1979 Marshall JMP 2203 - the 'Bright Cap' revisited!! 

When I have this, I tell the customer if you don’t like it, you’ve got the wrong amp or speakers. That amp is perfect as is. What a gem.

I really don't understand why anyone would be trying to dial back the gain to get a clean sound from these amps. They sure weren't designed with that use in mind. People say they are a one trick pony, but damn, what a trick! Good to see you using a chopstick to point out things in the chassis. My father was an old school military radio electrician, he emphasised to me to never go randomly touching things with your bare hands. He was trained to use a non conductive tool in one hand, and have his other hand in his pocket. That way even if he did get a shock, it wouldn't be as serious as if he was holding the chassis with his other hand so the voltage wouldn't pass through his body and potentially kill him.

Another great one Jason ! Here in Quebec , I'm lucky enough to have a great Electronic Engineer as a tech . He was the designer for all the pedals at Radial Engineering and invented the amp stage switcher for the big names in the 80's. Anyway , all this to say that I had him build me a 2204 JMP with SS and Tube Rectifier on a three way standby switch , standby being middle position . He also drew a schematic years ago so a knob on the back would blend the Bright cap less or more so you can adjust it to taste depending on the guitar or cab you're using and it's brilliant . There is so many forum threads on the subject of clipping or leaving the bright cap in but having a knob to add the brightness and grit you want is fantastic and it works great ! Just wanted to share my story on your wonderful channel . Have a great weekend everyone !

That amp sounds absolutely fantastic.

The brightness is what makes it sound great. All those upper mid and high harmonics. My 2203 from 1983 is amazing because of this. You can always turn down treble but it's hard to add without mods.

I one million percent agree it sounds like a great JMP leave it alone.

Great video! I Fantastic sounding Marshall! I 100% agree with your suggestion about leaving this amp like it is!

Great video and information Jason.

Thank you very much for your love for the amps and tones! It makes everyting so beautiful

This is one of the best sounding amps I've heard on your channel 👍

Wow...what an amp. I liked it stock too.

Great video! Thank You! 🙋🏻‍♂

Sounds as it should, even better after being biased. I think a lot of guitarist listen to their amp without putting them into the mix. Good explanation as usual 😊

Ideal sounding 2203 to me, in great condition too. Love those pointer knobs!

Sounds excellent

I have this exact model and year. Mine is a US version which originally shipped with 6L6s, the only thing I have changed was a setup and rebias for EL34s. Otherwise completely stock. The chouce of rube in V1 can make a huge change to the sound. I typically run my pre gain at 9 or 10, with a Tubescreamer pushing the front. Sounds massive! Plus, I have it paired with one of those oversized Mesa 4x12s with Celestion V30s. Mine does not have stacked resistors BTW.

Awesome amp !!

Sounds Killer-Rock on Jason 😎

Yeah, that's one great sounding amp! I set mine up pretty much exactly like how you dialed this one, though it can also depend on the guitar I use and/or speaker cab. With my Bogner os2x12 with Scumback m75's I can run the P, M, and T up higher as that is a darker sounding cab. For smaller gigs I bring a 1x12 with a Cream Alnico and that cab is a brighter cab, so I roll back the P and T a bit (and keep the master lower so that I don't get fired).

I bought two of these about 14 years ago ... picked one and kept it. Sounds at least as good as this one ❤ Incredible instruments

Massive sound killer playing !

Awesome. Mods are great, but a stock MV rips, when you dial it into it's sweet spot. Almost exactly how I run mine. Wise old Mr. Ho once told me "master at 4, preamp at 6" when I had him service it shortly after buying it for $750. He closed shop, gonna miss him. For a guy that didn't play guitar he new exactly what we wanted.

Thanks for servicing the amp for me Jason! Sounds killer especially biased well. As mentioned by @unclebensrice you cant really treat it like a gain control. I initially dialled it in like I would my jubilees (this is my first 2203 circuit) with the gain somewhere between 4-6, and yeah its pretty damn bright. Cranking the gain up to 8 really fills it out and doesnt really add that much more gain.

Looks factory to me, I've seen a few weird things in JMP's. They do tend to be stupidly bright sometimes, I remember back in the day we used to try them out and find one that sounded "good". The 800s were more consistent when they were new, but they can drift wildly. Sometimes that sounds good too so I don't usually change them unless the out of spec is going to cause problems.

