Mesa Rectifier and Tube Bias...

  • Thread starter Thread starter dead-pan
  • Start date Start date
dead-pan
dead-pan
Well-known member
Have a Mesa? Use Mesa branded tubes and all is good?

Hmm, I would have thought this to be the case.

I have a 2019 50th anniversary Triple Rectifier that I fought with to get it to sound great. Had been thinking I should swap out the power tubes to see if I could get better results.

Measured the bias and the stock tubes were running at 16ma at 150 watts and 19ma at 50 watts. Pretty low. Swapped in an old pair of Mesa 430s that ran at 30ma at 50 watts and the amp came alive.

Note, this is boosted.



Anyone have a preferred bias for their Rectos?
 
Last edited:
There is a color code one Mesa tubes for a reason. It tells you the bias setting in the Mess circuit
 
BesaMoogie said:
There is a color code one Mesa tubes for a reason. It tells you the bias setting in the Mess circuit
Click to expand...
Do you have a link to the specific bias specification per color?

I haven't saw anything specific and find it odd that stock the tubes would be biased at 16ma.

Was hoping others may have experimented with actual bias probing to find their desired sound. With Mesa branded tubes or others.
 
dead-pan said:
Do you have a link to the specific bias specification per color?

I haven't saw anything specific and find it odd that stock the tubes would be biased at 16ma.

Was hoping others may have experimented with actual bias probing to find their desired sound. With Mesa branded tubes or others.
Click to expand...
This is from coldest to warmest:
Red
Yellow
Green
Gray
Blue
White

I can’t tell, what bias ratings they refer to, especially because bias changes, when you use different rectifier and powersettings.

Which two colors do you have?
 
I always shoot for GRY 6L6 in Rectos as they run high 30s mA in bold / diode. GRN will also work at low 30s mA. Each color code moves roughly 6 mA.

To get into the teens I'm guessing you had RED.

Unlike Mark generations, I've found Recto bias to be pretty consistent across the generations.
 
BesaMoogie said:
This is from coldest to warmest:
Red
Yellow
Green
Gray
Blue
White

I can’t tell, what bias ratings they refer to, especially because bias changes, when you use different rectifier and powersettings.

Which two colors do you have?
Click to expand...
The 16ma are yellow and the 30 ma are green.
 
In that case (assuming you're testing on bold / diode) I'd suggest that the YEL you have are tired & weak.

Shop around for a new sextet of GRY. I prefer the STR445 (JJ) for metal and the STR448 (TAD Redbase) if you want a little more detail.
 
GJgo said:
In that case (assuming you're testing on bold / diode) I'd suggest that the YEL you have are tired & weak.

Shop around for a new sextet of GRY. I prefer the STR445 (JJ) for metal and the STR448 (TAD Redbase) if you want a little more detail.
Click to expand...
Amp has less than 10 hours on it...but possible. Just put in a gray and it measures 32ma.
 
dead-pan said:
Amp has less than 10 hours on it...but possible. Just put in a gray and it measures 32ma.
Click to expand...
Ok. Looks like your amp is slightly colder (~5mA) than average of most Rectos, that just means you could go as hot as BLU and be OK. GRY would be perfectly fine though.

Remember that Mesa power sections don't require power tube break up like Marshall power sections do, that said, when 6L6 start to get in the teens that's too cold for me. Anything ~25-38mA I don't sweat that much anymore.

But yeah what you're seeing is correct in that not all Mesas are good with all Mesa color codes. I've tested a ton and have a pretty good catalog of what goes where.

Generally speaking are you liking the amp? Compared to the 2 channels you've profiled?
 
GJgo said:
Generally speaking are you liking the amp? Compared to the 2 channels you've profiled?
Click to expand...
I liked the amp prior but found the mids tough to deal with. Now I know why. I really like it now.

I had a 2010 Triple that I regrettably sold which is why I bought this one.

I have a 1995 Dual, and a 1999 Triple that I love as well.

This Multi watt Triple is very raw and aggressive but quite a bit looser than the others. Boosted it has that girth, meat and depth while retaining decent tightness.

The 2 channel Triple is tighter and less extended in frequency response but just sits where you want it.
 
I know nothing about Mesa Bias - is it truly ‘fixed’ meaning you need to swap resistors to adjust what any given set of power tubes is seeing? Or is there a trim pot in the chassis somewhere that allows for adjustment?
 
Since the stock tubes are running cold I thought I would see how they do when switched to EL34 bias. They run hot with bold and solid state rectification, around 56ma. If set to spongy and tube rectification it runs at 32ma and sound good.
 
PDC said:
I know nothing about Mesa Bias - is it truly ‘fixed’ meaning you need to swap resistors to adjust what any given set of power tubes is seeing? Or is there a trim pot in the chassis somewhere that allows for adjustment?
Click to expand...
No trim pot. "Adjust" the Bias with the Mesa color code. It is the easiest way and there is no hassle going to a tech.
 
  • Like
Reactions: PDC
GJgo said:
Ok. Looks like your amp is slightly colder (~5mA) than average of most Rectos, that just means you could go as hot as BLU and be OK. GRY would be perfectly fine though.

Remember that Mesa power sections don't require power tube break up like Marshall power sections do, that said, when 6L6 start to get in the teens that's too cold for me. Anything ~25-38mA I don't sweat that much anymore.

But yeah what you're seeing is correct in that not all Mesas are good with all Mesa color codes. I've tested a ton and have a pretty good catalog of what goes where.

Generally speaking are you liking the amp? Compared to the 2 channels you've profiled?
Click to expand...
I actually have a Recto with a adjustable bias and I prefer it set to about 26-28mA. Going higher will take away the rest of the fizz but leaves the amp sounding to polite. The fizz ads up to the feel of having bite and is part of all Rectos and maybe even all Mesa amps.

And, at a certain point, the bottom end does not get any thighter either by increasing the bias. And for tight Rectos you should use a boost anyway.
 
dead-pan said:
Since the stock tubes are running cold I thought I would see how they do when switched to EL34 bias. They run hot with bold and solid state rectification, around 56ma. If set to spongy and tube rectification it runs at 32ma and sound good.
Click to expand...
Not sure, if bias is the only factor when changing from el34 to 6l6...
 
errrrrl said:
I never knew about the color code thing... 👀
Click to expand...
Like others mentioned, try to opt for green or gray with 6l6. It`s the sweet spot IMO.
With el34, green is already near the limit of the tube, when the amp is run in bold/ss. Mesa suggest running the amp in tube rectificaiton mode, when using el34s
 
Let's say you had Mesa amps, but none had Mesa tubes in them for reference. How would you know to get the right Mesa tubes? Is there a spot for the color code on the circuit? Would you just have to measure and see? Guess and check?

Asking for a friend...
 
BeZo said:
Let's say you had Mesa amps, but none had Mesa tubes in them for reference. How would you know to get the right Mesa tubes? Is there a spot for the color code on the circuit? Would you just have to measure and see? Guess and check?

Asking for a friend...
Click to expand...
Each vendor has their own "rating" system so you have to work with them to get it right, which could take a couple tries and you can't return used tubes so... I've logged rating systems from a few of the popular vendors in various Marks & Rectos.
 
You must log in or register to reply here.
 
Back
Top