What type of capacitor should I use?

Mylar is DuPont's brand name for a stretched PET plastic. P is for poly :)

Were you NOT paying attention previously when we ALL told you to use the yellow plastic caps? 630 volt.

Or are you just being stubborn?

Paper dielectric capacitors are crap. They ALL need to be replaced. Trying to "just replace the bad ones" is a fool's errand. They're all bad or will fail after they're "back in service" again.

I have a Collins R-390A receiver on the bench. It's full of paper capacitors. The IF module alone had 18 of them. They have all been replaced. "But it's Collins" and "Those were mil-spec" and and and every other excuse for not changing them. Changing them made a profound difference in how well the radio works.

These parts are bad. Anyone that tells you otherwise is either lying to you or is delusional.

--
Jeff-1.0 
wa6fwi 
http://www.foxsmercantile.com

I WAS paying attention and I even contacted that seller and found out they are made in China.

No, not being stubborn , I just dont want caps made in China. Not much of anything made in China is a quality item. That seller has good prices and a fair selection, but I still dont want China caps, which will likely contain duds, and I'll end up replacing all of them in 5 years or less, again.

And that site dont give enough info to translate to other sites. They are just called "Axial Film Capacitors" on that site. When I look at other sites, I see them sold with some sort of "poly" name, and I see the word "film" used, as well as "foil". So, what do these compare to in the words used to sell other brands?

That word "film" bothers me, anyhow. Just what the heck is this film? Is it just some sprayed on metalic particles? The old paper caps contained foil, which to me means something that looks like tin foil used in the kitchen. Maybe I'm wrong, but if my radio or (whatever) was designed for caps made with foil, I'd prefer to use caps with foil, and whatever plastics they used to replace the paper. In other words, I want caps that most closely mimic the original caps, except without the paper.

Those paper caps may be crap now, but considering many of them lasted 50 years, they were not all crap, to last that long. I doubt any China made caps will last even close to 50 years. I may be wrong, but based on nearly all China products, I doubt any of them will last 5 years. Everything made in China is just throw away short lived junk. Made to fail one day after their warranty expires.

I'm sure it did make a difference to the better, but for how long?

But rather that toss out my opinion, which is based on my overall feelings about China products, you tell me how these caps have worked for you. (assuming they are what you have used). What precentage of them have been duds? If you have tested them, how accurate are they? Have you had any fail? How long have you used them? Will they really handle the max voltage they are rated as? How do they perform under heat and other extremes? DId your Collins work as designed, or did you have to re-align it or do any modifications because the caps are not the "foil" type, and thus are not what the circuit was made to use?

Sellers (of anything), always rate their goods at "Top Quality", but advertising is mostly all lies. I want references from you, and anyone else who is NOT connected to the seller.

Although this is drifting from the topic, I just bought an old Sencor Substitution box. It's for Resistance, Capacitors, (including lytics), one silicone and one selenium diode, and a few other features. I took a modern VOM with capacitor tester, and found all the paper/wax caps in that box are still very accurate. However some of the lytics are not even close. The resistors are all close too. Considering these parts have seen little voltage and use, I see no reason to change any of the small caps or the resistors. I do plan to change the electrolytics though, because I know they deteriorate just from age, whether they are used or not, because of the chemicals in them. (and my tests confirm they are not even close to their rated UF values, some as much as 50% off.

But I see no reason to change those small caps (.05 .001, etc). Not for the brief times thay are used. and they are all very accurate in their values.

I have tons of new old stock caps that I keep for nostalgia reasons (dad's) , but if I place them on my LC75 and run working voltages into them, most o f them will draw excessive current and never "reform". Most are also wildl y (by today's standards) off value. I don't know if they drifted over time or if they're typically that far off when new.

Of all the mistakes you made in your rant, the biggest is confusing Walmart Chinese products with individual components. Unless you have a natural ra cist bent, be aware that having Chinese DNA does not preclude one from maki ng quality or innovative assemblies or components as needed.

