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 Post subject: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 3:53 pm 
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Posts: 183
Location: New Virginia, IA
Is there a guide to replacing capacitors?

I see these old wax coated paper capacitors with a ring around one end and the word 'ground'. Do these get replaced with the blue electrolytic capacitors? Should I hook the '-' lead to where the 'ground' lead was hooked up?

I see some capacitors with two capacitances marked on them and they have 3 leads so I assume I can use two capacitors to replace them.

As long as the capacitance is the same and the voltage is the same or higher I figure I should be good.

I have a couple of capacitors that say ".01 800 DCWV". Are they .01 MFD?

When you replace capacitors is it best to leave enough of the original capacitor leads and hook up the new capacitor to those leads or should I completely remove the old leads? I think electrically it shouldn't matter but it may be considered 'bad form'.

What are the gotchas?

I'm new at this and I'm very surprised my restoration books don't begin to cover some of the obvious nitty gritty details of replacing capacitors.

Thanks,
Dan


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 4:02 pm 
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Location: Pocasset, Cape Cod, MA
The ring or "ground" end simply means the outer layer of foil, which acts as a shield. Those are standard paper capacitors and are usually replaced with Mylar, though ceramic disks will almost always work as well.

Removing the entire old lead wire looks somewhat better, but it takes longer, there's a risk of breaking a socket terminal or overheating it, and no one except the next restorer will ever see it anyhow. Hook splices or laps to the stub of the old wire work just as well. It's entirely your call.

Dual bypass capacitors can be replaced with individual caps.

800V paper capacitors can be replaced with 630V Mylar without any problems.

Yes, "microfarads" is assumed if it's not stated.


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 5:03 pm 
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Thanks Alan!


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 5:38 pm 
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I hate to disagree with Alan, but...

You should never use a lower voltage rating than the original part.
Those parts cost more originally, and they were used for a reason.

This is particularly true in the audio output stage, where you may find caps rated 1000 volts or more.
These protect the output transformer in the event of static crashes, noise spikes, etc.

- Leigh

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 6:31 pm 
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Location: New Virginia, IA
Okay. I do have some 800 VDC and one 1000 DCWV (DC working voltage?). I'll stick with the voltage ratings.

Another question I have is that one capacitor has these markings:

50 150 Red
30 150 Green
Negative Black

Is that 50 MFD 150 V, 30 MFD 150 V? Since the Black wire is Negative is this an electrolytic?


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 6:43 pm 
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DWSmith wrote:
Is there a guide to replacing capacitors?

There is an established practice.
Quote:
I see these old wax coated paper capacitors with a ring around one end and the word 'ground'. Do these get replaced with the blue electrolytic capacitors?

No. These are NOT electrolytics. I replace all wax caps with the vellow 630 volts ones, most of the time (except AC mains filters - see below).
Quote:
I see some capacitors with two capacitances marked on them and they have 3 leads so I assume I can use two capacitors to replace them.

Yes.
Quote:
As long as the capacitance is the same and the voltage is the same or higher I figure I should be good.

Yes, but in some case you can go up somewhat in capacitance, e.g. screen decouplers and B+ filters. For the latter, don't exceed the allowable maximum capacitance for input caps at the rectifier cathode.
Quote:
I have a couple of capacitors that say ".01 800 DCWV". Are they .01 MFD?

They are 0.01 microfarads. 800 volt? If they are coupling caps, the yellow 630 volt ones are fine. If they are RF filters across the AC supply, use the special types for this or up the rating to 1000 volts.
Quote:
When you replace capacitors is it best to leave enough of the original capacitor leads and hook up the new capacitor to those leads or should I completely remove the old leads? I think electrically it shouldn't matter but it may be considered 'bad form'.

I do this nearly all the time unless the original lead will easily come off the tag strip or tube base with a dental pick. Don't risk breaking a tube base tab - nasty repair!
Quote:
What are the gotchas?

Can't think of any... Make sure new axial lead electolytics are secure, not floating about!
Quote:
I'm new at this and I'm very surprised my restoration books don't begin to cover some of the obvious nitty gritty details of replacing capacitors.

Some books do...
Hope this helps,
Cheers,
Roger

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Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 6:45 pm 
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DWSmith wrote:
Okay. I do have some 800 VDC and one 1000 DCWV (DC working voltage?). I'll stick with the voltage ratings.

Another question I have is that one capacitor has these markings:

50 150 Red
30 150 Green
Negative Black

Is that 50 MFD 150 V, 30 MFD 150 V? Since the Black wire is Negative is this an electrolytic?


This is a dual-section lytic. Sounds like the typical filter lytic from an AA-5 radio.

