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Advice for a JMP 2204.

grimlyflick

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Oct 27, 2005
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After being intitially a bit dissappointed with the sound of my newly accquired 2204, I have decided to stick with it and see how it goes, but I like some opinions etc on what I plan to do.

JMPfront.jpg


I'm going to get the amp serviced first but would like a tiny bit more "crunch" from it when run at full blast. Can anyone suggest replacement valves that may do this or will it be a matter of the tech just getting the bias right?

I've a friend who works for another large amplifier manufacturer and can get the amp serviced for free/a few beers, or shall I bite the bullet and risk any expense of sending back to Marshall?

The cabinet is showing its age (after 31 years of gigging) and I would like to "refurb" it (new handle, corner protectors as two are missing). I've another friend who has a custom cab company and he will recover it etc for next to nothing. But my question is, he can do it any colour I want, as well as Marshall black, but I really fancy having it white and getting my cab (which also bears the scars of years on the road) done to match too.
How would this affect the resale price should I ever (not that I do) plan to sell it? Bearing in mind that the original vinyl is not in fantastic condition.

Cheers!!! :salude
 

DannyBoy

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The best thing you can do is make sure it's biased properly, and use an eq pedal.
 

Mike Shaw

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The bias is a biggie since Marshalls tend to come a bit cold from the factory. Of course, if your tubes are older - replace 'em then bias them. I like the "Winged C" tubes. These USED to be Svetlana but there was some kind of fight regarding the name so the NEW Svetlanas are completely different! Can't tell the players apart without a scorecard! Anyway the "good" ones are SED that have a letter C with wings emblem. I've heard that the GT EL34M's are pretty nice as well but can't confirm. JJ's are nice as well but seem to be a little darker sounding.
Preamps .... JJ's are good but a bit darker sounding. GT 12AX7M's are supposed to be good but apparently have some QC issues. I've heard they are working to correct but can't confirm. New Tung Sols are supposed to be excellent.
Of course these are all new production. NOS opens a whole new world of options at a considerably higher cost.
There is a a bright cap / resistor set up connected to the either the Vol pot or the Master pot (don't recall exactly). If you're amp seems bright at lower volumes you can either remove or alter values. As you crank the vol or preamp the effect of the cap on brightness is diminished so in theory at full volume the cap is completely out of the circuit. You can clip one end of the cap / resistor while leaving the other attached to see which way sounds better.
Whew!!!
A recovered cabinet will likely reduce resale value but because the amp is not one of the holy grail amps going for massive dollars to collectors it likely wouldn't be that much. This is assuming the recovering was a top notch job and looked factory fresh.
FYI - I'm presently working on a 2203 with KT66's. Haven't played it an a bunch of years but I seem to recall that th 66's really kicked archie over the EL34's.
Hope this helps! Mike
 

pigman

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I,ve owned and gigged with mine for well over 15yrs or so,these amps are not plexi's by any means but they are desirable to people who like the versility of MV amps. I personally would keep it in it's factory condition because they're value is increasing as years go on, that said ,I agree Svetlana Winged "C"s EL34's are great new production tubes, with proper biasing I have enjoyed mine over the years and they won,t break your bank account. I presonally like to use good NOS pre amp tubes, Mullard,Brimar,Tunsram etc in V1 &V2, and use a RCA 5751 in the PI (V3) to smooth out any harshness. If the amp is too brite at lower volumes I would reccomend changing the brite cap to a lower value. Stock is 1000pf, and a 100pf suited my taste, one note though is that when the preamp is dimed the brite cap IS out of the picture and has no effect.Another major factor is the speakers and/or cabinet your using, I am a firm believer of G12h30's, always have loved thier sound and tight lower end. This is what has worked for me over the years. :2zone Give it a worth while try, they aren't for everybody, BUT it is a great classic Marshall in it's own rite. I,ll never cut loose with mine! Pigman
 

Mike Shaw

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Hey Piggie! Can you refresh my mind .... Where exactly is the bright cap located? Going from memory (uh-oh!) there is a cap connecting two lugs on the vol pot, and a cap / resistor connecting the "high" input jack to the master vol pot. Which one is the "bright cap"? I wan't to say the cap / resistor to master vol. but am not positive (damn burned up mind!!!). Pictures would be great if you got them. Thanks! Mike
 

pigman

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Mike, the brite cap is the lone cap on the 2 lugs of the volume pot, The cap and resistor combo is treble peaking type curciut, I did a mod to the cap/resistor at one time replacing it with a 68k resistor and to me it effected thetone too much for my taste and changed it back. But I changed the brite cap to 100pf years ago and it suited me. I did save the original cap, just because I'm one of those nuts that like to be able to restore any mod for the sake of "keeping it original" I don,t have the link but the web site is Tonelizard.com he refers to the JMP and JCM800's, which were very much alike if not the same during the JMP and JCM transition. Hope that helps. Pigman
 

pigman

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Grimlyflick, I might add if your anywhere close to Central, Oregon , I'd be happy to help you out dialing that baby in! Pigman
 

Mike Shaw

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Beautiful! Thanks for the info. Looks like I've got some 'sperimentin to do!
 

Tex Ecco

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grimlyflick,
I belive you have got yourself a real treasure. I have one of these and I have to say they are truely amazing amps once you get them tuned up.