When rebuilding a 50 year old radio, we find many original caps inside. Ve ry few can pass a voltage test, and really, when is the last time these rad ios were used daily? 30 or more years ago? Most of the old radios you wil l find to restore haven't been used in decades. Those paper caps were shot long ago even if the circuit still struggles to life with them.

A few things:

Today, capacitors are commodities. Meaning that the technology involved in making them is fully established, well understood, extremely reliable and ( now) very simple. Meaning, again, that the lowest-cost producer making a ge neric product will pretty much win the market. Meaning (a third time), that the cost of 'faking' such a device will likely approach or exceed the cost of making the proper product in the first place.

So, those capacitors that require very little technology - small-value film caps, for instance - will be cheap and plentiful. And, apart from very spe cific requirements - aerospace, medical, ultra-precision and similar - ther e is no reason to choose one item over another from one source over another as, at that level, they are all pretty much from the same place.

Electrolytics do have a greater variation, include different technologies, different chemistry, materials and such, have many different applications, and sub-categories within those applications. With that in mind, one may ch oose from different sources.

Specialty caps are a different matter altogether, and unless one is in the Aerospace, medical, ultra-precision or similar industries, not really relev ant to vintage equipment. Russian PIO caps presently in vogue with the audi o hobby are a case in point. Utterly silly indulgences but plenty of yiches .

Meaning that unless you wish to pay aerospace prices, purchase the item tha t meets the needs at the best price from a *RELIABLE* supplier. *RELIABLE* supplier will protect you from counterfeits - usually at a very small premi um, but well worth it. And if that part happens to be from China, comfort y ourself that it is due to the commoditization of the product - and your pre ferred suppliers simply cannot make a profit in that line. The bottom line is that your vintage item is singing again, far more reliable than it ever was in the past, and, very likely far into the future.

One example: I pay about $1.75 extra per transistor from Mouser than for th e same part-number from another supplier. Why? Mouser is a major contributo r and founder of anti-counterfeit parts organizations.

If Mouser sells me a part, I feel pretty sure it will be as represented, wh atever the country of origin. Yes, I tend to hold my nose and grumble, if t hat is China. But increasingly often, the alternative is nothing at all, or old-stock material no better than what is being replaced.

Does your meter test those caps and resistors at any sort of operating volt age? Before you describe them as 'very accurate', they must be tested at op erating voltages.

Peter Wieck Melrose Park, PA

Speaking of unsafe tires, they do seem to have a limiated lifetime even if not used very much. Friend jsut went through that with a tire company. He had a tire that is starting to seperate. He talked with the tire maker. While the tire had plenty of thread and mileage let on it, it was over 7 years old. The company told him that after abut 5 to

6 years many tires will just go bad. In a way I wish that I had been aware of that a year or two ago. I am retired and do not drive that much and have a car and truck. I put some tires on them that was rated very high in the milage thinking I would not have to worry about tires for a long time, but seems that they may age out with over half the thread left on them.

Speaking of China. They make some items that seem to be as good as any,and they make a lot of junk. I have several pieces of equipmant from China that seems to be as good as any. Friend ordered some transistors and all of them were bad junk that did not even test on a transistor tester.

As many power tubes are not made in the US anymore a company contractes with a China company to make some. They seem to hold up very well.

Give this site a try.

Until you go into their product list and find all of the 'usual suspects' from the 'usual sources'.

The (very, very) few US-origin film caps offered are either extremely expensive, low-voltage, of unusual values (5.5 uF film? Really?) or all three.

Seriously, there is no 'there' there.

Peter Wieck Melrose Park, PA

Right on the first page:

"Think all capacitors made in the Far East are cheap, noisy, low quality."

'If you are looking for quality components, then TEDSS.com is for YOU.'

"Americans put a man on the moon in 1969 with American-made capacitors. The greatest military power in the world was made by using High Quality American Made apacitors."

Wow. I suppose the grammar and spelling are about what you'd expect from a Usenet loon, but subpar for a vendor trying to sell quality.

And, for what it's worth, I DON'T think ALL capacitors made in the Far East are cheap, noisy, low quality. And as soon as I hear that the Chinese have mastered the art of making "High Quality apacitors.", I'll be doubling up on my Mandarin lessons.

