79 to 81 JMP 2204 ~= 81 to 84-ish JCM 2204?

[maico996]

If you're looking for a 2204, you could also consider a combo. I have an '82 4010 1x12 which is basically a 2204 in a box. I chopped it into a head a long time ago. It came stock with GE 6550s. Quite a while ago I switched to KT88s. My plate voltage reads right around 386. A very long time ago the voltage switch was removed because a mic stand fell over in our truck and broke the switch. The only other "mod" was piggybacking a resistor on the bias circuit so I could increase the adjustment range for the KT88s. I can post gut shots if needed.

 

[Ken Bob]

The schematics I've seen disagree. 4ohm tap for EL34, and 8ohm for 6550s. Not only that, but I personally own a 79 2203, 77 2204, and 76 2204 (formerly a 2104). I've also been inside of a 77 2203. All 4 are US Marshalls, and all 4 either still had the negative feedback on the 8ohm tap (with no signs of the 4ohm tap being messed with), or had it elsewhere but showed clear signs of having been monkeyed with.

I don't have any for my three heads. The 79 was badly monkeyed with. Someone changed the impedance selector switch years back, and actually had all the taps in the wrong spots. So you can't go on that one. The 77 2204 had an OT swap, and a really bad EL34 conversion, and was on the 4ohm tap.

The 76 was definitely on the 8ohm tap, but I didn't take any photos. The 77 2203 was as well, but it doesn't belong to me and I believe has since been sold.

For my three heads, I changed them all to the 16ohm tap, anyway. I actually prefer it there.

So, unfortunately, I can't give you any pics to back up what I saw. I'm just saying I don't think it's a myth. The schematics say 8ohm for 6550, and I've seen it in person. But if you've seen clear examples that contradict this, maybe we just add this to the pile of inconsistencies from that era.

Check these out, though. 1976 2203 schematic, w/ 6550s, showing the 8ohm tap:

https://www.drtube.com/schematics/marshall/2203u.gif

And this one, from 1981, with EL34 values used in the bias circuit, and showing the 4ohm tap:

https://www.drtube.com/schematics/marshall/jcm800pw.gif

Maybe the intention was 4ohm for EL34, 8ohm for 6550, and some went out that way, and some didn't?

@TommyVonVoigt, there you go, those are good examples of the differing schematics I've come across myself showing NFB off both the 4-ohm and the 8-ohm taps for the 2203. That's exactly why I brought up the question earlier in this thread, and posted the vid of the Marshall amp designer talking about changing the NFB when the JMP's evolved to the JCMs. There are tons of other threads, both in this and other forums, with dudes definitively stating that 4-ohm was for EL34s, 8-ohm for 6550s, and then other dudes stating the exact reverse. And then others (like @Derrick111) making the case that they should all be off the 4-ohm tap (besides those amps that were messed with along the way). It's a dilemma!

I actually just re-tubed my '79 2203 yesterday. So when I was in there, I snapped a pic of the impedance selector:

Looks like it's on the black (4-ohm, no?), and it looks to have the factory varnish on it. This is a USA-spec with 6550s, btw.

Great info you posted above about the changes in filtering. Is it your estimation that these changes were responsible for the increase in brightness with the JCMs? If so, that would mean that only the later horizontal input models had increased brightness, and not the earlier models, since they had the same filtering as the JMPs.

 

[Derrick111]

I don't have any for my three heads. The 79 was badly monkeyed with. Someone changed the impedance selector switch years back, and actually had all the taps in the wrong spots. So you can't go on that one. The 77 2204 had an OT swap, and a really bad EL34 conversion, and was on the 4ohm tap.

The 76 was definitely on the 8ohm tap, but I didn't take any photos. The 77 2203 was as well, but it doesn't belong to me and I believe has since been sold.

For my three heads, I changed them all to the 16ohm tap, anyway. I actually prefer it there.

So, unfortunately, I can't give you any pics to back up what I saw. I'm just saying I don't think it's a myth. The schematics say 8ohm for 6550, and I've seen it in person. But if you've seen clear examples that contradict this, maybe we just add this to the pile of inconsistencies from that era.

Check these out, though. 1976 2203 schematic, w/ 6550s, showing the 8ohm tap:

https://www.drtube.com/schematics/marshall/2203u.gif

And this one, from 1981, with EL34 values used in the bias circuit, and showing the 4ohm tap:

https://www.drtube.com/schematics/marshall/jcm800pw.gif

Maybe the intention was 4ohm for EL34, 8ohm for 6550, and some went out that way, and some didn't?

