, there’s a long and short story, and the audible differences between the tubes oddly ends up being the short story. The long story may well provide you with some new insights as to how to approach tube tone and regardless of your tube preference, you may find  yourself appreciating both for their inherent specialties.

It’s ironic that MESA has long been thought of as a company specializing in preamp sounds (not accidentally – since the all-tube, cascading high-gain preamp originated here). But it has always been our view that an amplifier’s magic comes from the perfect harmony between preamp and the power section.  The many patents we hold covering all aspects of the power amp – from Channel Assignable Wattage, Switchable Rectifiers, Switchable Classes of Operation and even Wiring Styles hints at our inclusion of the power amp as a huge part of the tonal greater good. The power tubes’ type and role is indeed an important one, but it’s only part of a larger picture.

These days, the subtleties of power-tube distortion and clip are often overshadowed by the greatly expanded range of preamp gain available in modern amp designs. Most modern distortion circuits and sounds are usually generated by massive preamp gain being amplified through very clean power sections that are operating below their power rating (threshold of clip).  This translates into less potential for power section/tube qualities to be a major part of the sonic style – even with Master and Output levels turned way up. Extremes of distortion and harmonic layering from the preamp are amplified with articulate detail through this cleaner power section. For Rectifier high gain sounds (and Roadking & Roadster), especially when using the amp for its original intended purpose (massive gain sounds in Orange and Red channels), switching between 6L6s and EL-34s may produce only slight differences, if any. Power tube influence can be masked at lower playing volumes with high preamp GAIN settings.

How about those differences?

While 6L6 and EL-34 power tubes are more likely to surprise you with their similarities in an A/B situation, you’re actually more likely to FEEL the differences between them. Audible differences do exist though and for those of you looking for the quick answer to the title of the post, these next two paragraphs are for you.

Mesa 6L6s on a matching traySonically speaking, 6L6s are well-known for being versatile and balanced across their entire range of low, mid and high frequencies. They are often loosely referred to as being ‘fat and round’ with a musically blooming bass response but they are also well regarded for being brilliant, detailed, sparkling and ‘open’ in high-end and presence frequency ranges. With the 6L6 being so well balanced yet bass-full and high-end brilliant, you might be thinking to yourself that the 6L6 has everything anyone could ever want from a tube… and Mesa’s history tends to agree.  The 6L6 is easily the most versatile tube for any styles from pristine clean  for jazz to mind-numbing metal and anything in between. The same headroom that delivers full range clean tones simultaneously offers the same clarity to support huge but accurate low-end with modern high gain applications. Versatility being one of the cornerstones of Mesa products, the vast majority of Mesa amps have either been designed specifically with 6L6s only, or, those amps with the Switchable Bias are originally shipped with 6L6s from the factory. Beyond its expansive sonic signature, 6L6 tubes are consistent, reliable and a mainstay for tube guitar amplifiers since the inception of guitar amplification.

A tray of EL-34 Power tubes waiting to be packed While Mesa admittedly has a bias toward the 6L6 as the go-to, big bottle tube, there are characteristics of EL-34s that are undeniably rooted in rock ‘n’ roll that make the skinnier bottle ‘34 well worthy of it’s position in rock history. In bass frequencies, EL-34s tend to offer less bass in low frequency ranges (in the sub-low regions) compared to 6L6s, BUT –  the higher bass this tube DOES generate is  more focused, tight and extremely punchy. The frequency of this punch is similar to the kick drum punch range – closer to the  beaters’ attack frequency than the sub-air that comes out of a kick drum’s front head. Another key signature of EL-34 character  is its considerable peak in upper midrange and low treble regions in addition to an overall brighter disposition. It’s this upper-mid/low-treble peak that is the true signature of the EL-34 gain and it’s also the range where harmonic layering in distortion sounds begins to stack up in earnest. It’s also this frequency range that has the potential to produce what many refer to as “icepick” frequencies – unpleasant brightness that stings your ears. Careful settings of middle, treble and presence controls is crucial to avoid exposing you, your bandmates and your audience to these “icepick” settings. When tastefully set, there is an unmistakable and musical edge, cut and bite from EL-34s which lends itself well to medium preamp gain settings, heavy handed attack, and power tubes pushed into overdrive as amp Masters get cranked. This is where the EL-34 shines!

But enough about what you hear, let’s talk about feel.

Threshold of distortion, clip and overdrive.

Street sign of a car going off a cliff

One of the important and likely more noticeable differences players will experience when properly comparing 6L6s and EL-34s is threshold of clip and distortion. This living, breathing aspect of tube tone might not be as obvious to players new to tube amplification and/or those who haven’t been able play their amp very loud or at gig levels yet. So… let’s start by defining some of the concepts in the title above.

“Threshold of distortion” – as it relates power amp sections – is the point where the Output and/or Master settings of the amp, with settings dialed for clean sounds in the preamp, is being turned up loud enough to begin saturating the power section and power tubes, generating distortion. Clip is a term that describes the subtle initial onset of this distortion and the transition from clean sound to distorted sound. Overdrive is a term generally used to describe distortion sounds beyond this soft clip –  but before full gain saturation and layering we all call distortion. Overdrive is often the term used to describe distortion that is smoother and warmer and better for single-note solo tones or purring rhythm sounds. Hopefully these descriptions shed light on some of the more obscure details behind great distortion tones. Now, let’s compare our two tube competitors in the arena of feel.

Stiletto chassis in burn-in - waiting overnight for playtest in the morning. Technically speaking, EL-34s are served higher voltages and utilize more current than their 6L6 counterparts. Non-technically, they run hotter! This hotter/higher current operation is one of the reasons why EL-34 tubes (and the amps that use them) offer such a wide range of overdrive and crunch sounds from their power sections. The allure of EL-34s, particularly for gain sounds, stems from the tube’s earlier threshold to clip and distort when pushed. As you increase the amp’s overall volume, the potential and usable range for EL-34 power tubes to break up musically increases in a big way. This is the land where great, gut-punch gain sounds are born (think early AC/DC or vintage Van Halen). These fabled early rock distortion sounds were generated by power sections of amps being cranked up, since all-tube cascading preamp gain as we know it today was JUST being born by Mesa’s designer and high-gain preamp pioneer and innovator, Randall Smith.

6L6s offer a noticeably different range of distortion threshold and clip potential once you know ‘where’ to listen. The rich, full range of bass frequencies highlighted in 6L6s can generate a wide sonic footprint when pushed, but too much power section clip with a 6L6 can cause bass “bloom” that expands beyond a desirable sound. With smoother mids and low-treble frequencies compared to the EL-34, 6L6s also produce less obvious saturation when pushed. Power tube distortion and overdrive with 6L6s tends to be warmer, smoother and sweeter overall and is more commonly used in traditional blues and roots styles or wherever low to medium gain clip or pushed clean sounds are what the music calls for. For those looking to exploit the 6L6 clip threshold, single notes and solos can take on almost unlimited personalities. Solo tones from the likes of Andy Timmons, Robben Ford, or classic Steely Dan solos are great examples of the wide array of clipped and pushed clean sounds available from 6L6s while high gain sounds from the likes of John Petrucci and Dream Theater, Lamb Of God and Metallica are just a few excellent examples of 6L6s in action on the heavy rock front.

Switchable Bias

Mesa Boogie Rectifier Bias SwitchThe Switchable Bias feature in Mesa amps allows the user to choose between 6L6 or EL-34 power tubes with  just the flip of a switch (and once the corresponding tubes are installed). If your Mesa amp has this option and you are considering venturing into experimental mode, there are a few important things you should know. The first and most important rule to follow is; BIAS SETTING MUST MATCH TUBES IN USE! The reason this sentence is capitalized here and on the back of your amp where the switch exists is because premature tube and/or amp failure can occur QUICKLY if this switch is not set properly. In other words, ALWAYS make sure to set the  Bias Select switch to the position that matches the kind of power tubes installed in the amp. Your amp will have been shipped from the factory with 6L6s and the switch set to the same. If you’re wondering what might happen if you switch the bias to EL-34s with 6L6s in the amp,  DON’T DO IT! As mentioned before, EL-34s run ‘hotter’ than 6L6s and if you set the bias switch to ’34s but you have 6L6s installed in the amp, your tubes (and possibly internal components) are going to get cooked. On the other hand, if you set the Bias Select to 6L6s with EL-34s installed, EL-34s will be drastically underpowered and the amp will sound, well… underpowered and thin. Bottom line – MAKE SURE  you have the bias switch set to match the tubes you have in your amp and make no exceptions.

Which tube is for me? How to REALLY hear the differences? CRANK IT UP!

