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

[LoudStroud]

Very interesting information in the above comments that I was not aware of before. I have a 79 JMP 2204 that is a total keeper. Just recently considered picking up an 81 JCM800 2203 and was researching any differences to the earlier late 70s JMP‘s. The only difference I was finding were the capacitors… My 79 has beige colored caps where the 81 had the red caps. Assuming two different manufacturers that could have a minor effect on the tone. other than that, they appeared the same.

Was not aware that the JCM 2204 possibly had a higher B+ voltage, which could make it a little tighter on the low end, part of which likely contributed to the amp being so popular during the early 80s hair metal days. Now has my curiosity reignited about picking up an early JCM!

Other than that, it appeared the 79 JMP and the 81 - 83 JCM were essentially the same inside. After 83, I recollect, is when they began the horizontal inputs and mounting the pots directly to the circuit board. I believe I read that the filtering reduced as well on the 2203s. Maybe also the transformers changed?

 

[Deftone]

FWIW, I have a '79 JMP 2204, an '85 JCM800 2204 (both w/6550's) and a '90 JCM800 2204 (w/ EL34's). They all sound really close to my ears. I do like the '79 the best, followed very closely by the '90. The '85 was modded and returned to stock, so that may have made a difference. I'll probably sell that one.

If price is a concern, I wouldn't be afraid of a later model JCM800 2204 myself. The USA models came with EL34's around '89-'90 IIRC.

Also, Jason at Headfirst Amplification has a YT video on how to mod a later model JCM800 to early JCM800 specs.

 

[Ken Bob]

Very interesting information in the above comments that I was not aware of before. I have a 79 JMP 2204 that is a total keeper. Just recently considered picking up an 81 JCM800 2203 and was researching any differences to the earlier late 70s JMP‘s. The only difference I was finding were the capacitors… My 79 has beige colored caps where the 81 had the red caps. Assuming two different manufacturers that could have a minor effect on the tone. other than that, they appeared the same.

Was not aware that the JCM 2204 possibly had a higher B+ voltage, which could make it a little tighter on the low end, part of which likely contributed to the amp being so popular during the early 80s hair metal days. Now has my curiosity reignited about picking up an early JCM!

Other than that, it appeared the 79 JMP and the 81 - 83 JCM were essentially the same inside. After 83, I recollect, is when they began the horizontal inputs and mounting the pots directly to the circuit board. I believe I read that the filtering reduced as well on the 2203s. Maybe also the transformers changed?

Hey @LoudStroud, my '79 JMP 2203 has a mixture of the red and yellow lego caps. It's a USA spec w/ 6550s, and runs about 456 VDC on the plates. I still haven't confirmed which NFB tap it's using though. Does your '79 2204 have 6550s or EL34s? And do you know which NFB tap it's using?

 

[stickyfinger]

Around here late 70s-early 80s 2203/4 go for around 1000€, while you can maybe get a 1959 for a bit cheaper, and a two channel 2210 or an 900 for maybe 850;- or so, and that's about the same for like JVM heads and most others as well. A JCM2000 could be had for maybe 550 or so now and then. A 50w in 2x12" combo could be 1100-1200, there's been one for sale for like a year in my town now but he's asking 1200;- so it might still take awhile to move.

Anyway...I think those single channel 50w heads are just about the best rock-'n'-roll machines ever made. Downright hard to make them sound bad in any way. I've had a few, sold one for 850;- just six months back or so.

Where is "around here" and where do you find them?

 

[stickyfinger]

FWIW, I have a '79 JMP 2204, an '85 JCM800 2204 (both w/6550's) and a '90 JCM800 2204 (w/ EL34's). They all sound really close to my ears. I do like the '79 the best, followed very closely by the '90. The '85 was modded and returned to stock, so that may have made a difference. I'll probably sell that one.

If price is a concern, I wouldn't be afraid of a later model JCM800 2204 myself. The USA models came with EL34's around '89-'90 IIRC.

Also, Jason at Headfirst Amplification has a YT video on how to mod a later model JCM800 to early JCM800 specs.

