Mark IIA or IIB?

Scored this chassis from a studio closeout...

Wanted some feedback on what year this is and technically if it is a IIA or IIB...

The serial number puts it in the first batch of IIB's but as the pictures show there might be a different story...

Pots and transformers from 77', 78' & 79'

Capacitors from 78', & 79'

Fetron switch wired to V1 tube socket....

IIB knobs on the front, older style IIA knobs on the back

Etc..., etc...,etc....

It's a IIA!

Doesn't have an FX loop.

Yes, it is a II-A.

It must be one of the very last MKII-A's... my 1980 MKII-B is just a couple of numbers shy of it, according to the serial #.

Strange though... mine has the older silver capped knobs on the front and back. :?

Yes, at s/n 5823 the data on the chassis should show something like October 1980. Lovetoboogie: could you check the date written in the chassis in black Sharpie, please?

If I recall properly, I have seen a II-A with s/n 5574 born on 8/14/80 and have also seen another II-A with s/n 5022 born on 9/10/80.
Most probably, these inconsistencies could come up due to the move from Lagunitas to Petaluma that was happening at that time.

igfraso said:

Yes, at s/n 5823 the data on the chassis should show something like October 1980. Lovetoboogie: could you check the date written in the chassis in black Sharpie, please?

If I recall properly, I have seen a II-A with s/n 5574 born on 8/14/80 and have also seen another II-A with s/n 5022 born on 9/10/80.
Most probably, these inconsistencies could come up due to the move from Lagunitas to Petaluma that was happening at that time.

Click to expand...

I suppose that means that since my MKII-B is dated 10/7/1980... it must be one of the earliest examples of that model? :?

igfraso said:

Yes, at s/n 5823 the data on the chassis should show something like October 1980. Lovetoboogie: could you check the date written in the chassis in black Sharpie, please?

If I recall properly, I have seen a II-A with s/n 5574 born on 8/14/80 and have also seen another II-A with s/n 5022 born on 9/10/80.
Most probably, these inconsistencies could come up due to the move from Lagunitas to Petaluma that was happening at that time.

Click to expand...

Hi..thanks for the feedback...

There is no sharpie birthday on this chassis. It is not the first from 1980 that i have seen without a B-Day...

There is some faded sharpie near the tube sockets, 12AX7, etc...

I assumed this was a IIA but there are IIB staging resistors coming off the B+ rail going to the preamp( 1K vs. 5.6K) sending a much higher plate voltage down the rail...

Looks to have recent Mesa Filter Caps which leads me to believe this amp went back to Mesa at some point, and maybe thats when the front knobs were replaced..

So, this is a rather cool transistional IIA>IIB with some elements of both in the circuit design and dress...

Blueboxer said:

igfraso said:

Yes, at s/n 5823 the data on the chassis should show something like October 1980. Lovetoboogie: could you check the date written in the chassis in black Sharpie, please?

If I recall properly, I have seen a II-A with s/n 5574 born on 8/14/80 and have also seen another II-A with s/n 5022 born on 9/10/80.
Most probably, these inconsistencies could come up due to the move from Lagunitas to Petaluma that was happening at that time.

Click to expand...

I suppose that means that since my MKII-B is dated 10/7/1980... it must be one of the earliest examples of that model? :?

Click to expand...

As far as I know, the first II-B was produced on 8/14/80 with s/n 5575.

lovetoboogie said:

igfraso said:

Yes, at s/n 5823 the data on the chassis should show something like October 1980. Lovetoboogie: could you check the date written in the chassis in black Sharpie, please?

If I recall properly, I have seen a II-A with s/n 5574 born on 8/14/80 and have also seen another II-A with s/n 5022 born on 9/10/80.
Most probably, these inconsistencies could come up due to the move from Lagunitas to Petaluma that was happening at that time.

Click to expand...

Looks to have recent Mesa Filter Caps which leads me to believe this amp went back to Mesa at some point, and maybe thats when the front knobs were replaced..

Click to expand...

According to our records, this amp has NOT been here for service. Thanks!

At #5823, your serial number is way higher than my IIB, which is #5387. My chassis is dated June, 1980 on the underside. It was bought directly from Mesa, and I'm the sole owner.

@igfraso, you'll note that my serial predates the #5575 cutoff by a significant amount. That info, which comes from Mesa, is plainly wrong.

@lovetoboogie: not sure how your recollection squares with my amp. Could you be mistaken, re: dates?

@blueboxer: I don't think so. Mine is dated 6/18/80, by Mike B.