Thanks for the reminder Jeff. I need some caps from Sal.:-)

And if you look at their listings, the capacitors are made by a mix of manufacturers, some that I've heard of, some not. It appears that they are a surplus house.

--
Jim Mueller wrongname@nospam.com 

To get my real email address, replace wrongname with dadoheadman. 
Then replace nospam with fastmail.  Lastly, replace com with us.

If "the quality" is capacitance, or leakage current, or standoff voltage, or self-resonant frequency, or series resistance, the radio cares.

It doesn't care about 'made in China'.

well, if you must replace them with more modern components, a decent ceramic capacitor should do fine. From what I have seen, ceramics were common in gear made in the 50's and 60's because of their small relative size and reasonable consistency in manufacturing.

You should be able to order them from companies like Digikey, Mouser, etc.. Just make sure the voltage ratings are high enough, and you should be ok.

I've seen on-line "photo piles" of before/after restoration efforts in which modern components were "hidden" inside of hollowed-out components. Maybe you can stash a modern ceramic inside of the paper/wax tube, and seal it up with a bit of hot glue...

Your assumptions are wrong

NT

Ceramic capacitors are mostly cheap crap. Some have a wide change in capacitance, at different voltages. Some are microphonic, and their normal failure mode is a dead short. About the only place they should be used are for DC bybass, or in low power tuned circuits.

--
Never piss off an Engineer! 

They don't get mad. 

They don't get even. 

They go for over unity! ;-)

Then, what you are looking for would be what's sold as "film and foil" capacitors.

Digi-Key sells e.g. the CDE "WMF" series, which use metal foil, a polyester dielectric film, "non-inductive" winding (which usually means that the foil sticks out past the end of the film, and the turns of the foil are bonded directly to the wire lead), and epoxy seals at either end. These, or similar, might be the closest thing to a "plastic drop-in replacement" for your old paper-and-foil caps.

The film-and-foil design is often preferred for applications where there's a high peak current (e.g. pulse applications) as the current carrying capability of the foil is considerable.

The other (more common) option is "metallized film". In this design, the dielectric film (polyester, polypropylene, etc.) has a thin conductive metal layer deposited on one side - typically via vaccum deposition I believe. It's not discrete particles of any real size. Two layers of this film are then spiral-wound together, with the wire leads being bonded to the leads at the ends.

Metallized-film (sometimes "stacked film") tend to be less expensive, and (I think) more capacity available per volume at any give voltage rating because the conductive layer is so thin.

They are also said to have a reliability advantage, at least potentially. If a pinhole develops in the film and two adjacent layers short together, the short-circuit current can burn away the conductive film right around the hole, "healing" the short. Apparently this only works well when the film is a material with a high oxygen content.

Hmmm. I've not found them crap. Excluding MLCCs, which are a different anim al to the rest, ceramics are immune to the melting problems of some plastic film caps, their light weight aids robustness, they're small, they typical ly handle way above rated voltage without trouble if ever necessary. Slight microphony is not a problem in lots of applications - it is only very slig ht. The C/V gotcha only applies to some, and obviously one need be aware of it at design time and choose accordingly.

All parts have their issues, and ceramics behave fine and are very reliable in a lot of situations. As with everything, not in every situation.

NT

s r

tallized-capacitors/

Plastic film caps (but not polystyrene) are the best choice for valve radio s. There is no upside in this situation to separate foils, they destabilise capacity value some, are unable to self heal, are bulkier per farad and co st more. Pick high voltage ratings to ensure they all last a lifetime.

Trying to replicate all the defects of the original caps is pointless, ther e is no upside to it. That isn't true of some parts but it is of caps.

NT

If the originals were paper, I always use film capacitors. I've had too many shorted Ceramics in HV circuits, and I've replaced too many shorted disk capacitors in 5V circuits. Some have burnt holes in PC boards, when they are on a high current rail. "The C/V gotcha" can cause distortion in audio circuits, or cause an AGC circuit to 'pump'.

--
Never piss off an Engineer! 

They don't get mad. 

They don't get even. 

They go for over unity! ;-)