That video is not accurate of how they typically sound. One, the 86 is not that dull and the V1 plate hot shield is likely the reason. That is probably a mod. Could be wrong. the 2204 is using the 86 power transformer and has way more voltage that a early 2204 so it is much brighter.

 

[Deftone]

That video is not accurate of how they typically sound. One, the 86 is not that dull and the V1 plate hot shield is likely the reason. That is probably a mod. Could be wrong. the 2204 is using the 86 power transformer and has way more voltage that a early 2204 so it is much brighter.

the point of posting the video was to show that you can convert a later model 2204 to earlier specs if you so desire.

 

[racerxrated]

Very interesting information in the above comments that I was not aware of before. I have a 79 JMP 2204 that is a total keeper. Just recently considered picking up an 81 JCM800 2203 and was researching any differences to the earlier late 70s JMP‘s. The only difference I was finding were the capacitors… My 79 has beige colored caps where the 81 had the red caps. Assuming two different manufacturers that could have a minor effect on the tone. other than that, they appeared the same.

Was not aware that the JCM 2204 possibly had a higher B+ voltage, which could make it a little tighter on the low end, part of which likely contributed to the amp being so popular during the early 80s hair metal days. Now has my curiosity reignited about picking up an early JCM!

Other than that, it appeared the 79 JMP and the 81 - 83 JCM were essentially the same inside. After 83, I recollect, is when they began the horizontal inputs and mounting the pots directly to the circuit board. I believe I read that the filtering reduced as well on the 2203s. Maybe also the transformers changed?

I've had over 60 stock, modded Marshalls all pre 1990 to 1967. The JMP 2204 from 76 does not have the same preamp as all the rest from 77-90, I believe they are not cascaded like the rest. That being said, like others mentioned the 2204s up till 81 or so had much lower plate voltage...I had a 78 that was around 360v. Sweet sounding amp though. By contrast all the 82-83s I had measured out much higher; closer to 470. Monster amps that are brighter and more aggressive than the JMPs. But, the JMPs are more vintage sounding since many of them can be found with mustards in them. While they all have the same basic tone there are differences; with the red lego caps going in the early JCMs vs other brands that went into the pre 81 JMPs.
All are great though in their own way.

 

[dro]

Couldn't find anyone who wanted one, so I traded mine for a Martin OM-28

 

[LoudStroud]

Hey @LoudStroud, my '79 JMP 2203 has a mixture of the red and yellow lego caps. It's a USA spec w/ 6550s, and runs about 456 VDC on the plates. I still haven't confirmed which NFB tap it's using though. Does your '79 2204 have 6550s or EL34s? And do you know which NFB tap it's using?

I bought my head (Fawn tolex) in the early 90's and am pretty sure it had already been converted from 6550's to EL34's. It's been quite a while since I've opened it up, so not sure about the NFB tap.

About 15 years ago, I replaced all the beige chiclet coupling caps with SOZO's. It was a remarkable difference and at first questioned if I had made a mistake (I still have the originals). But as the caps have broken in over time, I absolutely love the added early 70's smoothness to the tone. Not brittle whatsoever. That said, with this much time past, it would be nice to compare to the original caps.

As I recall, the plate voltage is somewhere in the typical 375-385 VDC range.

 

[stickyfinger]

the point of posting the video was to show that you can convert a later model 2204 to earlier specs if you so desire.

Got it. My post was to point out even if it has the same circuit they don't sound the same without correct voltages.

 

[Derrick111]

I have an ‘87 2204 that’s so nasty it sounds almost modded…..for sure a keeper…..but it’s not. Don’t be scared of the other years…..my $.02

I have plexis, 70s JMPs and 80s JCMs... I love them all and 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. I like the aggressiveness though and keep them that way for the added flavor in my arsenal.

Thanks for that tip. Last night, I was doing more reading and listening to what I could from the late 80’s to compare, and honestly they still sound awesome and pretty much the same. I couldn’t discern much of a difference.

I’ve seen one or two comments that the late 80’s ones had a more scooped sound, but that doesn’t seem right. Consensus seems to be that the whole range pretty much sounded the same… which is great if I can save a few bucks and still get that same kind of sound. Plus I need some funds for the 4x12!

