Bias on a Mesa Mark series

anomaly

anomaly

Well-known member
Is there any benefit to having a adjustable bias mod on a Mesa Mark series amp, or a Recto? I know they're biased on the cold side, but I wonder if a hotter bias would help them in any way?
 
I always thought so. Warms up a rectifier for sure . Don’t necessarily need to do a bias mod. Just get some hotter tubes that increases the ma’s on the bias.
 
Emg77 said:
I always thought so. Warms up a rectifier for sure . Don’t necessarily need to do a bias mod. Just get some hotter tubes that increases the ma’s on the bias.
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I really dig the sound of class A on my Mark IV, and that is using the two outer tubes which are biased a lot hotter than the middle two. The only thing I don't like is the lack of punch and volume that class A has.

As far as Mesa branded tubes, which are the hotter color codes? and are all the color coded Mesa branded tubes safe in the amplifier?
 
That’s the thing. I stepped away from Mesa tubes. I don’t remember exactly the color codes on the Mesa tubes. But they always seemed colder than what I needed to get into bias range.

With other tube manufacturers they give a rating on the tubes. Most tube places you can request what range you want. If I recall for me when I ordered for my Boogies. It seemed to be in the 36 ish range.

To find out exactly, you need to know the plate voltage. If you don’t have a bias meter that tells you the PV. You can use a multimeter on pin 3 of the power tube.

The equation is this.

6L6 = 30 watts

30w divided by PV times percentage (60%-65%) or .60-.65

I believe the Mark IV is around 460 for plate volts

30 divided by 460 X .60 = 39 ma’s at 60%

And yes the EL-34’s running on the outside sockets are certainly running hotter.
 
All the Mesa tubes are in their range. I got some Tung Sol tubes that were a higher number and it worked out to be hotter. My Mark V sounds great now.
 
Yes and it’s pretty simple to do on the mark 3’s. Can’t comment on others. From the factory bias, both sets of 6L6’s I had ran hot as fuck. I think my winged C’s were somewhere in the 65-70ma range not even fully warmed up. In my opinion the bass improves greatly when lowered down to 40ish and they don’t get ice picky like Marshall’s do with a colder bias.
 
I noticed a difference when a bias pot was added on my mark Iva, but it was over all pretty subtle, so not sure I would mess with it if I had to do it over again.

When running the mark iv into a suhr rlir, I found it pretty interesting that I liked the master at 3 versus having it higher, that really surprised me.
 
anomaly said:
As far as Mesa branded tubes, which are the hotter color codes? and are all the color coded Mesa branded tubes safe in the amplifier?
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(Cold)
RED
YEL
GRN
GRY
BLU
WHT
(hot)

Very generally speaking, each successive color picks up about 6mA. Also, I do not believe they sell WHT anymore. They were too hot for most amps. Realistically BLU is borderline for most amps.

Are they all safe in all Mesas? No. The main warning here are the Class A slots for 6L6 in Mark II & III. You want to stay with red, maybe yellow. On the Mark IV & VII however the Class A slots are colder & you could be fine with GRN.

That said, even in the A/B slots on vintage Marks you can start getting up over 40mA with GRY and up. There are trends, and there is also amp to amp variance.

Rules of thumb for as hot as you want to go for 6L6 in Class A/B:
Mark II & V- GRN
Mark III, IV, VII, JP2C & Dual/Triple Recs- GRY

Is bias worthwhile? From an OCD standpoint I'd appreciate it, but it's not really necessary. I do prefer to set up tubes that are in the mid 30s (or more specifically 60-65%) however these days I don't sweat it down to the mid 20s. Mesas don't require power section overdrive like Marshalls do so while there are some nuances to feel with different bias settings it's subtle in these amps. In a nutshell as long as it's hotter than where it'll get crossover distortion and colder than 70%, you're probably fine, plus colder tubes should be more reliable.

I will also mention that in the Badlander, the GRY EL34 it came with were running 18mA. I spoke to Mesa about it and they said they did that (super cold) on purpose because that's where the best tone was. I scoffed, and then I tried different hotter tubes, and damnit if they weren't right.
 
The crossover distortion of cold biased tubes is part of the mesa (and peavey 5150) sound. Getting hotter will remove some of the fizz and tighten the bass. Overall the amp will start to sound darker the higher the bias gets. But at some point, you will lose the aggressive character of the gain struckture as it smooths out.
Instead of a bias mod, maybe go for hotter running tubes.