Perhaps I should clarify further... the Tube Amp book was referring to the practice by the USA Marshall distributor in the early 70s for modifying the amplifiers for 6550s. To do so, they clipped/changed the bias resistors and installed 6550s. All of the original examples I've seen or owned have been biased super cold. So cold that they weren't even putting out full power to the speakers. The Tube Amp book claimed that the distributor also moved the presence wire, but they didn't! They then gave instruction on converting back to EL-34s, wrongfully instructing readers to change the presence wire to the 8 ohm lug, but it hadn't been changed in the first place and was already in the factory soldered position with red dye on the 4 ohm tab of the impedance selector. But this propagated the myth. Readers also understood the book as stating that USA Marshalls with 6550s were converted by the USA distributor. always However, by the mid 70s, Marshall had already began to install the bias resistor values for 6550s at the factory, so it was no longer done by the distributor from then on. More myth propagation.

What this means is that Marshall changed from wiring the presence wire from either the 16 ohm presence tab or to the output jack (effectively making the connection to whichever impedance was selected), then in the very early 70s they began to wire it to the 4 ohm impedance tab for more aggression. Yes, there are schematics showing it wired to the 8 ohm lug, and I think Marshal started doing it both ways by the mid 70s or so... but the lion share I see and the ones I own are on the 4 ohm tab. The problem is, by the mid 70s, Marshall stopped using solder dye, so it is hard to definitively tell if a connection is original or changed in some cases. A lot of the Marshalls on the Amp archives have the 4 ohm tab connection, but a few also have the 8... trouble is, many of the photos are garbage and you can't tell the condition of the solder let alone barely tell the wiring from the small, low res photos.

Below is a photo of my '73 Marshall made for sale in the USA. Here you can see the purple presence wire is tied to the 4 ohm tab of the impedance selector. The red solder dye is clearly seen intact on the connections indicating a factory choice by Marshall.




Below is a photo of my '78 Marshall also made for sale in the USA. Here you can see the purple presence wire is also tied to the 4 ohm tab of the impedance selector. The solder connections look absolutely factory and match my other Marshalls, but since they stopped using the solder dye, it's harder to be definitive.



This was a discussion of the 70s era Marshalls made for USA. Relevant I feel, because it sheds some light on what the OP was asking about regarding 70s vs 80s Marshalls. To understand the difference, you have to define the facts behind the predecessors. I also feel it's helpful to know this so we aren't just assigning characteristics to amplifiers because a schematic reads one way or a book states something. Reality beats paper claims.

Back to the OPs question... my late 70s JMPs don't sounds all that different from my early 80s JCMs. The farther away in year you get, the more difference. People see the JCM as a different amp, but really it started out simply with different cosmetics. The thing is, Marshall ever so quick to give musicians what they want, added more treble and sizzle that was in such demand back in the 80s. So within a few years of the JCM, they went through some minor but noticeable changes that make people think these are much different than the JMPs. From about '85 on, the JCMs have more treble and sizzle, but not like a different amp and this can easily be tamed by removing one or two caps. I like them all though and keep them as Marshall designed them. I hope that some of this was interesting and that some of it helped.

(**Edited to fix photos that weren't showing up**)

 

[kysrsoze]

Back to the OPs question... my late 70s JMPs don't sounds all that different from my early 80s JCMs. The farther away in year you get, the more difference. People see the JCM as a different amp, but reall it started out simply with different cosmetics. The thing is, Marshall ever so quick to give musicians what they want, added more treble and sizzle that was in such demand back in the 80s. So within a few years of the JCM, they went through some minor but noticable changes that make people think these are much different than the JMPs. From about '85 on, the JCMs have more treble and sizzle, but not like a different amp and this can easily be tamed by removing one or two caps. I like them all though and keep them as Marshall designed them. I hope that some of this was interesting and that some of it helped.

Thanks, Derrick (and everyone else as well). This turned out to be one hell of a thread, with dug more interesting and useful info than I expected. Yours and some of the other responses made me a lot more comfortable with the later 2204s. Given I already have an SV20, I think the more aggressive sound will be a nice complement to it, and if I ever want to, I can mod it to earlier sound character. I ended up finding and buying an ‘89 2204 that looked really clean and unmolested. I’m so geeked to get it next week!