Many people are running these JMP‘s with vintage 30 speakers , which are overly bright anyway. I used to run a graphic eq to sculpt the input to my taste as well. My bright cap is untouched since 1980

Jason, WRT bright cap the following is worth trying: a/ use a series resistor to tame it, value experimentally derived, b/ connect it said RC network from * before* the 470k // 470p network. This will even out the HF boost response across the gain controls range. No bright cap to me doesn't sound quite right and IMV it needs some amount of HF boost but not too much. You can also connect the bright cap with a pull switched 1M gain control. Plenty of options. Have fun.

I have a 1980 2203 and this amp looks the same as mine but those piggy back resistors...I do not have. Beautiful amp!

I’ve had my stock 79 JMP for nearly 10 years now. It was my all time fave for most of that time and beat out 2203’s from 80 and 82(as well as a Ceriatone 2203 and a few ‘800 killer’ boutiques)for the top spot. Yes, it is a bright amp and like in the video I tend to run the Preamp around 7 to take the edge off the stock brightcap. Fantastic sounding amp that cleans up great and gobbles up boosts. That said, lately I’ve been going for a more Malcolm rather than Angus sound and the Preamp needs to be a little lower for that, say 5, and that can be a little edgy. So my stock 71 1987 became my go to for that sound and a few weeks ago I got a stock 70 Super Bass, and that is instant Malcolm.

I had my amp tech change the value of the bright cap on my 1981 Jmp to get it to sound warmer. Then I run it into a Mesa 2x12 cab loaded with Weber Thames 4 ohm speakers,which are voiced like Fane speakers like you hear with Hiwatts. What a massive difference! I still get the highs I need but they blend in with the Bass and Mids much better. I also got rid of my Vintage30 Celestions in my Mesa cab. Too harsh sounding. I dont understand why people like those speakers at all

Man that thing has some amazing high end.

Ends Up sounding good

Had one of these. 79 JMP 100. Bought from willies American guitars st paul, Mn about 20 years ago. $500. Mint. Thing could really thump! I was trying for the Randy Rhoads sound. Like a fool, didnt know and i got rid of it for JMP-1 setup, which was killer!! What they ask for these now.... i had a piece of valuable history.

I have an original 800, like this same year, it was super bright , but as you said once the preamp gets passed 12 it eases of a bit. Speaker cab selection is important as well. I used to run mine with the presence and treble at 2 to 3 , the preamp gain at just past Noonish, bass literally full on. I hit the front end with Klon or , surprisingly good effects with this is the Keeley DM drive. Its was still a little harsh. So I had mine modded with a bright switch and a Metropolis loop ( which is switchable). Now it sounds perfect and you can still get that incredible bite. I did have the normal channel modded to be a switchable boost, but it has the wrong value pot , which makes it unusual able. You just need to literally touch it and it adds 3 db.

Love removal machine!

Sounds just killer 😎

I think it sounds great, but please mention to the customer that it might help them to run the preamp high and turn down on the guitar - that way it minimizes the treble boost of that stage and also makes for a cleaner guitar sound, if that is what is desired. It may lead to it sounding a bit noisy though...

That’s a cool amp! A local cover band I used to follow played thru these & the lead player, who was a heavy set fella, got a huge fat tone out of that thing lol! I used to think, maybe it’s because of his size? Did he clip the bright cap? Anyway, I really enjoy your videos & greatly appreciate you sharing your knowledge!

These late 70’s Marshall’s are the coolest ever. People (especially modern amp designers) don’t seem to understand how a Marshall is supposed to sound. The lack of presence and sparkle is why I’ve returned almost every new Plexi clone I’ve ever tried out. They all sound like there’s an inch of cement and 4 blankets over the cabinet, just total mud. Friedman’s are the worst about this. Plus, people act like it’s almost impossible to get proper AC/DC tone at low volume and it’s some kind of unachievable holy grail tone, but that’s probably because they’re playing through these dark and dull modern plexi “interpretations”. The Brent Hinds Terror is the only one I’ve tried that gets it right, and was predictably discontinued and hated for being too bright and also improperly advertised as a metal amp. Adrian is one guy that knows what he’s doing and I wish he’d make more Orange Marshall’s lol.

Killer background!!!

Hey Jason, as you indicated and voltages I saw...this amp is spot on the epitome of a Marshall! NO changes needed. Bias it for tone/life and if the customer feels something is off...it's gotta be something else, like speaker/cab or upstream and guitar/pickups, because this Marshall is healthy as fuck!👍 I've seen stacked resistors in Marshall amps I think factory, but not as many as this one. But I do think looking at them and era specific n solder joints that they are in fact factory original!?

