TheSoulsRemain said:
the tubes are sorted into "color groups" depending how "hot"/"cold"
Our tubes don't run hot or cold...They run RIGHT
:mrgreen:
You can't "run" your amp hot or cold with Mesa tubes.
The 3 letter codes :
Mesa/Boogie tubes have a three letter color code at the base of the tube used to group the tubes into matched pairs. These color codes do not apply to different tonal variation (the number and two letter codes with the color code are Production Batch #'s and Tester's initials respectively).
The only ways to BIAS correctly your amp are :
Buy only Mesa tubes matched for your amp.
Buy at a good shop tubes matched for your amp (ie : eurotubes.com)
Biasing your amp correctly by measuring the Bias.
Ok, I don't think you quite understand some of the bias terms here. I'd suggest you first read the bias adjustment white paper, published under "Articles" on the Mesa site. Next:
What Mesa is talking about here is tubes that run
too hot or
too cold. Often when talking about tubes in an amp that run too cold, for instance, you say "the tubes run cold". As in saying that they run cold in relative to the amp's current
bias range.
To get this straight: no company can make/sort production tubes that match every fixed amps bias PERFECTLY, SPOT ON. That's just not possible, and it is, from a marketing point of view, not profitable either, concidering it's not really
necessary: as even though the bias is fixed it has a certain tolerance range. Thus, desirable results can be achieved by narrowing the bias range of the tubes. Which is exactly what Mesa is doing. They have established a specific bias range for the tubes so that
every Mesa-rebranded tube will run "right" as they say it. In other words:
every Mesa tube will run well within a fixed-bias-amp's tolerance range. Now, if you read my first post on this matter, you'll see I've mentioned exactly that, thus only confirming their statement. Which is: they simply have a much narrower bias range (if you clicked on my link, you would possibly had noticed that) on their tubes that is well within what their amps' fixed bias setting can handle. So: they vary, but in a very narrow range. Got it?
Good. So in that narrow range, there is still variation, which was what I was saying in the sentence you quoted (e.g. one color code is a tiny bit hotter or cooler tube than another color code).
That's also why the color codes are used to match the tubes into pairs, as even though an amp with fixed bias can tolerate the whole Mesa-tube range, the push-pull circuit (read on this in Randall Smith's article: Class A: Exposed and Explained) is much more sensitive to bias variations, which is why the pairs must be within one color group.
Hope I'm making myself clear enough now!
If you're still in doubt, you're free to browse the Tubes-section on this forum, where several forumites have tested the color coded tubes to confirm the bias variations. I also have several emails from the guys at Mesa recommending specific color codes for my older Mark IIC+.