 

[Ken Bob]

Thanks, Derrick (and everyone else as well). This turned out to be one hell of a thread, with dug more interesting and useful info than I expected. Yours and some of the other responses made me a lot more comfortable with the later 2204s. Given I already have an SV20, I think the more aggressive sound will be a nice complement to it, and if I ever want to, I can mod it to earlier sound character. I ended up finding and buying an ‘89 2204 that looked really clean and unmolested. I’m so geeked to get it next week!

@kysrsoze, congrats!!

 

[Derrick111]

Thanks, Derrick (and everyone else as well). This turned out to be one hell of a thread, with dug more interesting and useful info than I expected. Yours and some of the other responses made me a lot more comfortable with the later 2204s. Given I already have an SV20, I think the more aggressive sound will be a nice complement to it, and if I ever want to, I can mod it to earlier sound character. I ended up finding and buying an ‘89 2204 that looked really clean and unmolested. I’m so geeked to get it next week!

Really cool, keep us posted! I should also mention that often people go directly to mods to make an amp sound more to their taste when a simple speaker change can make all the difference in the world and keep things stock. Just something to consider. Also, the reason JCMs shot up in price about 15 or so years ago was that people realized how they just needed to play them at volume to unlock the insanely great, aggressive sound. All things you can look into with your awesome new JCM800. I love them. Good luck.

 

[lesexypaul82]

The 2204 in the video that was posted from Headfirst.. I actually own that amp now.. I bought it from him at the start of last year..I since have also gotten a 83 2204.. I can tell you which one sounds better to my ears (to anyone's that hears it actually) and that is the 83. I actually cannot describe the difference because its been awhile since the other one has been started.

Interesting little fact about the 2204 in the video, it has USA stamped on the build sticker,,,, but runs EL34 and my understanding is thats how Jason received it.

DISCLAIMER: Both 2204s sound great.. at a pub a few beers in ya you wouldn't pick it.. the Vertical input 83 just has that special touch to your ears and hands.

 

[lesexypaul82]

oh the 83 NF is on yellow (4ohms i believe).. but my switch is wired different.. Maybe an aussie thing and 240v supply..
the jumper wire from top to bottom then runs to output tip.. Grey wire is connected down the bottom.

 

[kysrsoze]

Really cool, keep us posted! I should also mention that often people go directly to mods to make an amp sound more to their taste when a simple speaker change can make all the difference in the world and keep things stock. Just something to consider. Also, the reason JCMs shot up in price about 15 or so years ago was that people realized how they just needed to play them at volume to unlock the insanely great, aggressive sound. All things you can look into with your awesome new JCM800. I love them. Good luck.

Thanks. Yeah, I don’t anticipate I’ll want/need to mod it. Now I’m trying to settle on which speakers (most likely in a 4x12). For now I have a 2x12 with Greenbacks I’m using with my SV and another 1x12 with an Eminence Governor. I really like what I’ve heard of G12-65’s, but they seem hard to come by.

 

[BlueX]

Thanks. Yeah, I don’t anticipate I’ll want/need to mod it. Now I’m trying to settle on which speakers (most likely in a 4x12). For now I have a 2x12 with Greenbacks I’m using with my SV and another 1x12 with an Eminence Governor. I really like what I’ve heard of G12-65’s, but they seem hard to come by.

FWIW: Last year I got a '79 2104 (Scandinavian, with EL34) with stock G12-65's (T3120). I love the sound from this combo, altough I usually don't like gain through open back. To me, the 65's matches this amp particularly well. I've run this amp through 1936 (closed back) with GB's, but it's not the same. If you can find some 65's I'd say get them.

 

[kysrsoze]

FWIW: Last year I got a '79 2104 (Scandinavian, with EL34) with stock G12-65's (T3120). I love the sound from this combo, altough I usually don't like gain through open back. To me, the 65's matches this amp particularly well. I've run this amp through 1936 (closed back) with GB's, but it's not the same. If you can find some 65's I'd say get them.

I'm going to try. Maybe someone will not be that aware of what they have - seems sometimes people are almost ready to give away a 4x12.

 

[Mats A]

They changed the filtering on the 100W JCM 800’s when they started doing the horisontal inputs. The 50W amps were not changed and stayed the same.

 

[TommyVonVoigt]

Great info you posted above about the changes in filtering. Is it your estimation that these changes were responsible for the increase in brightness with the JCMs? If so, that would mean that only the later horizontal input models had increased brightness, and not the earlier models, since they had the same filtering as the JMPs.

That’s a great question, but not one that I can easily answer. This is because they just kept changing things, and you don’t even find 100% consistency within a given year. In fact, regarding filtering, there was also a transitional period. I’ve seen heads with only 5 filter cans.

