Mesa 400+ tube config

[paradigm_shift]

Can anyone tell me how the tubes are paired/orientated. Left to right or front to back? Got two Microphonic tubes. Just not sure if its a pair or two pairs needing replacement .

Cheers
Chris c

[danomite64]

I think it is the center 2, then the next 2, then the outer 2. I would assume if that's the case, the 2 rows are separate. I'm not sure if MESA told me that when I got my 400+ (I definitely called them about buying a new set of tubes way back then), or if Mars Music told me.

[paradigm_shift]

what I guess I'm asking .. where (x) is tube and + is pair:

a)
(x)+(x) (x)+(x) (x)+(x)
(x)+(x) (x)+(x) (x)+(x)

or b)

(x)(x)(x)(x)(x)(x)
+ + + + + +
(x)(x)(x)(x)(x)(x)

From a top point of view

[Classickbass]

Originally Posted by paradigm_shift

what I guess I'm asking .. where (x) is tube and + is pair:

a)
(x)+(x) (x)+(x) (x)+(x)
(x)+(x) (x)+(x) (x)+(x)

or b)

(x)(x)(x)(x)(x)(x)
+ + + + + +
(x)(x)(x)(x)(x)(x)

From a top point of view

B, they are matched front to back.

[Calaverasgrande]

On my bass 400 non plus its
(x)(x)(x)+(x)(x)(x)
if you had to pull tubes it could be ()(x)(x)+ (x)()(x). It all sums to a buss per side.
Have you checked the pre tubes already? v1 is the closest to the input jacks, I would check that first.

[BillJarrett]

(A)(B)(C)(C)(B)(A)

Hope that helps.

[paradigm_shift]

(a)(b)(c)(c)(b)(a)
(d)(e)(f)(f)(e)(d)

So if Im reading that correctly ^ that is how the tubes are orientated ?
Basically its tubes (d) & (e) on the left side that are picking up noise. If I was to replace Both d's for example and use the "good" tube from d & e as a pair , is this likely to cause any issue? If so what sort of effect is likely to occur?

[Nightlyraider]

There are people posting the 400(non-plus)'s configuration with the ABCCBA ordering. The 400+ is two sets of 6.

AAAAAA
BBBBBB

The tubes are paired with eachother one A to one B. You want the A and B tubes that line up to be equal.

[anderbass]

Its like this on a Mesa 400+:

(a)(a)(a)(a)(a)(a)
(b)(b)(b)(b)(b)(b)

All 6 powertubes In the front row are wired together in parelel as your Push side.
All 6 powertubes in the back row are wired together in parallel as your Pull side

Select any pair of tubes, one from each row and its a push/pull pair.

Each row of power tubes are completely wired together with long metal rods shown in my pic below:

(the green wires you see here in my pic are not factory installed. They were added by me as part of a Cathode-lift mod I did to my 400+. my amp mod info is here: SWITCHABLE MAX OUTPUT MOD, FOR a 300/w TUBE AMP.

[BassmanPaul]

sorry but there is no such thing as a "pair" on any tube amp with more than two outputs. The only exception is amps with two or more bias pots. The SVT, for example, has two bias pots so you can work with triples. On the 400+ that has the standard bias arrangement, any one tube from one side of the OPT primary is equally a "pair" to any other tube on the opposite side.

[Calaverasgrande]

^^^^^ these two posts say it better than I did.