Mark IIb serial numbers

[erickompositör72]

Hello,

I'm wondering if there is info about exactly what serial numbers encompass these preamp boards:

RP9A / SP9A
RP9C / SP9C

...and any others, for the sake of having it all in one place.

I know my serial #1015X has the RP9C
I had a #8936 that had the SP9A

 

[robredo_mattila]

I have a Mark IIB with the SP-B8 circuit board.

Serial # 696x
Chassis date: 5/12/81

 

[Dude2Dude]

I have a Mark IIB with the SP-B8 circuit board.

Serial # 696x
Chassis date: 5/12/81

Should that be RP 8B, robredo? I think that's the number on my circuit board (Serial #53xx), 1980 MK IIB, loaded, from June, 1980

 

[robredo_mattila]

Should that be RP 8B, robredo? I think that's the number on my circuit board (Serial #53xx), 1980 MK IIB, loaded, from June, 1980

Apologies for the late reply. This is the number inside my Mark IIB. It's with my tech currently getting a clean bill of health. Looking forward to getting it back soon.

 

[sloanthebone]

My IIb is:

Date 10/81
RP-9B
Serial: 8231
says HRGX on the side

 

[jmf1928]

Is there any detail around the revisions and how the tone evolved? I have an 83 that I am pretty sure is a 9C, and it’s a wonderful amp. Definitely as metal-capable as I ever expect to need as well.

 

[RicherHertz]

Is there any detail around the revisions and how the tone evolved? I have an 83 that I am pretty sure is a 9C, and it’s a wonderful amp. Definitely as metal-capable as I ever expect to need as well.

+1 on what @jmf1928 is asking.

"Is there any detail around the revisions and how the tone evolved?"

 

[maswaim]

Hello,

I'm wondering if there is info about exactly what serial numbers encompass these preamp boards:

RP9A / SP9A
RP9C / SP9C

...and any others, for the sake of having it all in one place.

I know my serial #1015X has the RP9C
I had a #8936 that had the SP9A

My Mark IIb is a 929x with the RP9C board. Date is 5/13/82. HRG on side.

 

[XRL]

Hello,

I'm wondering if there is info about exactly what serial numbers encompass these preamp boards:

RP9A / SP9A
RP9C / SP9C

...and any others, for the sake of having it all in one place.

I know my serial #1015X has the RP9C
I had a #8936 that had the SP9A

Interesting, your 1015X s/n is very close to mine, made in late December 82. Mine is a base 60w model. Only option was cream tolex. Same board revision as well.

 

[erickompositör72]

My Mark IIb is a 929x with the RP9C board. Date is 5/13/82. HRG on side.

Aha, a 9C pre-1000! I was wondering if that was the cutoff

 

[RicherHertz]

Here's a headscratcher for this thread. Serial # 540X w/ Export Transformer dated 6/24/80.

Preamp Board # RP 8C. Mike B. has been in this one (loop mod & preamp tweaks).

Looking at Mesa’s serial # range, it looks like this may be a very late IIA or early IIB?

 

[XRL]

Apparently a IIB, and of course, the loop is the signature feature of that mark.

https://mesaboogie.zendesk.com/hc/en-us/articles/218914817-When-was-my-amp-made-

 

[user 41014]

Here's a headscratcher for this thread. Serial # 540X w/ Export Transformer dated 6/24/80.

Preamp Board # RP 8C. Mike B. has been in this one (loop mod & preamp tweaks).

Looking at Mesa’s serial # range, it looks like this may be a very late IIA or early IIB?
View attachment 1263View attachment 1264

Good job on book-ending the IIB start and RP board, a little earlier start than on the support site. I have an undated 58x coli with the RP-8C which I always thought must be one of the 1st coli's.

On my '76 Boogie restore thread we found the transition to 9A boards at August 1, 1981 (finish date) give or take a week at 7500.

This amp seems to define the 1st IIB reverb board as the RP-8C. The SP-9B was used until 7/23/81 at least based on another member's amp (743x) while my 8/6/81 752x has SP-9A.

The latest IIA I've seen is 4/28/80 5108 with RP-6A. It's looking like it went from RP-6A to RP-8C so the only thing left for me is to see if the 6/80-early '81 are SP-8A that may not exist or the 8B that clearly exists. I also have a SP-8B K12x - it's undated and since I don't believe in pre K100 coli's is likely in the first 30 or so coli's made.

The SP/RP-7, maybe the 8A (and RP-8B) too must have got scrapped.

 

[user 41014]

8/18/81 K152 also had what looked to be RP-9A tracing which I have on a 10/5/81 61x big brother and have also seen on a no serial 10/7/81 coli.

But sloanthebone's 8231 with the 10/81 start date shows mesa moved on quickly from the RP-9A. At only 2-3 months build the RP-9A is a more rare IIB. Next is to nail down the transition to SP/RP-9C.

