rabies
Well-known member
enjoy.
class A or A/B in 45 watts?
- Thread starter rabies
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>Photi G<
Well-known member
Class A. That's the way it's always been in Simul-Class amps. The lower wattage is always Class A. Even in the Mark V, 90 is Simul, but 45 and 10 are in Class A.
ifailedshapes
Well-known member
>Photi G< said:
FAIL! :mrgreen:
45 watts is Class A/B
90 watts is Simul-Class
rabies
Well-known member
ifailedshapes said:
that's what i was hoping, as i'd be using 45 watts more often and prefer A/B.
survey says?
ifailedshapes
Well-known member
Survey says go to Mesa's website and read the products specs. It's in there. You could also download the manual. It's always better to go to the source than rely on what people on here think. 
This is what my manual says.
"In the 45 Watt setting (switch down) only the outer pair of 6L6s are on, and it’s these that run in the extended Class A with their bias reduced. Thus, they run a little hotter but also smoother, especially across the threshold into clip without sounding harsh."
What exactly is extended class A, I wonder?
"In the 45 Watt setting (switch down) only the outer pair of 6L6s are on, and it’s these that run in the extended Class A with their bias reduced. Thus, they run a little hotter but also smoother, especially across the threshold into clip without sounding harsh."
What exactly is extended class A, I wonder?
ifailedshapes
Well-known member
Weird! Here's what the website says:
"Choose 2 power tubes operating in time-honored Class A/B producing 45 Watts or 4 tubes running in Mesa’s legendary, Patented Simul-Class Power that blends the best of Class A and Class A/B simultaneously to produce 90 Watts of pure tonal magic."
"Choose 2 power tubes operating in time-honored Class A/B producing 45 Watts or 4 tubes running in Mesa’s legendary, Patented Simul-Class Power that blends the best of Class A and Class A/B simultaneously to produce 90 Watts of pure tonal magic."
rabies
Well-known member
which is why i ask here. i'll call them up tomorrow.
Extended class A is marketing speak for class AB. A pair of 6L6 tubes can not make make 45 watts in class A without going well over max ratings.
The tubes will be running in class A until perhaps 20 watts (give or take) is reached then the mode of operating starts getting in the B area.
The tubes will be running in class A until perhaps 20 watts (give or take) is reached then the mode of operating starts getting in the B area.
rabies
Well-known member
MrMarkIII said:I think you guys are reading the old version of the manual.
Here's the version I downloaded, Pages 3 & 4:
"So let’s quickly go through the power levels: The 90 WATTS position is the full Simul-Class mode with all four 6L6s combining the two different bias settings to deliver the maximum power and headroom. It is substantially sweeter and warmer and a little more scooped than a standard 100 Watt amp yet it has plenty of punch and authority without any harshness.
45 WATTS turns off the outer pair of 6L6s so only the middle two are running. These are the ones with the lowered bias so, while they are still Class AB, their Class A region is extended. In Channel 3, they can be switched to run in Triode configuration which cuts their clean headroom roughly in half.
Combining these two opposite styles of wiring in one amplifier gives you the best of vintage and modern amplifier styles. Headroom and power are there when you need it… but there is always a naturally pleasing and musically curvaceous quality to the sound that is magic to your ears and to your hands. Simul feels great and is inspiring to play!
10 WATTS reconfigures the whole set of 6L6s so that the two nearest the 5U4 run pure Class A, single-ended—no longer push-pull. This is the ultimate low wattage output circuit that duplicates the essence of the best really old vintage circuits. Here, the second harmonic (an octave above the note played) is NOT cancelled out (as it is in push-pull circuits) and provides a magical halo surrounding
the notes. Onset of clip is so gradual that it’s hard to pin down the transition from clean to overdriven."
Hope this helps
sorry but no. that is from the MK V manual obviously.
rabies
Well-known member
answer is here from mesa rep towards the end: class A/B in 45:
http://www.premierguitar.com/Video/20090205/535/Mesa_Boogie_Electra_Dyne_Amp_Demo.aspx
http://www.premierguitar.com/Video/20090205/535/Mesa_Boogie_Electra_Dyne_Amp_Demo.aspx
ifailedshapes
Well-known member
If you think about Mesa's latest offerings, they only market a product as Class A if the amp will run in true single-ended Class A, i.e. one tube. An amp that runs on two tubes minimum by definition cannot be "true" Class A.
rabies
Well-known member
I've never fully understood Class A and A/B even though I've owned both types. I can surely tell the difference in the sounds of both.ifailedshapes said:
Are you saying 4 power tubes need to be present for true class A? Sorry for my ignorance.
ifailedshapes said:
I'm not sure about your exact thoughts here, but a push pull 2 tube class A amp is a perfectly valid class A setup.
For those that want a bit more technical explanation about what class A and class AB is about, here is a very brief explanation. For a push pull amp (the ED is push pull) the output section must have two output devices (6L6 or EL43 for ED). In normal operation each tube takes a turn at turning on while the other tends towards off. If the tubes are biased quite hot, say a bit over 50% such that the "off" tube never completely turns off then that amp is running in class A. If the tubes are biased cooler, say 20% then one tube will be fully shut off a good deal of the time. That is class AB operation. The amp will be running in class A until the output power is increased to the point where one tube is shut off.
When one of the tubes is shut off it tends to upset things a little that can result in a less smooth or nastier sound. To my ears the sound is a bit grainier and there is a bit less clarity.
Extended class A as Mesa advertises really just means that the output tubes are biased hotter so that the output stage stays in class A mode to higher power levels.
J.J said:
Revising a slightly old thread here. I found the above explanation to be helpful and wondered if anyone had measured the bias on the tubes in the different power settings? How much hotter is the bias in the 45w setting than in the 90w setting? Yes I could do it myself but not while at work sitting at my computer.
