I meant non-electrolytic signal caps, not power supply caps. Some techs replace every single capacitor in vintage amps, and I don't agree with that. That's part of the vintage sound.
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Capacitor life and death
- Thread starter Jammin Johneboy
- Start date
I meant non-electrolytic signal caps, not power supply caps. Some techs replace every single capacitor in vintage amps, and I don't agree with that. That's part of the vintage sound.
Mr. Foxen
Commercial User
Yeah that one too, like playing an old vinyl record (12" CDs for the younger ones).
I do agree with BbbyBld though if they ain't broke and produce the desired sound (signal caps) I don't break them.
I have capacitor meters that can do leakage testing. They are used for testing signal path coupling capacitors. Not what we are talking about here.
I have a Blue ESR meter that I built as a kit. It does a pretty good job for the money. I find it useful for some things. If the internal resistance is high in an electrolytic cap, it isn't a good thing. But for all the time it takes to test an electrolytic cap in an amp, it is more cost effective to simply change it. It isn't the same story for more complicated pieces of equipment.
A valuable vintage amp that someone wants to preserve is a different story. This usually isn't a gigging amp. Owners typically want it to work and to be able to play it once in a while. In a case like this, you don't necessarily need to do a full replacement. In this case it would be worth it to spend the time checking out the cap and possibly going through a reforming process to bring the cap back to health. It depends on the value of the amp and the condition of the cap.
And yes, I also hate to see ALL the caps changed in an amp. Change the coupling caps that are leaking otherwise leave them alone.
I have a Blue ESR meter that I built as a kit. It does a pretty good job for the money. I find it useful for some things. If the internal resistance is high in an electrolytic cap, it isn't a good thing. But for all the time it takes to test an electrolytic cap in an amp, it is more cost effective to simply change it. It isn't the same story for more complicated pieces of equipment.
A valuable vintage amp that someone wants to preserve is a different story. This usually isn't a gigging amp. Owners typically want it to work and to be able to play it once in a while. In a case like this, you don't necessarily need to do a full replacement. In this case it would be worth it to spend the time checking out the cap and possibly going through a reforming process to bring the cap back to health. It depends on the value of the amp and the condition of the cap.
And yes, I also hate to see ALL the caps changed in an amp. Change the coupling caps that are leaking otherwise leave them alone.
Subbed... & waiting for the first "vintage caps sound better" post
I have the original caps in my 67 pro. I'm not sure if it woul sound better with new ones.
People putting FT caps in Marshall have reported liking them
My concern is from a 1983 peavey T-40 that has caps on everything. All functions work but I get a constant hum and some distortion at some settings. It goes away in humbucking mode. That makes sense but shouldn't be there when both bridge and neck pickups are in single coil to cancel each other out.
Your amp is quiet in "humbucking mode" - so the amp isn't introducing hum by itself.
If power supply caps were bad then you'd hear hum with nothing plugged in.
Hum will be there with no bass plugged in if the amp power supply caps are at fault. If the hum comes from your bass it will be amplified. Your bass may have a faulty ground to the bridge.
When the things crackle, or change tone, then it's a fault, so fix it, until that point, don;t go looking for faults - it's futile.
I have two vintage stereo receivers (one Sony, one Harman Kardon), and both are from the early 70s...1971-1973 or so. The Sony clearly needs a recap, it frequently distorts and cuts out in one channel. The Harman Kardon (which is the slightly older one) continues to chug along perfectly, although I know that sooner or later it will need a recap too.
So...30-40 years, give or take a few?
So...30-40 years, give or take a few?
This is an extreme case, but here is my story...
I was recently given a 1954 Magnatone. The supply cap can looked original and the amp made no sound. I rebuilt the supply with modern caps but left the cap can so the amp would look right.
The amp then would crackle and only make a shallow ghost of the sound of the guitar plugged in. So I replaced all the bumble bee coupling caps. There are no cathode bypass caps. The amp came to life but had weird ugly distortion and sagged REALLY hard.
So I checked the resistors. Almost every one of those beautiful old carbon comps had drifted significantly. I had 3 220K resistors that had aged to over 450K. One was in the cathodyne phase inverter - where it is important to have a matched pair. So I replaced resistors. And the amp began to almost sound good.
Then I checked the volume and tone pots. All spec'ed at 1M, all were super high. One was over 2 meg!
So now I have a pretty decent weird vintage amp sorta like a tweed deluxe, except full of 220K plate resistors and a crude treble bleed tone control. But pretty much ONLY the chassis, transformers, and tube sockets are original.
In summary:
The second law of thermodynamics spews some confusing words about "ordered states", "equilibrium", and "entropy". In common bass-player language all this hooey can easily be reduced and translated to:
"Everything turns to sh!t"
I was recently given a 1954 Magnatone. The supply cap can looked original and the amp made no sound. I rebuilt the supply with modern caps but left the cap can so the amp would look right.
The amp then would crackle and only make a shallow ghost of the sound of the guitar plugged in. So I replaced all the bumble bee coupling caps. There are no cathode bypass caps. The amp came to life but had weird ugly distortion and sagged REALLY hard.
So I checked the resistors. Almost every one of those beautiful old carbon comps had drifted significantly. I had 3 220K resistors that had aged to over 450K. One was in the cathodyne phase inverter - where it is important to have a matched pair. So I replaced resistors. And the amp began to almost sound good.
Then I checked the volume and tone pots. All spec'ed at 1M, all were super high. One was over 2 meg!