Keep in mind, that in the dual rectifier (not badlander) the el34 are running much hotter. Mesa recommends using the rectifier settings in this scenario which brings the PV down (Mesa green el34 in Bold/Silicon pass the 70% lightly when I measured).
In the Mark simulclass series, the outer tubes are destined for el34. It is possible to put in 6l6 tubes, but again they will run much hotter. So maybe it would be enough to only change the inner pair with hotter tubes.

If you don’t have a bias meter, get one and measure your amps. That way you get a first idea where you stand.
 
Wouldn’t you want power section as stiff and cold as possible in such a highgainer? Especially for rhythms?
 
CrystalSky said:
Wouldn’t you want power section as stiff and cold as possible in such a highgainer? Especially for rhythms?
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Kinda, but i like there to be a touch of sponginess or bounciness, you know what i mean? Which the IV does have. I was just curious basically.
 
GJgo said:
(Cold)
RED
YEL
GRN
GRY
BLU
WHT
(hot)

Very generally speaking, each successive color picks up about 6mA. Also, I do not believe they sell WHT anymore. They were too hot for most amps. Realistically BLU is borderline for most amps.

Are they all safe in all Mesas? No. The main warning here are the Class A slots for 6L6 in Mark II & III. You want to stay with red, maybe yellow. On the Mark IV & VII however the Class A slots are colder & you could be fine with GRN.

That said, even in the A/B slots on vintage Marks you can start getting up over 40mA with GRY and up. There are trends, and there is also amp to amp variance.

Rules of thumb for as hot as you want to go for 6L6 in Class A/B:
Mark II & V- GRN
Mark III, IV, VII, JP2C & Dual/Triple Recs- GRY

Is bias worthwhile? From an OCD standpoint I'd appreciate it, but it's not really necessary. I do prefer to set up tubes that are in the mid 30s (or more specifically 60-65%) however these days I don't sweat it down to the mid 20s. Mesas don't require power section overdrive like Marshalls do so while there are some nuances to feel with different bias settings it's subtle in these amps. In a nutshell as long as it's hotter than where it'll get crossover distortion and colder than 70%, you're probably fine, plus colder tubes should be more reliable.

I will also mention that in the Badlander, the GRY EL34 it came with were running 18mA. I spoke to Mesa about it and they said they did that (super cold) on purpose because that's where the best tone was. I scoffed, and then I tried different hotter tubes, and damnit if they weren't right.
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Thanks for the post. Ya, right now I'm running green 6l6's in the outer slots and grey in the inner slots. That's what Mike B recommended for those tubes when I got the amp serviced. I also got some yellow code 6l6's and more grey code tubes that I'll use when it's time to change them out.

Brings me to another question, how often do you change your power tubes? because I've had mine in the IV for a good 5 years now and they still seem to be running strong.
 
 
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psychodave said:
Holy crap, haven't seen you post in ages. Hope all is well.
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Have not needed power tubes in ages. Bought a box full of these when they were much cheaper, get it? NOT for sale. Got some good used 416's in that same box, also NOT for sale.:cool:
 
When I had my C+s, I had a good supply of 415s on hand; I started to find other Sylvania GCs to add to my stash. I found that ones that would measure at 30-34ma sounded best with my Marks. At around 40ma or more, the amps started to sound harsh.
 
psychodave said:
Holy crap, haven't seen you post in ages. Hope all is well.
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Yes , my work job has picked up steam, big time, and I'm up in the fog of the steam! I do what I have to do to keep the ship upright. Being an old-head hotrodder, and seeing a 2001 Viper under a cover every morning sucks(meaning that I don't have the time to enjoy it). I am 52 yrs old with bad genes, so get every day, while you can.
 
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anomaly said:
Thanks for the post. Ya, right now I'm running green 6l6's in the outer slots and grey in the inner slots. That's what Mike B recommended for those tubes when I got the amp serviced. I also got some yellow code 6l6's and more grey code tubes that I'll use when it's time to change them out.

Brings me to another question, how often do you change your power tubes? because I've had mine in the IV for a good 5 years now and they still seem to be running strong.
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I've never actually "worn a set out". I've had a few go bad on me though. That said, I usually have a bunch of amps around so any one isn't getting a ton of hours.. Every year or two I'll pull and test just to make sure one hasn't drifted & pulled the balance off.
 
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