Sweetwater is showing "new" mesa tubes

bandit2013 said:

This is a convoluted concept so it may be a long post:

If I understand the color codes correctly, Red has the least early gain characteristics. White has the most early gain characteristics. Considering a fixed bias amp, The reds will not get into clipping as easily as the whites. In other words, you will have more headroom with Reds vs Whites. The color codes I think run Red, Yellow, Green, Gray, Blue, White. The green and gray codes sort of fall into the middle. Not sure how much of a difference there is within the narrow band of tube gain for the fixed bias design. Another key to understand is how the tube responds to frequency. I would assume the gain response is different at lower frequencies vs higher frequencies. The STR440, STR443 are similar such that the low frequency response is much stronger than say the STR448. So when a tube with early onset of gain or tendency to clip for a given signal level is used an a bass dominant amp, it can get muddy until the signal strength of the upper frequencies gets higher in magnitude. Example, the STR440 or STR443 having the same color code would be bass dominant in the JP2C at a reduced volume. The only way to compensate for this was to use shred mode in order to get more influence on the upper frequencies. Even at gig level, it became a burden to some extent. The STR440 had an advantage over the STR443 as it seemed to reveal more upper frequencies and harmonics at gig level. Comparing that to the STR441 in the JP2C they seemed too relaxed. Not best for this amp. The STR448 on the other hand, did not follow the same frequency gain characteristic. It was more balanced. So at reduced volume the low end and upper end was at the same volume and note definition was retained. At gig level the low end bloomed as well as the rest of the frequency range such that it was an epic experience. WOW, I cannot believe what I am hearing sort of deal. Note that a Mark amp sounds best when it can get into power tube saturation and clipping. Ideal when the power tube does not have a low frequency dominance. There is plenty of low end, probably more than I expected but it is quite different than the STR440. Just a tad looser but yet just as tight. Hard to describe.

For the Roadster, that is a different amp in its entirety. More of a low end sub-harmonic generator due to the cold clipper and the following tone stack lends itself to difficult to manage when the power tubes tend to be more low-end dominant. STR440 yellow would have more headroom than the gray. Not sure how much of a difference but you can hear it. What I mean by too much, too much bottom end and the early clip effect did not provide enjoyment. More of a muddier tone and lack of definition. I did not want to push the amp with stupidly loud settings in hopes the top end would eventually be noticeable. It does not take much plate current to make a difference in characteristics. In some respects, it could be related to being more familiar with one given color code in the amp vs the other. If there was not much of a difference between the color codes, why have them in the first place? When you feel you need to dial out specific settings on the parametric tone controls (Bass, Midrange, Treble) it may be the power tube is too dominant in one particular frequency that lends itself to be undesirable. Sometimes you can compensate but sometimes you cannot. The early onset of clipping of the Grays was one of those cases for me. Yellow in the Roadster had more content without the mud. Never tried the reds though.

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bandit2013 said:

I think it was yesterday, was looking for the information on what the Mark IV power tube choices were and noticed a different STR# STR454. Any clue what those were? Never mind, I found them, they were the SED =C=6L6GC tubes.

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Joey1970 said:

The STR-454 6L6 and STR-442 EL-34 tubes were the best since the Sylvanias, in my opinion. I bought up all the Sylvanias that I could afford, back when you could actually find them. Mainly for the life expectancy of them. Hell, that is what the early Marks were designed around.

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