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Marshall Cap Job

ToneKing

Member
Messages
1,424
How can you tell when your amp is needing a cap job? What symptons would you notice? I've got a marshall 2554 jubilee series combo that has been sporadically getting moisy hum. I've changed out all of the tubes, but would not eliminate them from being the problem. I've had some quality issues with jj's lately. Thanks for any input.
 

ked

Member
Messages
911
If the amp is 10 to 12 yrs old, it may need a cap job, depending on the quality of the electrolytics. If you see any of the cap bulging or leaking, it's time to change them for sure. Bad electrolytics can cause humming. Make sure the cap in the bias circuit gets change at the same time.

Ken
 

John Phillips

Member
Messages
13,038
10 to 12 years old is WAY too soon IMO.

I would never even consider doing a cap job on any amp under 20 years old at the absolute minimum, unless there was a failed cap.

How many amps over 10-12 years old are still being used all the time with no problems? Almost every single one. How many over twenty? Most of them. Many amps up to even thirty years old and more are running (apparently) perfectly well on their original caps, with no sign that they actually need changing.

I would certainly advise someone to change them if they're thirty years old, but not much before that.

Modern electrolytics have a longer working life than those old ones too.
 

vintage66

Member
Messages
6,733
Not to hijack, but my Jcm800's 25 years old-how do you tell if it needs it and is there a danger of messing up the amp if I don't?
 

phsyconoodler

Member
Messages
4,305
It's a preventative maintenance thing.You don't say "oh my oils' got 10,000 miles on it,but it's still clean,so i'm not changing it".Same with filter caps.Why take a chance?Sure there are lots of amps with good filter caps after 20+ years,but not all of them are good.
 

vintage66

Member
Messages
6,733
It's a preventative maintenance thing.You don't say "oh my oils' got 10,000 miles on it,but it's still clean,so i'm not changing it".Same with filter caps.Why take a chance?Sure there are lots of amps with good filter caps after 20+ years,but not all of them are good.
Well I just bought it-is there a way for a tech to tell if it's been done? How much does it cost? Will it change the sound-modern caps vs ones made in 1983?
 

John Phillips

Member
Messages
13,038
It's a preventative maintenance thing.You don't say "oh my oils' got 10,000 miles on it,but it's still clean,so i'm not changing it".Same with filter caps.Why take a chance?Sure there are lots of amps with good filter caps after 20+ years,but not all of them are good.
No, but the vast majority are. 20 years is at the early end of the range you might need to even think about changing them, and I would only consider doing so if one has failed. I don't think I've ever seen an amp that needed a full recap that early, and only a handful of individual cap failures.

Even at up to thirty years I won't normally change them if no other serious work needs doing to the amp, it's in good original condition, and has clearly been used regularly and carefully - but I will if the amp needs work for other reasons.

Forty years is pushing it though. The failure rate really starts to take off about then. I would recap it even if no other work needs doing at all.
 

Swarty

Member
Messages
1,131
you guys probably haven't had your prostates checked lately either!
Just last week... ouch! and the blood work too...

But as for the amp, it sounds superb; tight, punchy and very quiet... even played bass with it the other day through one of my son's experimental cabs. It was an amazing round yet crisp bass tone! For a customer's amp I always provide the appropriate schmeel...something to the effect of, "Cans typically outlive axials, however there are techs out there that recommend replacing filters every ten years, which I believe is to benefit the tech rather than the customer, but they do have a limited lifespan and changing them is considered routine maintenence. The downside to leaving them alone is if one goes it could potententially take a transformer with it."

Amps with axial filters are a different story... if it is pre 1980 or so it is just time.
 




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