A Nixie Tube Clock

Players using medium gain amp circuits and moderate to low GAIN settings and higher MASTER settings are more likely to hear the variation between these two power tubes as well as being able to take advantage of the musical expressiveness that the threshold of distortion provides. Our new Electra Dyne offers an excellent range of transitional soft-clip sounds and is a great example of an amp that ships with 6L6s but can truly deliver EL-34 greatness across the gain spectrum once installed. On the flip side, the Lone Star – a  veritable library of American clean, clipped, and classic overdrive tones – can be ‘tightened and brightened’ and nicely ‘crunch enhanced’ with the addition of EL-34s, not to mention what ’34s can do in a 10 watt setting on the amp. For the new Mark V, Channels 1 & 2 are loaded with an amazing variety of clean, pushed and crunch tones that will stand up and ‘sing ‘n’ sting’ with EL-34s installed while channel 3 can also deliver great variations from EL-34s in medium GAIN settings. For Rectifier, Roadster, Rectoverb and Solo50 owners considering switching to ‘EL-34s,  try this; Raw or Vintage on the gain channels or Brit and Pushed in the clean modes, switch Rectifier Select to Vacuum Tubes, drop it to 50 watts and turn it up! Explore the mighty hand of power tube distortion.

So which tube is for you? Well… what kind of music do you play? If you play classic rock from the ’60s and ’70s, there’s a good argument for you to look into EL-34s.  If you play traditional Blues or maybe Jazz – or – mostly clean sounds and just a little bit of overdrive for solos, 6L6s are probably the best place to start. Modern rock? Probably 6L6s – BUT – like we said at the beginning, power tubes don’t make the amp, the circuit and the big picture does. Research is key and if you have questions, give Mesa Customer Service a call. We’re specialists in the details but also great at getting you pointed in the right direction if all the tube talk here didn’t set you sailing in the right direction.

Finally, besides tonal differences and feel, the elusive threshold of distortion is a subtlety that is felt more than heard. Many of the details we’ve discussed will likely remain undetectable to any of your senses, regardless of the tube, until your amp can be turned up to ‘threshold levels’ and gig volumes. For those of you who aren’t in a position to turn your amp up past bedroom volumes, you owe it to yourself to find a way (and the place) to crank your amp up and jam for a while to FEEL what we’ve just covered in this post. Mesa amps sound great at lower volumes but every amp is tested and designed more specifically for use in professional applications. This is where the magic of tubes and Mesa amps REALLY happens. Find a barn, rent a rehearsal room, book a gig or do whatever you have to do to experience power-tube influence over your preamp settings. Ditch the high gain (settings) from the preamp and FEEL THE POWER section in all its glory. We can assure you that you might not be the same guitar player afterward. ;)


{ 107 comments… read them below or add one }

Howell Selburn May 21, 2014 at 4:18 pm

I have a Mark IV with the EV 12″! Could stand to have a pot cleaned and one of the EQ sliders is a lot looser than the other although it works just fine. I’d like it to feel like the others though. I love the 6l6′s because I can go from. Keith. Richards to Carlos Santana in a heartbeat and everything in between. The EL34′s don’t do that and there are pedals that come darned close to the el34 sound. I love overdrive. Not Fuzz. Heresy, I know, but there it is. I’d love to know what the optimal 6L6 I should use is…. 420, 440… Don’t know. The gain noise can get up there although I can tone that down if I’d buy a reverb pedal. Thing is, I like your pedal!


Howell Selburn May 22, 2014 at 11:33 am

I love your built in reverb. Does up the gain noise factor, of course putting another 12ax/y/t 7 in there will do that. :)


Shaun Swegman May 20, 2014 at 4:27 pm

That’s an interesting point about sound vs. feel. I play a Les Paul with ’57 Classics and an SG with BurstBuckers, and if I were to record a bunch of tracks with both guitars and listen to them later, I’d probably have a hard time telling them apart. But while I’m playing them, the differences are obvious. The way they feel and respond is different, and that comes through.
I own three Mesa amps right now. One with EL34s (Stiletto Deuce), one with 6L6s (Nomad 55), and one with EL84s (Maverick). The Mav is still my favorite, but it’s nice to have almost all of the basses covered. Be nice if Mesa came out with a 6V6 amp in the 15-20W range.


Glauco November 25, 2014 at 11:33 am

“Be nice if Mesa came out with a 6V6 amp in the 15-20W range.”

This is EXACTLY what the Blue Angel is. . . ;-)


Kostas December 22, 2013 at 5:09 pm

i have a 2\90 simulclass(red light)who has all 6L6 tubes…if i want to make it sound exactly like the older model(blue light)can i put in 4 EL34 tubes at the same positions like this: http://www.eurotubes.com/MESA-2-90-S1.jpg
and i must to re-biasing?


Boogie Boogie December 30, 2013 at 11:38 am

Hi Kostas –

A couple of things. First of all, there isn’t intended to be a difference in the sound between a Version I & Version II. So, changing the tubes in a Version II 2:90 to EL-34s will not make the amp sound like a version I.

Second, the tube groupings for Version II amps are slightly different. Here’s a link to the attachment to detail the tube matching in pairs and sides A & B:

2:90 Tube Grouping




Rob Harvy August 7, 2013 at 5:00 am

Hi Boogie men, I’m now the proud owner of a Road King Series 1, Express 5.25×12″ combo, a Nomad 100 combo and my old Mk2C which funnily enough still kicks the butt out of my Marshall combo volume wise.

Recently the Road King started crackling and sputtering with both EL34 valves and the adjacent 6L6 valve apparently arcing and then the fuse blew. The amp has been travelling around from Hong Kong to Australia so could it be just a valve replacement issue. I had something similar with my MK2C and just replaced the power valves and that fixed it.

There really isnt another amp manufacturer on the planet that does such a complete range of amps to suit all playing styles, so thank you,




Me December 12, 2013 at 10:38 am

Rob. You never take your music equipment to HK – the only thing you take is yourself and your lies for whom so ever you are cheating on and or with.


Tommy Paez June 7, 2013 at 4:49 pm


I am a diehard Mesa believer and user. I have a Mesa Mark V head and a Mesa Nomad 45 head which I specially ordered recently from you. I use them both going through different amps independently and sometimes both at the same time. You can imagine the number of optional sounds I can get. But the reason for this email is that I have been thinking of switching the 6L6 for EL34 tubes in my Mark V and I wanted to find out if doing so would produce a tighter brighter sound like the EL84 on the Nomad 45?

Thanks for your help… Tommy


Boogie Boogie June 11, 2013 at 6:40 pm

Hi Tommy –

Yup – that’s what EL-34s do compared to 6L6s – tighter and brighter. It won’t make quite the difference you might expect but it will go in the direction you’ve mentioned.

Hope the amps are working great!



Cecil March 13, 2013 at 5:02 pm


I replace all four power tubes in my Mark IV with MB 6L6GC (STR440) tubes. After replacement, all of my gain was gone. Regardless of the settings, I could get not distortion, even with full gain, full lead, full power, tweed power, etc.

None of the tubes were red plating or arcing and had a normal glow.

I put the old tubes back and the gain returned. Is there a “burn in” period or some other reason for me not to think I got a bad tube?

Thanks, MBs Rock.


Boogie Boogie March 18, 2013 at 12:30 pm

Hi Cecil –

You most likely have a weak 12AX7 preamp tube that tested good when it left the factory but somehow failed prematurely and is the cause of your lower gain. The Power tubes will generally NOT be the cause of low gain like that. This kind of issue is nearly always preamp tube related.

It’s unlikely to be more than one tube so it’s just a matter of replacing preamp tubes one at a time until the problem returns which will tell you what tube is bad. Get rid of that one and contact the dealer where you bought it for a replacement if still within the 6 month use period.

This can happen from time to time. Just because a tube is new does not mean it’s good or will last it’s normal lifespan. That’s why we and ever other tube re-seller offers a warranty and why Mesa’s 6 month warranty on tube is one of the best in the business!

Hope this helps and let us know what you find.



Jason January 15, 2013 at 5:56 am

If I wanted to switch the Mesa 6l6s for a different brand of 6l6 (I don’t but just in case I did), would the amp need to be rebiased?


Boogie Boogie January 24, 2013 at 10:49 pm

Hi Jason –

You need to read this:


Should answer all your questions.

Let us know if that helps you and thanks for your inquiry.




Robert F. Dorner September 17, 2012 at 2:52 pm

Hello Boogie,
Newbie here, I Just purchased my first Boogie. It is a Solo 50 Series 2 Rectoverb single speaker combo. Not sure of year serial # R5004637. This beast is loud and very Fender Vibrolux clean (my other amp). I will stick with the 6L6′s until they need to be changed then I will try the EL34′s. I enjoy sustain but live in small house. This amp needs to be cranked, clean or dirty, to get that! Could you recommended an Overdrive effect that would allow me to keep the wonderful sound of this amp without having the police at my door? Also, would it be best to run through loop or straight from guitar?


Boogie Boogie September 17, 2012 at 4:30 pm

Hi Rob –

Great stuff and welcome to the family. Glad you hear the beautiful clean of this amp – it really is something special.

Can’t recommend a great pedal for it at the moment except to say that at low volumes, feel free to crank the gain all the way whereas turned up to live volumes this doesn’t always work. Also, this amp sounds pretty darn good at lower volumes and even though you don’t get the bass bloom when it’s turned up, it still sounds fat and full. You can run the controls to more extremes when the volume is low – just remember to set things more normally/safely when you turn it up.

