'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 a project thread to keep track of the restoration. As I said in the other thread, the amp is in working condition, but does have some issues, and also has had some work done to it that I would like reversed in favour of returning it as close to original spec as possible/practical. The 4x12 cab I got with the amp has some wonderful 1968 Celestion Greenback speakers in it, but the cab is really ugly, having being painted and recovered rather badly at some stage. So far, My Program of Work for the project is going to look something like this: Amp Head 1.) Recover head in original Marshall Levant tolex, including original spec gold piping. 2.) Replace hard wired power cord with kettle style power recepticle. 3.) Replace all pots. 4.) Replace all input jacks with original mono Marshall vintage style ones. 5.) Replace front face plate. 4x12 Cab 1.) Recover Cab with original Marshall Levant tolex, and install original spec gold piping. 2.) Replace grill cloth with original Marshall Salt and Pepper basketweave grill cloth 3.) Rewire cab to 16ohm.

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.

MikeM

+1

I would try not to change ANYTHING on a '65 or older amp.

Buzz

If you want to sell it overseas, originality makes a huge difference to the price - There are some silly prices for Vintage gear.
Any Marshall JTM45/JTM50 or '60s JMP will fetch loadsofbucks - 100's as well. OT is the most important item - you can pay easily USD1000 for an original OT on it's own!

vic

Buzz wrote If you want to sell it overseas, originality makes a huge difference to the price - There are some silly prices for Vintage gear.
Any Marshall JTM45/JTM50 or '60s JMP will fetch loadsofbucks - 100's as well. OT is the most important item - you can pay easily USD1000 for an original OT on it's own!

Agree 100%.....the overseas market is a lot more focussed on originality. Even a professionally recovered item is frowned upon and consequently is worth a lot less.

shaunf

Time for some more pics.

Here is the cab, all dings and chips filled with this absolutely brilliant product I found at Builder's Express. It's called Alcolin Quikwood Epoxy Putty Repair Stick. I cannot sing this product's praises enough. It comes as a stick of putty, that you cut off what you need, mix the outer and inner layers by kneading between your fingers and then you can go wild and do your thing filling, moulding, whatever you need to. 15min work time, final cure in 60min, after which you can sand, drill whatever and it's waaaay stronger than ordinary wood filler

Fast forward a couple of days and a lot of sweat:

Just a reminder of what they looked like a few weeks back...

Before:

After:

Family shot:

Nicholas-L

Dude this looks killer kick-ass ? :applause: :woohoo:

:goodtimes: awesome job

Norman86

Well done ?

Where did you get the gold piping though??

vic

Brilliant Shaun....! Let's drink to it ! :goodtimes:

shaunf

The cabinet now has the speakers back in and wired up, all badge bling installed etc. The only thing left to go is to repaint the recessed handles and it's done.

Finally got to plug it in and hear it and I've very happy with the sound of the vintage Greenbacks, they sound great! I guess it was a very lucky find to have a full set of 1968 Greenbacks with no voicecoil or cone damage and that still work perfectly.

Here's another pic of the cab:

I've decided to redo the front panel of the head box. If you take a look at the tolex above the gold piping that runs across it, you will notice it's raised in places. This was the very first thing I covered in tolex, and I've since improved my technique so I'm sure I can improve on it.

shaunf

Norman86 wrote Well done ?

Where did you get the gold piping though??

Sorry, I missed your question regarding the piping. It is freely available from a number of online retailers, including tubesandmore.com

Reinhard

Fantastic job!
Q What's better than a halfstack?
A Two half stacks!

Norman86

Thanks Shaun!
She's looking good hey!!!

shaunf

Thanks for the comments guys. Can't wait for the amp chassis to come back.

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