L

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 8:42 pm 
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Location: Pocasset, Cape Cod, MA
With the exception of AC line filters, a 630V metallized Mylar cap will replace any 800V paper and foil unit. When a foil capacitor arcs through, the paper carbonizes and the capacitor shorts out. You only get one chance. When a metallized capacitor arcs though, the metallized electrode vaporizes and clears the short. This can happen many times, so the weak points all get removed.

I once took a Mylar capacitor and drilled a 1/4" hole through it. When all the shorts cleared, the cap worked fine (with reduced capacitance of course).


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 9:27 pm 
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Quote:
What are the gotchas?


There are a few others.

There are other types of capacitors in old radios, besides paper and electrolytics. Testing and replacement strategy depends on what you've got.

Mica capacitors were used from the very beginnings of radio into the early 1960s. They appear as square or rectangular devices. Early ones were encased in bakelite; other kinds of plastics were used later on. They are marked either with stamped numbers or with a color code consisting of a series of dots. You can do a search on "mica capacitor color code" to see the breakdowns; several were used over the years.

Mica capacitors were originally used for just about everything before paper capacitors were developed, but since the 1920s, they've mostly been relegated to RF and IF circuits. Their performance is far superior to paper or electrolytics at high frequencies. Since RF circuits tend to be notoriously fussy about the characteristics of the components in them, and many old mica capacitors are still perfectly good and usable today, it is best not to replace them unless you've got an actual problem in a circuit and troubleshooting demonstrates that the capacitor is faulty. Square mica capacitors are no longer manufactured, so if you need to replace one, the modern variety, called a silver mica capacitor, is the answer.

Ceramic capacitors take many, many forms. Some appear as round, hollow tubes, some look like white resistors with strange color codes or with printing on them, some are cubic, and others are round disks with a wire on each side. They started turning up in radios from about 1938 on, and are still used to the present day. Their performance varies greatly depending on the kind of ceramic inside, and its particular shape and geometry. Many times they are used in RF circuits to provide temperature compensation for frequency stability. In the early 1950s, the ceramic disc capacitor was introduced. These were used by the billions in numerous applications.

Normally, ceramic caps do not fail often. They should not be replaced unless physically damaged or troubleshooting indicates that a particular cap is bad. If replacing one of the old tubular or cubic style ceramics, you might have to experiment with different replacements until you find one that has the right temperature characteristic. Ceramic disc capacitors often have three-letter codes on them such as 'Z5U' or 'NP0.' Again, there are tables of these codes available online. If the code can be determined, it is best to cross reference it to its modern day equivalent. A capacitor with a different code may change the performance of the radio in noticeable ways.

Paper-in-oil, or oil filled capacitors are used in a few radios. These look like rectangular metal blocks screwed or bracketed to the chassis, or sometimes they appear as metal encased tubulars. When new, they were considered indestructible, but many have proven not to be. They sometimes develop leakage, and should be tested for it. Modern metal film capacitors make good substitutes.

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 10:08 pm 
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DW Smith,

I can think of a couple of "gotchas": One is to always check the new caps for both value (cap-value meter) and discharge (with analog voltmeter) BEFORE installing. While seldom bad, "new" is no guarantee. Another issue that has gotten me a couple of times is that a new cap may check good, only to fail in the circuit, (usually these failures are the ones subjected to higher voltages.) To deal with this, I do three things: 1) On higher voltage ones, I use a variac, and that's for both tubular (regular) AND for electrolytics. 2) On the higher voltage ones, I do one at a time. Slow, yes, but if I have a failure, I immediately know which one. 3) After re-capping, I burn the set in for an entire 8+ hour shift, (sometimes twice), to make sure everything is going to hold.

Good Luck,

Mike Tremper KC2HFR


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Tue 12, 2013 10:45 pm 
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michtrempe wrote:
On the higher voltage ones, I do one at a time. Slow, yes, but if I have a failure, I immediately know which one.
Sorry to disagree, but... I strongly disagree.
Powering up an old radio with any original caps is an invitation to failure.

If a cap fails, you have no reason to believe it is the last new one installed. In fact that's pretty unlikely.
It's probably one of the originals that should have been replaced but has not been.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Wed 13, 2013 11:23 am 
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DWSmith wrote:


What are the gotchas?


Installing the damn E-Caps backwards (don't laugh, I've blown out my share...).