Finally, you might consider a pedal EQ to help dial in what lots of people call ‘bedroom metal’. An EQ set to the Classic V can be a great way to dial in the sounds that are fun to play at quiet levels. Get a Dunlop 10 band EQ ad you’ll have loads of choices for high gain sounds while still using the amps killer gain.

Hope this helps and enjoy the amp!



Troi Darlington August 12, 2012 at 8:04 pm

Hi there,
Thanks for taking the time to write this great article.

I just turned my Dual Rectifier Solo Head around and noticed it has mixmatched tubes. there’s 3 x 6L6 and 3 x 5LGB tubes. The bias is set to 6L6 and the power is set to bold.

Question: Is this going to cause problems and should I replace them all to the same ?

I purchased it second hand on ebay and am doing some research as to how long before I should replace the tubes. I am a total noob with the Mesa amps.

I am such a noob I actually made the mistake of trying to record without the speaker plugged in. It was running like this on an off over a period of 3 days. I had never heard of power attenuators used with amps because I had never tried to record like this before…. so again total epic noob fail… I was just toooo keen to record it, and the sound seemed to worsen as I went.

Questions 2: Have I killed my amp. Is there anything I can do to fix it ?
It is still running but I’m worried I’ve damaged it from this oversite.
Please advise.


Boogie Boogie August 13, 2012 at 4:13 pm

Hi Troi –

Sorry to hear of problems with your Dual Rec.

First things first. A DUAL Rectifier is designed to run on FOUR power tubes not 3. Never run an amp for any length of time on odd numbers of tubes.

Second – the 5U4G tubes ALWAYS go in the sockets closest to the AC power cable/jack going into the amp. 5U4Gs ONLY in these sockets. Plugging 6L6s into a 5U4G socket is bad. Same as plugging a 5U4G into a 6L6 socket. Not good- don’t do it. Know what tubes go in the sockets before you install/replace/turn on! Very important.

Third – NEVER run a tube amp without a speaker cabinet or speaker load. At the least you will wear the tubes in the amp dramatically. At the worst you can permanently damage some of the most expensive parts in the amp, namely the Output transformer.

Now – because Mesa’s are tough, the amp may be OK, BUT – this amp should be taken to a technician to be looked at. If you’ve used it with mismatched tubes and no speaker connected for a long time, at the least the tubes are probably not in great shape. You should consider buying new Mesa power tubes – 6L6 and having them installed along with the amp being checked out. Here’s a link to either USA Authorized Repair stations (if you are in the USA):


Or, here’s the link to contact the Mesa distributor in your country for directions and recommendations for Authorized repair outside of the USA:


Hope this helps and let us know what you find out!



Rey Cruz August 12, 2012 at 10:33 am

I have a Mesa Boogie DC3 with 4 EL-84. All the tubes the preamp and power are recently bought at Mesa Boogie. 2 tubes on the right are bright red and after a while I will loose some volume while playing. Second tube on the right is hotter so I took it off and the amp seems to be better. Can i use this amp on 4 hours gig the way it is without damaging the amplifier?


Boogie Boogie August 13, 2012 at 3:37 pm

Hi Rey –

Sorry to hear of problems with new tubes.

If you installed new tubes and they are glowing cherry red at startup or after warmup, move the pairs of tubes from the right to the left and see if the problem follows the tubes or stays in the sockets.

Also, plug your old tubes in and see if they display any issues. It’s possible that one of the new tubes you received is shorting out and needs to be replaced under warranty.

It’s also possible that one of your old tubes may have failed and when it did it damaged some of the resistors that control the voltages to the tubes. If so, the amp will need to be taken to a repair tech to be gone over before replacing tubes again as the tubes are no longer receiving the proper voltage.

If you didn;t have a problem with the amp before you changed tubes, it’s probably the tubes. If you did have a problem with the amp and you changed tubes and you still have a problem, the amp should be taken to a tech to be checked out.

Hope this helps.

Let us know what you find out.




Daniel May 17, 2012 at 6:30 pm

Hi Mesa Boogie guys. From much time I’m search a head for me. But, I not know what choice. I play: Jazz, Ballads/Rock, Blues, Ska, Reggae, Funk, Gospel, rock modern and a bit of classic (but specially the rock modern), rock/metal, post grunge and a bit of metal. Then, I want that please you recommend me one o various of your products mesa boogie to the musical styles that I play and what tubes recommend me for the head? Thanks for see. Greetings.


Boogie Boogie May 21, 2012 at 10:24 am

Hi Daniel –

Since you play so many styles, it seems like a very versatile amp is what you need and that is exactly what we do!

In my opinion you would probably be most happy with a Mark V. From there, maybe a Roadster or a Dual Rectifier but ultimately a Mark V is probably Mesa’s most versatile amp and would cover nicely all the musical styles you mentioned. It also provides switchable bias so you can try 6L6s or EL-34s for yourself and see which ones you like best or use the different tubes for different applications where it seems like you need them.

Thanks for the question and hope this helps.



Daniel May 22, 2012 at 1:55 pm

Thanks for answer my question. Well, I buy these heads is in a future, because, I not have much money for buy a mark v or roadster or dual rectifier, these head are for me the objetive, but, Right now, I can buy a Mesa Boogie Express 5:50 head. Sincerely, you believe that this head (the express) can help me in my needs? Thanks for see. Greetings.


Aitch February 29, 2012 at 3:27 am

I purchased a MkIII simul class a few years ago and, as a non-performing player have, until recently, used the amp at home at very low output levels.
My experience in amplified is almost non existant.I have recently begun jamming at the local village hall with a friend who is an experienced guitarist. I was unable achieve anything like the same level of gain as he was getting from his modern tube amp, in fact the gain from my boogies was virtually non existant. My friend was unable improve the gain. I also noticed that there was no discernable difference in output between the simul and A class settings.

I have ordered a complete set of replacent tubes as all of the power tubes and three of the pre-amp tubes are non Mesa Boogie.

I would be grateful for your opinion as to whether this will resolve the problem, or whether its down to the settings used, or a possible problem with another component. Also any tips on retubing.



Boogie Boogie March 5, 2012 at 2:29 pm

Hi Aitch –

While it’s impossible to tell based on the information you’ve provided, my first thought is that the Mark III is an amp that may not compare to a “Modern High Gain Tube Amp” in terms of ‘amount’ of gain. There are also a number of different versions of Mark III that might offer different amounts or type of gain in various channels as well. My guess is that your Modern Amp has been designed with more gain than the Mark III was ever designed to provide.

There should be a slight but noticeable difference between Class A and Simul-Class operation. Simul-Class will be slightly louder and tighter. The differences between them are small.

Changing the tubes will not likely ‘solve’ your problem of the amp lacking gain compared to the more modern amp. We can only guess that your Mark III is fine but just does not offer as much gain as the more modern amp you’re comparing it to.

Hope this helps. Let us know what you’ve found out.



Steve Coakley December 20, 2011 at 4:19 pm

I play Mesa/Boogie mk3 combo blue stripe(1988)since 1988…in a road case for shure…change the tubes 2 – 3 times , that s all…THX


Michael December 15, 2011 at 7:20 pm

In my dual rectifier I have the standard 6l6, 5u4, and the 12ax7 preamp tubes. In the preamp section one of the tubes must have been bad (I noticed that it doesnt glow as much as all the others) and I was wondering if it is okay to mix different brands of tubes? like 3 mesa, a jj, and a ruby but all the same model?
Im new to tube amps and this is my first one, any advice on this would be great!!


Boogie Boogie December 19, 2011 at 7:52 pm

Hi Michael –

Judging the quality of tubes by looking at them is something only experienced people are able to do and even then, they are just offering an educated guess. Tube glow is not great indicator of whether a tube is good or not.

Mesa always recommends using Mesa tubes for a number of reasons, the least of which is the sound of your amp and the tubes themselves are guaranteed to operate properly and tonefully in a mesa amp where non-Mesa tubes are NOT guaranteed. You should definitely seek Mesa tubes as replacements and if you are new to tube amps, check out this link on tube troubleshooting which will answer a bunch of your questions.


Hope this helps!


Mike December 6, 2011 at 2:05 am

Hi I am the new proud owner of a M3 Carbine Combo does Mesa offer a different variety of preamp tubes for different sounds or would it not make a difference because it’s only one tube thanks for any help.



Boogie Boogie December 6, 2011 at 3:32 pm

Hi Mike –

Thanks for the inquiry. Great questions.

Mesa does not offer different preamp tubes (or power tubes for the amps that use them) to provide different tones for a number of reasons. #1 being that the tubes we use are the best tubes available and deliver the best sound you can get and offering the greatest reliability. If there’s a better tube out there to be had, we’d be using it!

