Mesa Color Code Plate Current Values (420 vs 440)

[QuantumDot]

I need replacement tubes for my Mesa 2:90 and the current power tubes are the Mesa Boogie STR 420 6L6GC with the color code GR BLU.

I thought about buying the new Tube Amp Doctor 6L6GCM-STR REDBASE power tubes but TAD is having problems coming up with plate current values that match the STR 420's with color code BLU.

Per Tube Amp Doctor, they need tubes with PC values around 58 so that the tubes can be installed without doing any tech work.

Now they're telling me that the PC value of 58 is code blue for STR 440 tubes and not the STR 420s.

The STR 420s with color code BLU should have a PC value of around 40.

Since they just can't seem to get redbase tubes with PC values around 58, they offered me to now buy PC 40 tubes instead. I'm not sure what to make of it... their business is selling tubes and they couldn't care less if I fry the tubes in my Mesa 2:90, so I'm not sure if the color code BLU for the STR 420 corresponds to PC values of 58 or 40...

Does anybody know for sure which of these two PC values applies to the STR 420 with color code GR BLU?

 

[gabilotcu]

I have the same problem but with a dc5

 

[woodbutcher65]

Nothing terrible will happen if you go to the next hotter or cooler color range. Have you considered buying guaranteed tested used tubes on ebay? Those power amps aren't known for being very hard on tubes anyway.

At the very worst, you might want to add a fan to your rack if you run a hotter tube range.

 

[GJgo]

Mesa's color codes are all the same test range for any 6L6 they sell. They probably tested tired tubes when they made this determination.

BLU is as hot as it gets now, IIRC they no longer do white. In my testing BLU is pretty hot in most Mesa A/B slots and unsafe in a Class A slot (where you generally want RED or YEL).

 

[joey_truelove]

If TAD says it's so I would certainly trust their judgement on it - they have no reason to provide erroneous advice. Could be that the shorter bottle 420 is preferably biased colder still, it probably not being more than 25W in real terms.

 

[meesa_jarjar]

Mesa's color codes are all the same test range for any 6L6 they sell. They probably tested tired tubes when they made this determination.

BLU is as hot as it gets now, IIRC they no longer do white. In my testing BLU is pretty hot in most Mesa A/B slots and unsafe in a Class A slot (where you generally want RED or YEL).

Do you have a ranking / hierarchy of Mesa's tube ratings, or know where I can find one?

 

[GJgo]

Red - coldest
Yellow
Green
Gray
Blue
White - hottest

Some people don't care what their bias is, and some do. If you do, I'd recommend testing your amp. While Mesas are fairly consistent I have owned & tested enough of them to see amp to amp variance that is concerning if you're going for a certain bias range.

 

[meesa_jarjar]

I assumed Greens were the coldest based on measurements I made in the past, but now it looks like the ones I measured were very worn out.

 

[gabilotcu]

Red - coldest
Yellow
Green
Gray
Blue
White - hottest

Some people don't care what their bias is, and some do. If you do, I'd recommend testing your amp. While Mesas are fairly consistent I have owned & tested enough of them to see amp to amp variance that is concerning if you're going for a certain bias range.

Thank you!

 

[woodbutcher65]

Not sure how it matters tonally, but if you are likely to run your amp turned up high for an extended period of time, you might be better off to pick a cooler temperature range of power tubes because they're going to run cooler overall than a hotter tube range. This can make it a bit less likely for the tube to develop a short due to thermal distortion of its internal structures.

 

[TRENCHLORD]

The whole mesa color-code spectrum resides in a fairly narrow range that matches their fixed-bias system.
Any of their 6L6 tubes of any color will work fine. The colors are to ensure that pairs are reasonably balanced.

You can run a pair of reds in the inner slots and a pair of whites in the outer slots,,,,,,and the result will roughly be the same as a full quad of greens or grays. The colors are for keeping each "side" of the amp close to the other.

 

[user 41014]

The whole mesa color-code spectrum resides in a fairly narrow range that matches their fixed-bias system.
Any of their 6L6 tubes of any color will work fine. The colors are to ensure that pairs are reasonably balanced.

You can run a pair of reds in the inner slots and a pair of whites in the outer slots,,,,,,and the result will roughly be the same as a full quad of greens or grays. The colors are for keeping each "side" of the amp close to the other.