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\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Wed 13, 2013 6:00 pm 
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AC line capacitors have been mentioned in this thread. A lot vintage and recent equipment has capacitors from the AC line to ground prior to the switch and fuse as shown on the schematic. Heathkit and other manufacturers used capacitors to both lines with their 2-fuses in a non-polarized plug scheme. Even if nothing else is done to improve the safety of the configuration, these caps should be replaced with AC line rated Y2 capacitors. The Y2 rating indicates that the cap is self-healing following a voltage spikes that puncture the dielectric. Do a web search on the subject of AC line rated capacitors. The other type of "safety" cap has an X2 rating. These are intended for line-to line (i.e., across the line connection, not for AC line to ground.) Some caps have X1/Y2 type combinations (for example) which can be used for AC line to ground.

These caps are almost always used from both Line and Neutral to ground in a 3-wire polarized plug configuration in PC power supplies. I've pulled a bunch of them when scavenging these ubiquitous PC supplies for parts and the case. Mouser and other suppliers sell the Y2-rated caps. Current practice is to use the 630 volt AC line rated caps rather than 800 to 1000 volt paper caps as used in the vintage equipment.

I recently restored a Hallicrafters S-38B receiver (modifiying it for polarized plug operation and fuse and switch to the Line (hot) connection.) In the original configuration, that AC/DC receiver transformerless has the line bypassed to the isolated chassis by a high voltage cap, the value depending on the particular model of the S-38 series. The S-38C uses a .022 microfarad cap, and I had a Y2 630 volt AC line rated cap of that value, so that was the one I used on my B-model.

Ted, KX4OM


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Wed 13, 2013 10:19 pm 
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leigh,
From that standpoint, I definitely agree with you. All true. What I have had happen in the past was that I used to just replace all the caps at once, and usually that was wonderful. But 2 or 3 times, the set stopped working completely after the "shotgun" approach to recapping, and I had to go back one-by-one and see either where I made a mistake and/or if there was indeed a new one that went bad upon fire up. Just a different technique. Now, I even measure the value of the old one and write it down, just in case the new cap is not working. Very tedious.

Mike


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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Wed 13, 2013 10:56 pm 
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Hi Mike,

Unfortunately, we have seen examples of brand new caps failing. That's very discouraging. :cry:

I'm suspicious of caps that have no brand name or logo. I try to stick with brands that are known for quality.

The only universal rule is that no rule applies universally. :mrgreen:

- Leigh

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Thu 14, 2013 5:13 am 
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All right, all right. This fellow is asking for a litle help with capacitor replacement, and he's met with a long thread full of arguments and comments about how new caps are as bad as the old ones -- not to mention a lot of gobbledygook about specs of little interest.

Let's get down to brass tacks:

A capacitor is basically two metal plates that are very close to each other, but don't touch. Placing an electrical charge on one plate will create a similar charge on the other. For this reason, AC current will actually go through a cap but DC cannot. Several of these components are used in radios, and of course come in various sizes. There are two basic specs -- capacitance and working voltage. Capacitance is basically how much plate area you have. Working voltage is the amount of voltage you can safely apply without arcing or breaking down.

Back in the olden days, capacitors were made with two strips of foil and a piece of paper in between. This is rolled up into a cylinder and coated with beeswax to prevent moisture from ruining it. Over the years the moisture seeps in anyway, and the caps can leak or short. They are so troublesome that it is recommended they be replaced with new ones.

Capacitance is rated in Farads, although one farad is a whopper of a cap! Most are rated in microfarads, or smaller values in picofarads. Unless used in radio tuners, the exact value of a capacitor is not important, although you generally want to keep it as close as you can. One popular value is .05 uF (microfarad). A .047 is a good replacement.

As for working voltage, it can't hurt to go with a higher rating than needed. The only limitations are size and price; but new ceramic caps are a lot smaller than original wax-paper caps, so a higher voltage rating is fine. Most caps I keep on hand are 630 volts. The old caps may be 50, 100, 200, or even 400, and a 630 type will handle the job and then some. A few caps are rated at 800 volts, and this has been debated before. Personally I don't want to take a chance on seeing a radio a second time, so I'll use a 1000 volt replacement.

Paper caps have a band on one end, often marked "outside foil." The cap should be installed with this band toward ground. BUT -- newer ceramic caps aren't made this way, so it doesn't matter.

There are other caps you'll find in these sets. Some are little brown disks. Some are rectangular with dots, and resemble Dominoes. These are a better design, and typically used in the tuning section of a radio. I do not replace these unless I suspect a problem. Yes, I've seen them fail and do some wild things, but the rule of thumb is to leave them be unless you think they're bad.

Some radios used a better design capacitor, with a molded plastic case instead of the beeswax. Some are green or red with markings, most are black with colored stripes. They are often nicknamed black beauties or bumblebees. Although plastic coated, they are still made with paper and the coating will deteriorate with age, forming cracks and leting the moisture seep in. When rebuilding a radio, it is wise to replace these.

