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The late 70s Marshall JMP mastervolumes and the Marshall plexis?

Right now I have a JMP and it seems a little bright and if I had a lot more money I probably would have gotten a plexi seeing how most or all of my favorite artists get a nice tone from them and I wanted something similar so I tried and got the JMP and I like it but do plexis sound just as bright? I think they have different tube setups as well, would that make a difference? Is there any other parts that would be better in a plexi that a JMP wouldnt have like transformers, ect, if so would it be possible to buy some of those MM transformers and put them in the JMP without doing any mods? Im thinking of changing my cabs grill cloth to basketweave to help get rid of some of the brightness? Another thing is I dont use a lot of pedals, I have 1 eq to boost the front end of the amp, so when you listen to other artists play from similar amps do you think they got rid of some brightness by using more pedals? This is my first quot;realquot; amp so maybe I just noticed some brightness because I wasnt used to it, if anyone else has heard a JMP do they sound bright to you, or brighter than a plexi?

I'm not sure but I think your amp might have el 84 tubes. You can check if does by removing the metal grill on the back of amp and reading the sticker at the base of the tubes in there. Some tubes aren't marked there so you could just find the type by googleing picks of el84's and el34's to find the tubes you got in there. The el 34's are the more tradition tubes to get that classic marshall tone you want. I'm pretty sure you can get tones pretty close to plexi with the amp you got.

A MV JMP is a 2203 most likely. A little gainier than the plexis but still great sounding amps. I have a JCM 2203 and they are fairly simular amps. Changing the tubes and speakers can seriously warm those amps up.

What are you using now?

I've got a '77 JMP MkII 2104 2x12 combo with stock 6550s amp; Marshall/Celestion 65s............it's is anything BUT bright.

It's a friggin' '70s rock amp; roll machine!!!!

I use a marshall tv cab with 25w reissue greenbacks. Im not sure how old the tubes are but I think theyre el34s but im not sure.

EL84's? I doubt it. I remember standing at the edge of the stage at a small show where one of the guitarists (the guy in front of me) was using a MV JMP and an original Guv'nor and I've never heard tone that thick. It was not bright at all. The kind of music they play needs a decent amount of gain but not for shredding...just chunky progressive lines. Ever since I saw that I've wanted a JMP.

JMP's (and NMVs 72 and later) are brighter than Plexi's in general, but I wouldn't call them overly bright. Not by todays standards at least.

Which model JMP do you have? Head or combo? what speakers? Make sure of what tubes you have (very very few Marshall amps have ever had El84 tubes), most likely they are EL34s or 6550s. IME, 6550's can be a little bright but not in a good way. I suggest you talk to trace over at He can give ya the lowdown on transformers, etc.

I would start with re-tubing/biasing, etc...and evaluate your speakers. JMPs are great amps, and honestly I prefer the later NMVs and JMPs to the PLexi sound (though I love it too) because the sound *is* a little brighter, and the ampsn have a bit more gain.


Originally Posted by JeffB

IME, 6550's can be a little bright but not in a good way.Would you say Zakk Wyldes tone is bright???

If so, maybe I need to re-evaluate my definition of bright.....

The 6550s in my JMP have the fattest fullest tone I've ever heard since I put KT88s in my Hiwatt

I've owned a bunch of the post 76-pre 82 models, and played dozens of them with both 6550s and EL-34s. By far and away my favorite amps.

The big question is, how do you like the amp with no pedals, no EQ pedal- just the guitar into the amp?

If you don't like that sound, you're probably better off with a different amp.

Have you ever played a plexi? If you need a pedal to get the gain you want out of your JMP, you're going to have a more difficult time getting a usable gain sound at a reasonable volume without an attenuator or pedal.

I would strongly suggest plugging directly into the amp and tweaking the EQ to taste. On my two amps my settings are something like this:
Presence: 8-10
Bass: 8-10
Mids: 3-4
Treble: 3-5
Master: 0-4
Pre: 7-10
good advice above ...

I haven't owned Marshalls, but will take others advice that it's not an inherently bright amp.

That suggests that the amp may be biased a little cold. You may be able to solve the problem with a rebias. If the tubes aren't that new, you may then want to consider new tubes.

you should also take a look at your first preamp tube, see what it is, then take a look at the thread regarding preamp tube in The Vault


Originally Posted by PUCKBOY99Would you say Zakk Wyldes tone is bright???

If so, maybe I need to re-evaluate my definition of bright.....

The 6550s in my JMP have the fattest fullest tone I've ever heard since I put KT88s in my Hiwatt

Actually yeah I do consider ZW's tone pretty bright. However I haven't heard anyhing of his since No More Tears (the song, never heard anything else on the album)..so I'm going solely by what I know of his tone. And yes it's fat and full too...You can have a huge sound that also is bright/ , IME at least. You mentioned HiWatt, well...Pete Townshend. HUGE tone...bright as hell too

TGB (I believe) and I have had this discussion before...the 6550s have a slight frequency shift in the high mids...and this is where my quot;distastequot; for 6550's comes in. It's not that I don't like the tone, it just not the Marshall tone I prefer.


Originally Posted by The Golden Boy

Gahh..everytime you post that pic I That Park head just rules

This might be a dumb question but Ive never had an amp rebiased, what is that?


Originally Posted by JeffBActually yeah I do consider ZW's tone pretty bright. However I haven't heard anyhing of his since No More Tears (the song, never heard anything else on the album)..so I'm going solely by what I know of his tone. And yes it's fat and full too...You can have a huge sound that also is bright/ , IME at least. You mentioned HiWatt, well...Pete Townshend. HUGE tone...bright as hell too

TGB (I believe) and I have had this discussion before...the 6550s have a slight frequency shift in the high mids...and this is where my quot;distastequot; for 6550's comes in. It's not that I don't like the tone, it just not the Marshall tone I prefer.

Chimming in late on this one. Zakk used Marshalls and Ampegs in the studio for that album. His tone from any of the Black Label Society stuff, or Pride and Glory for that matter, is anything but bright. There's some top end in there for sure but the entire spectrum is so full and fat. Get quot;The Blessed Hellridequot; (BLS album) and crank it up really loud. Amazing tone on that album.

I will agree that the MV's are brighter than the Plexi's, whether it be a JMP or JCM800 (same amp, different label). That is easily rectified by changing the 470p cap in the first gain stage, or removing it altogether. They do get 'warmer' as you turn them up though.

The 6550's will also give a little more headroom before breakup than EL34's, so that will hold some brightness but adjusting the presence and treble (2 and 5 or 6 respectively) makes them sound very smooth.


Originally Posted by JeffBGahh..everytime you post that pic I That Park head just rules

Me too. I hate it when he does that.




Originally Posted by guitarplayerThis might be a dumb question but Ive never had an amp rebiased, what is that?

It's setting the amount of current the tube sees.

Kind of like setting the timing chain on an engine. Sort of.