What are caps & why replace them?

I've been searching around the Audiokarma forum and in particularly the Marantz forum. I'll be replacing the lamps of my 2238B receiver in the near future with LED lamps. While researching on the forum I keep coming across discussions about caps & folks replacing theirs. What are caps & why are people replacing them? Is there a thread already explaining this with a good tutorial (pictures included) that someone could point me to, if a thread exists? If not, could this the beginning of such a thread?

Caps is short for capacitors. Generally when you're talking about solid-state equipment, replacing caps means replacing ELECTROLYTIC caps. Electrolytic caps contain a liquid electrolyte which dries out over time. As the caps dry out, the capacitance value may change, or they may start to leak DC current across them. Both of these conditions <can> have negative effects on the performance of the amp.

The most common caps to replace are the power supply filter caps... these are the largest cylindrical caps, two or four of them (or, I guess, one if it's a quasi-complimentary single rail design), often located adjacent to the power transformer. These caps perform two functions: they smooth the jagged waveform of the rectified AC, and they provide a reserve of power (they're like batteries in that they store charge).

dspear99ca said:

Caps is short for capacitors. Generally when you're talking about solid-state equipment, replacing caps means replacing ELECTROLYTIC caps. Electrolytic caps contain a liquid electrolyte which dries out over time. As the caps dry out, the capacitance value may change, or they may start to leak DC current across them. Both of these conditions <can> have negative effects on the performance of the amp.

The most common caps to replace are the power supply filter caps... these are the largest cylindrical caps, two or four of them (or, I guess, one if it's a quasi-complimentary single rail design), often located adjacent to the power transformer. These caps perform two functions: they smooth the jagged waveform of the rectified AC, and they provide a reserve of power (they're like batteries in that they store charge).

Click to expand...

Excellent explanation dspear99ca, right in the money! I would ad unless you are very good at reading a schematic and very handy with a soldering iron, replacing the caps should be left to the experts. Actually, any repairs as when you have an older unit there maybe more needed than just caps.:yes:

and to add just a little. Most of the caps used are called electrolytic capacitors. They use a paste inside them. The expected life span of one of these is 20 years. most of the vintage gear we are using is over 30 years old - at least 10 years past it's life expectancy.
Now there is debate on if a cap past it's life expectancy will change the sound of the unit (I personally believe it does so I change them all, but many believes it does not).
There is a small chance that a bad capacitor could "explode", a better chance it could leak. many use their equipment and never have a problem, there are more then a few posts with pictures showing people who have had problems.
For me, if it is something I am keeping, I replace every electrolytic cap in it. Besides the big ones (the filter caps), it is actually very cheap to buy replacements. Now I used to solder for a living, but I had never re-capped one before so I just dug in a unit and learned as i went. Power amps are usually the easiest just because the boards are usually really easy to get to and obvioulsy not as many caps as a receiver. receivers can be more difficult just because they can be much harder to get to.
If you happen to have a piece of gear around to play around with, I personally recommend getting the service manual, learn how to solder and practice on it. If you happen to have quite a bit of gear, it will cost a whole bunch of money if you have to send it out. If you learn how to do it, you can save hundreds, if not thousands of dollars.
You could always go to goodwill and just buy the cheapest thing they have to practice on. Is a great skill to learn if you like vintage gear. Is not really hard, just have to be patient and pay attention to what you are doing

Thanks & DeOxit questions

Great explanations! Really appreciate it. I know I'm not ready to do cap replacements, yet. But with more research & practice eventually I'll have the confidence. Good advice on obtaining some inexpensive equipment from second hand store (possibly alley finds?) to practice on. For the time being I'll be doing the lamp replacements with LEDs from AK member Don H. I haven't ordered them yet, but once I do & crack open receiver I'll post pictures. I hope their aren't any leaky caps. I've been the only owner of this receiver since I purchased it new in the mid-70's. Sound quality seems to be about the same. Have caps been improved upon since these original? Maybe once I post pictures someone will be able to tell if there's any parts that need replacing (upgrading?). Along with the lamp replacements I'll be using DeOxit for the first time. Besides DeOxing pots/controls & RCA connectors, is there other parts I should DeOx? Circuit board? Caps? Power supply?

Electrolytic capacitors have gotten smaller in recent decades, but you can find the proper sizes from Digikey, I just did mine. The only ones that matter size-wise are the two big PS caps as they're held in place with fitted rings. The other electros are just held in place by their leads, so size doesn't matter.

What are the signs of bad, dried out, or leaking caps? Smell, lost of sound quality, etc?

Most times the clues are subtle. The sound changes, but it's like a glacier... you look at it and it's not moving, but come back in 6 months and it's moved a foot. You don't realize the sound has degraded until you replace the caps.

The power supply filter caps have really obvious symptoms of failure, the biggies. They are subjected to the roughest treatment... you'll note the catalogs advertise that some capacitors are for "high ripple applications", well the power supply is one of those. The rectified quasi-DC voltage coming out of the diode bridge is a mighty ugly-looking square wave pattern, look up bridge rectifier on wikipedia there's a good explanation. The filter caps store charge and "smooth" out the jagged waveform to a nice consistent DC voltage. When they fail you can hear the 60Hz oscillation derived from the AC line voltage. Replacement of these large charge reservoirs often improves the bass response.

Some caps do obviously leak, and you can visually inspect. Some caps are glued down to the PCB, and sometimes it's tough to tell the difference between leaking electrolyte and glue. Glue has much more volume and tends to be somewhere between yellow and tan, leaking electrolyte tends to be dark brown in a thin coating.

You can test caps with both a capacitance meter and an ESR (equivalent series resistance) meter to determine their health. The ESR meter is (IMHO) much more useful, and it can be used on components in-circuit, i.e. you don't have to de-solder anything to test.

dspear99ca said:

Electrolytic capacitors have gotten smaller in recent decades, but you can find the proper sizes from Digikey, I just did mine. The only ones that matter size-wise are the two big PS caps as they're held in place with fitted rings. The other electros are just held in place by their leads, so size doesn't matter.

Click to expand...

I use the smaller caps for the PS locations, too. A couple of turns of rubber weatherstripping (not foam) holds them into the clamps like concrete.

Also look out for the tops (and sometimes the bottoms) of capacitors that bulge. Bulging capacitors are well past their best and as soon as you notice them it's time for replacements!

Hi guys,

Good info here, but wanted to make a little comment about 'leakage' You may have a cap that appears to be physically not leaking. The cap could still have electrical leakege, from the cap being old and not doing it's job. Same would go for the old paper/foil caps. They might look perfect, but have electrical leakage.


I restore vintage radios, and have replaced some caps in solid state equipment.

In the worst case scenario a bad electrolytic cap in the power supply will have a loud hum. That hum is usually not affected by the volume control.
If the cap becomes shorted, you run the risk of damaging the power transformer or other components. So with many older pieces of equipment, I feel it is best to replace the filters at a minimum to prevent possible damage. A set using original caps may 'work', but could fail at any time, and taking out the transformer can happen in less than a second.

New caps are cheap insurance to prevent damage.

Take care,
Gary.

Question.

Does beefing up the power supply with higher [x]farad-value caps do any real world improvement? I put a larger value (3300uf) in my little Lafayette integrated amp. It was still notable smaller than the original 2200uf unit.