Some circuitry weirdness:



I can't understand why someone would have fitted this capacitor between the power selector and ground, but at some stage of its life, it went Boooom!

This place has been kinda dead lately, so not sure if there are any amp nuts left in these parts. If you're all still here, show yourselves and then I'll post up some more pics and we can chat about old amps 'n stuff like in the good 'ol days! 8)

shaunf wrote: This place has been kinda dead lately, so not sure if there are any amp nuts left in these parts. If you're all still here, show yourselves and then I'll post up some more pics and we can chat about old amps 'n stuff like in the good 'ol days! 8)

Yeah keep posting, we are looking ?

Does this amp work at all? It may need some TLC like the one you built a new circuitboard for. Looks really decent otherwise (barring the missing knobs and things).

Ok cool. Welcome EZ, hope other guys will chime in too. It's no fun doing this otherwise.

The first thing that got removed was that popped capacitor. It shouldn't have been there in the first place. Now that it's gone, lets take a look at the rest of the circuit:

Original Power Transformer. You'll also note that in this pic, I had replaced that horrible blue Neutrik Powercon socket with a NOS Bulgin socket. I also replaced that mains fuse holder that had previously been replaced with an incorrect sized unit, and as result had a bit of old brown circuit board around it to make it fit in a hole in the chassis that was too big for it.



Original electrolytic caps still in place. I reformed all of these caps and they seem to be working ok for now. Now what is that weird blue cap in the bottom right of the image?

Casting our eyes further to the left, we are greeted with this sight:




Most of the solder joints still contain the red dye Marshall originally marked them with. If you're wondering, the blue and yellow capacitors are made by Cornell Dubilier and are 100% original to the amp. There are a few amps that were made around the same time that also have these caps, instead of the regular mustards one usually sees. The only component that has been replaced on the entire turrent board is one of the plate resistors on V1. The V1 tube socket has also been replaced at some prior stage.

By the time this second picture was taken, I had already replaced the 2 left most input jacks that had been previously replaced with incorrect regular jacks. I installed 2 new Cliff jacks.

The Tremolo circuit is currently disconnected and so this amp is currently operating as a straightforward Superlead.

Restored rear view:

Front view, now sporting the replacement input jacks as well as a full set of vintage knobs:



Fortunately both the front and rear plexi panels are both in exceptionally good condition, with no cracks, or oxidisation of the gold paint.

Completed my usual startup procedure for amps that haven't been powered for a long period, including reforming the main electrolytics. I checked the onboard electrolytics for signs of physical leaks and couldn't see anything. Bias circuit was providing stable bias voltage. Once I was satisfied that the caps were ok, and that there were no shorts or anything major wrong, I brought up the voltage slowly on my variac with no tubes installed. All seemed good, so I installed a good known set of tubes, reran my tests, biased the amp and plugged in a guitar, and instantly she sprang back to life. 8)

Over the weekend, I tackled some of the headbox cosmetic issues. In the first picture I posted, you will see that the headbox piping around the front panel had at some stage been "upgraded" to the white piping that the newer Marshalls from the late 70's and forward had begun to come out with. What is not obvious from the photo, is that the front panel had also been recovered with vinyl, instead of the original tolex. Although this vinyl quite closely resembled the tolex of the rest of the box, it was still noticeable to me, and so off came the vinyl, careful to preserve the original gold "string" that goes across the panel underneath the logo. I then recovered the front panel with original Marshall Levant tolex, reinstalled the gold string, and replaced the white piping with the proper gold mylar piping, and fitted an original Marshall logo. Here she is in top of a angled cab also from '68 that I had previously restored:

A pic with her and a few of her cousins. She is at the bottom of the pile. Above her is an absolutely pristine '75 JMP50 Lead spec that belongs to a friend of mine, that was visiting for some TLC, and on top is my '69 JMP50 small box.

Finally, here is a family shot of my current amp lineup:

Dang. That's nice. Congrats. Good find and awesome work. Your collection is really enviable now.

