Mesa Boogie amps.

Mesa amps are fixed bias and generally they are very cold. The exceptions to this are the EL84 amps like the DC2 and DC3's and also the F30 and Loan Star Specials to name a few. You can actually get the bias up where it should be with warmer grade's of tubes.

The Dual and Triple rectifiers are set very cold in the 6L6 mode even when in the solid state rectifier mode and the bold setting. So even the hottest 6L6's on the planet will still not get the bias as high as it could safely be run. When in the EL34 mode the bias is quite warm with even a moderate grade of EL34's which is why Mesa will tell you that if you're going to use EL34's that you have to run them in the tube rectifier mode. The reason for this is because when the stock 5U4 rectifiers are switched in the plate voltage drops from about 475 on average to about 415 volts so in turn the bias goes down.

I quite often use the JJ GZ34's in place of the 5U4's to get a punchier and less mushy sound in the tube rec mode and the voltage drop is only about 10 volts down from the solid state diode mode. If the amp is played at high volumes with the GZ34's depending on your line voltage you may need to jump the fuse up from 4 amps to 5 amps which is what I do in my Dual Rec because no matter whether I'm running a combination of 6V6's and KT77's or KT66's and KT88's I'm always in the tube rec mode and usually in the Bold setting where the voltage is at it's highest.

The Dual and Triple Rec's are actually quite versatile with all of the combinations of tubes that can be run including the JJ 6V6's in the EL34 mode, 6L6's. EL34's, E34L's, KT77's, KT66's and KT88's. We also do Integrated quads with different combinations of power tubes like a pair of KT77's and a pair of 6V6's which is one of my favorites.

The Single Rec's that are switchable from 6L6 to EL34 mode can also use pairs of 6V6's, KT77's, KT66's and KT88's for a lot a tonal variations. The bias does not have to be modded and made adjustable if the proper grades of tubes are used. So if you order any of these tubes online from Eurotubes then make sure to leave us a note in the comments box on the checkout page to let us know what amp they are for so we can select the proper grade. Of course if you want ultimate control then a bias mod will allow you to dial any grade in.

The front ends of the Rectifier amps are quite happy with the ECC83S's and especially the high gain ECC83S's used in specific locations. The ECC803S and Gold pin versions of these tubes are also a great V1 tube if a fat thick clean is the mission.

I get lots of questions on the Mark series amps and mainly on the MK IV. The two inside sockets on these amps are biased VERY cold and need real hot tubes where the two outside sockets are biased much warmer to be able to use EL34's. We use a lot of hotter grades of E34L's and KT77's in the outside sockets on these amps along with very hot 6L6GC's or for the big box MK IV heads (not combo's!) where the tubes sockets are over 2 1/4" apart from center to center then you can run a pair of the JJ KT66's in the middle two sockets which is a great combination.

Here is a great option for you Mesa Dual Rec players! I have been wanting to get around to this for a while and with the help of my son Eddie who has become more involved with Eurotubes over the past couple of years we finally got to it!

This option is running the JJ 6V6's and GZ34's in the Dual Rec!

Click on the pics to enlarge.

The pics above show a quad of the JJ 6V6's running with two of the JJ GZ34's. These are running in the EL34 bias position and the Bold setting and in the tube rectifier mode utilizing the two GZ34's which gets the plate voltage to 450 volts and the current draw to 28mA per tube which is perfect! Using the solid state rectifier gets them a little too hot.

Using the GZ34's will get you that tube rectifier sound without the saggy feel that the stock 5U4 rectifier tubes give you so it's like playing in solid state bold but you get the rectifier tube dynamics.

The sound? Very cool! The JJ 6V6's have a very big low end that is tight and well defined. The mids and highs are thick, sweet and harmonically rich and at higher volumes they crunch up like only a 6V6 can do. To date this is the warmest clean tone I've heard from a Dual Rec.

So if you want to get a little more of that cranked up tone a bit earlier and want a great clean to go along with a very warm and punchy drive tone from you Dual or Triple Rec the JJ 6V6's and GZ34's may just be what your looking for!

As a side note the preamp tubes we used were three of the graded high gain ECC83S's in V1, V2 and V3 with a standard ECC83S in V4 and a high gain balanced ECC83S in V5. This is the most popular set of Mesa front end tubes that we do and they are available in the online store under the title "Mesa high gain front end".

Yet another option for Dual, Triple and Single Rec heads is the KT66! They have a big tight low end and a huge open mid and high end that crunches up at high volumes just like the original Genalex. These tubes draw a lot of natural plate current so the warmer grades get the cold fixed Mesa bias right up where it should be in the 6L6 mode. The pic below shows a quad of them running in the tube rectifier mode with a pair of JJ GZ34's and you can also run them in the solid state rectifier mode if you like or with the stock 5U4's.

The bases on these tubes are the same large metal base that is used on the KT88's but it's black in color. A very cool look! Because of the large diameter base the bear trap spring tube retainers will not fit around the base of these tubes so they can either be pushed down as shown in the pic or removed. If you want to use these in Mesa combo's you would need to remove the retainers and install spring style retainers if the amp is a gig amp and constantly moved around.