Not scooped, just a bit more treble response. See my comment above.

 

[Derrick111]

I know the USA amps had 6550 powertubes and feedback on the 8 ohm. Uk had EL34 4ohm.

Another thing to consider is some amps had .68uf on the presence control early on but this may be a pre 79 thing.

If you are referring to the 70s Marshalls, I don't think that is correct... the 8 ohm tap being used when the change to 6550s happened in the USA is a rumor that started when it was published in the Tube Amp book in the late 80s or early 90s, but is actually wrong. All of my USA 70s Marshalls have the feedback to the 4 ohm tap from the factory, except for the very early 70s which still had it on the 16 ohm tap like the 60s. The only exception being that they did sometimes put the negative feedback wire on the output jack instead which means that whatever speaker setting you had selected was the tap that the negative feedback wire would be connected to. This is surely responsible for a lot of people having the impression that Marshalls sounded so different from on another. They had some variances in them, but this would really change things considerably.

The G12-65 was introduced in about 1978 and ran until 82 or 83. The G12-65 has wide dust caps and is usually less toppy. It may not be entirely coincidental that the amps got brighter during the G12-65 and the G12-80 era.

I think this is something that gets confused a lot as well. The "Marshall" labeled speakers from the late 70s to sometime in 1980 that people site as "G12-65" had small center dust caps and don't sound to me at all like the classic large dust cap G12-65 that was used in Marshalls from 1981 to early 1983. The "Marshall" labeled Celestions are bright and sound much like the blackbacks that preceded them. The early 80s G12-65 are very round and not overly bright speakers.

 

[stickyfinger]

.

 

[stickyfinger]

If you are referring to the 70s Marshalls, I don't think that is correct... the 8 ohm tap being used when the change to 6550s happened in the USA is a rumor that started when it was published in the Tube Amp book in the late 80s or early 90s, but is actually wrong. All of my USA 70s Marshalls have the feedback to the 4 ohm tap from the factory, except for the very early 70s which still had it on the 16 ohm tap like the 60s. The only exception being that they did sometimes put the negative feedback wire on the output jack instead which means that whatever speaker setting you had selected was the tap that the negative feedback wire would be connected to. This is surely responsible for a lot of people having the impression that Marshalls sounded so different from on another. They had some variances in them, but this would really change things considerably.

My (January?) 81 2204 JMP had 100k 8 ohm with original GE 6550s. My 72 also had 6550s but was converted to el34 with the solder on 8ohm tap being messed with. Id say your wrong about this one.

 

[Ken Bob]

I have plexis, 70s JMPs and 80s JCMs... I love them all and 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. I like the aggressiveness though and keep them that way for the added flavor in my arsenal.

Super interesting. And definitely soooo much contrary misinformation about this subject in this forum and many others. So if you're correct, then:
1) Re: JMP vs JCM, It's not the same circuit, despite so many folks' assurance that it most definitely is. (yes, I understand we're talking small changes)
2) The difference in bite/brightness between the earlier JMPs and the JCM 800s isn't just because of the lego caps, like so many others insist.

If you are referring to the 70s Marshalls, I don't think that is correct... the 8 ohm tap being used when the change to 6550s happened in the USA is a rumor that started when it was published in the Tube Amp book in the late 80s or early 90s, but is actually wrong. All of my USA 70s Marshalls have the feedback to the 4 ohm tap from the factory, except for the very early 70s which still had it on the 16 ohm tap like the 60s. The only exception being that they did sometimes put the negative feedback wire on the output jack instead which means that whatever speaker setting you had selected was the tap that the negative feedback wire would be connected to. This is surely responsible for a lot of people having the impression that Marshalls sounded so different from on another. They had some variances in them, but this would really change things considerably.

Also very interesting, and this seems to contradict what the former Marshall amp designer recounted in the video I posted earlier in the thread. I wonder if he is mis-remembering a change to the NFB when the JCMs came along...

 

[Derrick111]

My (January?) 81 2204 JMP had 100k 8 ohm with original GE 6550s. My 72 also had 6550s but was converted to el34 with the solder on 8ohm tap being messed with. Id say your wrong about this one.