I've been toying with the idea of building another amp but with the exchange rates and house prices and a few other things I haven't made any decisions :/

I also have an old Marshall that needs fixing. Im not sure it will be a nice amp if I get it working again, I guess I'll decide what to do with it when I get it working and see what it's like.

Looks really good Shaun. Its always nice to see an amp this old looking sharp.
2 questions:
1. What did you do to the electrolytics? Have you checked them?
2. Where did you source the mylar piping. PM me if you want.

lapdawg wrote: Looks really good Shaun. Its always nice to see an amp this old looking sharp.
2 questions:
1. What did you do to the electrolytics? Have you checked them?
2. Where did you source the mylar piping. PM me if you want.

Hi,

I found a procedure for forming caps on the Metroamp forum ages ago, that relies on disconnecting the relevant electrolytic, the temporary installation of a 100k 1w resistor, and then measuring the voltage drop across this resistor over time. When it gets to almost 0v, the cap is properly formed.

I didn't want to have to do this each time I get an old amp though. It's too invasive for me, too much unsoldering of original joints, so I built a test board that comprises a PT, rectifier and the relevant resistors. Connected to my variac, all I need to do is disconnect the caps I want to reform, and connect it to my test board. I can do up to 4 caps simultaneously using this board.

The piping I got is the stuff available from AES. I had some left over from a previous job and so used that. It's not perfect, but I am on the hunt for some better stuff that more accurately matches the vintage stuff. If I can't find any, it stays, otherwise I'll replace it again.

As an aside. I did a side by side comparison between this amp, and my 50w JMP over the weekend. Oh the joys of being able to crank these beasts! One thing I'll say that whoever says there is little difference in volume between a 50w and 100w is smoking their socks. My 50w JMP cranked is farking loud, much louder than the 18w, and the 30w Trainwreck, each also plugged into a 4x12, but this 100w is in another league altogether. It's not a headroom thing. Both amps start breaking up at around the same point on the volume controls, the 100w is just generally a hell of a lot louder.

In the modern day when we are trying to curb volume rather than increase it, this is obviously not desirable, but I thought it was interesting nonetheless.

/useless bit of info.

I love these threads, I just have nothing worth while to contribute so I lurk.

Keep up the excellent work.

Dude, you don't have to contribute a thing. I just sometimes think if we as gear heads can't chat to each other about this type of thing then who can we chat to? My wife just looks at me like I am mad when I bring up the subject.

shaunf wrote: Dude, you don't have to contribute a thing. I just sometimes think if we as gear heads can't chat to each other about this type of thing then who can we chat to? My wife just looks at me like I am mad when I bring up the subject.

Oh I know that feeling all to well ?

I will comment more freely on such threads in future ? ? ?. Just looking at these turret boards makes me want to embark on another project. I know it sucks when you get limited feed back on a kiff thread, I felt that way with my DIY MegaDrum E-Kit and my Home made bass :-\

I'd love to hear one of these things cranked up!

Nice Shaun, that amp collection looks amazing ? Your neighbours must love you ?

Cool guys. It's certainly not a recognition or approval thing from my side, I just like conversing with others, like minded or otherwise. I really enjoy what others have to say and your views, no matter how different they are from my own, so please feel free to chat away. My posts are not intended to be instructional at all, they are intended to hopefully generate conversation.

A few of you have mentioned my "collection". Funnily enough, I don't consider myself to be any sort of collector. Certainly that's not what I set out to do at all. Sure, I've gathered a couple of amps, but I do feel they are different enough in character to warrant having the choice, and they all get played regularly. I have a bit of a soft spot for old Marshalls and I really enjoy restoring the ones I come across and getting them to play right and look right, faithfully to the way they are supposed to be, unmolested in any way.

I suppose that now that this one is up and running the way it should be, to a great extent the fun is over for me. I already have a 50 watter that sounds awesome, and that I didn't mind fitting a ppimv, because it required so much work to raise from the dead. I'm lucky in that my neighbors are fairly far from me, and so I can generally play as loud as I want to, but still use some form of volume control for my own sake more than anything else. I couldn't fit something like that to this amp, because its so close to original. I guess what I'm saying is that this one will probably go up for sale at some point in the not too distant future.