Also, particularly in the Carbine, as you’ve pointed out, you’re not likely to hear a huge difference in tone by changing the preamp tube. You *MIGHT* notice a difference – then again, you might not. It won’t be a huge deal either way. Best to stick with Mesa tubes to maintain your warranty and to trust that we use the very best tubes we can source in every amp we make.

Thanks again and hope you’re loving your M3!


Gennadiy Solovey December 4, 2011 at 6:33 am

hi,PLEASE HELP ME,i am looking four set of tubes to my MESA BOOGIE 2;90 Simul.amp.at that moment i have jj 6l6 set ,but i need to change to ORIGINAL MESA BOOGIE set of tubes to 2;90 Simul .amp.Thanks


Boogie Boogie December 6, 2011 at 3:23 pm

Hi Gennadiy –

If you are not in the USA, please contact your local distributor for pricing and availablity.

If you are in the USA, you can purchase tubes from your local dealer or by calling Mesa/Boogie directly at 707 778 6565, Monday-Thursday, 9am-5pm Pacific time.

Hope this helps!


Jose Jimenez November 29, 2011 at 6:28 pm

Nice article! I just wanted to let you know that I am enjoying my Mark I Re-issue, even with 6L6′s and I use a fuzz box and eq for the metal sounds.

It’s versatile, the chime is just fantastic, and if I turn it up even slightly it gets nicer and nicer sounds, w or w/o the pedals . With the pedals, my RI could easily mimic the sounds of vox, marshall or fender.

It’s nice to know, if I had to that I could swap out the power tubes for a set of EL34s if I set the power switch to ‘tweed’.


Boogie Boogie December 1, 2011 at 7:44 pm

Hi Jose –

Glad you’re enjoying the Mark I. Simple yet still very versatile.

Just to clarify, EL-34 tubes are not an ideal tube for the Mark I unless it is otherwise modified and biased for that tube. EL-34s have higher/hotter bias requirements than 6L6s and when in TWEED, the voltages/current to the tube sockets actually goes DOWN. This reduced voltage/current is what makes it possible to run 6V6s in the TWEED mode. If you run EL-34s in the TWEED mode, the tubes will be running even COLDER than they would if you were in full power. So… unfortunately, EL-34s are not a reasonable option for use in the Mark I or any other amps that are NOT equipped with SWITCHABLE BIAS like Rectifiers and other Mesa’s.

Hope this helps and thanks again for the kind words.




Tobey December 8, 2011 at 8:51 pm

But in the Mark I manual it states that EL34s can be used with great success, just output power is reduced to ~80/40 (100/60 switch, respectively). It doesn’t mention the POWER/TWEED switch so in direct response to the OP, I would assume this means leave it in the POWER position (which, of course, corresponds to what you stated).

Just got my first Mesa a couple hours ago (and coincidentally a MkI Re-issue) so I am quite curious as to the above. :) Not that I have any immediate need to switch to EL34s but I like to know what I can and can’t do.

Thanks for the article! Very informative!


Boogie Boogie December 12, 2011 at 4:43 pm

Hi Tobey –

Keep in mind when that manual was written… ;)

As mentioned previously in comments here, EL-34s draw MORE current than 6L6s. Since Mark One’s and Mark I Re-issue’s are all biased for 6L6s, plugging EL-34s into a 6L6 biased socket will mean that the EL-34s will run cold. That doesn’t imply they will sound bad but they will not be operating at their suggested current/voltages, although, since running colder, they should be plenty reliable.

TWEED power will reduce the voltages/current available to the tubes even MORE. Already cold running tubes will run EVEN colder and in some cases, using tweed power may not provide even the minimum voltage/current needed to properly run an EL-34. There are always many variables but the short answer is TWEED power is not necessary to install EL-34s in a Mark I re-issue and, in fact, Full power is suggested if you plan to experiment with installing EL-34s in a 6L6 biased amp.

Hope this helps! Let us know how it sounds when you try it out. Cheers,



Stevo November 9, 2011 at 1:16 am

I have a Mesa SOB with the Black Shadow speaker and the Limit knob feature. I want to re-tube the entire amp. I’m most interested in obtaining an over driven metal/hard rock tone from the amp. What kind of tubes do you recommend? Are kt88 or 6550 an option? As long as they are biased 4-6 they should work fine in the SOB? ALso I have 3 pre amp tubes as there in no reverb. What do you recommend for pre tubes?


Boogie Boogie November 11, 2011 at 9:07 pm

Hi Stevo –

The S.O.B. is not really capable of modern hard rock and metal tones, regardless of the tubes in use. First of all, it is not the tubes that deliver the sound, its the circuit. Beyond that, Mesa always recommends using Mesa tubes as all Mesa amps have a fixed bias and using Mesa tubes ensures that the tubes in use match the fixed bias of the amp.

As for getting hard rock and metal tones out of the amp, your best bet is to use some pedals or external distrotion generators as the S.O.B. was designed and built many years BEFORE we had what we all now consdier to be hard rock and metal tones. It’s a great clean amp and maybe some blues overdrive as well but for modern gain, something external is what it takes.


Spencer October 28, 2011 at 12:57 pm

Hey I am currently debating between buying a Mesa Boogie F 50 which runs on 2 6l6 tubes. I have heard from some people that it is impossible to convert this amp to run EL34′s. Is this true? How would i convert it if it is possible?


Boogie Boogie October 31, 2011 at 12:31 pm

Hi Spencer –

The F-Series amps do NOT have a switchable bias function like many other Mesa amps.

While we can’t say that it’s impossible to convert for EL-34 operation, we don’t encourage it and this is something that a technician would have to modify and for which there is no instruction available from Mesa.

And, as the post describes, we don’t think you will experience as much of a tonal difference as you might hope for, given what it will likely cost to get the amp modified to operate EL-34s. We would suggest you stick with the stock 6L6s and look to outboard effects (EQ, Gain,Boost or distortion) to get the sounds you are looking for if you don’t get them already with the amp.

Hope this helps,



leon lewis October 27, 2011 at 7:53 pm

What are the best rock and roll sound for a 50 caliber regular.I just want to update the amp.


Boogie Boogie October 31, 2011 at 12:35 pm

There are two types of .50 Caliber. Early versions used four EL-84 power tubes. Later Versions used two 6L6 power tubes.

Mesa doesn’t offer different choices of either of these tubes – we offer THE tube that we feel makes the amp sound it’s best. If your amp uses 6L6s, you would buy this tube:


If your amp uses EL-84s, these are the tubes you’re after:


Hope this helps!



Chad September 13, 2011 at 10:26 am

Hey guys.
I’ve been toying greatly with the idea of getting either a dual or triple rectifier.
One thing that’s crossed my mind is, is it possible to mix tubes?
What I mean is, could you have 2 EL34s and 4 6L6s?



Boogie Boogie September 19, 2011 at 11:25 am

Hi Chad –

Mixing the two different types of tubes (EL-34 and 6L6) is only possible in the Roadking and some Simul-Class amps – NOT the Dual or Triple Rectifier. That said, I doubt you would hear much of a difference with the mix of tubes if you could. The majority of the tone of the amp comes from the preamp and your settings. The tubes will only provide subtle differences, especially when blended like that. As romantic as it sounds to do tube blending and as much as people suggest that it’s the power tubes that make the sound of the amp, Mesa tends to find that it’s the overall design, quality of parts and the preamp which shapes the majority of what the amp sounds like. The power tubes do the job of making all that other stuff loud! ;)

Thanks and hope this helps.



JAMES WATSON September 8, 2011 at 11:02 am

Hi, just a quick question. I just got some new tubes for my express 5 50. I just noticed that one of the tubes is marked yellow and the other is green, is this right or should they both match the same colour? thanks


Boogie Boogie September 8, 2011 at 4:39 pm

Hi James –

Tubes should be sold, purchased and installed in matched pairs in corresponding sockets in the amp. Very important!

Mesa sells it’s tubes in pairs so if you purchased the tubes as a pair, you should have received a pair of tubes with matching color codes. While it’s not impossible for the factory to have packed a box with two tubes of different color codes, it’s highly unlikely. We might suggest contacting the establishment you purchased the tubes from and request a properly matched pair.




Victor August 21, 2011 at 4:23 am

Hello Friends i have a Mesa Boogie DC-5 Dual caliber ,since Mesa Boogie no Longer use Mesa 6L6 STR 420 my original Tubes , And mesa Recomend STR 440 Do i need changes in Bias Head ? because Bias is Fixed, do i need a Tech ? for change anything in Bias ?

thanks from



Boogie Boogie August 31, 2011 at 1:01 pm

Hi Victor –

All Mesa amps benefit from a fixed bias which allows for ANY Mesa tested tube to be compatible with any Mesa amp ever made. There is no need for any bias adjustment as long as Mesa tubes are being used. STR420 tubes were tested to the same degree that STR440 tubes are tested today so they are a direct plug-and-play. Get some 440s, plug em in and you will be ready to rock!




