77 Marshall JMP 2204

[Rob_Zingler]

Hi all,

First vintage Marshall here, had an SV20 and liked it a lot so thought I’d try the real thing, and although I’ve only plugged it in shortly and not pushed it or anything yet it’s sounding pretty nice.

Been searching for a reasonably early 2204 with original transformers and mustard caps for a while and hopefully I’ve made an ok decision on this one, but I wanted to ask on here if you could inform me what you thinks been done/changed on the amp. At the end of the day it’s 45yrs old so I’m aware things happen to amps through the years, I’m just looking to tonally make it as close to original as I can.

Things I’m aware of are that 2 of the 0.022 mustard capacitors in the tone stack have come out at some point, so I’ve ordered 2 NOS replacements to hopefully take that back to how it should be. I’m also aware that the ohm and voltage selectors are modern replacements. Otherwise its a bit beyond my level of knowledge.

I’m going to be taking the amp to a tech and having a decent service, perhaps change filter caps and rebias with some nice power tubes, so if I can identify anything that needs work I can get it all done together


Cheers
Rob

 

[AndyD]

Hi, I used to own a '77. It too had mustard caps. Capacitor wise, they are all original to the amp except for the first two coupling caps (0.022) and the presence cap which should be a mustard cap IMHO. Mine had a 0.68uf presence cap which wasn't unusual in '77. As for the resistors, I count at least 11 non original. They should all be either red in colour (Piher) or the large yellow resistors (Iskra) and often a mix of the two. There is a shielded wire coming off the Hi input. Not original but usually a good idea to prevent oscillation issues. The electrolytic bias caps are new and should be 10uf 100-160V rated. The output valves have had screen and grid resistors added and could do with being tidied up. Mine came without, but I added them for modern valve use. If you are restoring, there is quite a lot to do. If you just want a great sounding amp to get on and use....use as is! Hope that helps. More comments to follow I am sure.
Oh, and welcome to the forum!

 

[Deftone]

Congratulations. IMHO the greatest amp ever made.

Here's a couple shots of my '79 2204 if you would like to compare...

 

[Central Scrutinizer]

Welcome Rob.

Good looking amp.

Looks a beast !

Party on Rob ! 😎

@Rob_Zingler

 

[LPMarshall hack]

Dammit! Why does everyone have a 2204/3 but me!!!

 

[Central Scrutinizer]

Dammit! Why does everyone have a 2204/3 but me!!!

Santa just don’t like you !

Ever since you peed on him when you were 3.

 

[Rokinroller]

Ah , those r just them cheaply made expensive old amps .

 

[stickyfinger]

I'm not a expert but that's either not a 77 or the head box isn't original.

The front control panel cut out should still be the sharper plexi style,

 

[AndyD]

Not one reply from the OP. Why do I bother?????

 

[Rob_Zingler]

Hey man, be cool. I was always going to reply once I'd checked through the replies, I'm a busy guy working on the frontline of the NHS, and have 2 young boys. I just don't come to post on internet forums very often, I appreciate all the responses though I'm starting to get a feel for what I have now.

Andy your reply was really helpful actually thanks. I don't think any kind of restoration is realistic, I'm just looking to make it tonally the best sounding I can. I think it's fair to say before looking into it that I thought a resistor was just a resistor, what I'm getting now is that although subtle they make a slight difference. Am I correct in thinking that all the resistors that have been put into my amp are still carbon films? Is there a particular type or brand of resistor that's really popular for these, or if I'm able to get say some NOS, which of the changed resistors are the ones most likely to affect the tone if I was to swap some out, the ones by where the orange drops currently are?

 

[Rob_Zingler]

By the way with the resistors, I think I've identified that most of them are 0.5w. Does it matter in terms of function or tone if you replace a 0.5w with a 1w, or is that a no no?

 

[Mitchell Pearrow]

@Rob_Zingler


To The Forum
HNAD
Nice amp nonetheless one of my favorite 50 watters .

Cheers
Mitch

 

[AndyD]

Hey man, be cool. I was always going to reply once I'd checked through the replies, I'm a busy guy working on the frontline of the NHS, and have 2 young boys. I just don't come to post on internet forums very often, I appreciate all the responses though I'm starting to get a feel for what I have now.

Andy your reply was really helpful actually thanks. I don't think any kind of restoration is realistic, I'm just looking to make it tonally the best sounding I can. I think it's fair to say before looking into it that I thought a resistor was just a resistor, what I'm getting now is that although subtle they make a slight difference. Am I correct in thinking that all the resistors that have been put into my amp are still carbon films? Is there a particular type or brand of resistor that's really popular for these, or if I'm able to get say some NOS, which of the changed resistors are the ones most likely to affect the tone if I was to swap some out, the ones by where the orange drops currently are?

