'69/70 Marshall JMP 50 Restore Project

shaunf · 2011-11-11T17:19:50+00:00

So, following from my NAD thread earlier in the week, http://www.guitarforum.co.za/amps-speakers-and-valves/noad/ I thought it might be interesting to start...

'69/70 Marshall JMP 50 Restore Project

shaunf

Sebastian wrote: Looking really great so far, Shaun! Fantastic work! especially on the new front panel! Have you tried the amp at the marked settings? See if the previous owner knew what he was doing or not ?

(Btw check out JJ "E34L's", a variant on EL34's. More body and very nice. For when the time comes to replace valves ? )

Hi Seb,

The faceplate is still the old, original one. I just cleaned it up and had all the markings reprinted.

I haven't tried those settings. I literally got the amp, tried it for an hour or so, and the next day started stripping it for the restore. The amp chassis is with Glen Turrell at the moment getting some work done, but I'll be sure to try them when I have it back and back in the head box. You must come and give it a try sometime when it's back together, probably later this month or in January.

Thanks for the tip re the tubes. I'm definitely going to replace the power tubes and have been trying to decide what to put in. If I end up going with new production tubes, I'm pretty sure it will be the EL34L's.
Also looking into the preamp tubes and trying to decide whether to replace all/any of them. The amp currently has a NOS Mullard, a NOS Phillips tube, and a Haltron.
Just by way of a general update to this thread, this is where I currently am:

Amp head box stripped, sanded, dings filled and recovered
Speaker baffle painted matt black and new Salt and Pepper Backetweave grill cloth installed
Rest of the speaker cabinet stripped and in the process of removing old glue, sanding and filling dings and chips

Will attempt to take pics this weekend, if it will just stop raining for 5 seconds! :?

shaunf

Some more pics...

Headbox complete:

Speaker cabinet stripped and in the process of being sanded and dings filled:

Speaker baffle recovered with Marshall Basketweave grill cloth:

I'm quite pleased with the way the headbox came out considering this is the first time I've ever worked with tolex.

Stretching the basketweave grillcloth over the baffle was an absolute bitch of a job. I managed to get it really nice and tight but it's a job I really wouldn't want to do again.

What do you guys think so far?

vic

Fantastic ! Few people can really appreciate the amount of work that goes into a project like this. Well done so far.

makepeace

this is looking super cool. hopefully you'll be posting before and afters at the end?! good luck! you're nearly there. also, i might also suggest a cap job if it hasn't already been done recently. a set of spragues and sozo's would probably do wonders.

AlanRatcliffe

Yeah, a real labour of love. Well done so far!

shaunf

makepeace wrote: this is looking super cool. hopefully you'll be posting before and afters at the end?! good luck! you're nearly there. also, i might also suggest a cap job if it hasn't already been done recently. a set of spragues and sozo's would probably do wonders.

Thanks guys. Makepeace, the amp is currently with a tech to have a look at and he did mention possibly recapping especially the big cans. Quite a few of the caps on the turret board seem to have been replaced with square yellow ones, that I think say Phillips on them. I'm clueless on the electronics side so will mention the spragues and sozo's and see what he says. If you click the link in the first post you will see all the "before" shots as well as a pic of the amp guts. Would appreciate any input or advice you guys have for me, so please keep it coming.

Reinhard

Nice job dude!

Buzz

Shaun - do not be in too much of a rush to replace those Philips yellow caps - they can certainly be original.
They are known as "Chicklets" and do crop up fairly regularly in early 70's marshalls. You should try to keep the amp as original as possible.

There have been many strange caps used in Marshalls - here is a pic of my '67 T head with some odd caps - all original

If you look closely at those Philips/Mullard ECC83, you will find a code etched into the glass, which can tell you the date and where they were made.
The PT has been replaced as well as quite a few pots. Have a look at the OT - should be 784-139 to be original to that amp.
I have a bunch of Marshalls from this era, so if you want any info, I can help you out.

I suspect this amp was rebuilt many years ago - the chassis appears to be galvanised or something. Not too easy to make out in the pics.
The turret board also looks like it is fibreglass, which I think is not correct
Buzz

shaunf

Buzz wrote: Shaun - do not be in too much of a rush to replace those Philips yellow caps - they can certainly be original.
They are known as "Chicklets" and do crop up fairly regularly in early 70's marshalls. You should try to keep the amp as original as possible.