Sho August 11, 2011 at 9:33 pm

I’m a proud owner of a Lone Star v2 (10/50/100W). I’d like to try some other 6L6 and also EL34 from different brands but I didn’t want to spend tons of money buying 4 tubes of each type/brand.

Can I run the LS with only 2 power tubes (50W)? If so, which sockets should I use? Outer ones (1 & 4) or inner ones (2 & 3)? Does it hurt to leave the unused sockets without any tubes inserted?

BTW, nice article! Inspiring! Thanks.


Boogie Boogie August 15, 2011 at 12:13 pm

Hey Sho –

You can run the amp in just 50 watts which uses the outer sockets (1 & 4) when in that position.

HOWEVER – DO NOT switch from the 50 watt mode with only the outside tubes installed. You will only be able to listen to the amp in this position with only those two tubes in. Use of caps is to point out that you could do damage to the amp if you switch to other wattages with no tubes installed. Use caution here…

If you have the same type of tube (6L6 or EL-34) that you can keep in the inner sockets, you can try a pair in the outer socket and still have all wattages available to you while the 50 watt position is, of course, the position that allows you to hear what the tubes you are reviewing sound like.

Thanks for the kind words. Hope this helps and glad you’re diggin’ the Lone Star. Great amp!



Gary June 21, 2011 at 11:34 am

hello, I have a older triple rectifier, and the question I have. Is it true you can pull the 2 middle tubes for less power with out hurting anything, and will it effect my tone that much?


Boogie Boogie June 21, 2011 at 3:06 pm

Hi Gary –

Regardless of your amplifier being old or new, any Rectifier can have ONE pair of it’s tubes removed to reduce the wattage of the amp by “50 watts”. A Triple Rectifier should not have more than one pair removed or damage to tubes and/or transformers may result.

When removing pairs of tubes to reduce wattage, a few other elements must be understood and implemented:

- Tube sockets are matched via outer and inner pairs. In a Triple, with all the POWER tubes labeled 1-6 left to right, the matched sockets/pairs are 1 & 6, 2 & 5 and 3 & 4. In a Dual, it’s the same with one less pair to start with – 1 & 4 and 2 & 3 are matched. When pulling tubes, make sure to pull an appropriate matched pair.
- When a pair of tubes is pulled out, the impedances of the speaker outputs as written on the back of the amp change (internally). What was originally labeled an 8 ohm jack on the amp has now become a 16 ohm jack – a 4 ohm jack has become an 8. SO… if you have one 8 ohm cabinet and you pull two tubes, you now need to plug your 8 ohm cab into one of the 4 ohm jacks on the back of the amp. Make sense? VERY IMPORTANT!!!

If you don’t understand the above, its very important to make sure you do before you ‘experiment’. The sounds one can get by lowering the wattage this way is VERY cool and it’s worth trying. However, the damage you can cause to tubes and/transformers if this isn’t performed properly can be very unpleasant. If you’re not sure, call Mesa customer service to walk you through the process until you do understand it. We encourage people to experiment with this setup because the sounds generated by lower wattages is a part of rock n roll history that is well worth exploring in electric guitar.

Hope this helps and let us know how it goes!




Dave June 17, 2011 at 1:44 pm

Hello, someone is selling a Mark IV head locally, and I can see from the pictures that all four power tubes are EL-34s. Everything I’ve read shows that only the outer pair are intended to be swapped with EL-34. Would this cause troubles if it has been used like this for a while? Are there mods people do to support this that I should ask about before considering purchasing?


Boogie Boogie June 18, 2011 at 9:03 am

Hi Dave –

In a Mark IV, EL-34s are best used in the outer sockets only. If the amp has 34s across all 4 sockets, this will not harm the amp but the inner 2 tubes will be running cold and not necessarily improving the tone or providing EL-34 character. Hope this helps.



Derrick April 24, 2011 at 11:54 am

Awesome stuff to read up on I’ve been playin for a while now on tube amps mostly boogie’s and it helped to understand tube amp lingo like clipping,saturation,ect one thing it didn’t cover is scooping mids I here this term alot and don’t have a clue what this means but anyway cool stuff I got a lot out of it!


panos April 13, 2011 at 11:01 am

hello i am a happy owner of a mark v…i d like to change the stock tubes by el34/84…certainly i ll go for mesas tubes but which ones? green ones?yellow ones??which color is compatible so i can do no harm to my amp?do i need to to biasing or its all ok if a turn the bias switch to el34?

thanks guys!!!!


Boogie Boogie April 13, 2011 at 2:03 pm

Hello –

Regarding changing tubes in a Mark V, only 6L6 or EL-34 are an option. EL-84s have a different base and pin style and are NOT compatible with the power tubes sockets of a Mark V.

Regarding the tubes themselves, if you are using Mesa tubes, there is no biasing needed. All Mesa amps, unless otherwise modified, (which we DON’T do) have a fixed bias. The tubes we sell are ALL tested to work perfectly within the range of the fixed bias of all the amps we make. The color codes are used to closely match tubes in pairs and quartets. The color codes DO NOTsuggest that there are different tones to be had from different color codes – we are not offering tubes that provide different tones. We want the amps to sound the same as when you bought them when you go to maintain and change the tubes.

As for changing the tubes from 6L6 (stock) to EL-34, if you are using Mesa EL-34 tubes, remove the 6L6s, flip the bias switch to EL-34, install the EL-34s and power the amp on and you are ready to enjoy the amp with EL-34s.

Hope this helps and glad you are enjoying the amp!



Carlos Rocha February 1, 2011 at 11:56 am


I’m Carlos from São Paulo, Brazil! I got a Mesa Boogie EXPRESS 50:5 2×12 and I’d like to get some informations about this amp. Could I change the tubes 6L6 for EL34 with FIXED BIAS in 50:5, for sound tests? What I need to do to change the tubes of this model amplifier?
In Brazil we don’t have MESA BOOGIE technical assistance , what can I do to replace these tubes or parts ?

Thank you!


Boogie Boogie February 1, 2011 at 2:22 pm

Hi Carlos – Congrats on the Express 5:50! Hope you’re enjoying it.

The Express series does not have a Switchable Bias like other Boogie amps. Without a Switchable Bias option, you are not able to install EL-34s. Your amp is designed to use 6L6s ONLY.

There is a new distributor in Brazil who CAN provide you with technical assistance as well as sales. You can find their information here:


Hope this helps and enjoy the amp!


Boogie Boogie April 13, 2011 at 2:09 pm

Hi Carlos –

Congratulations on your Express 50 – hope you are enjoying it!

It is not possible to run the Express 50 with EL-34s. The amp does NOT have a bias switch like other Mesa amplifiers. It is specifically designed to operate ONLY with 6L6 power tubes.

You DO have a distributor in Brazil for parts and assistance. Please look up the distributor at this link:





Greg K. January 10, 2011 at 4:56 am

I’m a proud owner of a great Roadster 2×12 combo. Even though I have it for almost two years it shows me something new every time I turn it on. It’s great to have such a variety of tones ready at hand. I’m interested in the technical background also. I was just thinking on the gain structure and the potmeters’ interaction when I found this article. So staying with the Roadster I have some possibilities to change the volume and saturation. I have the gain and the master per channel, and I have the FX send level and the output – if the FX loop is enabled. If the loop is off then the gain feeds the preamp and the master feeds the power amp I guess. Quite straightforward. But what if the loop is on? The manual says that the FX send level pot takes it’s signal off of the preamp. Are the FX send level and the output pots just attenuators or they control some gain also? So should I max out the FX send level to get all the signal come through this junction or sould I leave it on normal? Can I make the power tubes saturate on a reasonable level? I mean I can never turn it up louder than 12 o’clock because it would blew me off of the stage even on 50 watts. I think these questions should be worth thinking on… And if you guys could give me some hints… Nevertheless Roadster is a great amp and it’s a pleasure to play with it! Rock on, Mesa!
ps.: Do us a favor and include a tube layout and task chart in the next version of the Roadster manual!


Boogie Boogie January 20, 2011 at 4:07 pm

Hey Greg –

Thanks for the kind words and glad to hear you’re getting the ‘something new everytime I turn it on’ experience. That’s one of the many things Mesa’s are all about…

Great question about Loop and FX Send and Output controls – very important stuff. Because the FX return is tube buffered, where the send level is set can have a significant effect on tone and gain. The Send level is there to provide the needed signal from the send to interface with the WIDE range of input sensitivities on different FX devices. Generally, you’ll want the send set nearer to 12:00 (labeled Normal on the amp). You may need to turn it up or down a little bit from normal depending on the FX in use.

If you turn the send up more than say 2:00-3:00 – or – all the way up, you will be increasing gain and volume at the return stage of the amp. This can and often does (when turned up too high) cause microphonic or other problems and is not recommended – hence the ‘normal’ label on the Send Level. There may be cases where it’s usable and you are technically increasing preamp saturation here, but this approach is generally not recommended. Just because the control goes there doesn’t mean it will be useful, usable or sound good… ;)

As for power section saturation, settings of 50 watts and Vacuum Tube Rectifiers is far more likely to give you the tube saturation you’re after than the FX approach.