The latest SP-9A I have is 1/26/82 in K23x and I've seen 8551 with the same finish date but no gut shots. I have not seen a SP-9B as of yet.

 

[James]

Here's a headscratcher for this thread. Serial # 540X w/ Export Transformer dated 6/24/80.

Preamp Board # RP 8C. Mike B. has been in this one (loop mod & preamp tweaks).

Looking at Mesa’s serial # range, it looks like this may be a very late IIA or early IIB?
View attachment 1263View attachment 1264

Early IIB, as it had an effects loop to begin with. The IIA had a different layout with preamp out/power amp in jacks. How does it sound? I've got a IIA with the tube version of the FX loop mod. Great sounding amp.



As for the original question, here are the IIBs that I've had

-743x. 60 watt with loop mod and SP-8A board. All 12AX7s. Dated 7/23/81

-779x. 60 watt. All 12AX7s, so probably the SP-8A. Dated 9/10/81.

-86xx. 60 watt. V2 12AT7, so the circuit had changed. I'm guessing the SP-9A. Can't remember the exact build date, but definitely 1982.

-1050x 100w. V2 12AT7. RP-9C board. 1983 build (exact date tbc)

The RP-9C is definitely my favorite. Sort of falls in between the older MK 1 type sound and the later amps. Low end is more usable and still has a plenty of drive. Fairly neutral sounding too.

 

[user 41014]

As for the original question, here are the IIBs that I've had

-743x. 60 watt with loop mod and SP-8A board. All 12AX7s. Dated 7/23/81

-779x. 60 watt. All 12AX7s, so probably the SP-8A. Dated 9/10/81.

James, I made a mistake stating your 743x was SP-9B (which I've never seen) and you have it listed as SP-8A (another I've not seen). In nailing down the transition to the 9A boards tho you said this was a 7/23/81 SP-8B.

Your 779x should be SP-9A for September 81.

My 12/28/81 K22x SP-9A uses the 12AT7 for V2 and since they changed the RP boards around October build start I'm guessing they re-spec'd V2 at the same time, roughly Halloween finish builds and later (RP-8B and SP-9A which continued into '82).

Sloanthebone's 8231 however has 12AX7 written across V1/V2. I cant see V3 assuming AX7 while the V4 reverb is 12AT7 maybe to lower the voltage for this stage only to move it to V2 shortly after. A little voltage balancing act in late 81? I think it was a Mark III I just read about that MB pulled back on how hot the reverb driver was so this balancing act looks to have continued for years.

 

[sloanthebone]

 

[James]

James, I made a mistake stating your 743x was SP-9B (which I've never seen) and you have it listed as SP-8A (another I've not seen). In nailing down the transition to the 9A boards tho you said this was a 7/23/81 SP-8B.

Your 779x should be SP-9A for September 81.

My 12/28/81 K22x SP-9A uses the 12AT7 for V2 and since they changed the RP boards around October build start I'm guessing they re-spec'd V2 at the same time, roughly Halloween finish builds and later (RP-8B and SP-9A which continued into '82).

Sloanthebone's 8231 however has 12AX7 written across V1/V2. I cant see V3 assuming AX7 while the V4 reverb is 12AT7 maybe to lower the voltage for this stage only to move it to V2 shortly after. A little voltage balancing act in late 81? I think it was a Mark III I just read about that MB pulled back on how hot the reverb driver was so this balancing act looks to have continued for years.

Sorry, yeah - SP-8A was a typo. Will edit the post. 743x from July 81 is definitely the SP-8B

It's difficult to say about the 779x - sold that one around ten years ago. Do we have any examples from around that time? I know it was all 12AX7s. The sound was closer to the above amp (before the FX loop mod) than the later ones.

Which version is 8231? I had one in the 8600 range and all I remember is that it was an 82 and had the 12AT7 in V2. Interestingly that amp originally had a 250k pot for volume 1.

Here's the 83 RP-9C I mentioned. 1050x. V2 is marked for either tube, but I've only used 12AX7

 

[Lyon76]

Hey James you have the same lettering on your amp as mine. So does the b of 83 represent feb of 1983? Mine says D of 83 with same initials . Mine is a 107**

 

[user 41014]

Which version is 8231? I had one in the 8600 range and all I remember is that it was an 82 and had the 12AT7 in V2. Interestingly that amp originally had a 250k pot for volume 1.

8/1/81 brought the SP-9A and RP-9A.

By thanksgiving '81 reverb amps started in 10/81 like 8231 had the RP-9B while the SP-9A's continued. I have a late Jan 82 one still with SP-9A and can't speak to past that.

This prob needs updating but will help with your Q and the main Q of this thread:

As you can see by 10582 (if someone didn't change them on that amp) they moved to Mark IIC / Mark III knobs while it looks like your 1050x still has Fender looking "innies" with a zero. That narrows that transition down to 80 amps.