Advice on 1969/70 made 100w super lead

[Smellytele]

The head cab looks like it has plastic corners on three sides; when did Marshall start using those? For some reason I thought it was later 70's. And the logo looks too large for 69/70

 

[PrestonCowboy]

From what I see...
- valves have been replaced (before I bought it - has 4 Pinnacle branded EL34 tubes, dated Feb (19)82.

Everything else appears as original from what I can tell.

QA label has a date of 12/12/1969 on it !

I've NOT had the frame out of the wooden carcass yet - advice on what to do or not to do most welcome before I do that !!! (I assume it's just a couple of bolts and all the lot slide out ??
Or should I leave alone as I've never messed with this stuff before ? (I'm a mechanical (rail vehicle) engineer, happy to take things apart, just wary with something this old / something I've not worked on before).

 

[PrestonCowboy]

I'd definitely welcome all thoughts and advice - I'm getting to a point where I have the time to re-start playing (it's going to be re-teaching an old, not very talented, dog, the tricks he learned in the 1980s !)

Should I try to find a good amp tech in the region that knows what they are doing with OLD amps ?
Should I contact Marshall direct (they used to have a service dept down in Bletchley) or would they swap out 80% of the parts and make the thing rubbish ?



Or at least try getting new capacitors in case these are dry.

Should I just plug in and get playing ?

I'm on a new-old bakalite round 'keyed' power plug (not the more modern update to the IEC / 'KETTLE PLUG' Power lead). Thoughts on that ?

Anything else ?

When I get playing again, I'm realistic that I'm not going to be filling concert halls - this will be a hobby into early retirement, and I may be better served with a small 10w or 20w combo that can be switched down to use in our small house (3ft thick stone walls are good for not annoying neighbours). Though I'm also open to opinions on whether an attenuator is worth while instead.

 

[Matthews Guitars]

Pull the chassis out and take a bunch of clear photos of the amp internals and post them here. Also a few of the top surface showing transformer markings, etc.

If it's been decades since it was last plugged in, don't. That's a worst case scenario for those blue filter capacitors. At the absolute minimum they need to be reformed by bringing the amp up slow on a variac. They would have almost certainly depolarized by now, and if they were to get hit in the face with full operating voltage they'd probably blow their guts out and the corrosive residue would do NO good for the amp's components. The amp should see a qualified technician if you actually want to run it.

Yes a good attenuator is a good investment. I run 100 watt Marshalls in my home every few days. The attenuator keeps my hearing in good shape.

 

[Ned B]

As all have gathered by now it's a December 17th, 1969 test dated amp with the smooth top handle as normal for this period. Someone obviously added those corners. The cones should be inspected. The '68 silver back T1281s may be factory recones as are mine from that period that I have posted about in the past. If the cone code ends in "003" the lead cone, it is likely a recone done maybe as early as '69 at Celestion. The "014" bass cone would have been the original cone for the T1281. The silver magnet cover may be what Celestion used for their in-house recones. Instead of using a 014 bass cone they went with the 003 lead which would be a mis-match to the T1281 model.

 

[PrestonCowboy]

This code 32 102 014 is printed on the cone, if that is of any help !

 

[BlueX]

This code 32 102 014 is printed on the cone, if that is of any help !

Correct cone code! If you got the same code (production week "32" might differ) on all speaker cones then that's a really nice cab, worth some money if speakers still in good condition. Cab looks great, with logos ("Marshall" and "100") still in place, kind of rare.

 

[BlueX]

Very nice stack with this 100W amp and the cab. I think you should remove corner guards and that white "Marshall" logo from the amp head. Will look better. Looking forward to pictures from inside amp chassis!

You should not just plug in and start up this amp. If it's been sitting for decades it needs an inspection and slow startup (by someone who knows how to). Hopefully some British forum member can advice on a good tech in your area, if you're not able yourself.

If you want to keep and play that amp I suggest an attenuator between amp and cab. Marshall 100W into one 4x12 with vintage greenbacks might be too much for the speakers.

 

[scozz]

The head cab looks like it has plastic corners on three sides; when did Marshall start using those? For some reason I thought it was later 70's. And the logo looks too large for 69/70

Yes, logo should be the small one I’d think.

 

[TAZIN]

View attachment 157067

What's with the two little blocks of wood fastened to the baffle? Was the cab ported at one time?

