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PostPosted: Tue Sep 29, 2009 12:42 pm 
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Mark III

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I read that mesa amps are biased cold, is that why they can sound sterile with the mesa valves??


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PostPosted: Wed Nov 11, 2009 12:52 pm 
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The concept of "hot" and "cold" bias is amp tech voodoo. Tubes are biased primarily so that they stay pretty linear as they deliver the intended power to the speaker. There are a range of bias conditions that control this, including plate voltage and current. Usually the circuit is designed by drawing a load line on the tube characteristics listed in the datasheet, and finding a reasonable area in the curves. Biasing with high voltage and/or current dissipates more power than low voltage and/or current, and each affects both lifetime and linearity. There is usually a range of voltages and currents that give a decent combination of life, linearity and power. The bias can also affect crossover distortion, though this is often more a characteristic of tube and transformer tap matching.

The range of proper bias is usually not terribly large in the sense that you can detect it with an ammeter, but not with your eye. If you bias based on the color of the arc in the tube, you are way outside of the specified bias range of the tube.

If changing bias makes you like the sound better, go for it. But be aware that you may be trading tube life or amp life. Dissipating more power in the tube makes it die quicker, and more likely to supernova, taking some amp components with it.

A manufacturer who wants a reputation that includes reliable amp performance will be careful to bias tubes so that they are not pushed terribly hard, but still give the rated power output. If you don't like that, fine - change it. But don't get mad at the company, and be aware that you are almost always trading reliability for whatever you feel you get from rebiasing the amp.

There is no single "ideal" or "correct" bias point. It's all tradeoffs.

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PostPosted: Wed Sep 29, 2010 3:03 am 
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elvis wrote:
The concept of "hot" and "cold" bias is amp tech voodoo....
The range of proper bias is usually not terribly large in the sense that you can detect it with an ammeter, but not with your eye. If you bias based on the color of the arc in the tube, you are way outside of the specified bias range of the tube.
If changing bias makes you like the sound better, go for it. But be aware that you may be trading tube life or amp life. Dissipating more power in the tube makes it die quicker, and more likely to supernova, taking some amp components with it.
A manufacturer who wants a reputation that includes reliable amp performance will be careful to bias tubes so that they are not pushed terribly hard, but still give the rated power output. If you don't like that, fine - change it. But don't get mad at the company, and be aware that you are almost always trading reliability for whatever you feel you get from rebiasing the amp.


Hmm... You must work for Boogie tube marketing division... right??
A lot of the things you say make no sense... I'm just trying to get folks to the thruth and not picking on ya!!
Different tubes will draw different current from the same circuit at IDLE ( no guitar signal ) !!! By having a Bias pot you "adjust" the circuit so that the IDLE current drawn by the tube is within specs for a given tube. THATS IT! ITS SIMPLE.
Mr Smith says... "Ok i wont give you the option to change the circuit... but I will sell you tubes that I know will be in the proper operating range". Well thats kinda cool in its own way... but it also leads to folks believing in non-sense.


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PostPosted: Wed Sep 29, 2010 3:10 am 
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UKBoogieboy wrote:
I read that mesa amps are biased cold, is that why they can sound sterile with the mesa valves??


it would make sense that their fixed bias would be on the low (cold) side of the idle current draw range for given tube type. This would give them more "room" to certify the tubes they coming in. And also decrease the chance of plate glow should one ( god forbid ) throw in a set of JJs or some other brand.


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 Post subject: Re: Re:
PostPosted: Wed Sep 29, 2010 3:19 am 
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droptrd wrote:
I agree. It's all about the $$$$$$$$$$. Thats the American Way! But I have yet to get a set of JJ 83's that last longer than a month or two.


Disregard if you amp is Class A...

May be the JJs are drawing too much current in your amp and burning out.
Different tubes, even from the same manufacturer from different production cycles can have vastly different current draws. If you cant adjust the circuit ( bias ) how can you blame the tube???


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PostPosted: Tue Nov 16, 2010 4:56 pm 
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I have to say that I find the life of my JJ's has been more than satifactory . I have had a set in my Triaxis for 5 years and a set in my Mk111 for around 3 without any issues. I have also used them in my 290 prior to selling it, never have they sounded lifeless or dull either ????
So all I can really say about Boogie'sclaims are that I find them to be untrue.


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PostPosted: Tue Nov 16, 2010 5:18 pm 
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Well I'm happy to see the openness of the info!! I used to play a fender HR 212 and my tubes of choice were GT 6l6 in the power sec. and Rubies in the pre amp.... Nice to know I can do the same with my V....Thanks again for sharing that!!!! :D

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PostPosted: Wed Feb 02, 2011 5:58 pm 
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I used to own a peters dual channel amp. It had built in bias ports. I experimented with high and low bias settings. I never heard much of a difference between high or low bias settings until I got uber low. ymmv


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PostPosted: Thu Jun 16, 2011 10:35 am 
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all that said.......what are the EL34`s being put in the new RA-100?jeffp


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PostPosted: Sat Jun 18, 2011 8:53 am 
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Good info.

I use JJ KT77s in my recto and I'm much happier with them than with the stock tubes. I've gotten several years per quad so reliability isn't an issue and my tone stomps all over the stock recto tone TBH. :lol:

Even if the life expectancy wasn't up to par with Mesa's stock tubes, I'd gladly buy new tubes a little more often and enjoy great tone. My .02.

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PostPosted: Wed Nov 23, 2011 8:55 am 
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JJ's a ghreat tubes I ran two Lynch Box heads for 4 years with JJ EL34L 12AX7S in them... no issues what so ever. Do they sound the best... thats anyone's opinion... I like Mesa tubes and JJ Tubes but they sound different... I also like Groove Tubes but have to say I have not had much luck with them.

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PostPosted: Wed Sep 05, 2012 3:55 pm 
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Thanks for taking your time to ask and posting.

VR, Ron


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PostPosted: Tue Oct 16, 2012 8:19 am 
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I have only very good experience with JJ tubes. They really improved a lot over the last years. the 12AX7s are very linear "hifi" so maybe for some people they lack a bit character. The powertubes are strong and healthy and last quite long if they're biased right.
The problems start when you put strong tubes (which means they draw lots of current) in a fixed bias circuit like Mesa Boogie. Chances are good they bias on the hotter side, so they wear out faster.

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PostPosted: Fri Mar 08, 2013 5:19 pm 
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wow, here we are 7 years later......

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PostPosted: Fri Mar 29, 2013 2:29 am 
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For the mostpart, I've used primarily Mesa-branded tubes and have bad zero issues (not even a bad tube, preamp or Poweramp). I have used Winged Cs, Sovtek, EH, Rubys (obviously), and several others. Over the years, I have purchased all of my amps used but one, and they have always come loaded with the original Mesa-branded tubes. It's amazing to me that after 27 years, these tubes are still going strong!

As far as the preamp tubes go, most of my amps are running the "Russian II" 12AX7s, whole some positions of V1 and V4 are running the 12AT7s. There is a considerable amount of liveliness that comes from the Russian II 12AX7s as compared to the current Mesa-branded tubes. IIRC, the Russian IIs are rebranded EHs, right?

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