The smaller Mesa amps using EL84’s are also fixed bias but are not as cold so by using hotter tubes they sound real good and the JJ EL84’s are by far the best EL84 being made today. They rival most all of the classic EL84/6BQ5 tubes and sound great in the little Mesa’s.

Here is a shot of Kris Siewell's custom Loan Star Special. It's clad in African Ribbon Mahogany and has a flame Maple front. We just did tubes and an Alnico Silver Bell and Blue Dog for him and he loves the tone!

Here are a couple of Mesa 295's and a Strategy 400 that we also used the KT88's in. The EL34 sockets in the 295 run pretty hot so even the coolest KT88's I had were pulling 90mA which is too hot so we ran the JJ E34L's in the outboard sockets and the KT88's in the inboard sockets in place of the 6L6's where they pulled a very nice 45mA at 530 plate volts. This combination sounded fantastic! The lows were very deep and tight, the mids were thick and very harmonically rich. The highs were creamy without being at all brittle. Overall the amp was very punchy with a great dynamic.

The Strategy was a bit different because the EL34 sockets were not biased so hot and the amp sounded best with the JJ 6L6GC's and a quad of the JJ KT88's in place of the EL34's where they pulled exactly the same 45mA at 530 plate volts.

KT88's in a Dual Rectifier??

Yes! KT88's in a DR... This is one way to make a DR into "Frankin Rectifier" The bias on the DR's is set very cool for 6L6's and EL34's but the average KT88 draws about double the natural plate current of the average 6L6 so when you run KT88's in a DR with the amp in the EL34 rectifier mode the bias comes up to where it should be and the bottom end gets VERY deep and strong along with a punch that is truly enormous! 

May the amplifier Gods have mercy on your speakers!!

I would also like to dispel a couple myths that I've read lately on the Harmony Central forum about KT88's ( yes I do read the forum every once in a while when I have the time ). First off Dual Rec's are capable of using either 6L6's or EL34's and LOTS of you DR players out there are using the JJ E34L's in your amps and have been doing so for years. A standard 6L6 draws .9 amps of heater current where the JJ E34L draws 1.5 amps. A KT88 draws 1.6 amps so as you can see a quad of KT88's will only draw .4 amps more that a quad of E34L's and is not going to cause a problem. Hell I even use a quad of KT88's in my 1982 Evil Twin which means that it's having to deal with a 6.4 amp draw instead of a 3.6 amp draw from a quad of 6L6's and it's been running STRONG for almost four years now. My 5150ex has a total draw of 6.2 amps running two KT88's and two E34L's once again this amp was made for a quad of 6L6's with a total draw of 3.6 amps and yes, it's a MONTSER and gets played very hard and often now for over two years. The bottom line is that most of the amps out there that can run 6L6's can run E34L's or even KT88's if there is room and the bias is set properly.

Now about that pesky bias question. Dual Rec's are a unique amp because of the different settings available with the "spongy" and "bold" settings along "6L6" and "EL34" settings and the "solid state" and "rectifier" modes. Since a KT88 will draw almost twice the natural plate current that an average 6L6 draws your bias will go up! An average E34L will draw only about half the natural plate current that an average 6L6GC draws. When a DR customer calls me and is looking for an improvement in his clean tone and an improvement in dynamics I will often recommend using the JJ 6L6GC's in a cooler grade and running in the "EL34" mode which will get a DR to draw about 32 to 40mA per tube depending on whether it's run is SS, REC, Bold or Spongy. This gets the bias much closer to where it actually belongs when using a cooler grade of 6L6.

An amp that has anywhere from 450 to 500 plate volts can run a JJ KT88 at between 50mA and 90mA per tube. Here's a quick run down on the bias of moderate grade JJ KT88's in a DR.

These setting are in the "6L6" mode.

Rectifier mode in spongy setting = 16mA which is VERY cold so you can imagine how cold a 6L6 would be!

Rectifier mode in bold setting = 18mA which is still VERY cold.

Solid State mode in spongy setting = 28mA still cold.

Solid State mode in bold setting = 32mA still a little cool.

These setting are in the "EL34" mode.

Rectifier mode in spongy setting = 44mA which is actually just getting out of crossover distortion and sounds very good.

Rectifier mode in bold setting = 50mA nice an aggressive with great dynamics.

Solid State mode in spongy setting = 78mA now this is getting some heat in the tubes and the dynamics are spectacular.

Solid State mode in bold setting = 88mA this is getting up to about 80% of max dissipation and will shorten the tube life about 10 to 15% and the tone will start to "brown" but it's a lovely sound!

Now I do want touch on one more thing that is a big myth. Just because a JJ KT88 will actually dissipate 50 watts does NOT mean that because you use a quad in a DR you will have a 200 watt amp! It doesn't work that way. To get more power from an amp the plate voltage needs to increase and you can't do that unless you replace the transformers to supply a higher plate voltage ( please no questions... ) For instance my Twin when loaded with JJ 6L6GC's will make right at 90 watts before clipping and loaded with a quad of JJ KT88's it makes 98 watts before clipping which is not much and is basically perceived as a little more headroom. You have to double your wattage to gain 3db so if you calculate the difference the KT88's will breakup only a fraction of 1db louder than the 6L6's.  

Anyone reading this has my full permission to post it on HC or anywhere else.