What to expect from a Cap Change

ironlung40 · 09-07-2009, 09:11 PM

Hey guys,

I've got a 78' JMP 2203 master volume head. I'll post some pics at some point.

Anyway, it is all original as best that I can tell. I'm thinking of replacing the caps as it probably needs it. can anyone tell me what tonal differences I can expect from recapping this amp? I own several tube amps, but I've never had to recap one yet.

I also own a few JCM 800 single channels, and to me this JMP is sounding a little thin, and bright compared to them. I guessing a retube is also in order.

Anyway, any comments or previous post links would be appreciated.

Sincerely,

Ironlung40

TubeStack · 09-07-2009, 10:13 PM

I just had my 2204 re-capped. The first thing I noticed, after having it done, was the increase in volume in the lower third of the knob (ie up to 2-4, or so). It was way fuller and louder, with more bottom end, in that range of the volume.

At a cranked volume, say 8 on the MV, it was tighter, beefier, quicker, and chunkier. Basically "more" of everything, and in a more balanced, full way. Was definitely worth it.

Vague, I know, but that's what I can recall. All in all, it can't hurt and any vintage amp could certainly use it.

ironlung40 · 09-07-2009, 11:05 PM

Thanks Tubestack, I think I understand the sounds and feel you are describing completely and is exactly what I'm hoping for.

How do I ensure that I don't devalue such a great amp that is now 30 years old with a cap change? I may want to sell it later. I guess the collector types like everything original, seemingly whether it works as good as it should or not.

TubeStack · 09-07-2009, 11:08 PM

Quote:

Originally Posted by ironlung40

Thanks Tubestack, I think I understand the sounds and feel you are describing completely and is exactly what I'm hoping for.

How do I ensure that I don't devalue such a great amp that is now 30 years old with a cap change? I may want to sell it later. I guess the collector types like everything original, seemingly whether it works as good as it should or not.

I'm not sure, maybe ask your tech to give you the old caps?

ironlung40 · 09-08-2009, 10:20 AM

Good Idea. Thanks.

MajorNut1967 · 09-08-2009, 12:30 PM

Just out of curiosity, why did or are you guys re-capping? And what caps are you doing Filter or Coupling? And 78' JMP 2203 is gona be very bright and thin at low to mid volume. When you crank it, the thing will sing. If you want get rid of some thin sound get rid of the treble peaking circuit.

What you can expect is the amp to sound much tighter the bass will be much more rounded and it also won't sound as warm as it did. You might notice that is seems like it is louder and a lot less hissy.

TubeStack · 09-08-2009, 07:09 PM

Quote:

Originally Posted by MajorNut1967

Just out of curiosity, why did or are you guys re-capping? And what caps are you doing Filter or Coupling?...

I was trying to track down a "swirl" sound that my amp makes when it's cranked (have posted about it in other threads). It's like a phase sort of sound, in amongst the distortion, sweeping from low, to high, to low, when you hit a note, or notes, and let it ring. Is especially apparent when using the neck pup. Only happens at 8 or higher on the MV.

The recap didn't kill the swirl though, which actually bothers me less now. Have come to realize it's exaggerated by the room in which I'm playing, and may just be a characteristic of some tube amps, that some players even desire.

Also just wanted to get all the upkeep/maintenance business done right off the bat, after I bought my 2204. New tubes, recap, ready to rock!

(Re. filter or coupling caps - not sure - I just asked for a "cap job." My tech is really great and has a huge love for Marshalls (esp. JCM 800 and earlier), he knows them inside and out. I should ask him, just to know.)

ironlung40 · 09-08-2009, 07:21 PM

Quote:

Originally Posted by MajorNut1967

Just out of curiosity, why did or are you guys re-capping? And what caps are you doing Filter or Coupling? And 78' JMP 2203 is gona be very bright and thin at low to mid volume. When you crank it, the thing will sing. If you want get rid of some thin sound get rid of the treble peaking circuit.

What you can expect is the amp to sound much tighter the bass will be much more rounded and it also won't sound as warm as it did. You might notice that is seems like it is louder and a lot less hissy.

I was referring to filter caps. As for the thin and bright sound, this JMP is much worse in this manner than my JCM 800 2203 which is essentially the same circuit. both are unmodded and thus have all of the "bright" caps on them. that is why I was leaning toward recapping and possibly retubing too. I bought it recently, so I really don't know how worn the tubes may be. I do know that I put the same preamp tubes in it that were in my JCM 800 and I noticed a big change with that. So I'm thinking a full retube and caps to be safe would get it sounding better for me.

anthonyr · 09-08-2009, 07:41 PM

On a 30 year old amp, are you taking a chance running it with the original filter caps even if there is no sign of leakage or bulging? Obviously they're way past the 10-15 year life expectancy.

ironlung40 · 09-08-2009, 08:11 PM

Quote:

Originally Posted by anthonyr

On a 30 year old amp, are you taking a chance running it with the original filter caps even if there is no sign of leakage or bulging? Obviously they're way past the 10-15 year life expectancy.