I don't have the hotter tubes- mostly greens and yellows with some greys.
My tests (I used a red stripe to test) came in at roughly 15mA to 30+mA and it's my understanding the hotter tubes would push it to slightly over 40mA. I don't consider that a narrow range of dissipation.

If we assume 470 plate volts and for amps other than mesa the standard 70% dissipation you get 45mA. Closer to what I expect for a mesa at 50% is 32mA. Unless I'm missing something it is reckless to suggest 58mA tubes in any mesa that is not an original Bass 400 or that does not have a bias pot. I wouldn't even run 7581A's that high which would be 80% for the rare 35W bulb.

At a hot 90% for class A you get 58mA using the same tranny and 30W bulb.

Tubes drift and testing all new yellows and greens mostly I found better matches across colors individually and across new boxes than within the same color code or packaged set. Ymmv but staying in the same color blindly does not mean you are balancing each side which really can only be done with a bias pot for each side or tenuously rolling power tubes till the mA's match. I believe all the grid R's I've seen match (not dialed in for balance) while you can't expect each side of the power section to match perfectly without dialing one of those grid R's.

Matching tubes didn't come about till the 80's (GT) at which time tube amps were being overrun by SS and some prefer non-matched anyway. So whether any of this matters is up to your ears and fingers. Frying your amp is something I think we all care about.

 

[Theresa]

From Mesa Tech Support bulletin:

What color code rating do you need? We’ve got seven power tube color code ratings and these color ratings represent current flow. The reason for having these ratings is so that you can match up, as closely as possible, a pair of tubes for use in a push-pull circuit. It’s a spec issue and not a tonal one. Any tonal difference between our colors would be hard to notice and not significant. How accurately should tubes be matched? The Industry standard is plus-or-minus 10%. That means two tubes could be as far apart as 20% and still considered matched. Our matching process at MESA is twice as stringent at plus-or-minus 5% before a tube moves into our next color category and is matched with another nearly identical one. More important is that ALL our color categories are within the “sweet spot” of tube performance. We simply reject all the tubes that test either under scale or over scale.

Such strict selection and close tolerance permits us to permanently set the bias in each amplifier so it never needs re-adjustment. For the optimum in performance from your amp, it is important to use matched pairs of power tubes in the amp. Amps having more than one pair of tubes don’t have to use the same color rating throughout. For example, there are two pair of power tubes in a Dual Rec Solo Head. The two tubes in the inner tube sockets work together in this amp as do the two tubes in the outer tube sockets (from left to right, tubes 1 and 4 are working together and tubes 2 and 3 are working together). When you replace these tubes, you can load tubes of one color rating in the middle two sockets and another color rating in the outside sockets. Because of our tight tolerance, you can do this without having to worry about a change in performance or tone. Keep in mind that when replacing any of the color-coded power tubes; it is always best to swap tubes in pairs. This will ensure tubes working together are matched as closely as possible.

 

[user 41014]

The reason for having these ratings is so that you can match up, as closely as possible, a pair of tubes for use in a push-pull circuit. It’s a spec issue and not a tonal one. Any tonal difference between our colors would be hard to notice and not significant. How accurately should tubes be matched? The Industry standard is plus-or-minus 10%. That means two tubes could be as far apart as 20% and still considered matched. Our matching process at MESA is twice as stringent at plus-or-minus 5% before a tube moves into our next color category and is matched with another nearly identical one. More important is that ALL our color categories are within the “sweet spot” of tube performance.

A perfect example of why the advertising gets a bad rep at times. My tests of NOS tubes where much different. I'd have to check my notes for exact results but I want to say my variance was up to 60% difference in the same color. I put stickers on the bases so as not to be fooled into grabbing the same color since some greens and yellows matched perfectly with each other.

As stated in the technical bulletin you may not want your pairs to match. You personally may not even want to match a pair. An example would be players that rely on power tube break up and play at different volumes. If one tube is getting worked harder you might get the break up at lower volumes and the 2nd (same side or pair) works like helper spring on a work truck that only kick in effectively with heavy loads.