OK, you are now talking about both 80s and 70s, but I made the clarification regarding 70s. Your one '72 that has a messed with solder tabs.is not exactly definitive proof that using the 8 ohm tab was the practice on 70s USA Marshalls. I'm not saying Marshall never ever used the 8 ohm impedance connection, but it was certainly not the standard practice in the USA like the Tube Amp Book claimed and was then propagated through the net, and you don't tend to see photographic proof that it was done this way form the factory on 70s USA Marshalls either. On the other hand, I have several factory soldered examples ranging from early to late 70s with the purple presence wire soldered to the 4 ohm impedance jack and factory red dye. Plus there there are countless photos online showing them done that way as well.

 

[TommyVonVoigt]

If you are referring to the 70s Marshalls, I don't think that is correct... the 8 ohm tap being used when the change to 6550s happened in the USA is a rumor that started when it was published in the Tube Amp book in the late 80s or early 90s, but is actually wrong. All of my USA 70s Marshalls have the feedback to the 4 ohm tap from the factory, except for the very early 70s which still had it on the 16 ohm tap like the 60s. The only exception being that they did sometimes put the negative feedback wire on the output jack instead which means that whatever speaker setting you had selected was the tap that the negative feedback wire would be connected to. This is surely responsible for a lot of people having the impression that Marshalls sounded so different from on another. They had some variances in them, but this would really change things considerably.

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.

 

[Derrick111]

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.

Well, Marshall schematics aren't known for covering all their circuit iterations. Do you have photos of your factory 8 ohm presence connections? I've love to see them. Are you sure you are looking at the correct tabs/transformer wire colors to make this observation? The corresponding tabs can be tricky to identify. Seems odd that I would possess all of the USA Marshalls with factory red dye over 4 ohm tap presence connections sent to the USA. Maybe I'm just lucky!

 

[TommyVonVoigt]

Aside from the NFB question, the capacitor makes and models definitely did change from JMP to JCM era though, and of course there was the change in filtering with the horizontal input amps that I think someone touched on above. Is that really all? I used to have a 2204 JCM with EL34s that was, in fact, brighter and more aggressive than the '79 JMP 2203 I currently have (which has the plastic lego caps).

The horizontals had different filtering and less 10k B+ filltering. Combined with a higher voltage power transformer the latter amps were brighter and more crisp. I'm not sure if any had lower voltage transfomers.

I don't want to derail this thread too badly, but I do want to just jump in on this filtering thing real quick with some specifics. It's a very common misconception that when they changed the filtering, they decreased it. I see that posted all the time (not on this thread, fortunately). That is actually only half true. For the 100 watt heads, they actually increased the filtering on the Mains and Screens, and did something really wacky with the PI.

Prior to the change to horizontal inputs, the 100 watt heads (2203, 1959, 2210, etc), had 2 50+50 caps for the mains, and two for the Screens. Each can wired in parallel, bringing it up to 100uF, and then in series with the other cap, dropping it back down to 50uF, but at double the voltage capacity. When they reduced the number of cans, they still had each one wired in parallel. That doubled the filtering to 100uF for both the Mains and the Screens.

For the earlier heads, there was a 50+50 cap wired in parallel just for the PI. 100uF on that node. Then, moving further along the line, we find a 50+50 for the preamp, which was split. One side for V1, and the other for V2. Two triodes per node. What they did when they monkeyed around with the filtering is actually kill that dedicated PI cap entirely, and put the PI on the same node as V2, using one half of that 50+50 cap. So they chopped the PI filtering in half, and stuck 4 triodes on one node. It's even worse for the 2210, which does have the PI on its own node, using half of a 50+50 can. But, the entire rest of the preamp is all on one node (7 triodes!!), using the other half of that 50+50 can. There is actually an 8th triode (the reverb driver) which is tapped into the Screens node.

 

[TommyVonVoigt]

Well, Marshall schematics aren't known for covering all their circuit iterations. Do you have photos of your factory 8 ohm presence connections? I've love to see them. Seems odd that I would possess all of the USA Marshalls with factory red dye over 4 ohm tap presence connections sent to the USA. Maybe I'm just lucky!

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?