Good question. I would expect you would be, but I see these old amps with the original caps all the time. Mine does not show any physical signs of bad caps, but I have had it apart to adjust the bias, and I measured the voltage on the caps which was very very low, which leads me to think that they are not holding a charge like they should which may be due to leakage?

What damage would occur to the amp if a cap goes out?

Anyway, Hopefully a more knowledgeable someone will chime in.

TubeStack · 09-08-2009, 10:26 PM

Quote:

Originally Posted by ironlung40

... I bought it recently, so I really don't know how worn the tubes may be. I do know that I put the same preamp tubes in it that were in my JCM 800 and I noticed a big change with that. So I'm thinking a full retube and caps to be safe would get it sounding better for me.

Have you had it biased since you bought it? Could be running pretty cold...

MajorNut1967 · 09-08-2009, 11:04 PM

Quote:

Originally Posted by anthonyr

On a 30 year old amp, are you taking a chance running it with the original filter caps even if there is no sign of leakage or bulging? Obviously they're way past the 10-15 year life expectancy.

Hey AnthonyR,

One of our friends from either Norway or Finland, not sure which one. But he has 1967 100 watt with the original Radio Spares 32 mfd 450vdc and according to him the are still 100%! So it's relative I guess but I am still with if they are 10 + years change um.

5er driver · 09-09-2009, 02:08 AM

Quote:

Originally Posted by MajorNut1967

What you can expect is the amp to sound much tighter the bass will be much more rounded and it also won't sound as warm as it did. You might notice that is seems like it is louder and a lot less hissy.

Quote:

Originally Posted by MajorNut1967

.......I am still with if they are 10 + years change um.

That's exactly what I got when I recapped (filters) my 14 year old SL-X last month and my '79 Twin Reverb a couple of years ago. You don't notice the gradual loss of bass and increasing hiss over the years until one day you realize "that's not how it sounded when I bought it"......of course when everything else is in order. 10 years is a good cut off point. If they don't need replacing (technically speaking) at 10+ years and you do swap them out, you will probably notice an improvement in sound. If they do need replacing because they are falling apart, you will most definately hear an improvement.

PaoloJM · 09-09-2009, 08:29 AM

I tend to think of filter caps like the tyres on your car.
Will the car still work and drive from A to B when the tyres are thread bare? You bet, of course it will.
Will it give you as good a ride and operate as effeciantly and reliably as the day you got it? No way in the world.
Is there a distinct poosibility of a blow out and major accident some time? Maybe not today but maybe some day, who knows?

Older amps, 10-15 years or more, that have been left idle for some time (> months) without play will feel the effects sooner as the electrolyte is a bit like honey in that it dries up and crystalyses at the outside when it's just left there. This decrease the effective capacitance, leading to more hiss and less punch and definition to the amps tone.
I've a '81 JCM 800 that's been payed regularily and is showing only a slight increase in hissing (I'm giving it a cap job next week anyway) but I had a '89 JCM 800 in the other day that had been left idle for nearly a year was in bad need of filter cap replacment, lots of hiss, little note definition, lack of punch, tone a bit thin.

When you hear guys re forming caps, they are slowing increasing the applied voltage over time to re form the electolyte, just like you might put a crystalised jar of honey in the oven for some time to liquify it again.

Contrary to popular belief, new caps do not require reforming, but old caps may be recovered this way.

09-07-2009, 09:11 PM	#1 (permalink)
ironlung40 Senior Member Join Date: Nov 2008 Location: Maryville, TN Posts: 615	What to expect from a Cap Change Hey guys, I've got a 78' JMP 2203 master volume head. I'll post some pics at some point. Anyway, it is all original as best that I can tell. I'm thinking of replacing the caps as it probably needs it. can anyone tell me what tonal differences I can expect from recapping this amp? I own several tube amps, but I've never had to recap one yet. I also own a few JCM 800 single channels, and to me this JMP is sounding a little thin, and bright compared to them. I guessing a retube is also in order. Anyway, any comments or previous post links would be appreciated. Sincerely, Ironlung40

