Mesa power tubes and color coding (part 2)

[sundaypunch]

They are rating them so people will have the proper current draw in their amps. The various colors are "identical" tubes that idle differently. If you had a red and white set and put them in your Marshall, they will only sound identical if you adjust the bias pot to give each the same reading. If you swap the sets back and forth in your Boogie (or didn't adjust the bias in the Marshall) my guess is that they will likely sound slightly different.

It's like having two identical carburetors. If the idle is adjusted differently these "identical" carburetors will seem different. I think Chris is right in that there is no sonic difference in the various tubes. You will only hear a difference if they are running differently in the amp.

 

[sundaypunch]

A red vs. white color coded Mesa 6L6 is essentially the same tube. If you don't adjust the bias one happens to idle hotter in the amp. They will probably sound slightly different because of this. This isn't because the tubes are different, but because they are idling differently in the amp.

With most amps, you buy whatever tube you want and adjust the amp to have it idle properly. You can change how they sound pretty drastically if you have ever fiddled with a bias pot. If you had a Boogie with a Bias pot and adjusted a red pair and white pair of 6L6's to run at 30 mA they wouldn't sound different.

 

[sundaypunch]

So does Mesa label a certain pair or quad consistently GREEN if they have a certain plate current draw and transconductance?

In other words, are the color codes assigned according to specific test results/values?.

Yes, that is exactly it. Since Boogies don't have adjustable bias they need to sell you a tube that will idle properly. In my Boogie I occasionally will try a pair of NOS tubes that I have in other amps. I have a Bias-Rite that shows the current reading. Most often the pair of tubes I try runs way too hot or cold to use in the amp.

If you don't want to buy Mesa tubes you have to get them from a dealer (like Eurotubes, Lord Valve, etc.) that understands the Mesa system.

 

[stokes]

"If you don't want to buy Mesa tubes you have to get them from a dealer (like Eurotubes, Lord Valve, etc.) that understands the Mesa system."

Or add a bias pot to the amp.

 

[sundaypunch]

Yep, you can go with the bias pot. Judging from posts here there doesn't seem to be many people that do this. I'm not sure why? Obviously Boogie wants people to leave things alone and buy their tubes.

I have a Simulclass amp so the inner/outer pairs are biased differently. Do people that add bias pots to these just add one pot. or is there a way to add two (one for each pair). With "regular" amps you just buy a matched quad and bias to suit that quad. I'm not sure how you would go about it if you had a single bias pot?

 

[stokes]

When adding a bias pot you are replacing a single resistor that is responsible for setting the "fixed bias voltage",right?So whatever difference there is between the inner and outer tubes bias points are determined by other resistors between the bias "resistor" or bias "pot".If the tubes you want to use have a wider bias range between the two pairs you may have to adjust these as well.So sometimes with these simulclass amps there could be a little more to it than just changing the single resistor,but basically if you add the pot and check the bias of the two sets of tubes and they fall into a safe range for each pair,that is all there is to it.

 

[Rectumfryer]

I have a MarkIII Simul Class that I sent into Petaluma to get fixed and I told them to retube it while they were at it. It came back with all 6l6's. It went in with 2 el34's and 2 6l6's. I called and asked what the deal was with that, because I thought it had to have 2 of each. I was told it's ok to have all 6l6's. If I wanted them to send me some el34's to send back two 6l6's. It kinda tripped me out. Would this mean they are all biased the same?

 

[JOEY B.]

I have a MarkIII Simul Class that I sent into Petaluma to get fixed and I told them to retube it while they were at it. It came back with all 6l6's. It went in with 2 el34's and 2 6l6's. I called and asked what the deal was with that, because I thought it had to have 2 of each. I was told it's ok to have all 6l6's. If I wanted them to send me some el34's to send back two 6l6's. It kinda tripped me out. Would this mean they are all biased the same?

Do you recall the color codes of the 6L6's that were sent back with your amp? And did they put a different color code in the outer(class A) sockets? The Class A sockets are NOT biased the same as the inner pair.