JMP50 68-69' specs (work in progress...)

leonard.gulyas · Post by **leonard.gulyas** » Mon Aug 27, 2012 2:23 am

Hello fellow builders,

This is my humble attempt to recreate and hopefully fire up a Marshall JMP50 1987 or 1986 (not yet decided) amp with 68-69' specs with Larry grounding. Since not all the parts are in my posession I cant tell when I'm going to finish this project.

I am going to use this amp with a Mexi Strat with cs 69 pups aiming for a hendrixian sound so any suggestion would be welcome for specs that gets me closer to my goal.

Here are the materials used/will be used:

Metroamp JTM45/50 aluminium chassis with matching front and back plexi plate
Marstran 1202-118 PT and 784-139 OT, C1999 choke
Repro Turretboard from Brian (if it ever arrives

)
Valvestrom bits and pieces.
SED Winged-C EL-34, Svetlana 12AX7

Hopefully a Metro 4x12 pinstripe Replica cabinet with Scumback PVC (exact type not decided yet) speakers.

Please note that this is my very first attempt to build/solder anything so every critics/suggestion would help.

So here are the pics of the build in progress so far:

Regards

Fever Dog · Post by **Fever Dog** » Tue Aug 28, 2012 11:55 pm

Hello sir,
I'm pretty much at the same point you are with the same transformers. Please keep posting pictures. They are a huge help.

Dan

Coot Boy · Post by **Coot Boy** » Wed Aug 29, 2012 12:36 am

Doesn't tying your OT primary and secondary wires together create some kind o noise/hum? Sure I read that somewhere.

leonard.gulyas · Post by **leonard.gulyas** » Wed Aug 29, 2012 1:02 am

Coot Boy wrote:Doesn't tying your OT primary and secondary wires together create some kind o noise/hum? Sure I read that somewhere.

I am not sure. Maybe you could dig up that post or can somebody clarify this to me?

Much appreciated.

leonard.gulyas · Post by **leonard.gulyas** » Wed Aug 29, 2012 11:41 am

leonard.gulyas wrote:
Coot Boy wrote:Doesn't tying your OT primary and secondary wires together create some kind o noise/hum? Sure I read that somewhere.

Hi folks,

I went after this statement and asked Brian Wallace about his opinion on the matter. This is what he said to me:

"I've built amps both ways and have never had a problem with hum. On that note, it is a common practice to avoid placing outputs next to outputs of any type."

So it is definetly not an issue as far as I'm concerned.

Regards

leonard.gulyas · Post by **leonard.gulyas** » Tue Sep 04, 2012 10:28 am

So here we go...

I decided to order some extra elements for the build:

-IEC connector (For a much convenient transportation of the amp)
-Marshall modern voltage selector (Correct me if I am wrong but I can use all the 6 positions for the various voltage setting as the Marstran 1202-118 PT has 5 different primaries (100,120,220,230,240 VAC) even though the selector switch has only three setting written on it. So there is no need to waste any cable by cutting it sort or heat shrinking)

For the voltage switch I used a step drill bit as far as the connector hole goes I had to do it the hard way by a precision metal file.

I am really proud of the way they turned out.

Let the pictures do the talking:

Here are the holes after the work

And here are the installed parts

To be continued...

leonard.gulyas · Post by **leonard.gulyas** » Wed Sep 05, 2012 5:44 pm

So I moved on to unexplored territories...

Here are the pictures of the progress I made:

And the details as the following.

I routed the PT primaries to the newly installed voltage selector switch as the following:

PIN1 120V
PIN2 220V
PIN3 230V
PIN4 240V
PIN5 -
PIN6 100V

Even though the switch has only the 110V,220V,230V printed on it, it is functioning as a six way switch so why waste the possibilities of the extra voltage settings.

