NAD: Mesa Mark IV A/B

[Jimty]

What Headfirst is that? A Cali?

It’s his spin on the MCII, but the 25 watt version. Jason built it up as a smallbox because I wanted as many controls on the front panel as possible. Killer amp - it has Trainwreck transformers and is running 400v on the plate.

That’s a 2204 ‘78 JMP above it (in case anyone was wondering!)

 

[Bossman415]

Just took delivery of a Mesa Mark IV A/B - ie: one of the transitional amps that Mesa built between the Mark IV A and the Mark IV B. The serial number is solidly in the mid 58XXs.

There are a few amps I’d love to add to my shelf (KSR Gemini, Rev F Rectifier, Alta 100, Hellion) but a Mesa Mark wasn’t on the radar.

That said, I spotted this one for sale and did some digging and the idea of grabbing something a little out of the ordinary appealed to me. As I understand it, only a couple hundred of the transitional models were made and I guess not too many of those made it to the UK / Europe.

As I understand it I’m only the third owner and I know that servicing work (including the cap replacements and board clean up) was undertaken by a well known and respected amp tech. It used to be in a rack unit, but Zilla are building me up a headshell.

In case of interest, there’s a gut shot below and it has the 561137 and 562004R transformers. It also has the IV B fx loop.

I am very, very far from being any sort of expert, but from pictures I have seen I can see a fair few similarities to the Mark IV B circuit, a couple of similarities to the Mark IV A circuit and maybe a couple of places where this circuit doesn’t seem to be like either.

I’d be interested to hear from those with more knowledge about where the similarities and differences between this and the IV A and IV B circuits lie and if there are places where this circuit looks like something else (I heard of one A/B amp that had Mark IIC+ features).

It would also be interesting to hear from other A/B transitional amp owners as to whether this circuit is the same as the one in their amp, or whether they have further variations.

The amp sounds great, so all of the above is purely out of curiosity!

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Cheers,

Jimty

@Jimty I spoke with Mike B about this earlier last week. He said there's no such thing as an A/B transitional circuit.

There are 2 circuits A & B. As far as those transitional models go, Mesa always used whatever parts they had.

Hence the reason you see early Mark IVb's with Mark IVa faceplates, transformers, chassis and attached power cords.

This wasn't uncommon with other Mark models, like the IIC & III. The earliest of those models share parts from their predecessors.

Often times Mesa would take the faceplates and just stencil in the new pull feature above the knob, or use the remaining transformers, etc..

They did this to cut down on costs. Faceplates back in the early 80's were $25/pop, even at the volume they were buying them at.

This was a big contributor to the IVb going to a painted chassis and standardizing on the new transformer across other models.

It's definitely a cool amp and unique that it probably has the older transformers. Hope this info helps.

 

[Jimty]

@Jimty I spoke with Mike B about this earlier last week. He said there's no such thing as an A/B transitional circuit.

There are 2 circuits A & B. As far as those transitional models go, Mesa always used whatever parts they had.

Hence the reason you see early Mark IVb's with Mark IVa faceplates, transformers, chassis and attached power cords.

This wasn't uncommon with other Mark models, like the IIC & III. The earliest of those models share parts from their predecessors.

Often times Mesa would take the faceplates and just stencil in the new pull feature above the knob, or use the remaining transformers, etc..

They did this to cut down on costs. Faceplates back in the early 80's were $25/pop, even at the volume they were buying them at.

This was a big contributor to the IVb going to a painted chassis and standardizing on the new transformer across other models.

It's definitely a cool amp and unique that it probably has the older transformers. Hope this info helps.

That’s interesting and good to know. I’d read somewhere that there were a few out there that weren’t quite A or B circuits, but if anyone knows for sure it’s going to be Mike. That said - in the interests of safeguarding internet cork-sniffery - I’m sure we can all agree to bury this piece of information and keep talking about the rare transitional circuit….

 

[blackba]

Congrats Jim, I actually hadn't heard there were transitional models, but doesn't surprise me knowing Mesa.

 

[Jimty]

Ah nice! Sure itll look great in a new head cab.

I recently had a guy build a headcab for my Mark III, Craft Speaker Cabs. I think he only does stuff for Mesa's, can fully vouch for his level of detail and work.

So I decided to pick up a headshell from Craft Speaker Cabs after your post. Great guy to deal with. First class communication and I had my headshell within a week. The chassis fitted perfectly, the pre-drilled holes lined up perfectly with the chassis holes and the overall finish is first rate. Very impressed.

 

[easstudios]

So I decided to pick up a headshell from Craft Speaker Cabs after your post. Great guy to deal with. First class communication and I had my headshell within a week. The chassis fitted perfectly, the pre-drilled holes lined up perfectly with the chassis holes and the overall finish is first rate. Very impressed.

View attachment 254678

Looks fantastic! Glad it went well

 

[ClintN667]

That headshell looks perfect!