 

[TAZIN]

From what I see...
- valves have been replaced (before I bought it - has 4 Pinnacle branded EL34 tubes, dated Feb (19)82.

Everything else appears as original from what I can tell.

QA label has a date of 12/12/1969 on it !

I've NOT had the frame out of the wooden carcass yet - advice on what to do or not to do most welcome before I do that !!! (I assume it's just a couple of bolts and all the lot slide out ??
Or should I leave alone as I've never messed with this stuff before ? (I'm a mechanical (rail vehicle) engineer, happy to take things apart, just wary with something this old / something I've not worked on before).

You should post photos of the circuit to see if your amp has the factory mistake in which a 10K resistor was used on the cathode of V2b instead of a 1K.
It's just the four screws on the bottom of the cabinet that hold the chassis in place. You just have to inch the chassis out slowly making sure you don't snag the metal faceplates on anything including the aluminum sheet that is stapled to the bottom of the cabinet.

 

[PrestonCowboy]

Thanks folks. I've knocked off work for the eve, wife and daughter away, just walking the dawgie, then time to get the screwdrivers out again !

For the csb's 2x port holes with the patched covers, it definitely looks like an 'after' mod (bodge !), judging by the different colour of the thin ply. It's honestly the 1st time I'd seen that - but last night was only the 2nd time the back has been off since 1984 or so when I got it. I recall my mates and I took the cover off when I got it, just to check there really were 4 speakers and the cones were not ripped (again back then it was just an old 2nd hand cab to the 14 or 15 or 16 year old me). As I'd mentioned before, I've done no mods, other than replacing 1 or maybe 2 front knobs, and at the end of last year I got a 2nd hand good quality Bulgin power plug, as I couldn't find the original power cable when we cleared my parents house.

The fabric / front panel looks glued in and I'm not going to try to touch that.
It's had a pvc cover over it when not used, hence why in a reasonable state.

I'll take the chassis out of the head and get a load of photos tonight, and will try to post.

 

[PrestonCowboy]

Hi again.
I've got photos of the amp having removed the chassis from the case, and will upload over a couple of posts: (just got to do some file shrinking as most are too large when I try to post)

- I checked the pre amp tubes:- all the same, Brimal, ECC83, stamped as Made in England.

- no labels or markings rhat ai can see on the transformers.

- non-transformer end of the chassis has a small orange sticker with initials - can't make out what (D... maybe ???)

 

[PrestonCowboy]

Photos as below #1

 

[PrestonCowboy]

Photos#2

 

[PrestonCowboy]

Photos #3

 

[PrestonCowboy]

Photos #4 (last ones)

 

[BlueX]

Looks very nice, thanks for sharing! Still red dye on almost all solder joints.

V7 socket seems to be replaced, with burn marks around. Wonder if it took out something else as well?

 

[TAZIN]

Hi again.
I've got photos of the amp having removed the chassis from the case, and will upload over a couple of posts: (just got to do some file shrinking as most are too large when I try to post)

- I checked the pre amp tubes:- all the same, Brimal, ECC83, stamped as Made in England.

- no labels or markings rhat ai can see on the transformers.

- non-transformer end of the chassis has a small orange sticker with initials - can't make out what (D... maybe ???)

The initials are DM. He was one of the inspectors working at Marshall. He's the same guy who used to do the final test inspection on the amps in 1968.

 

[TAZIN]

Photos as below #1

Looks original with the exception of the one octal socket (V7) and both front panel switches. The transformers are original Dagnall's (T2623 & C1998).
For the resistor mistake on the V2a cathode, you have to look under the second 0.68uF capacitor since there are two resistors hidden underneath. One resistor will be a 100K (Brown, Black, Yellow, Gold color bands), and the other should be either a 820-ohm (Gray, Red, Brown, Gold) or a 1K (Brown, Black, Red, Gold). If it has the factory mistake, you'll see a 10K (Brown, Black, Orange, Gold) resistor. You can also use a multimeter to check the value of the cathode resistor. This photo shows the location of the V2a cathode resistor. You can see the 100K resistor clearly, but the V2a cathode resistor is underneath the large 0.68uF cap. The Red lines on the photo show where you could put the leads of a multimeter to check the value of the cathode resistor.