Hope this helps and thanks again for the kind words. Rock on…



Boba January 6, 2011 at 12:26 pm


Please help me.
I like the tone of the old MESA STR420 tubes.
But I can not buy them anywhere.
Which type of tubes are exactly same tone wise to the STR420?
Can I use them in my Roadking?
I would use original MESA tubes, but I find only STR440 and STR425 now.

Thank you.

Best regards.


Boogie Boogie January 18, 2011 at 1:30 pm

Hi Boba –

Mesa no longer uses or sells the STR 420 6L6 but the STR 440 is the equivalent to the 420 and is definitely recommended at this point to be used in Mesa’s. 440s will provide a more full sound overall and are also a more reliable tube at this point. You may be able to find the same tube (now a “new old stock” since they are no longer made as far as we know) but they won’t be Mesa tested.

Hope this helps.



Oscar Soto December 9, 2010 at 7:24 pm

Hey there!…Speaking of tubes I’ve got a question for you…I own a Dual Recto since about 1 1/2 years and couldn’t be happier with other amp. It is the first tube amp I’ve had so I try to constantly learn all sort of tube amp related stuff such as the differences, manteinance, etc. Lately I’ve noticed the sound of my amp is a bit muddier, I’ve read is a sign that power tubes must be replaced soon. The thing is, since I’m not the first owner of the amp I’m planning to replace all power, rectifier and preamp tubes, but I still doubt to do it because in the Recto manual is stated that “Pre-amp tubes don’t normally wear out as a rule. Therefore, it is not a good idea to change them just for the sake of changing them. If there isn’t a problem – don’t fix it.”. So the question is ¿Am I suppossed to experience some sort of trouble if I replace all the preamp tubes at the same time?

Greetings, keep rocking!



Boogie December 10, 2010 at 1:57 am

Hi Oscar –

Since you didn’t buy the amp new and everything is working well for the most part, in this case, changing all the tubes so you can record the reference of when the tubes have been changed and other good maintenance practices (some mentioned in this blog post here).

The one thing you might want to do to avoid any problems with high gain and microphonics is to buy an SPAX7 for the V1/Input stage of the preamp to insure you get a stable tube in this important position. Other than that, its fine to change tubes in this case. Mesa suggests you don;t change all the preamp tubes at once if you are trying to troubleshoot a specific problem because rarely is any tube rerlated problem more than 1 bad tube. It doesn’t make sense to change out all the tubes when only one is bad.

Hope this helps and glad you’re enjoying your amp.



Oscar Soto December 10, 2010 at 10:14 pm

Thanks for answering my question! I’ll keep that in mind!…Greetings from Mexico!



Chase November 23, 2010 at 5:04 pm

Didn’t Metallica use the Dual Recto’s on the Self Titled “Black Album”?
I could swear i seen a video of them in the studio using rectos with black diamond plate…hmmm


Rob Gnarley July 10, 2013 at 2:02 am

I believe between “And Justice For All” and the Black album, They used JMP’s and/or JCM’s. After that, they went haywire with experimenting. Their earlier sound, I’m pretty sure was the product of Mesa’s Mark 2 C+. Amazing circuit. Amazing sound.


TODD H November 10, 2010 at 6:41 pm

I’ve owned several dual rec’s, currently gigging with a 3ch dual rec circa 2001 (i think). every year I retube the whole amp rec tubes, power tubes and preamp tubes, and I’ve always stuck with 6l6′s. I play some heavy, heavy thrash metal-hi gain stuff. I always thought that my tone was a little bottom heavy and fizzy, even with the bass dialed down and treble rolled back a lil’. I tried using EVERY kind of distortion pedal to “tighten” the bottom -ts808′s, ts9′s, etc…. nothing was pleasing to my ear. Tried all kinds of different pickups in my guitars….still no luck. Last week i blew a tube (due to a flying object at a rowdy practice), and the local music store (that I work at) was out of 6l6′s only had mesa 34′s (the green coded). I’m BLOWN AWAY by the difference with the 34′s! so much more definition, both in leads and the chunky powerchord stuff. I can “FEEL” the difference in my playing. No more fizz, even at my hi gain settings! I’m sold on the 34′s in my dual rec, and I testify to the difference, at least for metal/thrash styles of playing.
Now my question–since im using 34′s now, i switched to the “tube rectifier” setting, as recommended on the back of the head. I have always used the “silicon diode” setting in the past. How often should I expect to be changing rectifier tubes, with use 3 hrs a day 3-4 days a week?


Boogie November 10, 2010 at 7:08 pm

Hey Todd –
Thanks for sharing the experience. Also… great question!

First – using the tube Rectifier with EL-34s is a suggestion, not a requirement. However, using tube Rectifier with EL-34s will increase the tube life of the 34s by a few months or so here and there.

The Rectifier tubes are not likely to wear out much faster using 34s or 6L6s and they tend to last easily twice as long as the power tubes. We recommend people consdier changing Rectifier tubes every other time you retube your power section and many Rectifier tubes have been know to last even longer.

Hope that helps and keep the rock on!


Chase October 22, 2010 at 10:15 am

I have owned a TRI-RECTO, and it had the 6l6 tubes. The other guitarist used the Peavey JSX head with ’34s…I have to say mine beat his in the single note and double picking. But of course, the Mesa was so much “darker” sounding than the JSX.


Boogie October 25, 2010 at 3:09 pm

Hey Chase – Thanks for the comment.

Brightness is nearly always in the hands of the person that sets the Treble and Presence controls and the Recto would be no exception. If you’re after some serious slashing high end cut and bite, the Recto can do that as well as being warmer, darker and smoother. We tend to start at where we think the middle ground is and leave enough room for personal taste on both sides of the fence.

Just glad the Recto still took out the JSX. ;)

Keep rockin’…


yourpalfranc September 18, 2010 at 7:04 am

I definitely qualify in the “tube new-b” category! I have a used F-50, that has some static when it’s been on for a long period. I’d like to replace the GT6L6′s that came installed since I have no idea how old they are, anyway. All my pals insist that I need to take it to a shop for bias-ing, but does the fixed bias feature mean I can DiY? Also, I assume the GT6L6 probably wasn’t original equipment?? Thanks, in advance, and I appreciate the education!


Boogie September 20, 2010 at 12:07 am

Hey Franc –

Great question!

All Mesa amps benefit from a factory FIXED BIAS which allows the user (even a tube NEW-B!) to change tubes themselves without need for re-biasing, shops, technicians etc. Proper and reliable operation is guaranteed when using Mesa tubes as our tubes are tested specifically to work within the range of the fixed bias of the amp. Competitively priced with a 6 month warranty (one of the best in the business) as well as insuring the original tone the amp was designed to deliver are all benefits of using Mesa tubes when troubleshooting and retubing.

6L6s were the original tube of choice for the F50 but the GT6L6 indicates another brand of 6L6 in use. Unless you see a Mesa logo on the tube, it’s not original issue.

Hope this helps.



Dwight September 14, 2010 at 2:07 pm

I had a power amp with KT88′s back in the day before getting my Mesa gear. Where do they fit into the picture and will Mesa experiment with these in the future?


Boogie September 14, 2010 at 5:16 pm

Hey Dwight –
Not sure whether Mesa will dabble in KT-88s or not as they are slightly less than standard these days (compared to 6L6 & EL-34) and not as readily available. Beyond tone and reliability, these kinds of things are important considerations for Boogie in the concept and design stages. Never say never, but for the moment, not something to be expected from Mesa in the near future.

That said, its a fine tube although not freely interchangeable with either 6L6s or EL-34s, at least not in Mesa amps.


Russ D September 15, 2010 at 11:29 am

I dunno, there has been kind of a glut of KT type tubes lately. Sino, Russo an Yugo varieties abound. There are some bulked up KT types such as the KT90 and KT100. I even know some folks that run KT88′s in their Bass 400 amps. Though I understand the Mesa line of sticking to tubes that can be reliably sourced in the long term. Who knows if new sensor will still offer KT types 5 years from now?


Russ D September 8, 2010 at 12:48 pm

EL34′s have a higher watt output capability than 6L6′s right?
I know that a certain Canadian bass amp could get 90 watts from a pair of EL34′s.
I would think a 6 or 8 EL34 bass amp would be awesome!


Boogie September 8, 2010 at 1:49 pm

Hey Russ –
Not in our experience. It all varies on a number of aspects beyond just the tubes but as a general rule, EL-34s tend to put out about 40 watts as a standard where 6L6s tend to put out 50 watts in most cases.