So there are a few possibilities:

1. My amp was a prototype or custom corder, perhaps an early experiment to see how the effects loop might be implemented. Since its back plate layout is absolutely standard on all the IIBs, though, it's highly improbable that it was a one-off or an experiment. Instead, I think it's just one of the first IIA-IIB transitional models.

2. The cutoff for the IIB was much earlier than Mesa's records indicate. This is true, but as to when they actually started making IIB chassis, it would have to be on or before June 18, 1980.

2. It's possible that your amp has been messed with a bit. Cosmetically, yours has late-model IIB all black knobs on the front, where mine (and all early IIBs) have silver inverted conical knobs -- like the ones on the back of your amp. (Obviously, since knobs are easily swapped, this doesn't mean much.) But you don't have an effects loop, which puts in it solidly in IIA territory, except its serial number is WAY higher than mine, and many other IIBs Your amp seems a bit of a mystery, actually.

Is it possible that it was kluged together out of two or more Boogies?

@blueboxer: I don't think so. Mine is dated 6/18/80, by Mike B.

Click to expand...

Ok, understood... I was just going off of igfraso's quote:

If I recall properly, I have seen a II-A with s/n 5574 born on 8/14/80 and have also seen another II-A with s/n 5022 born on 9/10/80.

Click to expand...

FYI... mine is MKII-B s/n 5889, built 10/7/1980. :wink:

It is odd, though, that his serial number (which is solidly into IIB territory) doesn't correspond with what should be the standard back plate configuration for a IIB, i.e., no Effects Send and Return jacks, only the Slave and Preamp Out/Power Amp In jack.

Can anyone make sense of this? Could you order a IIB without the loop? (I didn't think so, but who knows?)

Dude2Dude said:

It is odd, though, that his serial number (which is solidly into IIB territory) doesn't correspond with what should be the standard back plate configuration for a IIB, i.e., no Effects Send and Return jacks, only the Slave and Preamp Out/Power Amp In jack.

Can anyone make sense of this? Could you order a IIB without the loop? (I didn't think so, but who knows?)

Click to expand...

Agreed. Perhaps it has been cobbled together from different amps? :?:

The amp is certainly unique... no, i don't believe in my gut is it cobbled together by anyone outside of Mesa Boogie. The knobs on the front were definately replaced... the transformers all have 77', 78' & 79' EIA codes, as do the pots, EQ caps, etc...

wasn't much work done on this except for B+ Filter Caps(Mesa Branded Spragues), and a new resistor on the presence circuit. Everything else is original. Or as original as I can determine given the varying date codes on everything!

it sounds amazing. with the high plate voltage on the preamp the dynamics on both the lead and clean channel are mindblowingly good...

I am going to put it in a headshell I just had built. Gonna dress it out in Cherry and wicker...

Fun thread, thanks for the replies!

lovetoboogie said:

The amp is certainly unique... no, i don't believe in my gut is it cobbled together by anyone outside of Mesa Boogie. The knobs on the front were definately replaced... the transformers all have 77', 78' & 79' EIA codes, as do the pots, EQ caps, etc...

wasn't much work done on this except for B+ Filter Caps(Mesa Branded Spragues), and a new resistor on the presence circuit. Everything else is original. Or as original as I can determine given the varying date codes on everything!

it sounds amazing. with the high plate voltage on the preamp the dynamics on both the lead and clean channel are mindblowingly good...

I am going to put it in a headshell I just had built. Gonna dress it out in Cherry and wicker...

Fun thread, thanks for the replies!

Click to expand...

Very cool! Either way it looks like a wonderful, unique amp. Enjoy!

Blueboxer said:

igfraso said:

Yes, at s/n 5823 the data on the chassis should show something like October 1980. Lovetoboogie: could you check the date written in the chassis in black Sharpie, please?

If I recall properly, I have seen a II-A with s/n 5574 born on 8/14/80 and have also seen another II-A with s/n 5022 born on 9/10/80.
Most probably, these inconsistencies could come up due to the move from Lagunitas to Petaluma that was happening at that time.

Click to expand...

I suppose that means that since my MKII-B is dated 10/7/1980... it must be one of the earliest examples of that model? :?

Click to expand...

Blueboxer,
regarding the first Mark II-B, I have seen:
- s/n 5515 dated 7/8/80
- s/n 5505 dated 7/17/80
- s/n 5517 dated 8/80 (August 1980 with no date)

You can see the inconsistency in serial numbers and dates.

Are they prototypes or regular production amps? I really don't know.

Just thought I would add my Mark IIb info to the mix to see if it would help

SN: 5587
Date: 7/23/80