There have been many strange caps used in Marshalls - here is a pic of my '67 T head with some odd caps - all original

If you look closely at those Philips/Mullard ECC83, you will find a code etched into the glass, which can tell you the date and where they were made.
The PT has been replaced as well as quite a few pots. Have a look at the OT - should be 784-139 to be original to that amp.
I have a bunch of Marshalls from this era, so if you want any info, I can help you out.

I suspect this amp was rebuilt many years ago - the chassis appears to be galvanised or something. Not too easy to make out in the pics.
The turret board also looks like it is fibreglass, which I think is not correct
Buzz

Hi Buzz,

Thanks very much for taking the time to comment, I really appreciate those more knowedgeable than I, commenting and assisting me to learn more about this amp and to restore it.

The amp tech that currently has the amp is convinced that those Phillips caps are not original, but has also advised that they are good ones and shouldn't be changed unnecessarily, so they'll probably stay.

The chassis has been painted with Hammerite paint. The amp tech who has it seems to think he knows who did the previous work on the amp, and knows him well and will have a chat to him and see if he can get anymore of it's history.

The turrent board does look a little different to the pic you posted. I've looked at a lot of turrent boards on the internet and pre '69 boards seem to look like yours, however I've found a bunch of '69 and '70 original JMP's that have boards that look identical in colour and material to mine, so I think the board is original.

Look forward to your further input in this thread. I will be adding a couple of pics of the 4x12 cab recovering in progress tonight or tomorrow.

I don't have the amp in my possession at the moment, but will check out those valves and the code on the OT when I have it back, but that code you mention sounds familiar and it did have a number stamped on it.

Buzz

I think I remember reading somewhere that the chicklet caps that were originally in '70s Marshalls had the values printed on them, as opposed to later caps of the same type, which had the values impressed into the yellow covering. From your pics it looks like they are impressed, so maybe someone nicked the original mustards along the way. You can see what I mean here

MikeM

A bit OT, but welcome to the forum Buzz. ? You seem to be an interesting character with similar gear. Mind posting a couple of pics of your gear and an introduction for the rest of us folk?

Buzz

Thanks Mike
I love old valve amps, and have collected over the past 25 years or so. Mostly old Marshalls, but I also have an old Princeton black face from around '67 as well as a Vox AC50. Most of the amps were in really bad condition, and I have slowly been trying to get them back to as original as possible.
My price and joy is my 1967 JTM45 combo, not really a Bluesbreaker, as it is the first version. The cab had been recovered with something nasty, and i will one day recover it with correct period Tolex if I can find some - it is the Black tolex with the green bits in the depressions. I am just using it as a head at the moment - it is completely original inside, apart from a couple of resistors and a bias cap. (Jim Marshall kindly signed it for me some years ago)

Second is a JTM50 Black flag from '67 or '68, all original except PT has been rewound (badly) I will rewind correctly when I have some time - it is a laborious task.

Third is a JMP50 Tremelo, also 67 or 68 - PT replaced as well, but otherwise all original

No 4 is a JMP50 plexi circa 68, but with replaced OT and PT
No 5 is JMP50 from 69 or 70 with Metal panel ( Much the same as Shauns') I use this as my experimenter - been playing with cascade mods, switchable gain stages and generally fiddling with. I always find I go back to the 67 Bass spec, as that seems to be the best sound for me.

I also have a PA20 from 69 or 70 which is actually the best sounding amp of the lot - unfortunately it does not have quite enough volume clean to gig with. Perfect for recording with tho'.

The little Fender Princeton is actually a lovely little amp - I use it for practises - I have heavily modified it, with and extra gain stage at the expense of the tremelo circuit. I don't get on much with the AC50 - I'll just hang on to it and maybe trade it for something I need one day.