Last but not least, we have electrolytics. A chemical called electrolyte is added to greatly ijncrease capacitance, and over the years the electrolyte will dry up and fail. Typical sizes are 10uF, 50uF, 100 uF, or 1000 uF. These caps have a plus sign (newer versions have a minus sign) for polarity. Note the polarity; if installed backwards it might short or even explode. Sometimes two or three electrolytics will be housed in the same case with a single minus lead (or a metal case which is minus). You may replace these with two or three new electrolytics as needed.

When replacing an electrolytic, it is wise to stay close to the rated value of the original. Don't go crazy over it; a 4 volt type can be replaced with a 16 volt or 25 volt without a problem, but don't shoot for a 630 volt on one of these unless called for.

Some people cut the leads of the old cap and solder the new cap to these leads. I prefer being more professional, removing the old leads entirely. However you can go either way; whichever is more comfortable for you.

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Thu 14, 2013 5:19 am 
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Leigh wrote:
You should never use a lower voltage rating than the original part.
Did you consider that they may have had a stock of a certain type, so using them cost less than buying more stock with a lower working voltage? There is not 800 working DC volts anywhere in most radios. Of course, analyzing the schematic will help.

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Thu 14, 2013 10:46 am 
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There have been discussions on this before on other threads. Certain capacitors, particularly in power supplies and audio output stages, are rated 800v, 1000v, or 1600v. When a company makes 50,000 radios, you can be guaranteed each component is deliberate -- no leftovers here.

What is so hard about replacing a component with the RIGHT type?

Quote:
From that standpoint, I definitely agree with you. All true. What I have had happen in the past was that I used to just replace all the caps at once, and usually that was wonderful. But 2 or 3 times, the set stopped working completely after the "shotgun" approach to recapping, and I had to go back one-by-one and see either where I made a mistake and/or if there was indeed a new one that went bad upon fire up.


THAT is a valid comment, and good advice. It's wise to troubleshoot first, then once you know it's safe to power up the radio, and once you have it playing to the point where you can hear intelligence through the speaker, replace 2 or 3 capacitors then power it up again to ensure it still works. Things happen; maybe you soldered to the wrong terminal post, or maybe you've got two leads touching -- whatever. If the radio suddenly stops playing, check the 2 or 3 components you just put in. I've been doing this for way too many years, and recap in exactly this manner.

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Feb Thu 14, 2013 11:34 am 
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FStephenMasek wrote:
There is not 800 working DC volts anywhere in most radios.
Copying a reply I posted to a similar recent thread:

-----

Capacitors on the plate of the audio output tube(s) can experience very high voltage.

Under normal operating conditions the peak plate voltage can reach twice the applied B+.

Under abnormal conditions that cut off plate current completely, the voltage can rise beyond that norm by a substantial amount due to the inductive kick from the output transformer when current flow ceases.

Such events are quite common, occurring for example whenever lightning causes a static crash.

Capacitors from plate to ground for tubes of modest power and B+ of 350 to 400 volts are frequently rated over 1,000 volts, as much as 1,400 or 1,600 volts in some designs.

-----

To expand on this further...
When an output tube is idling, with no signal, its plate voltage is roughly equal to B+, say 350v for discussion.

When the grid signal goes positive, plate current increases and plate voltage decreases, say to 50 volts at the positive peak of the grid drive, which is 300 volts below B+.

In order to reproduce a distortion-free sinewave at the plate on the negative peak of the grid signal, the plate voltage in the example must increase by 300 volts above B+, to 650 volts.

This is just basic circuit analysis.

The absolute minimum voltage for a plate cap would be twice the nominal B+.
That allows no safety margin for high AC line or for noise-induced spikes.

You need to use a cap that equals or exceeds original voltage rating. It was used for a reason.

I believe your statement quoted above is incorrect.


- Leigh

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 Post subject: Re: Replacing old capacitors with modern capacitors.
PostPosted: Dec Thu 07, 2017 3:49 am 
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Posts: 2
THANKS TO ALL FOR REPLYING . I SHOULD HAVE GIVEN MORE INFO. I HAVE A RCA RADIOLA 17 AND IN A METAL CONTAINER IS A GROUP OF CAPS THAT ARE CONNECTED
IN A MANNER THAT I DO NOT UNDERSTAND. DID NOT WANT TO CAUSE MORE DAMAGE BY WIRING THE CAPS WRONG.I DO HAVE THE MANUAL FOR THE 17. IN ONE OF THE
DIAGRAM IT SHOWS CAPS 3.5 3.0 2.0 1.O MFD ALL CONNECT TOGETHER. HAVE NEVER DONE THAT. UNCERTAIN


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