Firstly, Mike was right on with the Svet Winged C power valves, they are the best option available today for these amps. Also be sure to use the best pre amp tubes you can afford, especially in V1 (most of the amps tone is generated here).

Pigman was also dead nuts on with the G12H 30 celestion speakers. If you can get a pair from the 1970's you'll never regret owning them. And a nice early marshall 2x12 (ply, not particle board) will bring out the best in the speakers.

The hi sensitivity input will have a bright cap across it, which infact cuts some of the highs. It's a very simple mod to disconnect or cut this to get more clarity and a little more apparent gain from the amp.

Finally have the electrolytic caps changed, especially if they are the originals. They don't last 30 years and really will make the bass sound tighter and more focused.

After all that, enjoy it. It's a truely great amp and not that far removed from the Plexi's so many people rave about.

Check out the Marshall forum on Plexi Palace for more useful info on these amps.
 

Ian Anderson

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Aug 5, 2001
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A cap job, new valves and correct bias will release the potential of that amp.

If you want a little extra gain, get your tech to change the cathode resistor on V1b from 10k to 4k7, this will give you some extra gain but still retain the basic tone of the amp. Also add a 0.68uF cap accross this resistor for a further gain boost.

I also like to add a 0.68uF cap accross V2a's 820ohm cathode resistor for a midrange gain boost.

Add a 100pF cap accross V1b's plate resistor to tame the top end a little.

Change the bright cap on the gain pot to 100pF.

Those simple mods will give your amp that extra gain you require. You'll still be able to get the 'stock' gain levels with your preamp volume set to 6.
 

grimlyflick

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Cheers for all the replies, guys. Plenty fo me to look into.

A question though, where is a good place to get the tubes you guys mention in the UK?

Pigman, many thanks for the offer, but I'm on the wrong continent I'm afraid. :pwink

I'll keep you all posted with a report after the servicing, rebiasing and maybe a cap job.

Cheers. :salude
 

Mike Shaw

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I don't live in Europe but Watford Valves seems to have a good rep. Hell, I wish they were in the states so I could buy from them!
 

Mike Shaw

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FYI - I finally got my 2203 with KT66's sorted out. Biased 'em up around 39 ma and clipped one end of the Pre-AMp pot's cap (the one connecting the two lugs) and plugged 'er in. I was using a "work" cabinet with one Weber P15N speaker at 8 ohms and it was OK but was missing something. Then I remembered that it is suggested to set the amp impedance to one setting UNDER the cab impedence when using KT-66's. Holy Lady!!!! This thing is unbelievable!! And I'm using old Sovtek LPS preamp tubes. It has that thick Soldano type of sustain but doesn't lack in the highs. And this is with a Strat! Wow! It should be obscene with a better preamp tube and my Marshall cab.
 

pigman

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Grimlyflick, Here in the states I get a lot of my tubes from Mike at KCA tubes, don,t know if he ships to the UK but look up his web site and ask him, he has a great selection and is a reliable supplyer. If I ever get back to Nottingham where my sister in law lives I look you up. Over at Pexi Palace the lastest is stuffing 6V6's in these amps . Haven,t tryed it and don,t know if I will, but you should jet over there and check out the blurb on that, kinda interesting.
Pigman
 

grimlyflick

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I presonally like to use good NOS pre amp tubes, Mullard,Brimar,Tunsram etc in V1 &V2, and use a RCA 5751 in the PI (V3) to smooth out any harshness.

Can you recommend which of these to use as pre-amp valves. When I go to Watford valves website I get very confused by all the different product codes for each make (ECC83, 12AX7, etc etc). I'm a complete novice at all this amp business and am totally in the dark.

I'd like to try to get the amp sounding great with good valves and a rebias before I start getting into changing caps etc.

:salude
 

pigman

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Basically, your ECC83 and 12ax7 are the same tube and what your looking for. the ECC83 is the European designation for the 12ax7. V1 which is your first pre tube furthest away from the power tubes , to the far left as you look in the back of the amp, will have the biggest effect on your tone, as your guitar signal see's this first, I presently am using Brimars, have for years and just like thier tone, they are NOS and aren,t cheap.If you have a local amp tech in your area, talk to him or her and ask about some new production pre amp tubes to mess around with, they're not to expensive. I went into our studio one nite and swaped pre tubes until I was satified with the tone I was getting, of course this happened for a while until I settled on what I presently use. It's fun and pre amp tubes do not need to be biased like power tubes, just plug them in and experiment. Good luck Pigman
 

grimlyflick

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Cheers Pigman,

Looks like the amp is off for a rebias and some Winged C's. Then the real fun starts with experimenting with the preamp tubes.

Thanks again. :salude
 

grimlyflick

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Right then, to go with my Svetlana Winged "C"s EL34's I've ordered some Harma ECC83/7025's to go in my JMP.

I'm hoping for a nice big, smooth, full sound without too much treble and a healthy amount of crunch.

After spending a day searching through various Forums and Watford Valves website and review section, I've taken the plunge.

As far as the refinishing goes I've decided to only recover the cabinet (not the front or back panels) and add new corners, handle etc to retain its original (well kind of) status.

Wish me luck, a review will hopefully follow soon with pic's.

And once again thanks for all your (very) helpful replies.

Cheers. :salude
 
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