I lost my cool! Apologies. You often get people coming onto the forum just wanting information and then disappearing without a trace. I was premature and I sincerely apologise for that. To answer your questions, yes the new resistors are carbon film just like the originals. They are 0.5w (yes, 1w resistors sound better than 0.5w, but Marshall used 0.5w resistors) rated just like the originals. In terms of tone, differences are subtle, but present. The original Piher and Iskra resistors were very good quality and usually hold their resistance values over time, and sound good. But it isn’t a “night and day” difference compared to the modern replacements. The capacitors and transformers have a much more significant influence on tone. Fortunately, you have mustard caps AND the original transformers. Valves are important also. If you can, put a Mullard in V1.
To conclude, you could use the amp as it is and enjoy it. If it was my amp, I would want to replace the resistors to original spec. However, working on pcbs is a pain, so if you are going to replace one or two, you might as well replace them all.
I found a photo of the inside of the ‘77 I had for reference, if that helps.

 

[79 2203]

If it’s anything like my 79 2203, you’re gonna love it. Great amps.

 

[Deftone]

You often get people coming onto the forum just wanting information and then disappearing without a trace.

This is true....it can be annoying at times. All good.

 

[marshallmellowed]

By the way with the resistors, I think I've identified that most of them are 0.5w. Does it matter in terms of function or tone if you replace a 0.5w with a 1w, or is that a no no?

Functionally, perfectly fine to go up in power rating. As for affecting the tone, depends on who you ask. I personally think it would be minimal, if even noticeable, assuming the measured values were the same.

 

[Angrycolon]

Such a coincidence! Yesterday, I pulled one of my '77 JMP's out of storage for some re-amping and your post came up in my newsfeed. Yes, I bought mine new when they came out! I've used mine for decades without issue. I did re-tube frequently. About 18 yrs ago I had one modded by FJA Mods with the "John Sykes" mod and added a boost pedal input. (It's the amp with an extra knob in the "Low Input" hole. It adds another gain stage and if you pull the knob, it clicks out adding another gain stage. On the back, there is a Mid-range scoop knob and a boost volume. Once dialed in this amp is a beast! Jerry has done fantastic work for artists for years, clean and professional and I believe it added value, but some may disagree. ) I did get it re-capped when I had the mods done. I ran the second JMP stock with just enough gain on the Master volume so you could hear it and ran the two through an "ABY" pedal. I could go clean or dirty by selecting the appropriate amp and using the guitar volume. By "A/B ing" together and rolling off the guitar volume you get the best tone I've ever heard...and I've heard many....IMHO. As I got older, I began using combo amps: Fender, Blackstar, and Orange as the Marshalls were just too much to load around for an old man. I've been offered a lot of money for them but I'll never sell them as I still have them in my home studio. Pristine in condition as they always were in road cases. Congrats on your acquisition! PS. You stated you haven't cranked them yet. When Marshall put the Master volume on this model running the 6550 tubes allowed you to get fantastic sound without cranking the shit out of them. With my pedal board, 4.5 volume was the sweet spot. Enjoy!

 

[Derrick111]

As a technician and a recording engineer, I am of the opinion that changing your resistors is going to yield no more than a placebo or psychological gain. If you have carbon film resistors that are of the minimum rated value (you do), then you are good to go. I am a stickler for originality, but you also have to be realistic. You are in for a lot of work for no gain in "tone". I have done these "mods" for customers in past years long ago and it never made a shit of difference. All you end up doing is spending money, taking time, and risking lifting the foil solder traces on the PCB by heating them up (even if careful, it happens on these old boards). If it were mine, I would check the tubes then check the bias, use a good electronics contact cleaner (with lube!) to clean the pots, and alcohol on Q-tips to clean the input/output and speaker jacks, then rock that thing. If the electrolytic caps need replacing, then do that too. But if that amp was played relatively regularly, they may be fine. BTW, don't make the rookie mistake in using WD40... Bad stuff for electronics! Replace those two orange drop caps if you like. Play it for a bit first, then change them and tell us if you notice any difference ;-)

 

[Angrycolon]

I'm not a expert but that's either not a 77 or the head box isn't original.

The front control panel cut out should still be the sharper plexi style,

Those are 1977 JMP's . I have two I bought new in 1977. Pictures below. Cheers!

 

[Relic61]

Those are 1977 JMP's . I have two I bought new in 1977. Pictures below. Cheers!