Wow, I just acquired a 76 2203 with the exact same four piggybacked 10K dropping resistors.

That sounds like rock n roll to me. Nothing wrong with that tone at all.

I've always found that the preamp volume on these Master Volume amps behaves much more like a tight loose control than a "real" gain control. Even by changing the bright cap to something smaller like 500p or 250p it still behaves somewhat like this. So instead of changing the bright cap I like to use a 250k pot and change the 470p on the 470k to a 2200p. To tackle the high end harshness on these amps I like to change the negative feedbackresistor to something like 39k or 47k off of the 4 or 8Ohm tap and add in a resonance pot. It makes the amp much more usuable (especially at lower volumes) in my opinion.

I think you fixed in the first minute and a half. That thing sounds great

Seen that Plate Snubber in a lot of JMP 22xx, it's also used to prevent oscillation, so I would not really exclude that this is a factory mod.PIHER They did some really awkward things sometimes so I would also consider the stacked resistors as factory, considering that the value is somehow in the ballpark and they are all the same type of PIHER resistors.

It's worth it to make note of the fact that by now any 50 year old Marshall with original plastic/bakelite/phenoloic power tube sockets should be considered for socket replacement with ceramic sockets. I've had more than one 50 year old JMP come across my bench with arced power tube sockets that have a definite burned smell on them. Try to crank the amp and things just go very badly due to more arcing in the sockets. So consider therapeutic socket replacement to keep the amp reliable at high volume. Even better to replace them with high quality ceramics.

Nice tone, I had some 800's back in the day but prefer the Plexi

Cool video that is a good sounding marshall with EVH great tone! One of things that got my eye was the guitar you were playing very nice guitar and with great tone! Is it stock?

I put the 330uf fat cap across a resistor that Friedman recommended and it beefed up the low and top end. Gives it more girth I guess

The factory Celestion speakers in Marshall cabs at the time this head was made were the very warm sounding, low-mid heavy G12-65, there’s a reason for that.

Hi Jason..love your videos.....Ive got a stock 2204 and theres a snubber cap on the plate resisitor of V1, though I think ive seen others without..strangely my volt drop of 2x 10k resistors next to the bias pot theres only a 10k and a bare wire in place of the other??..I know its stock as I bought it from new.

Also, i remember i had savage audio convert the KT88"s? I think stock, to EL34"s. Honestly.... couldnt tell a difference after spending $300. But oh well, we learn.

Jason, where is the best spot to put a clipping diode (and what type) that can “clean up” the best with a guitar’s volume ? Really curious….

That’s the only thing missing from the Suhr 68 amp. It NEEDS the bright cap. If people don’t like the stock bright cap just throw in a 470pf. Good in between.

Great video, what do you think of the new 20 watt JCM 800 SC20 ?

I have a 79 jmp 2204 and it is exactly the same with a snubber cap and doubled up dropping resistors that add to 8.9k. It must have been done at the factory.

Sounded perfect when he dropped it off. He just has the wrong amp for him

I have a feeling you could take a Pignose and make it RAWK!

Maybe put a tube rectifier might take out some harshness.

I prefer to have the bright cap removed. It opens up a lot of great blues & rock sounds at lower preamp gain levels. With the bright cap in you're missing out on some great tonal range.

I put a 220k resistor in series with my bright caps.

You know, it also doesn't hurt that you can absolutely play your friggin' ass off, brother. So. . .that might be contributing to the amp sounding good. 😃

plate snubber might be stock. the whole amp might be stock. i wouldn't touch anything. voltages all great. I'd advise the owner to use an eq pedal to dial out his ice pick

Hey I remember that axe.

Leave it alone it’s not supposed to to sound like doom music get a orange amp with vintage 30s you will have nothing but bass I own a 1978 it’s the kind of music back then

Large bright caps rule. It's what makes Marshalls sound.... well, Marshally. I even modded my JTM45 from 100pf to the full 4700.

Just turn it up! Doesn’t that take the bright cap out of the equation some what.

Leave it be....

That shitty Suhr sound piercing with any amp on any setting.

Maybe he'd rather play footsie with his pedal board.

SLP to my ears

"Ripping"?You must be joking.Just turn the treble down to 0 and presence 2-3"ala Eric Johnson"then it will be rippin.Or just mod it to a super bass.Then you can turn the treble up a little bit.