2:90 retube question

[badguitarist]

Hi guys! What tube positions need to be matched pairs on a Mesa 2:90?

 

[MrMarkIII]

If it's like the combo/head, the outside pair (pair "A") is the "Class A" pair, and may be EL-34s or 6L6s. The inside pair (pair "B") must be 6L6s.
Like this: A - B - B - A. (Also everybody's fave band . Sorry, couldn't resist.)
The "A"s should match each other, the "B"s should match each other, in pairs. The whole quad doesn't need to match, unless you're running all 6L6s, and need to spend the extra dough.
I gotta question myself: What's that switch up in the back next to the upper right power tube?

 

[ChesterH]

Call Mesa to be sure. There are 2 different configs out there, the ABBA config, and ABAB. I think the newer 2:90s are ABAB, but you should call to be sure.

 

[badguitarist]

Thanks mates for the info. I called Mesa. They said my version is
(A1)(A2)(B3)(B4)
(A1)(A2)(B3)(B4)

where A is channel A, B is channel B, 1,2,3,4 are matched pairs

 

[MrMarkIII]

Yeah, but what's that switch for? To disable the fan?

 

[badguitarist]

Yeah, but what's that switch for? To disable the fan?

Never touched it .

 

[MrMarkIII]

Does it cross the streams on the unlicensed nuclear accelerators?