The other thing I don't see mentioned much is voicing. If Mike voices a mid 80's amp with a STR-387 (415) at 25mA, not only does using other tubes stray from the original path, using a 15mA or 42mA will also be different. Whether you like it better or not is personal and signal chain dependent but you can't tell me there won't be a noticeable difference in the attack/decay dynamics.

I religiously use medium picks. It's the way I expect my hockey stick to release the force and I'll put up with many broken picks. You can tell me that tonally there is no difference from thin to heavy but at the end of the day words are just words.

 

[shawnohio]

What are words for. When no one's talking anyway? Heheh. Needed a flaming boogie solo right in the middle!!

 

[Theresa]

What is your method and procedure of testing? What equipment did you use to arrive at your readings? Was your test equipment calibrated? I have too many questions.

The STR 415 is definitely a different animal than any other STR's. Primarily being a USA (Maybe a Sylvania or GE/Phillips tube?). They are of course going to sound different but we are discussing the bin-out of plate current and matching stats. Characteristics of various tubes are a whole other matter I think.

To run an amp cooler results in better headroom and running it hotter would inversely result in earlier breakup of the power tubes. Conversely, running the cooler bias'd tube will make your tubes last longer as opposed to driving them hard.

 

[user 41014]

What are words for. When no one's talking anyway? Heheh. Needed a flaming boogie solo right in the middle!!

agreed. Feel free to add it!
Or maybe I'll work on the necromancer part II. It has been pounding in my head for a while making me learn the very simple part to scream, "brooding in the tower...". Maybe the neighborhood will get a break from me blasting the song if I learn the solo but I think their going to get an earful in a few minutes!

All the tests were done with a weber bias-rite in a red stripe. Actual conditions since I have no tube tester to lead me astray with non-actual operating conditions.

Since we are not talking about a vintage hitchcock that I would gladly have if it fell in my lap calibration doesn't apply. I trust the weber and it has agreed with my multi before.

 

[Theresa]

Not to put a point on the matter, but a benchmark baseline needs to be established before anything. Hence the need for procedures. Then you can tweak your hearts desire. Here is an example of dialing in an amp I resurrected for a client in a real world scenario, driving the amp and finding it's tube compliment "sweet spot" before buttoning it up.

 

[user 41014]

To run an amp cooler results in better headroom and running it hotter would inversely result in earlier breakup of the power tubes. Conversely, running the cooler bias'd tube will make your tubes last longer as opposed to driving them hard.

It sounds like you agree that despite the bulletin you posted there is a noticeable difference in tube colors when you describe headroom and saturation. I see your analog meters mean you are not trusting tube colors either. Tubes may be 10% matched from the factory. I can't verify that and I'm not the author of "tubes drift".

But I proved to myself being color blind is important if I want to match mesa branded tubes when it's time to put them in. Just like any other tube. Though when I've bought used 415's from Ness (or other tube sellers) of course he matched them before sending them out so the testing is fresh. At least then you have a relative mA to work from since you're not going to re-create his test environment and parameters.

You were correct on Sylvania. Phillips bought them for the US JAN contracts so technically you are right there also but anyone's name can be on a tube. The single and double halo getters for a top flash is the dead give away. Much different than the flying saucers of St Peterburgh.

Fancy amp stand but the deluxe looks like it had a life in the Florida sun.

As for procedures the large part of my amp stable is Marks 1981-89. I used only 1 amp to test on purpose from which I wouldn't expect much variance for all those amps. I don't disagree with you. My baseline was a PT from a redstripe creating the B+ and grid V with a simulclass OT and testing the A/B sockets.

As Mr. Van Zant might say, nuthin fancy. I don't feel disadvantaged without expensive tools. Volts are easy to measure; resistance is easy to measure. And thanks to a a very smart Mr. Ohm we know E=IR, therefore I=E/R.

It sounds like you are doing this professionally in which case I would want the tools that do the work for me too.

 

[Theresa]

Fancy amp stand but the deluxe looks like it had a life in the Florida sun.

I have no idea where the amp lived but I can tell you, it had a very hard life. (1972). I was really afraid to throw the switch fearing it might catch fire LOL. That there is a perfect application for a 100W light bulb in circuit! LOL I offered to restore the amp both cosmetically and electrically but he said "just get it up and running. I'm using it as a gig amp!" Needless to say, the guy got his amp back and is happy as a gecko in paradise!