Not aware of the bass amp you speak of but must admit that 90 watts from a pair of EL-34s sounds lofty. However, lots of things in amplification are possible given different approaches in electronics. Could be, I guess…

I can say with some certainty that Mesa will not be pursuing an EL-34 based bass amp anytime soon but I will say that bass played through EL-34 guitar amps and sometimes guitar cabs (using appropriate caution for amp and speakers, of course) is a secret weapon for quite a few in recording tight, punchy bass tone and/or for bass gain sounds. ElectraDyne or Stiletto for bass, anyone? ;)


Russ D September 8, 2010 at 4:23 pm

The amp I’m talking about is the Traynor YBA1a “Bassmaster MKII”
90 watts from two EL34. I understand at the time tehy were issued with Mullards or some other such “good” EL34′s. IIRC EL34′s were designed to be capable of a much higher dissapation then they are usually put in service with.
But hey, whatever kinda power tubes you guys wanna give us in an all tube bass head I am all for it. Just please no compressors, exciters etc!
Just tube to shining tube with amber waves of gain. (feel free to quote).


Joe September 5, 2010 at 1:02 pm

In regarding the article on 6L6 vs. EL34′s….since the EL’s run hotter, is there a tendency for them to need to be replaced sooner than 6L6′s, given the same amount and type of playing? Also is there more of a risk of a EL harming the amp if a tube fails compared to a 6L6? Finally,how does the circuity of a mark iV know which tube is in use since there is no EL34, 6L6 switch? Thanks


Boogie September 8, 2010 at 1:42 pm

Hey Joe – Great question and answered somewhat below in a few of the replies. Specific to the Mark IV and like the Mark III, the outer sockets of the Mark IV are the Class A sockets which are biased to ride the middle ground between 6l^ and EL-34 bias. So – he sockets/amp aren’t sensing anything, you’re just getting the option based on differences being split.

That said (and as discussed in more detail below), EL-34s may have a slightly higher rate of failure but in the last decade have been much improved. If the tone really suits you, just keep spares on hand and be prepared with some tube troubleshooting skills and some EL-34 tubes will last just as long or longer in the right conditions, care and use. Rock on!


Joe September 9, 2010 at 5:35 am

Hey..thanks for the reply..I really love the EL34′s in my mark IV. Great to get that insight. Keep these articles coming. I eat this stuff up! I crave to have a deeper understanding of these great amps.


richard schiller September 5, 2010 at 9:37 am

Just put in a quad of matched Electro Harmonix EL34s in my Tremoverb. A monster was born. So much power now directed to these small grinders. With an MXR Eq I can get most of my 6L6 sounds too by dialing in the sub bass and its surrounding harmonics. I can create every sonic tone possible with just a few pedals. No distortion pedals….this is the real thing. I also use a home theatre stereo EL84 amp. (The El34s smaller tube cousin). This is how music was intended to sound. Natural warm BIG and real.


Boogie September 8, 2010 at 1:37 pm

Nice use of the EQ, Richard. Depending on the quality of the EQ, lots of great variation can be achieved although some people just don’t like EQ! ;) It works though… Thanks for the suggestion and great comment!


Eric Kroon September 3, 2010 at 1:32 pm

How explain you the different sound in the mark III combo? These combo used 6L6 and EL34 tubes at the same time and you can switch between 60/100 watts (only EL34 or 6L6 and EL34 at the same time ). Regards Eric


Boogie September 8, 2010 at 1:35 pm

Hi Eric – See the reply to John below explaining the different sockets on a Mark III Simul-Class amp and how that works. Please note that ONLY Simul-Class amps are capable of this option – 60/100 watt amps are not Simul-Class amps and do not offer the same function.

The sonic differences between the tubes are the same regardless of what amp you plug them into. You can compare the sonic differences yourself by setting your switch to Class A on a Simul-Class Mark III and then switch the tube pairs from inner and outer sockets. Make sure to power the amp down when you go to replace the tubes and use caution with hot tubes (use a towel or something to protect fingers) and compare away.


Pete September 3, 2010 at 10:14 am

Mesa Boogie amps are..well…simply put:The best f*%#**g amps on the planet!(pardon my french but its appropriate to use such grammer when one really needs to express his/her feelings on a matter of such passion).
I have been playing thru a lonestar 2 x 12 (50/100 watt version) for the past 5 or 6 years now(Played thru a Mesa Tremoverb head and 2 x 12 Mesa Cab for 8 years before that).
My Lonestar is truley a workhorse, it shows up to the gig’s on time,plays its ass off for 4 hours and never complains.It is the most reliable amp I have ever owned.I keep it on channel 2 with the drive off which gives me this absolutley thick,round,fat,warm clean sound that has been known to make one drool.I use a few overdrive pedals in front for some dirt/crunch when needed—the Lonestar is extremely pedal friendly! I have received several comments on my tone(which as a guitarist just makes your night when it happens!)and knowing how dependable my Lonestar is actually makes me a better player.I also love the e-newsletter and reall liked the article about the differance between 6l6′s/EL 34′s.You guys have taught me a lot—Keep up the Great work that you do,your hard work and creativety are very much appreciated by the music community.
P.S. I also Love the fact that I can replace a tube and not have to Bias it!Very cool feature for working musicians!!


Boogie September 8, 2010 at 1:23 pm

Hey Pete – we appreciate the passion – it’s what makes the music so bring it on… Glad the Lone Star is serving well and the pedal friendly comment is a great one.

It’s true, some amps are better than others for pedals and if you dig pedals, for different gain sounds especially, the Lone Star is hard to beat! And, it’s a killer candidate for EL-34s and certain styles.

Also cool that you realize the number one advantage behind the fixed bias -it’s what we like to call tube-newb maintenance ready!
Thanks for dropping by and getting something out of the newsletter… there’s more where that came from. Rock on.


Russ D September 3, 2010 at 8:02 am

Awesome to hear these words on tubes. I do wish there had been some mention of the 6550 as it compares ot the 6L6. I tend to favor the 6550 in my bass amps. Speaking of;
I love my Mesa Boogie Bass 400 but its been almost 20 years now and its getting pretty long in the tooth. I would be first in line for a Mesa all tube bass head that incorporate gainier tones of your hybrid heads like teh big block (or the D180!).


Boogie September 8, 2010 at 1:20 pm

Russ – couldn’t agree more… There will be all-tube bass, that I can say. My order will be right after yours! ;)
Since we’ve had no 6550 tubes in use for decades, its not something that fits well into this discussion but it is a mighty tube and we hope to see it back in the fold someday soon.


Mars Passenger September 3, 2010 at 5:45 am

Mesa, Thanks for the news letter and especially for this writeup on tubes. In addition to the best tone ever, writeups like these keep me wanting more Mesa Amps. I purchased a Lone Star Special after reading the “Class A, Exposed and Explained” technical wrap by Randall Smith. I have received so many compliments on the tone of the Lone Star Special; its as if there is something magical about this amp that compels people to fall in love with its sound. Only Mesa delivers this. Thanks and keep it up!


Boogie September 8, 2010 at 1:18 pm

Hey Mars – Amazing! Thanks for the compliments and thanks for hearing the magic in the Special… Lots of players here agree about the Special and that thing is tough to beat, especially with a 4×10 cab (or the combo…). Glad you dig the write-ups – more on the way… All the best!


John Arevalo September 2, 2010 at 11:55 pm

I bought my MK III Simul Sync combo in ’87. It came with two EL34s and two 6L6s. I was 100% pleased with it but at the time there was a shortage of good tubes available, especially EL34s. In fact, I was told by Mesa to substitute 5881′s in all power tube sockets. This worked really well because not only was there a good supply, but they tended to be slightly “softer” and sounded great at lower volumes. Eventually I added a Simul Satellite. I soon discovered that it sounded louder than my MKIII. It had all 6L6s. I looked into it and found out that 6L6s were also ok in all power tube sockets. I eventually switched to 6L6s in the MKIII and now I’m extremely pleased with my tone.
This article stipulated that EL34s need a seemingly vastly different bias setting than the 6L6s, yet my amp works fine with either type. My bias in permanently set and can’t be adjusted. Can someone explain this to me?


Boogie September 8, 2010 at 1:14 pm

Hi John – Another good question and great insights.
The short answer is that EL-34s can be plugged into 6L6 biased sockets and will, in most cases, produce sound – although likely not great tone as the EL-34 in a 6L6 socket is not properly biased and is running on the ‘cold’ side at that point.
Simul-Class amps like your Mark III (and any Simul-Class amp) present two separate operating classes in each pair of sockets and ultimately, two different sets of operating voltages for each pair. A very simplistic way of describing an in-depth electronic and vacuum tube process is that the Class A sockets of a Simul amp employ higher operating voltages which run EL-34s closer to their suggested requirements (but still ‘cool’). 6L6s in those same sockets will run slightly ‘hotter’ than their normal suggested bias and voltages, but still within reliable operation. The operating voltages of the Class A sockets in a Simul-Class amp straddle the optimum voltages required for 6L6s and EL-34s.

It’s important to know that Class A/B operation takes place on the inner two tubes of most Simul-Class amps and Class A operation takes place on the outer pair of sockets and this is where you have the choice of 6L6s or EL-34s in these sockets. Hope this helps and great question!


