Questions about Mesa MKIV AB (transitional model)

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itsgoodnow

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Hey All,

Apologies if this post is in the wrong spot. I am aware there is a Mesa MK IV A version and a MK IV B version. There is a transitional period sometimes referred to as an AB version (where I assume mesa was using whatever parts were leftover), in the transition from A to B. Supposedly this was relatively limited to serials 6k-roughly 6200. My B is 6206 and appears at first glance to be one of these transitional models.

I was always under the impression the transitional models had no difference from a normal B (minus, essentially, cosmetics), but wanted to confirm that is the case. Someone posted, of all places, in a youtube video description there may be changes on these transitional models to the PI and the circuit itself that differs from the standard B. I was curious if this was accurate or not. I figured someone here who is way more knowledgeable might be able to confirm or deny. Thanks all.
 
Yes they are a little different than a typical rev B. Some of them still carry the rev A PT and there are various circuit changes they made during that time up until they settled on what the B would become. Your amp could very well be a transitional model IV.

You also gotta consider the fact that even if the circuit is a typical B, those early B's carry a lot of the same components that the A's do, while the later 2000's era B's have different brand caps, resistors and such, so the early B's sound a bit different than the later ones do, i've compared a few of them including my own amp which is probably a transitional model as well as it has the earlier Mark III PT on it and serial #.
 
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anomaly said:
Yes they are a little different than a typical rev B. Some of them still carry the rev A PT and there are various circuit changes they made during that time up until they settled on what the B would become. Your amp could very well be a transitional model IV.

You also gotta consider the fact that even if the circuit is a typical B, those early B's carry a lot of the same components that the A's do, while the later 2000's era B's have different brand caps, resistors and such, so the early B's sound a bit different than the later ones do, i've compared a few of them including my own amp which is probably a transitional model as well as it has the earlier Mark III PT on it and serial #.
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Good intel. I'm emailing Mike B now also. I am curious how the transitional models differ in sound even relative to an early B.
 
Mike emailed me back and thought I would share intel. He could not remember where they switched (but based on internet searches and serials it does appear to be around the 6k mark). "I will say there is not really any transitional model. The newer loop and splitting the rev and lead in v3 and V4 was most all it amounted to." There you have it folks.
 
itsgoodnow said:
Mike emailed me back and thought I would share intel. He could not remember where they switched (but based on internet searches and serials it does appear to be around the 6k mark). "I will say there is not really any transitional model. The newer loop and splitting the rev and lead in v3 and V4 was most all it amounted to." There you have it folks.
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So, it must be the components that amount to most of the differences in tone cause when you compare a rev A with an early rev B they do sound very similar, while the later B's sound different. At least that's what I've found.
 
So how to spot one of this transitional B`s? Does it still have the attached powercord?
 
BesaMoogie said:
So how to spot one of this transitional B`s? Does it still have the attached powercord?
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Yes and some still have the older PT, but according to Mike B there wasn't much of a change going on with the amp from A to B.
 
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