Help me decide what to do with this '76 JMP 50. What mods are available for me based on whats been done to it?

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RWMusic

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Hi, new poster, long time lurker.

Last year, during summer, I decided I wanted a hot rodded Marshall after I watched videos that Pete Thorn made on the Jose Marshall. I wanted George Lynch, Warren Dimartini style tones. I spotted an ad for a '76 JMP 50 on TGP. The ad stated that the amp was able to get "all eras of Marshall tones", and that it had an effects loop installed and a "high gain mod" on channel 1. It also had a master volume installed A former owner of the amp posted in the thread backing up the claims of the ad. When talking with the seller and previous owner I was told it could do "EVH and more". I thought this was was I was looking for based on the description, so I bought it.

When I got the amp I was completely underwhelmed. It did not have the hot rodded sound I was expecting. After showing the gut shots to some experts (which I should have done prior to purchasing, so my fault), I found out that it didn't have any high gain mod. It was a stock JMP 50 with an added tube for the effects loop and master volume. I also found out that the master volume wasn't a PPIMV but instead of was a typical 2203 style pre phase master. It ironically also had it's bright cap removed which makes it less aggressive. Contradicting the claim of a "high gain mod"

The master volume was unusable for what I wanted. If you lowered it, it also lowered the gain, so with the master down low and the channel volume up high, you basically end up with an edge of breakup tone at best. I was under the impression that I would be able to get saturated tones at home volumes.

Completely bummed me out, but decided to hold on to it because it's still a vintage Marshall.

Fast forward 1 year later. I am thinking that since the amp already has an added tube installed, and a MV pot, that maybe I can leverage this somehow and get a tech to turn it into something I would enjoy.

I'm not familiar with many mods so I was hoping to get people's advice on what could be some good options. I already own a stock '81 JMP 2203, and a '72 JMP 50, so I want something more high gain.

Or do you think it would be better to not further mod a vintage Marshall, get a tech to rip out the mods and return to stock? Then maybe buy a reissue marshall to mod, or a different amp?

Or just sell it?

Here are gut shots of the amp to get an idea:

https://ibb.co/s9yH6HMhttps://ibb.co/q1L00vnhttps://ibb.co/S7M2TYvhttps://ibb.co/XkPvndP
 
FIrst of all - welcome to R-T :yes: you came to the right place
Originally I came in here thinking "OD pedal only - don't mod it"
Now I see it has been modded, just not what you thought was modded.
I'd either put it back to stock and use OD pedals, or go ahead and finish her off since she's already been molested.
By finish her off I mean, get the mods done that you think are best.
As you know, not all Marshalls are created equal, so it is possible you just have dud.
I'm not the expert here though - you really need someone like @FourT6and2 or @braintheory .
You will get responses here for sure, but if not, post in the Tech Corner subform
 
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Relieving to see a first time post like this. Welcome to the forum! Lots of good info here, just not from me when it comes to amps :ROFLMAO: 311splawndude called you to the right people, though! GL and welcome!
 
Here's a few observations from just a quick look at those pics:
The amp could be put back to stock fairly easily but it would still be a bit of a job. The main board is fairly intact.
The MV looks to be a pre PI Master so yeah it will neuter the amp's gain as you turn it down.
The mod looks to me like it's just the effects loop. The blue wire connected to the junction of the V1 plate resistors is stealing power supply voltage for the extra tube there. But it doesn't go to the extra board...it goes straight to the tube so that indicates a cathode follower SEND with a gain stage RETURN which is typical for an effects loop. The MV is probably really a Return Level that feeds the PI.

My opinion is to get it returned to stock and use a Powerstation or equal. An effects loop in these types of amps is just stupid imo. All the magic in these amps happens in the PI and power section...all of which is AFTER the effects loop (i.e. the distortion is still AFTER the loop in these types of amps). The mod looks fairly well implemented and took a lot of work...but it's just a stupid mod to do in the first place. It's a shame to see that but it could be much worse.
 
Also, the extra holes for the effects SEND/RETURN can be made to be extra speaker jacks and that MV could be replaced with a NFB switch/control. Altho since the amp already has the 0.68uF cap on the Presence...the Presence control is essentially already a 'NFB control'. Usually Presence caps are 0.1uF and only increase the highs but the big ass 0.68uF cap increases pretty much everything except the lowest lows.

Also, my opinion is don't put a post PI MV in it (or get talked into it). Michael R/T always made those sound good in his clips but I have never liked them.
 
Tough situation. My favorite modded Marshall’s I’ve had were all by guys that either are no longer options or dead. It is to me at least surprisingly hard to get a modded Marshall to sound actually better than (or even as good as) a stock one with a good boost (even Mark Cameron has admitted this). Ground Zero gets a lot of praise here for mods (haven’t tried one myself yet). Otherwise maybe better to keep stock imo

A few things I’d recommend is to keep it with the vintage Marshall’s if you can for a more organic, raw sound (at least I prefer that) and honestly the most popular gear YouTube channels IME don’t really lead to the right direction if the goal is to really find the best gear for pure tone quality. They often cater more to the masses/getting views, so they often recommend stuff they’re paid to promote or try show cheaper or practical stuff sounding “almost” as good, but then you get it and learn the hard way that it wasn’t accurate
 
Luckily it looks like it hasn’t been butchered. I’d rip out the extra tube and loop, and return it to stock with a metro loop since the holes are already there. From there you can decide if you want to mod it, given there’s already a hole for an extra tube. Lots of guys here can do fantastic work with 3 or 4 tube Marshall circuits.
I bet once you get it back to stock and have a way to crank the volume you’ll be pleased. More often than not people wreck the character of the amp with baindaid fixes.
 
I actually had a power station that I sold. I felt like whenever I played through it with the amps cranked, there was no dynamics. Yet when I played the amp plugged direct to the speaker, even though it wasn't cranked, and I set the master volumes way lower, It felt more dynamic and alive.

Given this observation, I am concidering returning to stock, but keeping the MV and converting it to a PPIMV.
 
Hermansson could make that thing into a straight up sonic weapon of complete and total bad assery.

There are a few guys who do awesome mod work. Hermansson, Gower is also epic, and so is Friedman. I have owned or played all of these guys work and they are great. All honest and good guys to deal with.
 
If you’re looking for those tones, and Jose style mods I would consider sending it to Dave Friedman and having a BE mod done along with the sat switch. He has been in a lot of Jose mods and amps from that era for the tones you are looking for, or you can have your tech do something similar as those schematics are out there. Where abouts are you located?
 
jasonP said:
If you’re looking for those tones, and Jose style mods I would consider sending it to Dave Friedman and having a BE mod done along with the sat switch. He has been in a lot of Jose mods and amps from that era for the tones you are looking for, or you can have your tech do something similar as those schematics are out there. Where abouts are you located?
Click to expand...
I'm in the Chicago suburbs. I've been trying to find a local tech who specializes in Marshalls, but don't know of any.
 
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