John Arevalo January 5, 2011 at 8:21 pm

Here’s a few more questions regarding Simul-Class amps: Can you tell us what exactly is happening with a Simul Class circuit? Does it have to have EL34s to BE a Simul Class circuit? And finally, do you recommend rotating the inner and outer tubes for extending their service lives? (assuming you’re using all 6L6s, of course)


Boogie Boogie January 20, 2011 at 4:14 pm

Hi John –

Great questions. Simul-Class is the simultaneous operation of Class A/B and Class A power running together in a power section. The output of the two Classes is blended at the Output transformer and doing so gives you the best of both classes of operation in one sound.

One does not have to use EL-34s – they are merely optional and available to use depending on peoples preference.

If using 6L6s across the board, it’s not a bad idea to consider Class A/Class A/B rotation of the tubes in the amp every three or 6 months to keep even wear on everything, BUT – this is also not necessary.

Hope this helps.



Haywire_Harry September 2, 2010 at 10:56 pm

Good read..


Rich M. September 2, 2010 at 8:47 pm

Thanks for this article. Very informative, and nice to see you guys address the tube issues.
However, one thing you left out of the article was tube reliability issues.
Yes, you talk about adjustable bias switching, but not about tube reliability.
I think it is well known, from anyone who has read one of your amp manuals, and from this article, that Mesa prefers 6L6′s, for tone, as well as reliability over EL34′s.
I have been discovering over the last year or two that I seem to prefer the EL34 tone to 6L6 tone for the heavy stuff I play, because I like a very tight rhythm that cuts through the mix with ease, and the guitar being a midrange instrument gets help cutting through the mix with the upper midrange boost of EL34′s. I feel 6L6′s are a little loose for my tastes, and sometimes scooped in the midrange.
I tend to run all my Rectifier amps with a set of JJ-EL34L’s, as those are nice and tight and have a big bottom end as well.
However, I just recently had an issue with some EL34′s in my Mark V that has been making me concerned about tube reliability using EL34′s.
I bought 2 sets of the very expensive Mesa STR-450′s to use in my Stiletto Deuce II (which really helped that amp out amazingly!), but then sold it and bought a Mark V (kept the tubes). I popped the STR-450′s into the Mark V, and yes, I did make sure to switch the switch on the bias select to EL34…and a very short time later, with mild volumes (under 10oclock) i thought something sounded funny and took a look in the back to see one of the tubes glowing too bright. I switched off the amp, and re-arranged the tubes, thinking it was only a temporary issue, and then when i turned on the amp, it blew the fuse and I had to have the amp repaired for an issue.
Once repaired, I took out the stock 6L6′s again and then wanted to try some Winged C’s, and I had the same issue with those tubes as well. I dialed in the John Petrucci settings on his website, where the volume is around 10:30, and played for about 30 seconds, the sound cut out, and a tube was blown.
I immediately switched back to the 6L6′s again, and have not had an issue since. At any volume.
However, this EL34 reliability issue has now got me worried about using EL34′s again, since I have now spent almost $300 for tubes just to fail very quickly.
I’ve not heard many other people having issues like this, but I have heard of other amp makers talking about reliability of EL34′s as well, and they always seem to pick a preference of a specific tube over others due to these issues.

Just something that seems left out of the article.



Boogie September 8, 2010 at 12:46 pm

Hey Rich – Great stuff – thanks for the thoughtful reply and kind words.

Deep subject and worth further discussion – and perhaps a future Blog post. Here’s a few thoughts…
EL-34s, because they run ‘hotter’ and at higher voltages, do suffer from slightly less reliability than 6L6s. This is one small reason why Mesa has leaned toward 6L6s for most of our production for many years although it’s fair to say EL-34 reliability has improved somewhat in the last decade, hence Mesa’s Stiletto designs and expanded Switchable Bias amps. However, all our circuits, including those with Switchable Bias features, employ a few reliability secrets to bring EL-34s ‘up to speed’ reliability-wise.

Your experience with multiple failures may be just coincidental although understandable how you would be shaken by it. There are additional considerations/research/awareness that need to be considered when using non-Mesa tubes in Mesa amps. It’s imprtant to insure that you have tubes matched to work within the range of the fixed bias of the amp (and keeping in mind that Mesa warranties are voided with NON-Mesa tubes in use).

Premature failure of tubes (regardless of testing/matching) is why companies that sell tubes offer warranties on them. Unfortunately, tubes cannot be tested for their longevity or reliability and while Mesa’s advanced Robo-Tube testing system does offer some predictive testing in it’s through process, we also offer one of the best warranties in the business at 6 months for just these reasons.

All that said, reliable tube operation is somewhat uncontrollable but attention to amp operation, especially when first installing or making changes is very important. Paying close attention in the early days of new tubes (or changes) for any crackling noises, volume drops, dips or peaks or any other odd tonal or sound developments is very important. f possible, the user should do exactly what you did – jump to the back of the amp to look at the tubes while you reach for the standby and off switch and shut the amp down. Doing so will likely help you identify the bad tube before cutting off the voltage where further damage may be done and allow you to remove the bad tube straight away and engage in more advanced troubleshooting from there.

Thanks for the suggestion here, Rich. Good point and should you need any help with the troubleshooting stuff with tube failures etc, give the customer service department a call and we’ll be glad to help. Rock on…


David Allen September 2, 2010 at 6:00 pm

Awesome article fellas.. Just want to say that I have been putting my Mark V clean tone (6L6) against the fender twin reverb (6L6) in a back to back challenge. Both sing quite responsively. Bells, whistles… the whole gamut. I play Jazz/Blues fusion.. Clean.. Clean… Clean…. I will have to say I keep going back to the Boogie. Both sound awesome.. Awesome… However, (With my Gibson 335 and standard Les Paul) the Mark V just sounds a tad better than the Fender twin (single coil machine).. In my opinion… Rock on Mesa Boogie…. Rock on…
I would love to switch out the 6L6 tubes with the el 34′s on the Mark V to check out the metal I could produce.. However, I just love the clean way too much……


Boogie September 8, 2010 at 12:11 pm

Hi David – Thanks for the kind words and glad you’re finding the clean channel in the amp as versatile and vintage-capable as we hoped. The options between the three modes in Ch 1 are staggering and I bet it sounds amazing with the 335!
The 34s do some cool stuff for the clean as well but the definitely do ‘their thing’ when pushed. Rock on indeed!


Felix Uitz August 13, 2010 at 3:16 pm

Hey Boogie guys!
Please keep up with stories like this one.
This is just so amazing!

One question – well in all of your manuals the master volume is nearly always around 10 o clock. Is it possible to reach a nice amount of tube saturation??

Best regards


Boogie August 16, 2010 at 11:31 am

Thanks, Felix. Glad you enjoyed it.

10 o’clock on the Master and Output settings is a common setting in our manuals because we tend to use similar potentiometer values in most of our circuits in Master and Ouput controls and this setting tends to be where the amps begin their range of usable live volumes.

However, where the threshold of clip and distortion starts on either the Output or Master really depends on many other factors like which amp, settings, your guitar, your playing style and, of course tube types… just to name a few.
It’s hard to answer your question other than to say that 10 o’clock is probably where power tube and power section saturation has the opportunity to begin influencing your overall sound.

The best way to explore the concept of power section distortion (and where it really, obviously starts to happen on your Boogie amp) is to turn it up step back, close your eyes and rock out. Hope this helps!


Felix Uitz August 17, 2010 at 1:01 pm

Hey thanks for the answer- i think you are right thats probably the best way!! :-)
Just for an example – let’s take the factory setting WORKHORSE of the MARK V – Is there already a powersection distortion involved ?

I am asking because of the moderate settings of ch. volume and master and the 90w mode .

…and a other question when i am slowly increasing the master volume knob there is a significant volume jump (or step) between 9:30 and 10 o clock. Is this because the master knob is ment to be set past 10 o clock?

Best regards …. take care



Jason DeRo August 13, 2010 at 2:15 pm

Oh, tubes. I remember the 1st time I played on a tube amp. Actually was a Boogie. A 45 what Nomad 2×12 combo. EL84′s I believe were in it. I bought it from Guitar Center. Came from a Peavy 2×12 combo solid state. As well as a Fender solid state ultimate chorus. Looking back I still am amazed at the sound that 45 watt monster would throw. I gave the other guy in our band lessons on the side. He went and bought a marshall tsl half stack. Thats a tube, or valve as they call it, amp. He got his just a few weeks after mine. Our 1st gigg with these new tube amps left me a bit worried about reliability, and me having 45 watts to his 100 watts wondering if my Nomad could keep up. Everyone there including the sound guy I had never met showed much interest in my amp. I put a Boss EQ with an inverted v, mids pushed which gave my Nomad some extra bite or dirt(metalish tone) and chorus and delay. The other guitar guy in the band was a jellous type person so that really burned his butt. He was so sure his 4×12 marshall would drowned me out and to the contrare the masses were impressed by my Nomad. He didn’t last in the band much longer after that. I even offered to try to set his amp up. Seemed his playing went downhill from there. Guess that was a tube story…. Thanks


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