I am always on the lookout for old parts to keep my amps as original as possible, so if anyone has old blown up transformers or anything else, I am always happy to trade (got a bunch of 60'sMullard ECC83)

shaunf

Hi Buzz,

Apart from the fact that the amp was working and sounding good, apart from scratchy pots, when I got it, I have no idea how good the current valves are, and also have no idea if/how I can test them. Anticipating that I'd be needing to change some/all of them either sooner or later, and currently not having any spare tubes, despite owning several valve amps, I've ordered some Tung-Sol reissue 12AX7's and a matched pair of EL34B's, as well as a set of JJ 12AX7's and matched pair of EL34's. I figured these 2 sets would form a good starting point based on reading as much information around valve choice as I could find.

I don't have anything to trade, but would be interested in chatting further about some of those Mullard's you have, if you're interested in parting with any...

Buzz

Preamp valves seem to last for ages - I use Sovtek 12ax7 for amps that gig (don't want to risk the old stuff)
I don't think I have had a failure except for one that leaked air into it. I don't want to sell any, I would rather trade for parts I really need!
There are definitely tonality differences between different valves, but not necessarily better or worse, just different IMHO
I suppose it depends on what you are looking for.

The nice thing about having a Marshall that is not completely original is that you can play around with different values of caps/resistors to see what works best for you. Changing the coupling cap/Cathode byass values make more difference than finding ancient esoteric valves or caps I think!
As I said, I like the JTM50 bass spec myself, not as agressive as the 70's amps, and with a bit more body to it. This is with a Strat - maybe not the same for your LP

shaunf

Buzz wrote: Preamp valves seem to last for ages - I use Sovtek 12ax7 for amps that gig (don't want to risk the old stuff)
I don't think I have had a failure except for one that leaked air into it. I don't want to sell any, I would rather trade for parts I really need!
There are definitely tonality differences between different valves, but not necessarily better or worse, just different IMHO
I suppose it depends on what you are looking for.

The nice thing about having a Marshall that is not completely original is that you can play around with different values of caps/resistors to see what works best for you. Changing the coupling cap/Cathode byass values make more difference than finding ancient esoteric valves or caps I think!
As I said, I like the JTM50 bass spec myself, not as agressive as the 70's amps, and with a bit more body to it. This is with a Strat - maybe not the same for your LP

I can't really comment much on the tone of this amp at this stage. I've played it for about an hour or so to make sure it was working on the day I got it, and began dissassembling it the next day to begin restoring it the next day and it hasn't been plugged in since. What I do recall was that with the R9 LP plugged in, connected to my new 1960 cab and with the vol at around 6 or 7 I had vision's of Angus' curled lip ? It has quite a raunchy snarl to it. My other amp is a hotrodded JCM800 so perhaps my frame of reference isn't the best when it comes to aggressive tone though... :-[

I'm very interested in hearing what it sounds like through the vintage cab I'm restoring at the same time, and which I haven't heard yet. The Greenbacks it came with are the ones with the 55hz bass cones, so may add a bit of bottom end?

AlanRatcliffe

Nice to see you joining in Buzz. Just please take the time to squizz at the forum rules regarding affiliations.

Folks, Buzz knows Marshall amps better than anyone I know.

shaunf

Well as an update, I can tell you that the 4x12 is now covered with tolex and has the gold piping in the channels. I'm very happy with the way it's come out. My corner joins are all nice and straight, lie flat on the curved corner and join with no gaps at all, so that's a win in my book. I finished well after midnight and was too tired to take photo's but I'll get some up soon. The only thing I still need to cover is the rear panel of the cab, which I'll probably only get to on the weekend as it still needs to have the old glue removed and be sanded.

Buzz

Thanks Alan
OK like that?
Never thought to read the rules and regs
Who does?

For Shaun-
Post some gutshots when you get the amp back, I can maybe give you a couple of tips to play with!

shaunf

Buzz wrote: For Shaun-
Post some gutshots when you get the amp back, I can maybe give you a couple of tips to play with!

Will do. Unfortunately the forum seems to limit the size of the images to too small to see any real detail. Will have to post links to larger images.

vic

Keeping amps as original as possible...electronically and otherwise...I'm with you there.
I'm in to vintage AC30's and have had quite a few over the years...some were good enough to keep as is and some had to be restored extensively. However originality does not seem to influence many buyers. I never had a buyer wanting to know about the originality of an amp up for sale...they don't even bother to see if the speakers or transformers are original to the amp !..... ??? To me these are most important but some people just don't care.