Idle Plate Dissipation, Plate Current, & Mesa Color Code Chart project

[Mile High Effects]

I believe I’ve compiled a fairly accurate chart indicating approximate idle dissipation, idle current, and associated Mesa Color coding at ~475v Plate Voltage. This chart does not apply to Simul Class amplifiers, btw.

On my 90’s Dual Rec, I installed an external bias control to more-closely dial in the tone and response I like best; and which Mesa Color Code would reflect those numbers.

I believe the it was the designers intent of the idle plate dissipation to lie between Green & Gray although Mesa typically ships new amps and repairs with Red or Yellow coded tubes so they’ll run cooler and last a bit longer. White color coding was dropped, from running too hot for these amps, I presume?

This is taken at a plate voltage of about 475v with 124VAC coming from the wall with Silicon Diodes and Bold settings.

25w
EL34, 6CA7, KT77
6L6WGC, 6L6GCR, 5881WXT, 6Π3C-E
25% 13mA Red
30% 16mA Yellow
35% 19mA Green
40% 21mA Gray
45% 24mA Blue
50% 27mA White (dropped)

30w
6L6GC
25% 16mA Red
30% 19mA Yellow
35% 22mA Green
40% 25mA Gray
45% 28mA Blue
50% 32mA White (dropped)

Maybe @Boogiebabies and @electric mayhem can help me tweak this chart a bit if it’s a bit off? I’ve read some of the best info that was shared from their experience regarding dissipation/Mesa color coding on this forum. So thank you.

 

[electric mayhem]

I believe I’ve compiled a fairly accurate chart indicating approximate idle dissipation, idle current, and associated Mesa Color coding at ~475v Plate Voltage. This chart does not apply to Simul Class amplifiers, btw.

On my 90’s Dual Rec, I installed an external bias control to more-closely dial in the tone and response I like best; and which Mesa Color Code would reflect those numbers.

I believe the it was the designers intent of the idle plate dissipation to lie between Green & Gray although Mesa typically ships new amps and repairs with Red or Yellow coded tubes so they’ll run cooler and last a bit longer. White color coding was dropped, from running too hot for these amps, I presume?

This is taken at a plate voltage of about 475v with 124VAC coming from the wall with Silicon Diodes and Bold settings.

25w
EL34, 6CA7, KT77
6L6WGC, 6L6GCR, 5881WXT, 6Π3C-E
25% 13mA Red
30% 16mA Yellow
35% 19mA Green
40% 21mA Gray
45% 24mA Blue
50% 27mA White (dropped)

30w
6L6GC
25% 16mA Red
30% 19mA Yellow
35% 22mA Green
40% 25mA Gray
45% 28mA Blue
50% 32mA White (dropped)

Maybe @Boogiebabies and @electric mayhem can help me tweak this chart a bit if it’s a bit off? I’ve read some of the best info that was shared from their experience regarding dissipation/Mesa color coding on this forum. So thank you.

Hey Mile High, are you in Denver also or do you just have some really good bud?

All my input on what mA Mesa used are guesses, but educated ones and I'll use the 30W bulb as an example. Since they state you can use any branded tube common sense dictates they don't set the bias at either the hot end or the cold end typically.

I don't have hot tubes to check but I was guessing the rainbow range was teens to lower 40's mA. The greens I have tested teens to higher 20's mA's iirc, so 32mA for a white is about 10mA lower than I expected.

I think I remember @GJgo saying that he really liked upper teens in one of the rectos he had which made me think the factory has a favored bias point for each model they voice for. I haven't AB'd but I believe I want more juice from the Marks than teens and guessed they were shooting for upper 40's dissipation in the 80's Marks, the mid point of what I thought the mesa rainbow to be.

In contrast the 4x el84 50 caliber was likely biased at over 100%.

I didn't know white was dropped.

 

[Mile High Effects]

For four years, I both lived in Colorado and had good bud. lol. But that’s my company name. I work on and build guitar effects. Then started working on and building amps when covid hit. But now I have **** bud living back in Texas. lol

I think to better illustrate this, I’d be better off instead of trying to average the colors, give an average range. That White 32mA is an average so could see 30-40. In that case, I think maybe they do spread out a bit more on up to 65% MPD. In which case where I read that they dropped White would indicate they like to keep thinks cooler.

Which brings my next point on what you said about high teens on the current, that’s been my observation. Plenty of cut if jamming at low volume but when you crank it, it fills pretty nicely. Dialing back allows better dynamics and cleans are more present.

I may tinker with my estimations a bit more from observations from others. I’ve seen people report Reds as low as 9mA on Bold/Diode.