Mark IV - A / AB / B

Hey guys,

I've been doing some reading in there and wanted to see if anyone can clarify this stuff. The Mark IV thread says that the B models start at around 6XXX s/n but I figured I might be able to narrow this down a bit more for gearnerd sake.

I have Mark IV s/n 6044. I believe that mine is actually an AB or whatever we want to call it as a transitory period.

I grabbed some photos to make this more fun.

I think this is unquestionably a IV - A

Quad FX loops, Attached Power Cable.

I believe this is a IV - AB

Staggered FX loop and Attached Power.

And this is a final IV - B

Plug in Power.

Is this the general consensus for how this works? Theres a few other changes but Im not sure if they are mods. (Ground switch etc) Theres really no reason to even know this but I'm a curious person and figured this would be the place to ask / discuss.

This is what I posted 4 years ago about my no-A/no-B, or early B, Mark IV.

Mine is s/n 617X (March 93).
My early B version has all 12AX7 tubes while, I believe, the A version has a 12AT7 in the reverb. Output tranny is 562004R-1 and power tranny 561136. Chassis is black (A versions are silver?).

I don't know how all this compare to the B versions. For what I know, early B go between approx. s/n 5900 (Jan 93?) and 6800 (Nov 93?).

I figured I couldn't have been the first person to notice this. Thanks for the info!

Mine is a "B". According to Mesa, it was made in June of 2003. All pre-amp tubes on mine are 12ax7s. Serial number 114xx.

I've never really figured out what mine is. It looks just like the middle picture above. But I can't remember the serial number - where is it? (I probably have a picture of it somewhere, but it's hard to get at the back of mine for a casual check. - edit: found it, it's 6396.

sduck said:

I've never really figured out what mine is. It looks just like the middle picture above. But I can't remember the serial number - where is it? (I probably have a picture of it somewhere, but it's hard to get at the back of mine for a casual check. - edit: found it, it's 6396.

Click to expand...

That puts igfraso's SN estimate as dead on!

igfraso said:

This is what I posted 4 years ago about my no-A/no-B, or early B, Mark IV.

Mine is s/n 617X (March 93).
My early B version has all 12AX7 tubes while, I believe, the A version has a 12AT7 in the reverb. Output tranny is 562004R-1 and power tranny 561136. Chassis is black (A versions are silver?).

Click to expand...

My Mark IV has a 12AT7 written on the amp by the reverb tube, it is a '91 SN 58x.
On a side note, the output and power transformers are the same as on my blue stripe.

themisfit138 said:

igfraso said:

This is what I posted 4 years ago about my no-A/no-B, or early B, Mark IV.

Mine is s/n 617X (March 93).
My early B version has all 12AX7 tubes while, I believe, the A version has a 12AT7 in the reverb. Output tranny is 562004R-1 and power tranny 561136. Chassis is black (A versions are silver?).

Click to expand...

My Mark IV has a 12AT7 written on the amp by the reverb tube, it is a '91 SN 58x.
On a side note, the output and power transformers are the same as on my blue stripe.

Click to expand...

and gain stage tube is V3 for ry2 and 3, witch is easier to manage 8)

themisfit138 said:

My Mark IV has a 12AT7 written on the amp by the reverb tube, it is a '91 SN 58x.
On a side note, the output and power transformers are the same as on my blue stripe.

Click to expand...

Mine has this as well.

For you guys with a transitional model (in the 6000's), what transformers does yours have (if not posted already)? I'll have to check mine, mid-6000's.

Silverwulf said:

For you guys with a transitional model (in the 6000's), what transformers does yours have (if not posted already)? I'll have to check mine, mid-6000's.

Click to expand...

Here's what mine looks like ....