Help me identify my Mesa Mark II (probably a mark IIb)

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breogan

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Hi there!

I've just bought a Mesa Boogie Mark second hand, serial number is 3984. I suspect this amp has gone thru a heavy modding process. Both external and internal. I hope you can help me!!

What I know for sure is that this was originally a combo that was reconverted to rack-mount system (the chassis has an engravement that says "combo" next to a very long number.). The front panel looks like a Mark IIb.

Front panel

2005_0826mark0002.jpg


Back Panel

2005_0826mark0005.jpg


And this is the channel-switching pedal. (this looks original)

2005_0826mark0003.jpg



If we look at the botom of the chassis it can be seen that this amp was made in 79'. AFAIK Mark I were made at least up to 1979 so this may be one of the first Mark II or Mark IIb, is't it?

DSCF1644.jpg


This a view inside the chassis, I suspect some kind of modifications have been made, but I haven't gone thru the circuit yet. On one side of the chassis there is a stick of Nau Engineering, this may be the company that made the rack-mount change. I have asked them and I am waiting for response.

DSCF1633.jpg


Finally a general view of the chassis.

DSCF1638.jpg


Any info about this amp that you could tell would be greatly appreciated. Also some pictures of the original wiring too so I can compare to mine.

Thanks a lot!
 
Thanks! Definitely it is a Mark IIa...

One of my main problems is that I live in Europe and the PT is wired for 110V. Do you know if the PT has any primary wired for 220V or 240V?

Are there any Mesa PT schematics?

Thanks!
 
Definitely a 60 watt Mark IIA because of the Fetron, serial number and the effects loop. This is a great amp. I would suggest having a qualified tech remove the fetron and maybe they could rewire it for Europe. It doesn't look too modified to me.

I can't say enough good things about the IIA. Just a flat out awesome amp. I have the 60/100 watt version and had Mike B remove the Fetron and balance out the gain between channels and give it a general good bill of health. Well worth it. This amp sings. It will be nice to compare the clean channel of this Mark IIA against your Fender Bassman, It may surprise you.

Good luck and have fun.
 
Where is exactly the fetron? Mine has 3x12AX7 outside... Is it inside on the PCB board?

Sadly that Bassman isn't mine, pictures are from the previous owner.

I am going to check if I can rewire the PT.
 
There is a switch labeled TR1009 which chooses either the silicon Fetron or Preamp tube. Good luck if you are so inclined to rewire it. I would listen to the amp first however you might like it as is.

Check this out from The Boogie Files:

Mark IIA

The Mark II introduced channel footswitching, so you could go from rhythm to lead. It also wasn't referred to as the "Mark IIA" until the Mark IIB was issued. You could also get a separate head for this model, which could be hooked up to a number of different speaker combinations, although a 1x12 cabinet was typical. However, the reverb circuit is considered noisy and the footswitching made a popping sound when used; both of these features were later improved on in the IIB and IIC. The preamp gain on the Mark IIs occurs after the tone controls, unlike the Mark I. A MESA/Boogie person has stated that the IIA has a "tighter, more focused sound" than the Mark I. The clean channel on this is very nice, but some argue that EQ is needed on the lead channel to be able to dial the midrange out in order to get something other than the "Santana" tone. A landmark review of this amp was posted in the German literature, namely the Fachblatt Test.

The IIA and IIB, and some late-model Mark I amps used a silicon device called "fetron" in place of one of the 12AX7 pre-amp tubes, and included a switch for configuring the amp for either fetron or 12AX7 operation. The reason for using a fetron was to address some of the problems associated with microphonic 12AX7 tubes in a high-gain situation; somehow, Boogie users didn't care too much for the fetron, so its use was later discontinued.
 
breogan said:
Thanks! Definitely it is a Mark IIa...

One of my main problems is that I live in Europe and the PT is wired for 110V. Do you know if the PT has any primary wired for 220V or 240V?

Are there any Mesa PT schematics?

Thanks!

No dice Breoheem. The PT is 117V only and cannot be rewired. If you need a IIA schematic, just PM me with your e-mail address.

Nice amp !! :D
 
Boogiebabies said:
breogan said:
Thanks! Definitely it is a Mark IIa...

One of my main problems is that I live in Europe and the PT is wired for 110V. Do you know if the PT has any primary wired for 220V or 240V?

Are there any Mesa PT schematics?

Thanks!

No dice Breoheem. The PT is 117V only and cannot be rewired. If you need a IIA schematic, just PM me with your e-mail address.

Nice amp !! :D

That's what I suspected... :( Anyway I have a step down transformer for this amp... I just scored an empty cabinet on ebay that includes a EVM 12L and the SUS-4 mounting system. Plus a reverb tank!

With this the amp will recover its original aspect.


Carlosasi,

Thanks! that's what I though but, I was wondering which element of the PCB is the fetron. There is a small cylindric element with 6 legs and a metal cap but I suspect that is the relay.
 
That's way out of my comfort zone!

Sorry.

Here is a before and after of my amp with the Fetron removed if that helps.

Before with fetron


After fetron removed


It appears to be the black plastic housing with 2 resistors running to the pcb.
 
carlosasi said:
That's way out of my comfort zone!

Sorry.

Here is a before and after of my amp with the Fetron removed if that helps.

Before with fetron

After fetron removed

It appears to be the black plastic housing with 2 resistors running to the pcb.

That plastic housing is the switch for the fetron! :D

I've been reading a bit (not much info available)... It seems that the fetron is a device that was plugged in the 12AX7 socket instead of the tube. The tube and the fetron needed different working voltages so the switch is used to set the correct voltage for each device.

See this user panel.

i-4_B_L.JPG


I guess you technician removed the switch leaving it set for the 12AX7.

Mine came with a 12ax7 on the socket, so I have no chance to try the Fetron.
 
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