So now I have a pretty decent weird vintage amp sorta like a tweed deluxe, except full of 220K plate resistors and a crude treble bleed tone control. But pretty much ONLY the chassis, transformers, and tube sockets are original.
In summary:
The second law of thermodynamics spews some confusing words about "ordered states", "equilibrium", and "entropy". In common bass-player language all this hooey can easily be reduced and translated to:
"Everything turns to sh!t"
As electrolytic caps (I'm thinking about tube amps) age, they tend to drift up in value, and in a very sloppy way, which can cause motorboating, woofy low end, loss of headroom, etc. As they drift up in value, they drift down in power handling and will eventually fail. When they fail they will either open up (massive hum) or short (often taking other components with it.)
Working life of a cap is roughly 15-20 years. Caps tend to last longer in an amp that is played than one that is stored. From my experience, cap cans seem to last longer than discreet caps of the day.
I've had filter caps fail in SS power amps. One PV XR600 would occasionally spit DC that would destroy speakers without a sound. New caps remedied that. I've replaced filter caps in bass heads that were operating seemingly OK, that were stronger with renewed headroom with new caps.
Working life of a cap is roughly 15-20 years. Caps tend to last longer in an amp that is played than one that is stored. From my experience, cap cans seem to last longer than discreet caps of the day.
I've had filter caps fail in SS power amps. One PV XR600 would occasionally spit DC that would destroy speakers without a sound. New caps remedied that. I've replaced filter caps in bass heads that were operating seemingly OK, that were stronger with renewed headroom with new caps.
So glad i started collecting discarded valve radios on the street, in 1966. As the new 6 transistor radios were all the rage. Inside these older radios were all manner of components, body end dot resistors, paper tube capacitors, silver mica capies etc etc. In the fulness of time entering an electronics career, at the high end of industrial design and manufacture, each day i was wide eyed. Wall to wall quality USA T and M gear, i could test to destruction what ever i wanted to.
Had to also read and understand all the technical data for these components, being mil sampled and tested. As i read through this topic, some are on the money, many have inherited the old wives tales, base on nothing in particular as to technical merit.
In general, electrolytics were -20/+100% value tolerance. Complex reason for this, much to do with chemical formation of the insulation barrier between the plates.
So many the time, as i was being taught at college how a signal passes through a capacitor..... first principles were paramount in my training at engineering level. The question i posed to my college teachers, "if the capacitor has a non conductive insulation barrier between the conductive plates, how does the signal pass through it?!" To a man they could not explain that anomaly to me, i knew the answer that is why i asked them, i was 17yo.
In our amps we have either power supply "filter" capacitors and signal passing capacitors or coupling capacitors, of many and varied types in material and construction. To lump them in together and say change them all is short sighted.
Worst aspect i find most alarming is what quality capies are you using for the replacements? Good ones with long life are hard to locate in small repair quantities, never mind the less toxic materials used these days.
*** Lets see who knows how a signal "passes through" a capacitor in a signal path or frequency compensation gain control application. This is not an easy question by the way.
Regards.
Had to also read and understand all the technical data for these components, being mil sampled and tested. As i read through this topic, some are on the money, many have inherited the old wives tales, base on nothing in particular as to technical merit.
In general, electrolytics were -20/+100% value tolerance. Complex reason for this, much to do with chemical formation of the insulation barrier between the plates.
So many the time, as i was being taught at college how a signal passes through a capacitor..... first principles were paramount in my training at engineering level. The question i posed to my college teachers, "if the capacitor has a non conductive insulation barrier between the conductive plates, how does the signal pass through it?!" To a man they could not explain that anomaly to me, i knew the answer that is why i asked them, i was 17yo.
In our amps we have either power supply "filter" capacitors and signal passing capacitors or coupling capacitors, of many and varied types in material and construction. To lump them in together and say change them all is short sighted.
Worst aspect i find most alarming is what quality capies are you using for the replacements? Good ones with long life are hard to locate in small repair quantities, never mind the less toxic materials used these days.
*** Lets see who knows how a signal "passes through" a capacitor in a signal path or frequency compensation gain control application. This is not an easy question by the way.
Regards.
I'm not sure where you are coming from there: Mouser and Digikey both sell small quantities and they stock very high quality caps. Reasonable prices and the convenience of the Internet. Some of these are better than most any cap available 40 years ago--compare the newer higher-end Panasonics or Nichicons to the venerable Sprague Atoms, and the newer caps run circles around the old Spragues (better ESR, tighter tolerances, long life, etc). I'm not sure what you mean by "less toxic" unless you are talking about the lead-free stuff (I don't like lead-free solder either).
Certainly some folks post here and just repeat Internet lore, but I think many of us here have a pretty good understanding of a capacitor's operation and construction. Some of the posters on this thread design amps for a living. Some are engineers. Some repair amps for a living.
I think that it is true that modern capacitors are much better than the older ones. For a lot of products that are typically sold for recapping amps it's difficult to find a full set of specs. They indicate the tolerance and temp spec on the cap but don't supply data sheets. CE Manufacturing's multi section cap can is an example. In contrast, check out the Invalid Link Removed products. Just about anything you want to know when designing with them is available and the company is responsive to your questions. I like to use the snap-in ones such as the TS-ED or HD series. The high ripple current capacity is well suited to the demands of a bass amp. There are good products available from other companies as well.
Reverse wound Reverse polarity, I think. Basically it means "wired like a Fender Jazz Bass so that the two single coils hum cancel when their volumes are up all the way."
Not all basses that have single coil pickups are wired like this.