While I’ve never had enough amps in front of me to do any actual A/B comparisons, it’s hard to imagine that the filtering changes wouldn’t have had an impact on the tone and the feel. But, keep in mind that for every person you find that claims the horizontal input heads sound a certain way, you can find someone saying that about the whole 800 line, vs the JMPs. Plus, as Mats A pointed out above, 2204s did not get any filtering changes, and yet some people like to claim that all of the horizontal input heads sound different from the verticals.

Could there have been more transformer changes? At what point exactly did the voltage come back up? Did they use the same coupling caps all through the 80s, or did those keep changing like they did in the late 70s?

One thing is for sure - Marshalls are wildly inconsistent from one head to the next. Yeah, you can kinda know roughly what a head should kinda sound like ahead of time. A 2203 isn’t going to surprise you and sound like a JC-120 randomly. But play half a dozen 2203s, and they’ll all be different, in different ways. Knowing this, and knowing the way people tend to regurgitate info on the internet endlessly, it can be hard to know what to believe.

Personally, I don’t worry so much about any of this. If you’re handy with a soldering iron, you can alter these circuits any way you wish. You can even convert the later heads to the earlier filtering spec.

 

[Derrick111]

Quite an interesting topic.

That’s a great question, but not one that I can easily answer. This is because they just kept changing things, and you don’t even find 100% consistency within a given year. In fact, regarding filtering, there was also a transitional period. I’ve seen heads with only 5 filter cans.

While I’ve never had enough amps in front of me to do any actual A/B comparisons, it’s hard to imagine that the filtering changes wouldn’t have had an impact on the tone and the feel. But, keep in mind that for every person you find that claims the horizontal input heads sound a certain way, you can find someone saying that about the whole 800 line, vs the JMPs. Plus, as Mats A pointed out above, 2204s did not get any filtering changes, and yet some people like to claim that all of the horizontal input heads sound different from the verticals.

The filter cap change didn't make radical differences. You may notice a hair more tightness or other aspects you would expect from more filtering, but it's not like the world changed for Marshall when they implemented this. I have each and they are all great. It never occurs to me that there is a difference in the filtering. Not because I can't tell, but because other variables far outweigh it.

Could there have been more transformer changes? At what point exactly did the voltage come back up? Did they use the same coupling caps all through the 80s, or did those keep changing like they did in the late 70s?

Yes, they did use different coupling caps throughout the 80s. Their were red Iskra block caps. white block caps, yellow Philips block caps, lighter unknown brand red block caps, possibly another brand white block cap, and it was common for there to be some measure of a mix of usually two of these used up through the mid 80s before being a bit more consistent with some brand of white block caps. Around 1987, there was also a switch from primarily using Piher resistors to using a more typical carbon film type still widely seen today. While I'm not trying to open the "do resistors have a sound" debate here, some may see that as yet another small flavor difference. I don't think it is of any significance is even noticeable... especially with a distortion machine like the Marshall, because let's face it, who uses a JCM800 for it's cleans?

One thing is for sure - Marshalls are wildly inconsistent from one head to the next. Yeah, you can kinda know roughly what a head should kinda sound like ahead of time. A 2203 isn’t going to surprise you and sound like a JC-120 randomly. But play half a dozen 2203s, and they’ll all be different, in different ways. Knowing this, and knowing the way people tend to regurgitate info on the internet endlessly, it can be hard to know what to believe.

I feel like Marshall was actually somewhat consistent in comparison with a lot of other makers along the way, but people usually don't account for all of the differences in the health/servicing state of an amplifier which I feel can vary Marshall's character quite a bit. Even different tubes are enough to make quite a noticeable difference. More so than the amount of filter caps, as stated above. Some of my Marshalls do have slightly differing personalities, but since I service all of mine the same way myself, they tend to be a lot more consistent. I can't tell you how many customer's amplifiers I have found non-factory changes in and stuff that was just left for years, and correcting those also brings things back to a baseline.

 

[TommyVonVoigt]

feel like Marshall was actually somewhat consistent in comparison with a lot of other makers along the way, but people usually don't account for all of the differences in the health/servicing state of an amplifier which I feel can vary Marshall's character quite a bit. Even different tubes are enough to make quite a noticeable difference. More so than the amount of filter caps, as stated above. Some of my Marshalls do have slightly differing personalities, but since I service all of mine the same way myself, they tend to be a lot more consistent. I can't tell you how many customer's amplifiers I have found non-factory changes in and stuff that was just left for years, and correcting those also brings things back to a baseline.

