Marcus has it completely backward in regard to his understanding of how the GT ratings work in Mesas. A #1 has the least amount of headroom. 4 to 7 is the range that falls within area that most manufacturers use because it offers the best blend of distortion and headroom. 8 to 10 have the most headroom, with 10 being the cleanest.
Fixed bias means the amp’s bias has been set at a fixed point at idle. This can be set hard with a fixed resistor (IE: Mesa; The early Diezel VH4) or a variable resistor (Almost everything else that is Class A/B).
You can install a bias pot in a Mesa Recto and adjust the bias. It’s still a fixed bias amp. The power tubes won’t behave any differently.
Myles Rose talked about that a lot around 2003 on HCAF.
stephen sawall":2k4beu73 said:
Currently I am using Groove Tube 6L6GE rated 4 in my Tremoverb, Mark IV and Heartbreaker. I also have some JJ rated 7 I like in the Tremoverb. They allow for more range with the Treble and Presence pots.
RED
"Headroom" available: Very High
Clipping: Low
YELLOW
"Headroom" available: High
Clipping: Low
GREEN
"Headroom" available: Medium High
Clipping: Medium
GREY
"Headroom" available: Medium High
Clipping: Medium
BLUE
"Headroom" available: Medium Low
Clipping: Medium High
Best Regards,
Marcus Daniel | Customer Service
Mesa/Boogie | MESA ENGINEERING
4 -Red
4.5 -Yellow
5 -Green
5.5 -Gray
6 -Blue
6.5 -White
With Groove Tubes basically, a #1 will distort sooner, and a #10 later.
THIS IS COMPLETELY OPPOSITE WHEN IT COMES TO MESA FIXED BIAS AMPS. In fact, GT distortion rating of 4 has MORE headroom than a 6 rating, not less. Again, this is only relevant for fixed bias amps, and has to do with the percentage of max plate dissipation a tube is pulling at idle.
This applies when the tubes are installed into a FIXED bias amp such as a Boogie. This means that the Groove Tubes will draw close to the same current at idle as the corresponding color codes of MESA tubes. The red color code idles cooler and is further from clip (breakup) , and the white color code idles hotter and is closer to clip (breakup). Reds = headroom , White = quicker distortion. 8) This is what Marcus was saying.
The early and late breakup that Groove Tubes is talking about is the tubes installed into an ADJUSTABLE bias amp with the tubes biased to the same current draw. That is, if you took a #5 tube and a #10 tube and biased them do both draw 70% mpd, that the #5 would distort sooner and the #10 would have more headroom.
"7 is about as high as you can go and even with a 7 in the output section I would check the bias." -Myles Rose
I usually use the 4 rating or cooler bias because I prefer more punch and more dynamic range.
The 7 rating is more compressed feel and dynamics.
It's really just subjective taste and the way I play....with a lot of dynamics.