Need help dating a Vintage Marshall SuperBass...

[cluster]

Hello Everyone,

I'm posting here because i just received this vintage Marshall SuperBass for $900. The guy I bought it from told me it is a 1969 but I didn't believe him (hence the price). The amp also has a JCM800 MV mod. Most of it appears original with the original red dye on the solder joints but much of the front end has been moded and .022uF were put on to the output to convert it to super-lead specs. Two screen resistors were swapped as well as some resistors/caps in the front end. Also, some idiot cut out the serial number so I can't date it exactly, so I'm asking you experts to help me date this amp. It has a lay-down PT with 490VDC on the plates (tubes in). It also has original yellow caps (which I've never seen) that are not mustards. The only mustard in on the presence control. The PT/OT are original based on the red dye but there are no codes to be found anywhere on them. Can anyone here help me identify this amp?? My feeling, based on looking at my other vintage Marshalls is that it's a 71 but I'can't tell. My intentions are to rip out the mod and using what vintage parts I can find, bring it back to 69 Superbass specs. thanks

[cluster]

More shots:

[cluster]

[cluster]

Just had a look under the CTS pots. One said LN AB C2. I read some where that LN = Linear, AB=Allen Bradley (maker of the pot) and C2=date (C=month and 2=72??). Anyone out there know how to date CTS pots in vintage superleads??

[J M Fahey]

Is exact manufacturing date that important?
Or at all?

All that practically matters is that it is an old Marshall, that it seems to be working properly, that you can build there the circuit you want without much trouble.

The yellow caps are certainly not original, but look good quality.
FWIW the earlier owner must have replaced old mustards with these for some reason, most probably seeking an improvement.

I would not lose sleep chasing same spec old ones if these are good.

EDIT: as of the missing serial number, most probable explanation is that sometime in its long history, this amp was stolen.

[MarkusBass]

Have you tried looking at capacitors? Larger capacitors (e.g. in the power supply) have manufacture period printed. I would also look at the transformers and maybe at 5W resistors. I see 74 on one of them. Could it be a production year?

Mark

[dai h.]

the yellow caps are original for that period (they varied--some amps look more consistent in terms of cap brand composition, some look more of a hodge podge).

[Justin Thomas]

If those are real CTS pots, there should be a 6 or 7 digit number on them, opening with 137_ _ _ _. Check all of them. If they all seem pretty close and are original, that should help narrow it down. After 137, first & second digits are week (01-52), third & fourth are year of manufacture.

Electrolytic caps should also be stamped with numbers, although I don't know Euro/British coding norms...

Don't get too hung up on it, as Juan said, but I do enjoy the detective work!

Justin

[Pedro Vecino]

Must be between 71 and 73 approx. No matter. Is there a lot of slow and patient work to get it back with electrical and mechanical safety and sounding like it should. Yellow capacitors are polycarbonate Philips, and sound brighter and with more edge than polyester mustard handling overdrive. I say this as a curiosity. There is no reason to change.

[dai h.]

While there are yellow ones that are polycarbonate, I think those are metal polyester (as far as I can remember from my research--don't recall the specific series at the moment).

[Pedro Vecino]

I bought many of them long ago in a dutch warehouse and was advertised as polycarbonate. They put pictures of the components on old catalog pages of Philips, Siemens, etc. Is the only reference that I have.

[dai h.]

IIRC this was the best (most authoritative) info I found on the web (at the "wayback machine/internet archive--which by the way for anyone looking for old data--has old semiconductor databooks and such as well) :

https://archive.org/details/MullardB...nentsMarch1981

https://archive.org/details/MullardP...ponents1974-75

(Looking at p.20 onwards on the 1981 databook pdf and p.10 on the 1974-75 databook) it looks like they could be either metal polyester (PET) or polycarbonate depending on the voltage rating (250V = PET, 400V = polycarbonate).

The "341" on the cap itself seems to indicate the series. I have some of these (presumably earlier to later from top to bottom) :



(which are also marked "34189" (followed by value) as in your pic). So I suppose if the same holds for the ones in old Marshalls (around 1967-1973--the 680nF show up earlier, the 22nF only from early 70s AFAIK), then the 22n would be polycarbonate, and the 680nF would be polyester (PET). (I have tried looking for older databooks, but couldn't find one that old, so the 400V 22n in Marshalls being polycarbonate is a bit of a presumption.)

[big_teee]

What is the Serial number.
Marshall Specs

[J M Fahey]

What is the Serial number.
Marshall Specs

some idiot cut out the serial number so I can't date it exactly,

[trobbins]

In Australia, the IRC 5W WW resistors marked IRC Australia have a 4 digit number, and the first two digits always seem to correlate with the amplifier age (ie. earlier). If so, then amp is at least late 1974.