Thats actually a very good point. Everything that was done to these things in the roughly 4 decades since they were new. That surely must play a role in the whole “no two Marshalls sound alike” thing

 

[Derrick111]

Thats actually a very good point. Everything that was done to these things in the roughly 4 decades since they were new. That surely must play a role in the whole “no two Marshalls sound alike” thing

Yes, that and the fact that just servicing an old tube amp can make it sound very different. So can the various states of servicing. Unless two similar Marshalls are serviced similarly with similar tubes, then you can see why they can vary. Then if a resistor or cap value or presence wire, etc. was changed but not noticed, you can really see how people could get this impression. This is more noticeable in overdriven character than clean tones so Fender gets less of that stigma, but they have all the same issues really. Leo/CBS threw in whatever they could get cheapest from the parts suppliers that week like Marshall, and they gravitated to certain parts which would vary often depending on what they had available. I think that accounts for a lot more than parts tolerances which conventional wisdom assumes.

 

[Ken Bob]

That’s a great question, but not one that I can easily answer. This is because they just kept changing things, and you don’t even find 100% consistency within a given year. In fact, regarding filtering, there was also a transitional period. I’ve seen heads with only 5 filter cans.

While I’ve never had enough amps in front of me to do any actual A/B comparisons, it’s hard to imagine that the filtering changes wouldn’t have had an impact on the tone and the feel. But, keep in mind that for every person you find that claims the horizontal input heads sound a certain way, you can find someone saying that about the whole 800 line, vs the JMPs. Plus, as Mats A pointed out above, 2204s did not get any filtering changes, and yet some people like to claim that all of the horizontal input heads sound different from the verticals.

Could there have been more transformer changes? At what point exactly did the voltage come back up? Did they use the same coupling caps all through the 80s, or did those keep changing like they did in the late 70s?

One thing is for sure - Marshalls are wildly inconsistent from one head to the next. Yeah, you can kinda know roughly what a head should kinda sound like ahead of time. A 2203 isn’t going to surprise you and sound like a JC-120 randomly. But play half a dozen 2203s, and they’ll all be different, in different ways. Knowing this, and knowing the way people tend to regurgitate info on the internet endlessly, it can be hard to know what to believe.

Personally, I don’t worry so much about any of this. If you’re handy with a soldering iron, you can alter these circuits any way you wish. You can even convert the later heads to the earlier filtering spec.

@TommyVonVoigt, what you describe here is exactly what I've observed as well. For sure Marshalls from the "good old days" are famous/infamous for all the random anomalies you sometimes find inside - I picked up a really nice UK-spec '73 Super Lead in the past year, and the factory-installed presence cap was a 1.0 uF... not a mustard, not a 0.1 or a 0.68.

I sure wonder about other small changes as the line evolved (coupling caps, like you said, etc.)... @Derrick111 seemed to lend credence to this as well:

the mid/late JCMs are no less great than the early ones. Just brighter. The reason for the brightness are a few tweaks Marshall made in the tone shaping parts values. Very small/few tweaks. I am not for mods of nice old amps, but in a mid-late JCM you can remove a single cap or change a value and be pretty much where the early JCMs are.

Although it can be frustrating to read so much conflicting info online presented with absolute certainly as though it were fact (not referring to you, @Derrick111), if the old ones weren't random and different and sometimes weird, they'd be no different from the mass-produced computer-chip Marshalls of today.. and they wouldn't be nearly as badass

I think it's freaking awesome that the OP got a good discussion going here, and ended up with a new 2204. Now I hope they come back and show it off a little

 

[TommyVonVoigt]

@TommyVonVoigt, what you describe here is exactly what I've observed as well. For sure Marshalls from the "good old days" are famous/infamous for all the random anomalies you sometimes find inside - I picked up a really nice UK-spec '73 Super Lead in the past year, and the factory-installed presence cap was a 1.0 uF... not a mustard, not a 0.1 or a 0.68.

One thing is for sure - since I learned how to repair, restore, modify or build these things from scratch, I don’t sweat this stuff at all. It doesn’t matter to me what shape a head is in when I find it. As long as the iron is there and the chassis is solid, everything else is just details. The schematics are available, so it is a breeze to get anything you find into correct spec. Or, at least, correct spec according to the schematic.

Actually, even the iron isn’t a deal breaker. I’ll start from a stripped chassis if I find one.

So, when I open one up now and see all manner of horrors and questionable stuff, I find it amusing, and then get right to work