In the 50Watt Metro Kit instruction at STEP 7 section C. George tell us to sodler the PT primary common to the side of the Mains fuse holder. But when I asked Brian Wallace about this here is what he said to me about the subject:

"Marshall wired this backwards IMO. I would wire the common to the AC input neutral side(IEC connector) and run the Load side(Hot) to the fuse and then to the switch. This is a much safer way to wire the AC supply."

So I did it like that:

One question I had in mind. Is it ok to that I wired the AC input with standard 22 AWG wires from th Valvestorm plexi kit? Is there any benefit for a bigger gauge?

Update possibly tomorrow...

leonard.gulyas · Post by **leonard.gulyas** » Thu Sep 06, 2012 6:14 pm

So more pics of the progress I made:

Basically I went ahead with STEP 8 and thru A and B points (installed and wired up the power switch and just installed the standby switch) with the additional advice from Brian Wallace:

"wire the common to the AC input neutral side(IEC connector) and run the Load side(Hot) to the fuse and then to the switch"

I hope it is not a problem but I twisted both cables routed to the power switch.

... more updates on the weekend as I'll have more free time for the build.

Cheers

leonard.gulyas · Post by **leonard.gulyas** » Sun Sep 09, 2012 12:27 am

Welcome back folks...

I went ahead with STEP 8 points C,D,E (wiring the standby switch to the filter cap):

If anybody could chime in on the quality of these solder joints (I am really a beginner on this subject) do they look ok, as it seems the joints are dull compared to other ones. (Maybe this is caused by the NOS switch solder terminals, but believe me I did all my best to carefully clean them isopropyl alcohol and steel wool.)

So next was STEP 12-13 (as I already did STEP 9-11) installing pots and input jack assemblies, as I stated at the beginning of my posts I opted for Larry's ground so there are no buss wire solder on the back of the pots the as the ground goes to ground points 1,2,3:

Notice the nice looking scott knobs:

Input jack asembly with NOS AB CC 1M resistors:

STEP 14 has been also completed (but I forgot to take pictures of the V2 resistor installed):

It will be no more updated on progress for a while as I need the turret board (the one I ordered from Brian has been lost in transit so it needs to be reordered with insured/trackable postal service) also need the mustard caps to fully finish up my build so I am waiting for some funds to arrive and looking for some NOS mustard caps as I decided on the 1986 specs.

Regards and happy building...

Meanwhile I will practice with my public saxophone

till the time comes.

Big Mike · Post by **Big Mike** » Mon Sep 10, 2012 4:33 pm

Work looks very nice.

What I"m confused on...Where's the HT Fuseholder? DId i miss it?

Looks like you're buildign the 50 on a JTM45 chassis?

Mike

leonard.gulyas · Post by **leonard.gulyas** » Mon Sep 10, 2012 7:30 pm

Big Mike you are right, The HT fuseholder will be an internal one as I am building it on a metro jtm45 chassis.

Regards

Big Mike · Post by **Big Mike** » Sun Sep 30, 2012 6:54 pm

Makes sense. Beautiful work my friend.

I've F'd over my JTM45 with so many mods I'm going to undue it and rebuild it. Going to shoot for doing it as clean as you have.

You cut the IEC by hand?

bigsmitty · Post by **bigsmitty** » Sun Sep 30, 2012 9:46 pm

Nice looking build.

leonard.gulyas · Post by **leonard.gulyas** » Mon Oct 01, 2012 3:49 am

Big Mike wrote:Makes sense. Beautiful work my friend.

I've F'd over my JTM45 with so many mods I'm going to undue it and rebuild it. Going to shoot for doing it as clean as you have.

You cut the IEC by hand?

Thanks a lot for the kind comment.

The IEC cutout was made by hand wit a small half-round file from the initial round hole.

I would really love to continue but unfortunately I had stop with this build as life gets in the way (financial issues, moving).

Have a nice day.

jimmyride · Post by **jimmyride** » Mon Oct 01, 2012 10:02 am

Nice build.. looking forward to hearing the clips.

Metropoulos Forum