Music Man serial numbers demystified

Hello,
this is my first message in this great forum.
I didn't find any explanation here on the serial numbers, only the assumption that they are random numbers. I believed that they must contain some information, so I collected serial numbers here from this forum and from ebay to draw my own conclusions.
This is what I found out so far:
The serial numbers have a form like C004235, BN05663, DP05491, etc.
They have 7 digits.
The first digit (A, B, C, D, or E) is the chassis size (width):
A: small size e.g. 65 watts bass head
B: two channel amps, left channel without bright switch and middle control, e.g. 112-65, 410HD-130
C: the big two channel amp like the 212HD-130 or 212-65
D: the RD or RP series with 65 or 100 watts
E: the small RD with 50 watts
The second letter (N,O,P) denotes the output power (we should read 0 as Oh here and not as zero):
N: normal(??) = 65/75 watts, or 50 watts on the small RD, generally "little power")
O: 130/150 watts
P: 100 watts
The following numbers seem to be chronological *for each series*. It seems there were more B models like C models, so a 78 B-model has a higher number than a 78 C-model.
What I didn't find out is what exactly happened when they changed to new models (75/150 watts). It seems they kept the first two letters and possibly started the numbering with 0000 again. Here I need more data.
Generally this means it IS to some extend possible to identify the model according on only the serial number. Also the numbers have to do with the year of production, but only indirectly. We need to find out which number range corresponds to which year *for each series (A - E).
greeting from Germany,
Ingo

Well done Ingo!
I give you two S/Ns (both from Germany ;) I bought them on ebay):
HD One-thirty 2100-130 EX A001627
Sixty-five 2100-65 EX AN01950
As soon as possible I'll give you the S/N of a RD112-65 that is from 1980 (year written inside the amp).
Bye!

Both of your amps are A series. Do they in fact have the same chassis width, or should I modify something of my theory?
According to the rather low numbers they both should have the driver tube. Am I right?

They have the same chassis an follow the rules of your theory.
From the model chart found in this site it seems that the HD130 never have transistor phase inverter.
The sixty-five has transistor paraphase inverter, so I think it's a 1978/79.
There is a difference between their knobs: numbers on the knobs in the HD130 are bold-like respect the sixty-five's ones. I'm quite sure that HD130 is older than the sixty-five.
I compared the components inside the amps but I haven't found any differences.

Some news about the sixty-five head. It's a kind of hybrid (!) It has a preamp board rev BB-1 B, with LM307H opamps (metal can package), and the "filter circuit" (as mentioned in the schematic) BUT has no 12AX7, so the bias circuit in preamp board is unused and the two EL34 are biased by transistors. If you look the schematics of 2100-65 chassis , in the matter of fact, none of them is correct for this head.
This makes me think that has been produced in the period of migration from tube PI to opamp PI.
NOTE: In the previous post when I wrote about component differences I was referring to preamp board.

Hi Giorgio,
thanks for your table with the data you sent me.
The numbers on the transformers (and also on all potis) also have some information about the date of manufacture, e.g. 606-740 means 606: manufacturer code, 7: 1977 (or 67 or 87), 40th week
So the 65 can't be built before end of 77, while the 130 is from early 77 or later.
The change from tube inverter to SS inverter was to my knowledge in 77 (not in 76). However, many amps that came with a tube were called back and were equipped with the SS driver board - this was a free service by MM.
For this reason you might find SS drivers on 75 or 76 amps as well. On the other hand, the latest tube driver we find should mean that all amps up to that date were originally made with the tube - until now this seems to be early 77 (but I need more data).
The schematics with the SS board were from a later version, without choke and with the stand-bye switch at the front. My 1980 HD130 is one of these.
Ingo