09-07-2009, 10:13 PM	#2 (permalink)
TubeStack Senior Member Join Date: Jul 2009 Posts: 196	Re: What to expect from a Cap Change I just had my 2204 re-capped. The first thing I noticed, after having it done, was the increase in volume in the lower third of the knob (ie up to 2-4, or so). It was way fuller and louder, with more bottom end, in that range of the volume. At a cranked volume, say 8 on the MV, it was tighter, beefier, quicker, and chunkier. Basically "more" of everything, and in a more balanced, full way. Was definitely worth it. Vague, I know, but that's what I can recall. All in all, it can't hurt and any vintage amp could certainly use it. __________________ "And I'm sorry but I can't be kind about this, if you are bitching about "my Marshall is too loud" or "I need a hot plate or a PowerBake to manage the volume," then you don't need or deserve a Marshall all valve amplifier! ... You're like a guy that goes and buys 1970 Chevy SS 454 with 500 horse power and then puts his golf clubs in and drives around the golf course at 3MPH..." - MajorNut1967

09-07-2009, 11:05 PM	#3 (permalink)
ironlung40 Senior Member Join Date: Nov 2008 Location: Maryville, TN Posts: 615	Re: What to expect from a Cap Change Thanks Tubestack, I think I understand the sounds and feel you are describing completely and is exactly what I'm hoping for. How do I ensure that I don't devalue such a great amp that is now 30 years old with a cap change? I may want to sell it later. I guess the collector types like everything original, seemingly whether it works as good as it should or not.

09-08-2009, 10:20 AM	#5 (permalink)
ironlung40 Senior Member Join Date: Nov 2008 Location: Maryville, TN Posts: 615	Re: What to expect from a Cap Change Good Idea. Thanks.

09-08-2009, 12:30 PM	#6 (permalink)
MajorNut1967 Senior Member Join Date: Jul 2009 Location: South Pacific Posts: 1,043	Re: What to expect from a Cap Change Just out of curiosity, why did or are you guys re-capping? And what caps are you doing Filter or Coupling? And 78' JMP 2203 is gona be very bright and thin at low to mid volume. When you crank it, the thing will sing. If you want get rid of some thin sound get rid of the treble peaking circuit. What you can expect is the amp to sound much tighter the bass will be much more rounded and it also won't sound as warm as it did. You might notice that is seems like it is louder and a lot less hissy. __________________ MJN1967 aka BA (Bad Attitude) 1958 Fender 5E3 Deluxe 1968 model 1987 50watt. A Baby Major (Half-Power) I built from the ground up. JTM 45 Clone combo Ground up build. JCM 800 Clone Ground up build, with Wilder Mods. Custom Built Warmoth Strat 75' Fender Tele-Deluxe '70 style strat custom build w/Custom Shop 69's PU's

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09-08-2009, 07:41 PM	#9 (permalink)
anthonyr Senior Member Join Date: Jan 2009 Location: Clearwater Florida Posts: 148	Re: What to expect from a Cap Change On a 30 year old amp, are you taking a chance running it with the original filter caps even if there is no sign of leakage or bulging? Obviously they're way past the 10-15 year life expectancy. __________________ 1982 JCM 800 2203 w/ 1960ax 4x12 1990 Les Paul Studio 2002 Faded Flying V 2003 Duesenberg Starplayer Special http://www.myspace.com/springfieldcubs

09-09-2009, 08:29 AM	#14 (permalink)
PaoloJM Senior Member Join Date: Jun 2008 Location: Cork, Ireland Posts: 751	Re: What to expect from a Cap Change I tend to think of filter caps like the tyres on your car. Will the car still work and drive from A to B when the tyres are thread bare? You bet, of course it will. Will it give you as good a ride and operate as effeciantly and reliably as the day you got it? No way in the world. Is there a distinct poosibility of a blow out and major accident some time? Maybe not today but maybe some day, who knows? Older amps, 10-15 years or more, that have been left idle for some time (> months) without play will feel the effects sooner as the electrolyte is a bit like honey in that it dries up and crystalyses at the outside when it's just left there. This decrease the effective capacitance, leading to more hiss and less punch and definition to the amps tone. I've a '81 JCM 800 that's been payed regularily and is showing only a slight increase in hissing (I'm giving it a cap job next week anyway) but I had a '89 JCM 800 in the other day that had been left idle for nearly a year was in bad need of filter cap replacment, lots of hiss, little note definition, lack of punch, tone a bit thin. When you hear guys re forming caps, they are slowing increasing the applied voltage over time to re form the electolyte, just like you might put a crystalised jar of honey in the oven for some time to liquify it again. Contrary to popular belief, new caps do not require reforming, but old caps may be recovered this way. __________________ www.youtube.com/paolojm

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